JP3399374B2 - Light emitting device with quantum well structure - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for forming a quantum well structure light emitting device having a pn junction type DH structure having a quantum well structure made of a group III nitride semiconductor crystal as a light emitting layer, and particularly, to a high technology. The present invention relates to a technique for forming a light-emitting layer having a quantum well structure that provides light emission with excellent brightness and brightness.

[0002]

2. Description of the Related Art A light emitting diode (LED) that emits short-wavelength visible light in a blue band or a green band that has been put to practical use
Most of the light-emitting devices such as N-type gallium indium nitride (GaαIn _1- α), which is a type of group III nitride semiconductor,
N: 0 ≦ α ≦ 1) is configured as a light emitting layer (active layer). GaαIn _1- αN is the indium composition ratio (= 1-
α) Depending on how, a large forbidden band width of about 2.0 electron volts (eV) to about 3.4 eV, which is convenient for emitting short-wavelength visible light or near-ultraviolet light, is provided at room temperature. That is the reason (publication of patent application, 3rd year of Showa 55th)
834).

The conventional structure of the light emitting section is composed of n-type and p-type
GaαIn between the rudd layers_1-Holds the light emitting layer consisting of αN
The so-called pn junction type double hetero
It is generally composed of a hetero (DH) structure.
(Jpn.J.Appl.Phys.,Vol. Three
Four, Part 2, No. 10B (1995), L133
2 to L1335). On the other hand, the crystalline structure of the light emitting layer
If the conventional example of the structure is omitted, the indium composition is made uniform.
GaαIn_1-An example of constructing a light emitting layer from a single layer of αN is
(See Japanese Patent Application Laid-Open No. 9-36430). Well
In addition, from the viewpoint of the laminated structure, a single quantum well (Single
  QuantumWell: SQW) structure or multiple
Quantum well (MultiQuantumWell: M
A technique of configuring the QW structure has been disclosed (Japanese Patent Laid-Open No. Hei 10-1999)
9-36430 gazette specification reference).

If the light emitting layer is composed of the SQW or MQW structure, there is an advantage that light emission with particularly excellent monochromaticity can be obtained. In addition, a laser diode (LD) has an advantage of lowering the oscillation threshold (Yasuharu Suematsu, "Optical Device" (Corona Co., Ltd., May 15, 1997, first edition). Issue 8), p. 63).

An energy band structure of a conventional SQW, which is also a constituent element of MQW, is schematically illustrated in FIG. SQW
Is basically a layer 010, 011 exhibiting a barrier action, and
It is configured by joining with a well layer 012 which is a light emitting layer sandwiched therebetween. In the case of forming a light emitting layer having a quantum well structure, it is a conventional example that the barrier layers have substantially the same thickness (see JP-A-9-36422). Similarly, there is known an example in which the well layer is composed of Ga _0.93 In _0.07 N having substantially the same layer thickness including the well layer (termination well layer) that constitutes the termination of the quantum well structure (Japanese Patent Laid-Open No. 9-36423). (See gazette specification).

Further, FIG. 10 shows a rectangular potential configuration in the SQW structure illustrated in FIG. The barrier layers 010 and 011 are the forbidden band width 013 of the well layer 012.
It is usually composed of a material with a larger band gap 014, 015. On the conduction band 017 side of the potential well portion 016 in the region where the well layer 012 is arranged,
Quantum levels 019, 02 that maintain a certain level from the conduction band edge
0 has occurred. Also, on the valence band 018 side, quantum levels 021 and 022 that maintain a constant level from the valence band edge.
Is occurring. Due to the generation of the quantum levels 019 to 022, the transition energies 023 and 024 are transferred to the well layer 012.
It is common knowledge that the band width is larger than 013 (see "Optical Device", page 63). Therefore, the theory teaches that the wavelength of light emitted from the quantum well structure shifts to a shorter wavelength side than the wavelength corresponding to the forbidden band width originally possessed by the material forming the well layer.

Conventional III with a quantum well structure light emitting layer
In the light emitting element having the group nitride semiconductor DH structure, the potential configuration of the light emitting portion is as shown in FIG.
12 has a line-symmetrical rectangular potential structure as a center (Japanese Patent Laid-Open No. 8-11612).
No. 8 and Japanese Unexamined Patent Publication No. 9-8412). Alternatively, it has a potential configuration in which the levels of the conduction band and the valence band change uniformly and linearly (Ma
t. Res. Soc. Symp. Proc. , Vol.
449 (1997), pp. 1167-1172). On the other hand, on the other hand, even from such a general rectangular potential well structure, contrary to the theoretical consequence pointed out by the quantum mechanical theory, the regular () of the group III nitride semiconductor forming the well layer (light emitting layer) is formed. A nitride semiconductor light emitting device that emits light having an energy smaller than the original bandgap energy is known (Japanese Patent Laid-Open No. 8-316528 and EUROPEAN PATENT APPLICATION EP-0716).
See 457 A2).

[0008]

In a light emitting layer having a quantum well structure using GaαIn _1- αN as a well layer, one conventional technique used for controlling the emission wavelength is an indium composition ratio (= 1. -There is a means to change α).
For example, when it is desired to make the emission wavelength longer, GaαIn _1- α having a relatively large indium composition ratio is used.
Measures will be taken with N as the well layer. This is because the band gap of GaαIn _1- αN becomes smaller as the indium composition ratio increases, and the emission wavelength becomes longer accordingly (see Japanese Patent Publication No. 55-3834).

However, in order to obtain GaαIn _1- αN having a high indium composition ratio of, for example, about 0.4 to about 0.5, it is unavoidable to set the film forming temperature to a low temperature of about 600 ° C. (Materials). Letters,
35 (1985), pp. 85-89). It is known that GaαIn _1- αN formed at a low temperature of around 500 ° C. has poor crystallinity (“Journal of the Institute of Electronics, Information and Communication Engineers”,
Vol. 76, No. 9 (September 1993), 913-
(See page 917). The superiority or inferiority of the group III nitride semiconductor crystal layer forming the well layer is reflected in the high or low emission intensity of the light emitting device. Constituting the well layer from Gaα In _1- α N, which is inferior in crystallinity, hinders obtaining a quantum structure light emitting layer that provides light emission with excellent strength. That is, it is one of the problems in the prior art that it is difficult to obtain a light emitting device having a high brightness quantum well structure.

In the quantum well structure, a quantum level resulting in an increase in carrier transition energy is generated in the well layer (for example, see Japanese Patent Laid-Open No. 9-8412). Therefore,
In order to obtain the same emission wavelength, it becomes necessary to form the well layer from GaαIn _1- αN having a large indium composition ratio, as compared with the case where the light emitting layer is formed from a single layer. As mentioned above, in order to achieve a high indium composition ratio,
A GaαIn _1- αN crystal formed at a lower temperature has poorer crystallinity. That is, Gaα having a high indium composition ratio
Under the present circumstances, it is not possible to conveniently obtain short-wavelength visible light such as a green band, which is excellent in intensity, from a quantum well structure light emitting layer made of In _1- αN.

On the other hand, in accordance with another prior art, the quantum well structure is said to provide light emission of a longer wavelength than that corresponding to the regular bandgap of the group III nitride semiconductor forming the well layer, and the light emitting layer. (Japanese Patent No. 278069)
(See No. 1), it is necessary to invent a potential configuration different from the unreasonable rectangular potential well structure in which the emission wavelength cannot be theoretically achieved. The first problem to be solved by the present invention is also here, and GaαIn _1- αN having a relatively low indium composition ratio, which has an advantage of producing light emission excellent in monochromaticity, is simple in crystal growth, and is excellent in crystallinity. Even with this, for example, it is to provide a structure of a quantum well structure in which light emission in a blue-green band or a green band can be easily and stably obtained. Particularly, it is to provide a structure of a quantum well structure having a potential structure suitable from the viewpoint of a band structure.

The second object of the present invention lies in the conventional problem that the emission intensity is sensitively changed due to the crystallinity of GaαIn _1- αN constituting the well layer.
For example, it is to clarify the requirements that the well layer of the quantum well structure should have in order to provide emission of blue-green band or higher intensity from the viewpoint of crystalline material. An object of the present invention is to solve the above-mentioned main problems and provide a light-emitting device having a quantum well structure light emitting layer made of a Group III nitride semiconductor, which is excellent in emission intensity and emission monochromaticity. To do.

[0013]

DISCLOSURE OF THE INVENTION The present invention overcomes the above-mentioned problems of the prior art and provides a quantum well having an n-type light emitting layer having a quantum well structure excellent in both emission intensity and monochromaticity. The purpose of the present invention is to provide a structured light emitting device. In particular, the invention according to claim 1 makes sense to bring about light emission with energy lower than the forbidden band of the semiconductor material forming the well layer (active layer), which was unclear in the prior art, and A light emitting device provided with a light emitting layer having a single or multiple quantum well structure including a convenient band structure is presented. Moreover, the junction structure relating to the well layer which can bring about the band structure conveniently will be described.

