JP4449296B2 - GaN-based semiconductor light emitting device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor light emitting element and a semiconductor device, and is particularly suitable for application to a semiconductor laser, a light emitting diode, or an electron transit element using a nitride III-V group compound semiconductor.
[0002]
[Prior art]
In recent years, research and development of semiconductor lasers using nitride-based III-V compound semiconductors such as AlGaInN as active semiconductor lasers capable of emitting light from the blue region to the ultraviolet region, which are necessary for increasing the density of optical disks, have been actively conducted. Has already been put to practical use (for example, see Patent Document 1).
[0003]
[Patent Document 1]
Japanese Patent Laid-Open No. 9-219556
[0004]
[Problems to be solved by the invention]
However, the semiconductor laser using the nitride III-V compound semiconductor has a problem that the contact resistance of the p-side electrode is high, which is an obstacle to reducing the operating voltage. The contact resistance of the p-side electrode is high because, in the p-type layer with which the p-side electrode contacts, the activation rate of Mg used as the p-type impurity is low and the hole concentration is low, so that the specific resistance is high. It is a cause.
Therefore, the problem to be solved by the present invention is to provide a semiconductor light emitting element and a semiconductor device capable of reducing the operating voltage.
[0005]
[Means for Solving the Problems]
In order to solve the above problems, the first invention of the present invention is:
In a semiconductor light emitting device using a nitride III-V compound semiconductor,
The contact portion of the electrode on the first conductivity type side is composed of a first conductivity type first layer, a second conductivity type second layer, and a first conductivity type third layer in this order from the electrode side. Have structure
It is characterized by this.
[0006]
The second invention of this invention is:
In a semiconductor device using a nitride III-V compound semiconductor,
The contact portion of the electrode on the first conductivity type side has a laminated structure composed of a first layer of the first conductivity type, a second layer of the second conductivity type, and a third layer of the first conductivity type.
It is characterized by this.
[0007]
In the first and second aspects of the present invention, the thickness of the second layer must be sufficiently thin so that holes or electrons can easily pass through the second layer by the tunnel effect. Therefore, it is preferably selected to be 10 nm or less. Typically, the first layer, the second layer, and the third layer have different compositions from each other. These first layer, second layer, and third layer can be basically composed of various materials including nitride-based III-V group compound semiconductors. In particular, Al _X Ga _1-xz In _z N (however, 0 ≦ x ≦ 1, 0 ≦ z ≦ 1). Also, since the contact resistance of the p-side electrode is the most problematic, when the application of the present invention is particularly effective, the first layer is a p-type layer, the second layer is an n-type layer, and a third layer Is a p-type layer. In this case, preferably, the band gap of the first layer and the second layer, particularly the first layer in contact with the p-side electrode is selected to be smaller than the band gap of the third layer. This is because the acceptor level generally decreases as the band gap decreases, and as a result, the carrier concentration (hole concentration) increases. In this case, typically, the p-type layer constituting the first layer and the p-type layer constituting the third layer are doped with Mg as a p-type impurity, and n constituting the second layer. The mold layer is doped with Si as an n-type impurity, preferably both Mg and Si are 1 × 10 ¹⁸ cm ^-3 Dope to the above concentration. The first layer is Ga _p In _1-p N _q As _1-q (However, 0 ≦ p ≦ 1, 0 ≦ q ≦ 1), and the second layer and the third layer are made of Al. _X Ga _1-xz In _z You may comprise by N (however, 0 <= x <= 1, 0 <= z <= 1). Furthermore, the first layer is In _1-s Ga _s As (where 0 ≦ s ≦ 1) and the second layer is GaSb _1-r As _r (Where 0 ≦ r ≦ 1), and the third layer is made of Al _X Ga _1-xz In _z You may comprise by N (however, 0 <= x <= 1, 0 <= z <= 1).
[0008]
Nitride III-V compound semiconductors are most commonly Al _X B _y Ga _1-xyz In _z As _u N _1-uv P _v (However, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1, 0 ≦ u ≦ 1, 0 ≦ v ≦ 1, 0 ≦ x + y + z <1, 0 ≦ u + v <1), more specifically Al _X B _y Ga _1-xyz In _z N (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1, 0 ≦ x + y + z <1), typically Al _X Ga _1-xz In _z N (however, 0 ≦ x ≦ 1, 0 ≦ z ≦ 1). Specific examples of the nitride III-V compound semiconductor include GaN, InN, AlN, AlGaN, InGaN, and AlGaInN.