That is, the invention according to claim 1 comprises an n-type light emitting layer formed on one surface of a crystal substrate and sandwiched between n-type and p-type clad layers made of a group III nitride semiconductor crystal layer. and, in the light-emitting device of the pn junction type double hetero (DH) structure, the n-type emitting layer may have a multiplex quantum well structure, the well layer constituting the end of the quantum well structure (end well layer) An intervening layer made of an n-type group III nitride semiconductor is disposed in the middle of the p-type clad layer, and the interposing well layer is a layer.
The thickness is equal to or less than the thickness of another well layer, and the termination well layer has a conduction band of the Fermi level in a region near the junction interface between the n-type intervening layer and the termination well layer. It is characterized by being composed of an n-type group III nitride semiconductor crystal layer containing indium (In), which has a potential configuration in which it is convexly bent downward toward the low potential side toward (Fermi level).

According to a second aspect of the present invention, in the invention according to the first aspect, the termination well layer is an n-type confronting the n-type intervening layer and the n-type intervention layer with the termination well layer interposed therebetween. It is characterized in that it is sandwiched between the barrier layer.

Further, the invention of claim 3 is characterized in that, in the invention of claim 2, the n-type barrier layer is formed to have substantially the same composition and substantially the same layer thickness as the n-type intervening layer. There is.

Further, the invention according to claim 4 relates to a termination well layer including a potential structure which is dominant for increasing the emission wavelength. That is, claim 4
The invention according to claim 2 is the invention according to claim 2 or 3, wherein the termination well layer directs a valence band of the termination well layer to a Fermi level in a region near a junction interface with the n-type barrier layer. It is characterized by having a low potential region that is bent upward in a convex shape.

The invention according to claim 5 is the invention according to claim 4
In the invention described in, it is possible to provide light emission with a longer wavelength than that corresponding to the bandgap of the semiconductor material forming the well layer,
It is an invention that conveniently defines the size of the bending of the band.
That is, in the invention according to claim 5, the termination well layer is
The energy difference (ΔEc = | Eco−Ec |) between the original potential level (Eco) of the conduction band and the low potential edge (Ec) dropped to the Fermi level side, and the original potential level of the valence band (Evo). ) And the energy difference (ΔEv = | Evo−Ev |) between the low potential end (Ev) that has dropped to the Fermi level side, and the total energy difference (ΔEc + ΔEv) is 0.4 electron volts (eV) or more. It is characterized by having bends in the conduction band and the valence band.

The invention according to claim 6 is the same as claim 4
Alternatively, in the invention described in 5, there is provided a structure for obtaining light emission excellent in monochromaticity, particularly from a light emitting layer having a multiple quantum well structure. That is, the invention of claim 6 is the invention according to claim 4 or 5, prior Symbol termination well layer, the energy difference between the sum of the (.DELTA.Ec + delta
Ev) is set to be larger than the total energy difference of the other well layers.

[0020] The invention described in 請 Motomeko 1 to 6 or of the
It provides superiority in forming a termination well layer which is excellent in monochromaticity and is particularly convenient for increasing the wavelength of emitted light .

The invention described in claim 7 is the same as claim 1.
In the invention described in any of (1) to ( 6) , the requirements for constructing the termination well layer capable of increasing the emission intensity are presented. That is, the invention according to claim 7 is the invention according to any one of claims 1 to 6 , wherein the termination well layer has a main phase having an indium composition ratio (= X) of 0.3 or less, and the main phase Is a multi-phase structure n-type gallium indium nitride (Ga _1-X In _X N: 0 ≦ X ≦, which has a different indium composition ratio and includes a dependent phase in which a strained layer is present in the junction boundary region with the main phase. 0.
It is characterized by being composed of 3).

The invention described in claim 8 is the invention according to claim 7.
In the invention described in (3), the requirements for the well layer to further increase the emission intensity are presented. That is, the invention according to claim 8 is the invention according to claim 7 , wherein the termination well layer having the multiphase structure has an oxygen atom concentration of 5 × 10 ¹⁷ cm ⁻³ or more and 5 × 10 ²⁰ cm ^−. It is characterized by being composed of an n-type Ga _1-x In _x N (0 ≦ X ≦ 0.3) crystal of ³ or less.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION In the first embodiment of the invention according to claim 1 of the present application, a case where the quantum well structure is a single quantum well (SQW) structure will be described. FIG. 1 illustrates an energy band structure of the light emitting unit 1 of the pn junction type DH structure of the SQW structure 1b, which has a structure in which the barrier layer 10, the well layer 11, and the intervening layer 12 are sequentially stacked. The SQW structure 1b according to the present invention has one barrier (barr).
layer 10 and one intervening layer 12 sandwiching one well layer 11 from this structure.
a is formed. The light emitting layer 1a is the n-type cladding layer 1
3 and the p-type clad layer 14 are sandwiched between them to form the light emitting section 1. In the SQW structure including the only well layer, the only well layer 11 is the termination well layer 11a. The quantum well structure of the present invention is characterized by the termination well layer 11a.
The intervening layer 12 is inserted between the p-type clad layer 14 and the p-type clad layer 14. That is, in the present invention, the termination well layer 11a
Is not directly bonded to the p-type crystal layer.

FIG. 2 shows the quantum well structure of the first embodiment according to the invention described in claim 1 of the present application, which is a multiple quantum well (M
It is a figure for demonstrating the case where it is set as QW structure based on an energy band structure. Similar to the SQW structure, the intervening layer 1 is provided between the termination well layer 11 a and the p-type cladding layer 14.
2 is inserted. This MQW structure 1d
The light emitting layer 1a is sandwiched between the n-type and p-type clad layers 13 and 14 to form the light emitting section 1. Well layer 11 that is joined to the intervening layer 12 and constitutes the final end of the MQW structure 1d
a is a termination well layer. The well layer adjacent to the intervening layer 12 next to the termination well layer 11a as the first proximity well layer is the second proximity well layer 11b. The well layers (11c to 11e in FIG. 2) arranged between the second proximity well layer 11b and the n-type cladding layer 13 are the second proximity well layer 1
It is a well layer after 1b. These well layers 11a-11
e and barrier layer 10 are alternately layered to form a 5-period MQW structure 1
d is configured.

In FIG. 2, n-type and p-type cladding layers 1
3, 14 can be composed of n-type and p-type, for example, an aluminum nitride / gallium mixed crystal (Al _Y Ga _{1 -Y} N: 0 ≦ Y ≦ 1). The well layers 11a to 11e made of a semiconductor material having a bandgap smaller than those of the barrier layer 10 and the intervening layer 12 is a conventional means for creating a quantum level. In addition to nitrogen, other Group V elements such as arsenic (As) and phosphorus (P) are used as constituent elements, for example, gallium arsenide nitride mixed crystals (GaN _1-Y As _Y : 0 <Y <1) and phosphorus. It is also possible to form the well layer from an n-type group III nitride semiconductor material such as gallium nitride nitride (GaN _1-Z P _Z : 0 <Z <1). However, by containing indium (In) as a constituent element, an indium-containing group III nitride semiconductor material, particularly Ga _{1 -X} In _X N, which more suitably provides a forbidden band width suitable for emitting short-wavelength visible light, is obtained. The well layer is preferably composed of a mixed crystal.

The well layer and the barrier layer exhibit n-type conduction.
It is preferably composed of a Group III nitride semiconductor crystal layer.
The well layer and barrier layer are made of Group IV element silicon (Si) or tin (Sn), or Group VI element sulfur (S) or selenium (Se).
It can be composed of an n-type group III nitride semiconductor crystal layer doped with an n-type impurity such as. However, in order to avoid inadvertent formation of levels due to impurities, in the present invention, it is most preferable to form the well layer from undoped and high-purity Ga _{1 -X} In _X N mixed crystal. The barrier layer is
In particular, it is preferably composed of an n-type crystal layer having excellent conductivity.

In the present invention, the layer thickness suitable for acting as the barrier layer and the well layer is not particularly specified. Carrier movement (transport)
A suitable layer thickness for the barrier layer exhibiting a barrier effect to the light emission and the well layer for emitting light is Kronig-Penny (Kr).
Quantum mechanics theories such as the Onig-Penny rule are naturally teaching (K. Seeger, "Physics of Semiconductors (1)" (Yoshioka Shoten Co., Ltd., 199).
Issued the first printing on June 10, 1), pp. 12-21). In other words, the barrier layer generally has a layer thickness capable of exhibiting a tunnel effect of about 10 to 20 nm. The layer thickness of the well layer is generally 10 nm or less. The constituent requirements of the well layer, the barrier layer, and the intervening layer that form the MQW structure are the same as those when forming the light emitting layer of the SQW structure. The layer thicknesses of the barrier layers constituting the light emitting layer of the MQW structure need not be the same. Similarly, it is not necessary to unify the layer thicknesses of the well layers forming the MQW structure.