[0009]
The semiconductor light emitting element is a semiconductor laser or a light emitting diode. In addition to the semiconductor light emitting element, the semiconductor device may be an electron traveling element such as a field effect transistor (FET) or a heterojunction bipolar transistor (HBT).
[0010]
The third invention of the present invention is:
The contact portion of the electrode on the first conductivity type side has a laminated structure including a first conductivity type first layer, a second conductivity type second layer, and a first conductivity type third layer.
This is a semiconductor light emitting element.
[0011]
The fourth invention of the present invention is:
The contact portion of the electrode on the first conductivity type side has a laminated structure including a first conductivity type first layer, a second conductivity type second layer, and a first conductivity type third layer.
This is a semiconductor device.
[0012]
In the third and fourth aspects of the present invention, what has been described in relation to the first and second aspects of the invention is valid as long as it is not contrary to the nature thereof.
[0013]
In the third and fourth inventions of the present invention, the semiconductor layer may be basically any type. Specifically, for example, in addition to a nitride-based III-V compound semiconductor, It is a layer of various III-V group compound semiconductors such as AlGaAs-based semiconductors, AlGaInP-based semiconductors, InGaAsP-based semiconductors, GaInNAs-based semiconductors, or II-VI group compound semiconductors such as ZnSe-based semiconductors and ZnO-based semiconductors.
[0014]
According to the present invention configured as described above, the contact portion of the electrode on the first conductivity type side includes, in order from the electrode side, the first layer of the first conductivity type and the second layer of the second conductivity type. When a voltage is applied to the electrode during operation by having a laminated structure composed of the third layer of the first conductivity type, that is, a pnp structure or an npn structure, holes or electrons injected from the electrode to the first layer Passes through the second layer by the tunnel effect and enters the third layer. In this case, the energy of holes or electrons entering the third layer is higher than in the case where the contact portion of the electrode is composed of only the first conductivity type layer as in the prior art.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings of the embodiments, the same or corresponding parts are denoted by the same reference numerals.
FIG. 1 shows a GaN semiconductor laser according to the first embodiment of the present invention. This GaN-based semiconductor laser has a ridge structure and an SCH (Separate Confinement Heterostructure) structure. FIG. 2 is an enlarged view of the vicinity of the ridge portion of the GaN-based semiconductor laser.
[0016]
As shown in FIG. 1, in the GaN semiconductor laser according to the first embodiment, a lateral crystal growth technique (for example, Applied Physics Letters vol. 75 (1999) pp. 196-198), a GaN-based semiconductor layer is stacked. Specifically, on one main surface of the c-plane sapphire substrate 1, a stripe composed of an undoped GaN buffer layer 2 and an undoped GaN layer 3 formed thereon is formed and extends in the <1-100> direction. The n-type GaN contact layer 4 is grown as a continuous layer using the striped undoped GaN layer 3 as a seed crystal. Here, the surface layer portion of the c-plane sapphire substrate 1 on both sides of the stripe is also removed, and in this portion, the n-type GaN contact layer 4 has a structure floating from the c-plane sapphire substrate 1. Then, on this n-type GaN contact layer 4, an n-type AlGaN cladding layer 5, an undoped InGaN optical waveguide layer 6 as an n-side optical waveguide layer, for example, undoped In _x Ga _1-x N / In _y Ga _1-y An active layer 7 having an N multiple quantum well structure, an undoped InGaN optical waveguide layer 8 as a p-side optical waveguide layer, an undoped AlGaN cladding layer 9 as a p-side cladding layer, an undoped InGaN layer 10, a p-type AlGaN electron blocking layer 11, p A p-type AlGaN / GaN superlattice cladding layer 12, an n-type AlGaInN layer 13, and a p-type AlGaInN layer 14 are sequentially stacked as side cladding layers. In this case, the p-type AlGaInN layer 14, the n-type AlGaInN layer 13, and the p-type AlGaN / GaN superlattice cladding layer 12 form a pnp structure of the contact portion of the p-side electrode. The undoped InGaN optical waveguide layer 6, the undoped InGaN optical waveguide layer 8, the undoped AlGaN cladding layer 9, and the undoped InGaN layer 10 are all n ^- It is a type. The reason why the p-type AlGaN / GaN superlattice cladding layer 12 is used as the p-side cladding layer is to facilitate the passage of holes by the tunnel effect.
[0017]
Here, the undoped GaN buffer layer 2 has a thickness of, for example, 30 nm. The undoped GaN layer 3 has a thickness of 2 μm, for example. The n-type GaN contact layer 4 has a thickness of, for example, 4 μm, and is doped with, for example, silicon (Si) as an n-type impurity. The n-type AlGaN cladding layer 5 has a thickness of, for example, 1.5 μm, is doped with, for example, Si as an n-type impurity, and has an Al composition of, for example, 5.5% (0.055). The undoped InGaN optical waveguide layer 6 has a thickness of, for example, 30 nm and an In composition of, for example, 2% (0.02). Undoped In _x Ga _1-x N / In _y Ga _1-y The active layer 7 having an N multiple quantum well structure is composed of In as a barrier layer. _x Ga _1-x In as N layer and well layer _y Ga _1-y N layers are alternately stacked. For example, In as a barrier layer _x Ga _1-x N layer thickness is 7 nm, x = 0.02, In as well layer _y Ga _1-y The thickness of the N layer is 3.5 nm, y = 0.08, and the number of wells is 3.
[0018]
The undoped InGaN optical waveguide layer 8 has a thickness of, for example, 30 nm and an In composition of, for example, 2% (0.02). The undoped AlGaN cladding layer 9 has a thickness of, for example, 100 nm and an Al composition of, for example, 2.5% (0.025). The undoped InGaN layer 10 has a thickness of, for example, 5 nm and an In composition of, for example, 2% (0.02).
[0019]
The p-type AlGaN electron blocking layer 11 has a thickness of, for example, 10 nm, an Al composition of, for example, 18% (0.18), and the concentration of Mg doped as a p-type impurity is, for example, 1 × 10 ¹⁹ / Cm ^Three ~ 1x10 ^{twenty one} / Cm ^Three It is.
[0020]
The p-type AlGaN / GaN superlattice cladding layer 12 uses, for example, an undoped AlGaN layer with a thickness of 2.5 nm as a barrier layer, and has a thickness of 2.5 nm and Mg of 5 × 10 5, for example. ¹⁹ / Cm ^Three The doped GaN layer is a well layer, and these are alternately stacked. The average Al composition is, for example, 4.5% (0.045), and the total thickness is, for example, 400 nm. The n-type AlGaInN layer 13 preferably has a thickness of 10 nm or less, for example, 5.0 nm, an Al composition of, for example, 7% (0.07), and an In composition of, for example, 3% (0.03). For example, Si is 1 × 10 ¹⁹ / Cm ^Three Doped. The p-type AlGaInN layer 14 has a thickness of, for example, 50 nm, an Al composition of, for example, 5% (0.05), an In composition of, for example, 15% (0.15), and Mg as a p-type impurity, for example, 2 × 10. ²⁰ / Cm ^Three Doped.
[0021]
The layers from the upper part to the upper part of the n-type GaN contact layer 4 have a mesa shape with a predetermined width as a whole, and further, the p-type AlGaN / GaN superlattice cladding layer 12, the n-type AlGaInN layer 13 and the p-type in this mesa part. For example, a ridge extending in the <1-100> direction is formed in the AlGaInN layer 14. The width of this ridge is, for example, 1.5 μm. Here, the ridge, that is, the laser stripe portion, is located in a low defect region between the dislocation 15 propagated from the seed crystal of the lateral crystal growth to the upper layer and the meeting portion 16 of the lateral growth from the adjacent seed crystals. is doing.