The intervening layer 12 is made of, for example, a group III nitride semiconductor material having a bandgap larger than that of the n-type Ga _1-x In _x N forming the termination well layer 11a. In particular, as will be described later, when the termination well layer 11a is composed of a multi-phase structure composed of a plurality of phases having different indium concentrations, it is possible to use a material which constitutes the main phase which mainly constitutes the termination well layer 11a. It is composed of a group III nitride semiconductor having a band gap. In addition, the intervening layer 12 is transparent to short-wavelength light emitted from the well layer 11a, for example, Al _Y Ga _{1 -Y} N.
It is preferable to be composed of (0 ≦ y ≦ 1) material.
The intervening layer 12 is composed of an n-type crystal layer. Carrier concentration is less than about 5 × 10 ¹⁷ cm ^-3 , preferably 1 × 10 ¹⁷ cm ^-3
It is preferably composed of a high-purity group III nitride semiconductor material having a low carrier concentration of ^-3 or less. Layer thickness is about 5
It is 0 nm or less, preferably 20 nm or less.

Since it is preferable that the intervening layer 12 is composed of a high-purity crystal layer having a low carrier concentration, if the layer thickness is unnecessarily large, the forward voltage of the light emitting element increases, and the intermediate layer 12 is driven at a low voltage. This leads to inconvenience when obtaining a light-emitting element with low power consumption possible. On the contrary, if the intervening layer 12 is extremely thin, the continuity of the film is impaired, and the surface of the termination well layer 11a is not covered with a uniform layer thickness. Insufficient to generate uniformly. Therefore, the thickness of the intervening layer is preferably 2 nm or more.

FIG. 3 is a view for explaining in more detail the energy band structure in the vicinity of the bonding interface of each layer of the light emitting section 1 including the light emitting layer 1a of the SQW structure 1b according to the first embodiment shown in FIG. Band diagram (band dia)
gram). The characteristic of the band configuration according to the first embodiment is that the conduction band 16 is bent downward to the Fermi level 17 side only in the internal region of the termination well layer 11a near the junction interface 15a with the n-type intervening layer 12. The low potential portion 18 is formed by bending.

Further, FIG. 4 shows the MQ shown in FIG.
It is a band diagram corresponding to W structure 1d. SQ
Regardless of the W structure 1a and the MQW structure 1d, the characteristic of the band structure according to the first embodiment is that the conduction band 1 is formed in the termination well layer 11a near the junction interface 15a with the n-type intermediate layer 12.
6 is bent to the Fermi level 17 side so as to be convexly bent downward, so that the low potential portion 18 is formed particularly remarkably.

As described above, in order to form the low potential region 18 in the conduction band 16, it is necessary to sharply change the composition at the heterojunction interface 15a between the termination well layer 11a and the n-type intermediate layer 12. Is required. For example, n-type Al
_Y Ga _{1 -Y} N (0 ≦ Y ≦ 1) to the intervening layer 12, and
N-type Ga _{1 -X} In having a band gap smaller than that of the intervening layer 12
_In a heterojunction system with the termination well layer 11a made of _X N (0 <X ≦ 1), the atomic concentration of aluminum (Al) or indium (In) is the average concentration in the layer containing it as a constituent element. To 2 digits, the transition region width required to increase or decrease the concentration is about 20 nm or less, preferably about 15 nm.
Hereafter, it is necessary to set the thickness to about 12 nm or less. The width of the transition region is determined by the general secondary ion mass spectrometry (S
The measurement can be performed based on the analysis result of the distribution state of elements by IMS) or Auger electron spectroscopy (AES). If the width of the transition region is within the above range, the necessary conditions for creating a low potential part in the conduction band or the valence band can be met.

Electrons 19 can be accumulated in the low potential region 18 of the conduction band 16 locally provided in the region near the junction interface 15a between the intervening layer 12 and the termination well layer 11a. If a storage region for the electrons 19 is provided adjacent to the low-potential portion 18 especially adjacent to the junction interface 15a with the p-type clad layer 14 that supplies the electrons 19, the positive potential of the diffusion length is shorter than that of the electrons. There is an advantage that holes can be efficiently captured, and therefore radiative recombination of electrons and holes can be effectively performed in the vicinity of the accumulation region.

The low potential portion 18 of the conduction band 16
Is not formed by a change in the potential at a uniform rate, but is formed by a sharp band bending in a very limited narrow region near the junction interface 15a with the intervening layer 12 and the termination well layer 11a. ing. Therefore, the carriers (electrons) localized in this minute region can behave as low-dimensional, for example, two-dimensional carriers. Therefore, there is an advantage that a quantum well structure light-emitting layer having a high-speed response of light emission and a high-speed response is obtained because of its low-dimensional carrier traveling speed.

Second aspect of the invention according to claim 2 of the present application
In the arrangement relationship of the crystal layers shown in the embodiment of FIG.
It means that it is directly bonded to the shaped intervening layer. That is, in the light emitting layer having the quantum well structure, it means that the termination is composed of the well layer. This arrangement is illustrated in Figures 1 and 2. The reason for directly joining to the n-type intervening layer is that this junction effectively causes the conduction band to bend in the termination well layer. If the arrangement relation of the present embodiment is summarized in relation to the arrangement of the n-type barrier layer that constitutes the quantum well structure together with the well layer, the termination well layer is arranged between the n-type intervening layer and the n-type barrier layer. (See FIGS. 1 and 2). S
In the QW structure, the n-type barrier layer can be substituted for the n-type clad layer.

Third aspect of the invention according to claim 3 of the present application
In the embodiment of the present invention, the characteristic feature of the quantum well structure is that it preferably exhibits n-type conduction.
2 and the n-type barrier layer 10 joined to the termination well layer 11a are
It is composed of materials having substantially the same composition. For example, n-type and high resistance Al _Y Ga _1-Y N (0 ≦ Y ≦ 1)
Al _Y Ga when configuring an intervening layer 12, n-type barrier layer 10 to the aluminum composition ratio (= Y) the same from
_1-YN (0≤Y≤1). Alternatively, the difference in the aluminum composition ratio is approximately within ± 0.05, and the aluminum composition ratio is almost the same Al _Y Ga _{1 -Y} N (0
≦ Y ≦ 1). Regarding the conductivity of the n-type barrier layer 10, it is preferable that the intervening layer 12 is composed of a crystal layer of high purity and high resistance, whereas the n-type barrier layer 10 that faces the n-type barrier layer 10 closest to it is conductive. It is good to be composed of a group III nitride semiconductor crystal layer which is excellent in Specifically, n
The carrier concentration of the barrier layer 10 is at least about 1 × 10 ¹⁶ cm ⁻³ or more, preferably about 1 to ensure conductivity.
It is preferably more than about 10 × 10 ¹⁷ cm ⁻³ and about 1 × 10 ¹⁸ cm ⁻³ or more. However, the carrier concentration is 1 × 10 ¹⁹ cm
^If it exceeds ^-3 , on the contrary, the crystallinity of the n-type barrier layer 10 is lowered, so that the carrier concentration is preferably about 1 x 10 ¹⁹ cm ^-3 or less.

Taking the SQW structure 1b shown in FIG. 1 as an example, the effect of the present embodiment will be described. If the intervening layer 12 and the n-type barrier layer 10 are made of substantially the same material, the termination well arranged in the middle thereof will be described. On the layer 11a, the joining surfaces 15a, 1 on both sides thereof are provided.
The stress applied from 5b can be made substantially uniform.
Under the condition that the applied stresses are substantially equal, it is possible to more easily control the degree of band bending at the bonding interfaces 15a and 15b depending on the steepness of the interfaces.

Further, if the intervening layer 12 and the n-type barrier layer 10 joined to the termination well layer 11a are made of a group III nitride semiconductor material having substantially the same layer thickness, the n-type barrier layer 10 and the intervening layer 12 are formed. The stress applied to the terminal well layer 11a from both sides can be equalized. Therefore, it is advantageous to generate a uniformly bent band in the termination well layer 11a. Substantially the same refers to a difference in thickness of less than ± 10%.

In the fourth embodiment according to the invention of claim 4 of the present application, in addition to the conduction band, the technical means for determining the bending of the band substantially uniquely by the steepness of the bonding interface is used. Form a bend in the valence band. The band configuration according to this embodiment will be described with reference to the band diagram of FIG. The characteristic of the band structure according to the fourth embodiment is that the junction interface 1 of the termination well layer 11a with the n-type barrier layer 10 is formed.
Only in the region near 5b, the low potential portion 21 is formed by bending the valence band 20 to be convex upward on the Fermi level 17 side. Further, as shown in the third embodiment, the termination well layer 11a is sandwiched between the n-type intervening layer 12 and the n-type barrier layer 10 having substantially the same composition and layer thickness. Without being limited to this, the bending of the band can be conveniently formed on the valence band 20 side.

In the low potential portion 21 bent to the Fermi level 17 side, the holes 22 that perform radiative recombination with the electrons 19 can be effectively accumulated. This low potential part 21
Is lower than the original energy level of the valence band 20, and therefore the energy level of the holes 22 accumulated in this region is low in the first place. Further, as described above, the energy level of the electrons 19 accumulated in the low potential portion 18 near the junction interface 15a with the intervening layer 12 is also low. Therefore, the transition energy 23 between the electron 19 and the hole 22 in such a band structure is due to the band gap 2 of the group III nitride semiconductor material forming the termination well layer 11a.
Less than 4. Therefore, the emission wavelength is determined by the termination well layer 11
Light having a wavelength longer than the wavelength corresponding to the band gap 24 of the group III nitride semiconductor material constituting a is provided.

As shown in FIG. 3 , the degree of bending of the conduction band 16 in the well layer is determined by the original potential level (Eco) 16a of the conduction band 16 and the low potential end (Ec) that drops to the Fermi level 17 side. Energy difference from 16b (ΔEc = | Eco-Ec |) 16c. On the other hand, the original potential level of the valence band 20 (Ev
o) Energy difference (ΔEv) between 20a and the low potential end (Ev) 20b that has dropped to the Fermi level 17 side.
= | Evo-Ecv |) 20c, the valence band 20
The degree of bending is shown. ΔEc (= 1 on the conduction band 16 side
6c) and the energy difference ΔEc + ΔEv, which is the sum of ΔEv (= 20c) on the valence band 20 side, is the total energy difference referred to in the present invention. For example, a value obtained by subtracting the total energy difference ΔEc + ΔEv from the regular band gap 24 of the semiconductor material forming the termination well layer 11 a gives the transition energy 23.

In the fifth embodiment of the present invention, as described in claim 5 of the present application, the total energy difference ΔEc + is obtained.
From the well layer where ΔEv is 0.4 eV or more to the termination well layer 1
Make up 1a. At least ΔEc + ΔEv is 0.4
This is because the termination well layer 11a having a voltage of eV or more has a convenient effect of increasing the wavelength of light emission. In order to set the total energy difference ΔEc + ΔEv to 0.4 eV or more, the termination well layers are sandwiched by intervening layers and barrier layers having substantially the same composition and layer thickness, and stress is substantially evenly applied from both crystal layers to the termination well layers. Is more preferable. If such preconditions are in place, the steepness of the junction interface described later (edited by The Physical Society of Japan, “Physics and Applications of Semiconductor Superlattices” (published by Baifukan Co., Ltd., September 30, 1986, first edition, first edition) 4 prints), 139
(See p. 145), a well layer can be formed in which at least the total energy difference ΔEc + ΔEv is 0.4 eV or more.

If the degree of band "dip" is remarkably different in each well layer forming the multiple quantum well (MQW) structure, the level formed in the low potential region in the well layer is incidental to the well. It depends on the layer. Therefore, the transition energy of carriers may be different for each well layer,
There is a disadvantage that light emission having different wavelengths for each well layer results. In order to secure monochromatic light emission, in the sixth embodiment according to the invention of claim 6 of the present application,
The structure of the termination well layer is further defined based on the total energy difference ΔEc + ΔEv. That is, in the sixth embodiment of the present invention, the termination well layer of the multiple quantum well structure is configured by a well layer in which the total energy difference (ΔEc + ΔEv) is larger than the total energy difference of other well layers. To do.

Explaining with reference to the band diagram of FIG. 4, the degree 25c of the potential "dip" of the conduction band 16 at the junction interface 15c of the second proximity well layer 11b with the barrier layer 10a is determined as follows. The feature is that it is smaller than the depth 25a of the depression of the close well layer 11a. Moreover, the degree 25d of the valence band 20 drop at the junction interface 15d with the barrier layer 10b is also 25 d.
The feature is that the valence band 20 in the inside is smaller than the degree of depression 25b. In summary, the total energy difference (25c + 25d) in the second proximity well layer 11b.
Is smaller than the total energy difference (corresponding to 25a + 25b) in the termination well layer 11a. Carriers (electrons 19 and holes 22) are accumulated in the low potential portions 18 and 21 inside the termination well layer 11a preferentially over the second proximity well layer 11b, and the well layers 11c after the second proximity well layer 11b are accumulated. This is because the accumulation regions of the electrons 19 and the holes 22 due to the bending of the conduction band 16 are not inherently included inside the to 11e.

In forming the light emitting layer from the MQW structure, the n-type barrier layer adjacent to the subsequent well layers 11c to 11e including the first proximity well layer (termination well layer) 11a and the second proximity well layer 11b. According to the third embodiment, the region in which the electron 19 as a carrier for causing light emission is accumulated is almost at one place because of the potential.
You can concentrate on 8. On the other hand, the area in which the holes 22 can be stored is limited to the specific area 21. That is, since the carriers are confined in the specific potential regions 18 and 21 inside the termination well layer 11a, the electrons 19 and the holes 22 having substantially constant energy can be used to cause radiative recombination. As a result, the emission wavelength is uniform, that is, the emission is excellent in monochromaticity. If each of the well layers 11c to 11e after the second proximity well layer 11b is formed with a low potential portion in which the "falls" of the conduction band 16 and the valence band 20 are substantially the same, the formed quantum level is formed. Also has an advantage that light emission with a uniform wavelength is brought about because the wells are substantially the same. Ideally, there is no "fall" in the potential in the well layers after the second proximity well layer.

In order to form a marked "fall" in the potential of the termination well layer 11a, the steepness of the composition at the junction interface with respect to the termination well layer is made more excellent. For example, in the termination well layer made of a gallium nitride / indium mixed crystal, if the transition distance of the indium atom concentration is 10 nm or less, the total energy difference (ΔEc + ΔEv) can be 0.4 eV or more. On the other hand, when a deep potential drop exceeding approximately 1 eV to 1.5 eV is formed, the emission wavelength undesirably becomes a long wavelength, and short-wavelength visible light emission cannot be constantly obtained. For example, a room temperature bandgap of about 3.1 eV formed by forming a potential part lower than the conduction band by about 1.7 eV.
When the termination well layer is made of Ga _0.9 In _0.1 N crystal, the infrared light having a wavelength of more than about 800 nm is emitted.

In order to make the potential drop in the termination well layer in the MQW structure larger than those in the other well layers, the steepness of the junction interface on both sides of the termination well layer should be set to the other well layer. It should be superior to the case of. In order to intentionally generate a difference in interface sharpness, for example, there is a method of providing an interval in the film formation period, that is, a so-called growth interruption opportunity. According to the method of controlling the steepness of the bonded interface by suspending the growth, the steepness of the interface is generally improved by extending the growth suspending time. Without setting a growth interruption period,
When film formation is continuously advanced, the steepness of the bonding interface becomes poor. For example, Ga _0.9 I on the n-type GaN barrier layer
When the n _0.1 N termination well layer is continuously deposited, the transition distance of the indium atom concentration at the junction interface thereof may well exceed 20 nm and reach about 40 nm to about 50 nm. Therefore, the steepness of the other well layers can be set to a steepness by arranging the growth of the termination well layer with an adjusted growth interruption time and not intentionally setting the interruption time of the other well layers. Compared to that, it can be excellent.

Further, as described in the seventh embodiment of the present invention, in the structure of the MQW structure light emitting layer, particularly, the termination well layer 11a is composed of a material having a layer thickness different from that of other well layers. Then, there is an advantage that the emission wavelength can be easily changed. For example, if only the layer thickness of the termination well layer 11a is made thicker than the layer thickness of the other well layers without changing the group III nitride semiconductor material forming the intervening layer and the well layer,
The emission wavelength tends to shift to the short wavelength side. On the contrary, if only the termination well layer 11a is simply made thinner than the other well layers, the wavelength of light emission can be made longer. Therefore, in the light emitting layer having the quantum well structure, if the layer thickness 11a of the termination well layer that has a dominant effect on the emission wavelength is made thinner than the other well layers, the crystallinity will be deteriorated. It is convenient that a long emission wavelength can be achieved without the need to intentionally form a well layer from a Ga _{1 -X} In _X N crystal layer having an indium composition ratio.

When the thickness of the termination well layer 11a is reduced, n
The degree of stress experienced by the shaped barrier layer 10 and the intervening layer 12 increases. Therefore, the junction interface 15 with the termination well layer 11a is formed.
Band bending in both the conduction band 16 at a and the valence band 20 at the interface 15b with the n-type barrier layer 10 is further increased. Therefore, the energy level formed in the low potential portions 18 and 21 becomes lower due to the increase in the number of band bends. Therefore, the transition energy between carriers is further reduced as compared with the case of the thick film termination well layer, resulting in a structure which is convenient for obtaining long-wavelength light emission. That is, unlike the conventional case, it is not necessary to intentionally form a termination well layer from a gallium nitride / indium mixed crystal having a high indium composition ratio that is inferior in crystallinity, and a more superior configuration can be obtained in obtaining long-wavelength light emission. There are advantages.