[0022]
For example, SiO having a thickness of 40 nm so as to cover the entire mesa portion. ₂ An insulating film 17 such as a film and a Si film 18 having a thickness of 45 nm, for example, are sequentially provided. Here, the insulating film 17 is for electrical insulation and surface protection. The Si film 18 is for increasing the absorption coefficient of the first-order mode of the laser beam that causes the kink phenomenon at the side wall portion of the ridge and preventing the kink phenomenon. An opening 19 is provided in a portion of the insulating film 17 and the Si film 18 on the ridge, and the p-side electrode 20 is in contact with the p-type AlGaInN layer 14 through the opening 19. The p-side electrode 20 has a structure in which a Pd film, a Pt film, and an Au film are sequentially laminated. The thicknesses of the Pd film, the Pt film, and the Au film are, for example, 10 nm, 100 nm, and 300 nm, respectively. On the other hand, an opening 21 is provided in a predetermined portion adjacent to the mesa portion of the insulating film 17 and the Si film 18, and the n-side electrode 22 is in contact with the n-type GaN contact layer 4 through the opening 21. The n-side electrode 22 has a structure in which a Ti film, a Pt film, and an Au film are sequentially laminated. The thicknesses of the Ti film, the Pt film, and the Au film are, for example, 10 nm, 50 nm, and 100 nm, respectively.
[0023]
Next, a method of manufacturing the GaN semiconductor laser according to the first embodiment will be described.
First, an undoped GaN buffer layer 2 is grown on a c-plane sapphire substrate 1 whose surface is previously cleaned by thermal cleaning or the like at a temperature of about 500 ° C. by a metal organic chemical vapor deposition (MOCVD) method. For example, the undoped GaN layer 3 is grown at a growth temperature of 1000 ° C. by the method.
[0024]
Next, on the entire surface of the undoped GaN layer 3, for example, a SiO film having a thickness of 100 nm is formed by, for example, a CVD method, a vacuum evaporation method, a sputtering method, or the like. ₂ After forming a film (not shown), this SiO ₂ A resist pattern (not shown) having a predetermined shape is formed on the film by lithography, and using this resist pattern as a mask, for example, wet etching using a hydrofluoric acid-based etchant or CF _Four And CHF _Three SiO by RIE method using etching gas containing fluorine such as ₂ The film is etched and patterned. Next, this predetermined shape of SiO ₂ Etching is performed until the surface layer portion of the c-plane sapphire substrate 1 is removed by, for example, the RIE method using the film as a mask. As this RIE etching gas, for example, a chlorine-based gas is used. By this etching, a stripe-shaped undoped GaN layer 3 serving as a seed crystal is formed. The extending direction of the stripe-shaped undoped GaN layer 3 is the <1-100> direction.
[0025]
Next, SiO used as an etching mask ₂ After the film is removed by etching, the n-type GaN contact layer 4 is grown by the above-described lateral crystal growth technique using the stripe-shaped undoped GaN layer 3 as a seed crystal. The growth temperature at this time is set to 1070 ° C., for example.
[0026]
Subsequently, an n-type AlGaN cladding layer 5, an undoped InGaN optical waveguide layer 6, an undoped Ga layer are formed on the n-type GaN contact layer 4 by MOCVD. _1-x In _x N / Ga _1-y In _y N multiple quantum well structure active layer 7, undoped InGaN optical waveguide layer 8, undoped AlGaN cladding layer 9, undoped InGaN layer 10, p-type AlGaN electron blocking layer 11, p-type AlGaN / GaN superlattice cladding layer 12, n-type AlGaInN Layer 13 and p-type AlGaInN layer 14 are grown sequentially. Here, the growth temperature of these layers is, for example, 900 to 1000 ° C. for the n-type AlGaN cladding layer 5, 780 ° C. from the undoped InGaN optical waveguide layer 6 to the p-type AlGaN electron blocking layer 11, and over p-type AlGaN / GaN. The lattice cladding layer 12 to the p-type AlGaInN layer 14 are set to 900 to 1000 ° C.
[0027]
The growth source of these GaN-based semiconductor layers is, for example, trimethylgallium ((CH _Three ) _Three As a raw material for Ga, TMG), and Al, trimethylaluminum ((CH _Three ) _Three As raw materials for Al, TMA), and In, trimethylindium ((CH _Three ) _Three In, TMI), NH as a raw material of N _Three Is used. As for the dopant, examples of the n-type dopant include silane (SiH _Four ) As a p-type dopant, for example, bis = methylcyclopentadienylmagnesium ((CH _Three C _Five H _Four ) ₂ Mg) or bis = cyclopentadienylmagnesium ((C _Five H _Five ) ₂ Mg) is used.