This phenomenon of lengthening the wavelength is a phenomenon which is completely opposite to the phenomenon exhibited by the conventional quantum well structure having a general rectangular potential configuration. In the conventional quantum well structure having a rectangular potential structure, the level formed in the well becomes higher as the thickness of the well layer, that is, the well width, is reduced. Therefore, the transition energy of electrons between the quantum levels increases, and the emission wavelength becomes short. On the other hand, as described above, unlike the conventional quantum well structure, although there is disclosed a configuration which brings about emission of long wavelength with a decrease in well width,
While the band structure sufficient to bring about the phenomenon of lengthening the wavelength was completely unknown, the present invention clearly shows that it depends on the band structure based on the bending of the conduction band and the valence band as described above. is there.

In the eighth embodiment of the present invention, originally, in a light emitting layer having a quantum well structure which provides light emission excellent in monochromaticity, in particular, the termination well layer is formed of indium as described in claim 7 of the present application. It is composed of a crystal layer having a multiphase structure with a regulated composition ratio. This is because a remarkable effect can be obtained in increasing the emission intensity. According to the configuration of the potential band of the present invention, the intensity of light emission is hindered when the Ga _{1 -X} In _X N having a high indium composition ratio that causes deterioration in crystallinity is intentionally adopted as the termination well layer. Avoid irrationality. According to the present invention, the indium composition ratio (= X) is 0.
3 or less gallium nitride / indium mixed crystal (G) having a relatively small indium composition ratio that does not deteriorate the crystallinity.
a _1-X In _X N: 0 ≦ X ≦ 0.3) can be used as a termination well layer without difficulty to provide a quantum well structure light emitting device that emits light of a long wavelength.

The termination well layer made of Ga _{1 -X} In _X N (0≤X≤0.3) having an indium composition within the above range and having a multiphase structure provides light emission with particularly excellent intensity. . The multi-phase structure means a plurality of domains or phases having different indium composition ratios (= X).
It is a crystalline body formed by mixing e) (JP-A-10-562).
No. 02). If the phase (lump) that predominantly exists in a layer is the main phase, then the multiphase structure consists of the main phase and the phases that are subordinately scattered within that phase (dependent phases). In most cases, the dependent phase is in the form of a microcrystal, and this microcrystal is sometimes referred to as a quantum dot.
Since t) is exerted, luminescence excellent in intensity can be obtained. In addition, the main phase and the dependent phase generally have different indium composition ratios. Therefore, the lattice strain generated at the bonding interface between the main phase and the dependent phase also contributes to the increase of the emission intensity. Become.

The termination well layer having a multi-phase structure is made of, for example, a metal organic pyrolysis vapor deposition (MOCVD) method, a molecular beam epitaxial (MBE) method, or a halide or hydride (hydride) as a raw material. After the film is formed by the vapor phase epitaxial (VPE) method, the film can be constantly formed by heating and cooling under the optimized conditions.

In the ninth embodiment of the present invention, a Ga _1-x In _x N (0 ≦ X ≦ 0.3) crystal layer having a multi-phase structure, particularly containing oxygen atoms in a proper concentration. Ga _1-X In
_The termination well layer 11a is composed of an XN (0 ≦ X ≦ 0.3) crystal layer. The optimization of the oxygen concentration can be configured termination well layers 11 a that gives the luminescence of high intensity. In particular, an oxygen atom concentration, preferably less than 5 × 10 ²⁰ cm ^-3, and more _{preferably, Ga 1-X In X N} (0 to 1 × 10 ²⁰ cm ^-3 or less
≦ X ≦ 0.3) is suitable as a crystal layer for forming the termination well layer 11a. The oxygen atom concentration is about 1 × 10 ¹⁵ cm ^-3
Alternatively, when the termination well layer is formed from a Ga _1-X In _X N (0 ≦ X ≦ 0.3) crystal layer having an extremely low oxygen atom concentration of about 1 × 10 ¹⁴ cm ⁻³ or less, high-intensity light emission is rather generated. In many cases, it is recognized that the above does not occur constantly.
The range of oxygen atom concentration that is convenient for producing high-intensity light emission is approximately 5 × 10 ¹⁷ cm ⁻³ or more and 1 × 10 ²⁰ cm ^−3.
It is the following.

Ga _{1 -X} for controlling the oxygen atom concentration within a suitable range
As a means for obtaining an In _X N (0 ≦ X ≦ 0.3) crystal layer, for example, when a Ga _1-X In _X N film is formed by MOCVD, an impurity containing an oxygen-containing substance or a functional group containing oxygen is used. There is a method of using an organometallic compound containing a compound added with (function group) as a growth raw material. For example, trimethylgallium ((CH ₃ ) ₃ Ga:
Trimethylindium ((CH
₃ ) Ga _1-X In _X N with ₃ In: TMI) as In source
In the film forming technique of (0 ≦ X ≦ 0.3), TMG for setting the oxygen concentration from several ppm by weight to over ten and several ppm by weight and TMI for adjusting the oxygen concentration from several tens to around 100 ppm by weight are used as growth raw materials. As a result, the preconditions for containing the oxygen atom concentration within the above-mentioned preferable range are prepared.

Ga _1-X In _X N (0 ≦
X ≦ 0.3) Another means for controlling the oxygen atom concentration in the crystal layer is Ga _{1 -X} In _X N (0 ≦ X ≦ 0.3).
Is formed in a growth atmosphere in which an oxygen-containing substance is intentionally added. Oxygen-containing substances include carbon monoxide (CO), carbon dioxide (CO ₂ ) and water (H ₂ O), but oxygen-containing substances such as nitric oxide (NO) and nitrogen dioxide (NO ₂ ) Since it contains nitrogen (N) which is a constituent element of the group III nitride semiconductor, it is preferably used also from the viewpoint of suppressing volatilization of nitrogen from the growth layer during film formation. For example, even if ammonia (NH ₃ ) gas containing water at a volume concentration of several to several tens ppm is used as the nitrogen source, Ga
_1-X In _X N can control the oxygen atom concentration in the crystal layer.
The oxygen atom concentration in the Ga _1-X In _X N crystal layer can be quantified by an instrumental analysis method such as secondary ion mass spectrometry (SIMS) or Auger electron spectroscopy (AES).

[0057]

According to the band structure described in the first aspect of the present invention, the action of selectively accumulating electrons in the region inside the termination well layer is exhibited. As a result, the electrons localized in the low potential region are filled to a low potential level.

Further, according to the arrangement of the termination well layer described in the second aspect of the invention, it is possible to surely create the low potential portion in the termination well layer. Particularly, as described in claim 3, the intervening layer and the n-type barrier layer joined to the termination well layer are composed of materials having substantially the same composition and substantially the same layer thickness.
It exerts an action of applying a stress to the termination well layer substantially evenly, and creates a state in which the presence or absence of the bending of the band at the junction interface of the termination well layer and the degree of the bending can be easily controlled.

The invention described in claim 4 has the function of selectively accumulating holes in a specific low potential region in the well layer. At low potential sites, the level of electrons and holes present is low, so the transition energy between carriers is reduced, thus leading to emission of longer wavelengths than corresponding to the original bandgap.

Further, the invention according to claim 5 has an effect of surely accumulating carriers in the well layer, and an effect of providing a band potential configuration which acts predominantly to increase the wavelength of light emission.

According to the sixth aspect of the present invention, the potential relationship between the first and second proximity well layers is such that electrons and electrons are preferentially generated in the first proximity well layer, that is, the termination well layer. Exhibits the action of accumulating holes. This acts to make the light emitted from the quantum well structure more monochromatic.

Further, the termination well layer having a thinner layer thickness than the other well layers according to the invention of claim 7 has a function of providing a potential structure capable of easily achieving a longer emission wavelength.

Further, the structure of the termination well layer according to the eighth aspect has the function of increasing the emission intensity from the termination well layer. In particular, the terminal well layer having the oxygen atom concentration defined in claim 9 has a function of further increasing the intensity of light emission.

[0064]

EXAMPLE 1 In Example 1, the present invention will be specifically described by taking a light emitting diode (LED) having an SQW structure as an example. FIG. 5 is a schematic diagram showing a cross-sectional structure of the LED 40 including the laminated structure 41 manufactured in this example.

On the (0001) plane (c-plane) of the crystal substrate 400 made of sapphire (α-Al ₂ O ₃ single crystal),
A buffer layer 401 made of undoped gallium nitride (GaN) whose main interface is a single crystal and its upper layer is mainly composed of polycrystal or amorphous is formed.
Deposited at 50 ° C. Buffer layer 40 having a layer thickness of about 17 nm
An undoped n-type GaN layer 4 having a carrier concentration of about 2 × 10 ¹⁷ cm ⁻³ and a layer thickness of about 0.5 μm is formed on the first layer 4.
02 is deposited. On the undoped n-type GaN layer 402, the n-type GaN layer 403 in which the doping concentration of silicon (Si) is increased in the increasing direction of the layer thickness, that is, the carrier concentration is gradually increased in the increasing direction of the layer thickness. Have been deposited.

This n-type GaN layer 403 is used as a lower n-type cladding layer, and undoped n-type GaN (carrier concentration = 4 × 10 4) having a layer thickness of 20 nm is formed thereon.
^A barrier layer 404 of ¹⁷ cm ^-3 ) was deposited.

A well layer serving as a termination well layer 405 was deposited on the barrier layer 404 at 890 ° C. The termination well layer 405 is
Undoped n-type Ga _0.88 In _0.12 N with a layer thickness of about 7 nm
Composed from. Cyclopentadienylindium (C ₅ H ₅ I) having TMG as a gallium source and having a valence of 1
n) as an indium source (J. Crystal Gr.
owth, 107 (1991), pp. 360-364), the formation of the n-type Ga _0.88 In _{0. 12} N termination well layer 405, ends with stopping the supply to the atmospheric pressure MOCVD reactor of both raw materials Let After the formation of the termination well layer 405, a growth interruption period for stopping the supply of the raw material gas to the MOCVD reaction furnace is provided for 3 minutes, during which only ammonia (NH ₃ ) gas is circulated, and the inside of the MOCVD reaction furnace is made to flow. Further, the indium source and the gallium source were swept and eliminated without any residue.

After the growth was interrupted, n-type GaN made of the same material as the n-type barrier layer 404 and having the same layer thickness was deposited as the intervening layer 406. The carrier concentration of the intervening layer 406 is about 7 ×.
It was set to 10 ¹⁶ cm ^-3 . That is, the n-type intervening layer 406 is made of a material having the same conductivity type as the n-type barrier layer 404, but has a carrier concentration lower than that of the n-type barrier layer 404.
It was composed of a group III compound semiconductor crystal layer of higher resistance and higher purity.

The above n-type barrier layer 404 and the intervening layer 406.
The well layer 405 is sandwiched by the
Configured. The steepness at the junction interface 43 between the n-type intervening layer 406 and the well layer 405 is generally expressed as the transition distance required to reduce the atomic concentration by two digits when the indium (In) concentration is higher than the average concentration in the well layer 405. It was about 14 nm when measured by different SIMS analysis means. This steepness is sufficient to cause bending (bending) of the conduction band at the junction interface 43 between the n-type intervening layer 406 and the n-type well layer 405.

A magnesium (Mg) -doped p-type Al _0.15 Ga _0.85 N layer was deposited as a p-type cladding layer (layer thickness = 15 nm) 407 on the n-type intervening layer 406. On the p-type clad layer 407, the p-type Al _Y Ga _1-Y N (Y = 0.15 → the aluminum (Al) composition ratio is reduced substantially linearly from 0.15 to 0 in the increasing direction of the layer thickness. 0) layer as a contact layer (layer thickness = 0.1 μm, carrier concentration = 2 × 10 ¹⁷
cm ⁻³ ) 408 to form a laminated structure 41.

The n-type clad layer 40 exposed by performing the plasma etching process on the laminated structure 41 through the patterning process using the known photolithography technique.
N type ohmic electrode 4 on the surface of 3
09 is provided. Further, a p-type ohmic electrode 410 was provided on the surface of the p-type contact layer 408 to form the LED 40.

Between both ohmic electrodes 409 and 410,
A DC voltage of 3.5 volts (V) was applied and a forward current of 20 milliamperes (mA) was passed to cause the LED 40 to emit light. The center wavelength of the emission is about 450 nm, than corresponds to the Ga _{0. 88} In _0.12 N of bandgap at room temperature which constitutes a terminating well layer 405 (about 3.1 eV), about 0.3
As a result, long wavelength light emission corresponding to a transition energy as low as 4 eV was obtained. The full width at half maximum of light emission was about 13 nm. In a chip state, the light emission intensity measured using a general integrating sphere reached about 23 microwatts (μW). That is, in this embodiment, since the termination well layer having the valence band structure bent to the low potential side is used as the light emitting layer, the emission having a longer wavelength is accompanied by
An LED was obtained which provided light emission excellent in both monochromaticity and intensity.

(Embodiment 2) In this embodiment, the present invention will be specifically described by taking as an example the case where an LED having a light emitting layer having a multiple quantum well structure (MQW) including the potential structure of the present invention is formed. Explained. FIG. 6 shows L of this embodiment.
It is a schematic diagram which shows the cross-section of ED50. Crystal substrate 40
The structure from 0 to the n-type clad layer 403 was as described in Example 1.

N-type Ga constituting the n-type cladding layer 403
An undoped n-type GaN barrier layer 500 is formed on the N layer.
Then, a light emitting layer 52 composed of a multi-quantum well structure 51b in which a pair of stacked structure units 51a were stacked for four periods, in which undoped n-type Ga _0.90 In _0.10 N was used as the well layer 501, was arranged. The layer thickness of the barrier layer 500 was about 15 nm. The layer thickness of the well layer 501 was 4 nm. Barrier layer 500
The carrier concentration of the well layer 501 is 5 × 10 ¹⁷
It is in cm ^-3 . In this MQW structure 51b, a layer joined to the n-type cladding layer 403 is an undoped n-type Ga layer.
N is the barrier layer 500, and the termination well layer 501a is an n-type G
a _0.90 In _0.10 N.

The well layers 501c and 501d and the barrier layer 5 on the n-type cladding layer 403 side after the second proximity well layer 501b, which is the next closest to the termination well layer (first proximity layer) 501a.
No measures have been taken to achieve the sharpness of the joint interface with O.00. That is, the other well layers 501c to 501d including the second proximity well layer 501b are formed so as to be temporally continuous with the barrier layer 500, and the growth interruption operation is not performed. On the other hand, when forming the termination well layer 501a that terminates the light emitting layer 52 of the MQW structure 51b, after the formation of the n-type barrier layer 500a at the final end is completed, the termination well layer 501a is continuously formed in time. 501a does not form a film, and M of the source gas is used.
The supply into the OCVD growth furnace was intentionally stopped for 4 minutes. Depending on the presence or absence of this growth interruption, the termination well layer 501
The degree of bending of the valence band at the interface of a with the n-type barrier layer 500a toward the low potential side was set to be larger than that of the other well layers 501c to 501d including the second proximity well layer 501b. By the above growth interruption operation, the transition distance regarding the indium atom concentration described in Example 1 at the junction interface between the termination well layer 501a and the n-type barrier layer 500a was set to about 12n.
m.

On the termination well layer 501a, the aluminum nitride / gallium mixed crystal (Al _0.05 Ga _0.95 N) having a layer thickness of 20 nm, which is the same as the n-type barrier layer 500a at the final end, and an aluminum composition ratio of 0.05. N-type intervening layer 50 composed of
3 was deposited. The n-type intervening layer 503 is the n-type barrier layer 500.
Although it is made of a material having substantially the same composition as that of a, the carrier concentration is less than about 2 × 10 ¹⁶ cm ^−3, which is a carrier concentration lower than that of the barrier layer 500a.

An n-type intervening layer 503 is formed on the termination well layer 501a.
During the deposition, the growth interruption time was set as described above. The growth interruption time does not have to be the same, but n
The growth interruption time before depositing the shaped intervening layer 503 was set to 4 minutes as in the above case. From this, the termination well layer 50
From the junction interface with the n-type intervening layer 503, which is required to reduce the indium atom concentration by two orders of magnitude from the average concentration in 1a, n
The distance (transition distance) into the shaped intervening layer 503 is about 13n.
m.

On the n-type intervening layer 503, the p-type cladding layer 407 and the p-type contact layer 408 described in the first embodiment are provided.
Were sequentially laminated to construct a laminated structure 51.

P produced by processing the laminated structure 51
In the n-junction type DH structure LED 50, about 3.4 to 3.5.
When a forward voltage of V was applied and a forward current of 20 mA was passed through, blue light emission with a central wavelength of light emission of about 470 nm was obtained. That is, G that constitutes the termination well layer
a _0.90 In _0.10 N has a forbidden band of about 3.1.
Emissions corresponding to a transition energy of about 2.64 eV, which is about 0.46 eV below eV, were obtained. The full width at half maximum of the emission spectrum was further narrowed to about 12 nm. The intensity of light emission in a chip state was as high as about 25 μW.

(Embodiment 3) In the present embodiment, the present invention will be specifically described by taking as an example the case of manufacturing an LED having the constituent elements described in claim 7.

In this embodiment, in forming the MQW structure having four periods described in Embodiment 2, the termination well layer 50 is used.
The layer thickness of the n-type Ga _0.90 In _0.10 N crystal layer constituting 1a is set to the second proximity well layer 501b and the subsequent well layers 50.
1c to 501d, which is a thinner layer. That is,
The layer thickness of the termination well layer 501a was 5 nm, and the layer thickness of the other well layers 501b, 501c to 501d was 10 nm. Thus, the termination well layer 501 is different from that of the second embodiment.
An LED was constructed from a laminated structure in which only the layer thickness of a was changed.

About 3.2 between the n-type and p-type ohmic electrodes.
A forward voltage of V was applied, and a forward current of about 20 mA was passed to emit light. The center wavelength of the light emission is the same as in Example 2.
The wavelength was longer than that of the LED of about 490 nm. This wavelength corresponds to Ga _0.90 In _0.10 forming the well layer.
This corresponds to a transition energy of about 2.5 eV, which is smaller by about 0.57 eV than the normal bandgap width of N about 3.1 eV. That is, even if the composition of the gallium nitride / indium mixed crystal forming the termination well layer is not changed, the light emission from the light emitting layer having the multiple quantum well structure can be made to have a long wavelength by simply reducing the layer thickness of the termination well layer. It was shown to do. In addition, the full width at half maximum of the emission spectrum was about 14 nm, and the emission intensity in the chip state reached a high value of about 27 μW after performing the luminosity correction. Than this,
It has been shown that the structure described in this example can provide a quantum well structure light emitting device which is excellent in monochromaticity and intensity and which can emit visible light of a relatively long wavelength.

Comparative Example 1 LE similar to that described in Example 3
In constructing D, that is, in fabricating an LED having the MQW structure 51b in which the layer thickness of the termination well layer 501a is thinner than the other well layers 501b to 501d,
The interface steepness at the junction interface with the barrier layer 500a and the n-type barrier layer 500b on the n-type intervening layer 503 side of the second proximity well layer 501b is improved. That is, after the growth of the n-type barrier layer 500b is completed, a growth interruption time of 1 minute is provided, and after the growth of the second proximity well layer 501b,
Similarly, by providing a growth interruption time of 1 minute, the second
The steepness of both junction interfaces related to the close well layer 501b was made substantially the same. As a result, the MQW structure 51b including the second proximity well layer 501b having the low potential portion in both the conduction band and the valence band, like the termination well layer 501a.
Was formed.

The transition distance described in Comparative Example 1, which was obtained based on the analysis result by AES, was about 15 nm at both junction interfaces regarding the second termination well layer 501b. Judging from this, the steepness was inferior by about 3 to 4 nm as compared with the transition distance of the termination well layer 501a.

In the same manner as described in Examples 1 to 3, a pn-junction type DH structure LED was prepared and evaluated for light emission characteristics. In comparison with the characteristics of the LED of Example 3, the center wavelength of light emission was about 505 nm, which was a long wavelength, due to the influence of the band inflection formed in the termination well layer. On the other hand, as shown in the emission spectrum 53 in FIG. 7, in the LED of this Comparative Example 1, in addition to the main spectrum 53a which gives the central emission wavelength, the secondary wavelength of which the central wavelength is about 480 nm is shorter than the main spectrum 53a. It was confirmed that the various spectra 53b were generated. Due to the appearance of the secondary spectrum 53b, the full width at half maximum was inferior to about 21 nm as compared with the emission spectrum 53 from the LED 50 of Example 3.

As is clear from the comparison of the emission spectra of FIG. 7, the secondary spectrum 53b is LE of Example 3.
It has not occurred from D50. On the other hand, the second proximity well layer 5
When 01b is composed of a well layer having a low potential portion at the junction interface with the barrier layers 500a and 500b, a secondary spectrum 53b that disturbs the monochromaticity of light emission appears. Therefore, such a secondary spectrum 53b is interpreted as originating from the second proximity layer 501b having the potential configuration as described above. In other words, in the light emitting layer having the multiple quantum well structure (MQW), in order to improve the light emitting characteristics such as uniformizing the light emitting wavelength or narrowing the half bandwidth of the light emitting spectrum, It was taught that the potential drop of the conduction band and the valence band in the 2-proximity well layer should be suppressed as much as possible.

(Embodiment 4) In this embodiment, in particular, a quantum well structure LED having a light emitting layer (termination well layer) having the structure described in claims 8 and 9 and having excellent emission intensity is manufactured. The present invention will be specifically described by way of example.

In constructing a laminated structure for LED use (see FIG. 5) similar to that described in Example 1, the n-type barrier layer 4 was used.
The growth interruption operation described in Example 1 was performed until the film formation of the termination well layer 405 was started after the film formation of 04 was completed.

In this embodiment, the termination well layer 405 is composed of an n-type gallium nitride / indium mixed crystal (Ga _0.82 In _0.18 N) having a multiphase structure containing oxygen. Termination well layer 4
05 is formed by using the atmospheric pressure MOCVD technique,
Mainly methoxy: about 60 ppm by weight of organic compounds obtained by adding (methoxy -OCH ₃₎ group as oxygen-containing impurity
Trimethylindium ((CH ₃ ) ₃ I
n) was used as the In source. As a result, the oxygen atom concentration is about 8
× 10 ¹⁸ cm ^-3 and indium composition ratio of 0.18
An undoped n-type Ga _0.82 In _0.18 N film was formed.

The layer thickness is about 5 nm and the carrier concentration is about 5 nm.
After the termination well layer 405 having a pressure of × 10 ¹⁷ cm ^-3 is formed at 885 ° C., the growth temperature of the next n-type intervening layer 406 is 1070 ° C. at a rate of about 100 ° C./min. The temperature was raised in minutes. The time required for this temperature rise and the MOC of the source gas
A growth interruption time of 5 minutes in total was provided in addition to 3 minutes when the supply to the VD reactor was interrupted. By providing a period of growth interruption before and after the formation of the termination well layer 405,
The steepness at the junction interface between both the n-type barrier layer 404 and the n-type intervening layer 406 was set to about 14 nm.

Then, the same p-type Al _0.15 Ga _0.85 N cladding layer 407 as in Example 1 was applied at 1070 ° C. for 3 minutes.
Has grown up. p-type Al _0.15 Ga _0.85 N cladding layer 40
7, followed by aluminum composition ratio (=
X) from 0.15 to 0 toward the surface with a compositional gradient of p-type Al _x Ga ₁ -x N (X = 0.15 → 0)
The contact layer 408 was grown. p-type contact layer 40
After the film formation of No. 8 was completed, it was cooled to 950 ° C. at a rate of about 40 ° C. per minute. Continuously from 950 ℃ to 650 ℃ 15 ℃
Cooled at a rate of / min. The termination well layer 405 is subjected to such two stages of cooling with different cooling rates, and the termination well layer 4
No. 05 was a crystal layer having a multi-phase structure having different indium composition ratios.

FIG. 8 is a transmission electron microscope (TEM) image showing the crystal structure inside the termination well layer 405 after the above cooling process. The termination well layer 405 is
Ga _1-X I with indium composition ratio (= X) of 2 to 3%
The main phase S composed of n _X N and the indium composition ratio of about 15
It has a multi-phase structure including a dependent phase T composed of a Ga _{1 -X} In _X N microcrystal of about 25%. Subject phase S
The existence of a region U containing lattice strain, which is considered to occur due to the difference in lattice constant due to the difference in indium composition ratio between the two, was recognized in many of the boundary regions between and the dependent phase T. Further, the oxygen atom concentration in the termination well layer 405 is
Since the detection sensitivity was poorer than that of heavy metals, accurate quantification was not possible. However, oxygen is contained in the phase regions of both the main phase S and the subordinate phase T, and is strong,
It seems that there are more inside the subordinate phase T.

A quantum well structure LED was produced in the same manner as in Example 1. The emission wavelength is about 45 from the LED.
Emission in the blue-green band at 0 nm was emitted. This is about 0.34 eV compared with about 3.0 eV which is the original band gap of Ga _0.82 In _0.18 N forming the termination well layer.
The emission was equivalent to low transition energy. Further, the full width at half maximum of the emission spectrum was about 12 nm. While no significant difference was observed in these characteristics from that of the LED of Example 1, the emission intensity was
Of about 30 μW, which is about 30% higher than that of From this, in the first place, the termination well layer composed of Ga _{1 -X} In _X N having a multiphase structure, in which the indium composition ratio capable of maintaining high crystallinity is 0.3 or less, and which contains an appropriate amount of oxygen,
In particular, to provide a quantum well structure light emitting device with high emission intensity,
It was shown to be effective.

[0094]

According to the invention described in claim 1, the indium-containing group III having a high indium composition ratio and inferior crystallinity is exhibited while exhibiting the original characteristics of the quantum well structure which produces light emission excellent in monochromaticity. Even if the nitride semiconductor layer is not intentionally used as a light emitting layer, a bend in the band toward the lower potential side, which is convenient for promoting a longer wavelength of light emission at the junction surface of the termination well layer with the n-type intervening layer, is generated. Therefore, there is an effect that a quantum well structure light emitting device which is convenient for increasing the wavelength of light emission can be provided.

According to the inventions of claims 2 and 3, in addition to the invention of claim 1, the well layer at the end is an n-type barrier layer and an n-type barrier layer.
Since it is sandwiched between the interposing intermediate layers and has a structure that is convenient for causing band bending in the termination well layer, there is an effect that a quantum well structure light emitting device that is convenient for increasing the wavelength of light emission can be provided.

According to the fourth aspect of the present invention, since the holes can be effectively accumulated in the low potential part of the valence band, a transition energy smaller than the regular band gap is given,
There is an effect that it is possible to provide a quantum structure light emitting device having a structure that is particularly convenient for increasing the wavelength of light emission.

According to the fifth aspect of the invention, the degree of bending of both the conduction band and the valence band, which works well to secure the steepness at the junction interface and shift the emission wavelength to the longer wavelength side. As a result, the carrier transition energy is further reduced, and there is an effect that a quantum well light emitting device which is convenient for providing long wavelength light emission can be provided. In particular, according to the invention of claim 7, since the termination well layer is composed of a thinner layer that can more easily develop a longer wavelength of light emission due to band bending due to the steepness of the junction interface, Provided is a quantum well light emitting device that can easily achieve a longer wavelength.

According to the sixth aspect of the invention, in the multiple quantum structure, the degree of bending of both the conduction band and the valence band in the termination well layer is compared with that of other well layers. Since the expansion of the nonuniformity of the transition energy between carriers is suppressed, the quantum well structure light emitting device which is particularly excellent in monochromaticity and provides long-wavelength light emission can be provided.

According to the eighth aspect of the present invention, the termination well layer of the quantum well structure is not a single composition but a multi-phase structure having different indium compositions, and the indium composition ratio which does not significantly deteriorate the crystallinity is set. Since it is composed of gallium-indium nitride having a low indium composition ratio of 0.3 or less, high intensity light emission is brought about, and therefore, there is an effect that a quantum well structure light emitting device with high brightness can be provided.

Further, in the invention described in claim 9, as described in the invention of claim 8, the composition ratio of indium is low, and
In forming a termination well layer from a gallium nitride / indium mixed crystal having a multi-phase structure, a quantum well structure light emitting device further excellent in emission intensity is obtained, especially because the concentration of oxygen atoms contained in the well layer is set to an appropriate amount. There is an effect that can be provided.

[Brief description of drawings]

FIG. 1 is a diagram showing an energy band structure of a pn junction type DH structure light emitting part including a light emitting layer having a single quantum well (SQW) structure.

FIG. 2 is a diagram showing an energy band structure of a pn junction type DH structure light emitting part including a light emitting layer having a multiple quantum well (MQW) structure.

FIG. 3 is a diagram showing a potential configuration in the SQW structure according to the present invention.

FIG. 4 is a diagram showing a potential configuration in the MQW structure according to the present invention.

FIG. 5 is a schematic sectional view of the LED of Example 1.

FIG. 6 is a schematic diagram of a cross-sectional structure of an LED of Example 2.

7 is an emission spectrum of the LED described in Example 3 and Comparative Example 1. FIG.

FIG. 8 is a schematic diagram of a TEM image showing a crystal structure inside a termination well layer described in Example 4.

FIG. 9 is a diagram showing a basic energy band structure of a conventional single quantum well (SQW) structure.

FIG. 10 is a diagram showing a rectangular potential configuration of an energy band structure of an SQW structure.

[Explanation of symbols]

010, 011, 10, 404, 500, 500a, 5
00b: barrier layers 012, 11, 11a, 11b, 11c, 11d, 11
e, 501a, 501b, 501c, 501d: Well layers 013, 24: Original band gap 014, 015 of barrier layer material: Barrier layer band gap 016: Potential well 017, 16: Conduction band 018 , 20: Valence band 019, 020: Quantum level 021, 022 formed on the conduction band side: Quantum levels 023, 024, 23 formed on the valence band side: Transition energy 1: Light emitting part 1a: Light emission Layer 1b: Single quantum well 1d: Multiple quantum wells 11a, 405, 501a: Termination well layers 11b, 501b: Second proximity well layers 12, 406, 503: Intervening layers 13, 403: N-type cladding layers 14, 407: p-type cladding layers 15a and 43: junction interface 15b between the termination well layer and the intervening layer 15b: junction interface between the termination well layer and the barrier layer 15c: contact between the second proximity well layer and the barrier layer on the interposition layer side Interface 15d: Junction interface between second proximity well layer and barrier layer 16a: Conduction band level (Eco) 16b: Conduction band bend edge (Ec) 16c: Conduction band potential difference 17: Fermi level 18: Conduction band side Low potential part 19: electron 20a: valence band level (Evo) 20b: bent edge (Ev) of valence band 20c: valence band potential difference 21: valence band side low potential part 22: hole 25a: Deflection degree on the conduction band side in the termination well layer 25b: Deflection degree on the valence band side in the termination well layer 25c: Deflection degree on the conduction band side in the second proximity well layer 25d: Second proximity well layer Degree of bending on the side of the valence band 40, 50: LED 41, 51: laminated structure 400: crystal substrate 401: buffer layer 402: n-type GaN layer 408: contact layer 409: n-type ohmic electrode 410: p-type ohmic electrode 51a: quantum well constituent unit 51b: multiple quantum well structure 52: light emitting layers 53, 54: emission spectrum 53a: main emission spectrum 53b: secondary emission spectrum S: main phase T: dependent phase U: strain Area of inclusion

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Claims (8)

(57) [Claims] 1. A pn-junction double hetero (DH) having an n-type light emitting layer formed on one surface of a crystal substrate and sandwiched between n-type and p-type clad layers composed of a group III nitride semiconductor crystal layer. ) in the light-emitting device of the structure, the n-type emitting layer may have a multiplex quantum well structure, the well layer constituting the end of the quantum well structure (end well layer)
Intermediate between the p-type cladding layer, an intervening layer of n-type Group III nitride semiconductor are arranged, the layer thickness of the termination well layer, not more than the thickness of the other well layer, and the termination wells In a region of the layer near the junction interface between the n-type intervening layer and the termination well layer, the conduction band of the termination well layer is bent downward toward the Fermi level toward the low potential side. Indium (In) -containing n-type II with potential configuration
A quantum well structure light emitting device comprising a group I nitride semiconductor crystal layer. 2. The termination well layer is sandwiched between the n-type intermediate layer and an n-type barrier layer facing the n-type intermediate layer with the termination well layer interposed therebetween. Item 2. A quantum well structure light emitting device according to item 1. 3. The quantum well structure light emitting device according to claim 2, wherein the n-type barrier layer has substantially the same composition and substantially the same layer thickness as the n-type intervening layer. 4. The termination well layer is a low potential region in which a valence band of the termination well layer is bent upward toward a Fermi level in a region near a junction interface with the n-type barrier layer. It has, The quantum well structure light emitting element of Claim 2 or 3 characterized by the above-mentioned. 5. The energy difference (ΔEc) between the original potential level (Eco) of the conduction band and the low potential edge (Ec) dropped to the Fermi level side in the termination well layer.
= | Eco-Ec |) and the energy difference (ΔEv = |) between the original potential level (Evo) of the valence band and the low potential edge (Ev) that has dropped to the Fermi level side.
Evo-Ev |) total energy difference (ΔEc + Δ)
5. The quantum well structure light emitting device according to claim 4, wherein Ev) has a bending of a conduction band and a valence band of 0.4 electron volt (eV) or more. 6. Before Symbol termination well layer, according to claim 4 or 5, characterized in that a larger than the energy difference between the sum of the energy difference between the sum of the (ΔEc + ΔEv) other well layer
2. A quantum well structure light emitting device according to. 7. The indium composition ratio (=
N-type nitriding of a multi-phase structure including a main phase having X) of 0.3 or less and a dependent phase having a indium composition ratio different from that of the main phase and having a strained layer present in a junction boundary region with the main phase. gallium·
Indium _{(Ga 1-X In X N} : 0 ≦ X ≦ 0.3) quantum well structure light emitting device according to any one of claims 1 to 6, characterized in that consisted. 8. An n _-type Ga _{1 -X} In _X N having an oxygen atom concentration of 5 × 10 ¹⁷ cm ^-3 or more and 5 × 10 ²⁰ cm ^-3 or less in the termination well layer having the multiphase structure. The quantum well structure light emitting device according to claim 7 , wherein the quantum well structure light emitting device is composed of a (0 ≦ X ≦ 0.3) crystal.