[0028]
As the carrier gas atmosphere during the growth of these GaN-based semiconductor layers, the n-type GaN contact layer 4 and the n-type AlGaN cladding layer 5 are N ₂ And H ₂ The gas from the undoped InGaN optical waveguide layer 6 to the p-type AlGaN electron blocking layer 11 is N ₂ Gas atmosphere, p-type AlGaN / GaN superlattice cladding layer 12 is N ₂ And H ₂ The n-type AlGaInN layer 13 and the p-type AlGaInN layer 14 are N ₂ A gas atmosphere is used. In this case, the carrier gas atmosphere is N in the growth from the undoped InGaN optical waveguide layer 6 to the p-type AlGaN electron block layer 11. ₂ The atmosphere is H and the carrier gas atmosphere is H ₂ Is not included, it is possible to suppress the separation of In from the undoped InGaN optical waveguide layer 6, the active layer 7, the undoped InGaN optical waveguide layer 8 and the undoped InGaN layer 10, and to prevent the deterioration of these layers. Can do. Similarly, in the growth of the n-type AlGaInN layer 13 and the p-type AlGaInN layer 14, the carrier gas atmosphere is changed to N. ₂ The atmosphere is H and the carrier gas atmosphere is H ₂ Is not contained, it is possible to suppress the separation of In from the n-type AlGaInN layer 13 and the p-type AlGaInN layer 14 and to prevent the deterioration of these layers. Further, the carrier gas atmosphere is changed to N when the p-type AlGaN / GaN superlattice cladding layer 12 is grown. ₂ And H ₂ Therefore, the p-type AlGaN / GaN superlattice cladding layer 12 can be grown with good crystallinity.
[0029]
Next, the c-plane sapphire substrate 1 on which the GaN-based semiconductor layer is grown as described above is taken out from the MOCVD apparatus. Then, the entire surface of the p-type AlGaInN layer 14 is formed by, for example, CVD, vacuum deposition, sputtering or the like with a thickness of 0.1 μm, for example. ₂ After forming a film (not shown), this SiO ₂ A resist pattern (not shown) having a predetermined shape corresponding to the shape of the mesa portion is formed on the film by lithography, and using this resist pattern as a mask, for example, wet etching using a hydrofluoric acid-based etching solution, or CF _Four And CHF _Three SiO by RIE method using etching gas containing fluorine such as ₂ The film is etched and patterned. Next, this predetermined shape of SiO ₂ Etching is performed using the film as a mask until the n-type GaN contact layer 4 is reached by, for example, RIE. As this RIE etching gas, for example, a chlorine-based gas is used. By this etching, the upper layer portion of the n-type GaN contact layer 4, the n-type AlGaN cladding layer 5, the undoped InGaN optical waveguide layer 6, the active layer 7, the undoped InGaN optical waveguide layer 8, the undoped AlGaN cladding layer 9, the undoped InGaN layer 10, The p-type AlGaN electron block layer 11, the p-type AlGaN / GaN superlattice cladding layer 12, the n-type AlGaInN layer 13 and the p-type AlGaInN layer 14 are patterned into a mesa shape.
[0030]
Next, SiO used as an etching mask ₂ After the film is removed by etching, the entire surface of the substrate is again formed on the entire surface of the substrate by, for example, a CVD method, a vacuum deposition method, a sputtering method, etc. ₂ After forming a film (not shown), this SiO ₂ A resist pattern (not shown) having a predetermined shape corresponding to the ridge portion is formed on the film by lithography, and using this resist pattern as a mask, for example, wet etching using a hydrofluoric acid-based etching solution or CF _Four And CHF _Three SiO by RIE method using etching gas containing fluorine such as ₂ The film is etched to have a shape corresponding to the ridge portion.
[0031]
Next, this SiO ₂ A ridge is formed by etching to a depth just before the p-type AlGaN electron block layer 11 by the RIE method using the film as a mask. As this RIE etching gas, for example, a chlorine-based gas is used.
[0032]
Next, SiO used as an etching mask ₂ After removing the film by etching, the entire surface of the substrate is made of SiO, for example, by CVD, vacuum deposition, sputtering, or the like. ₂ An insulating film 17 such as a film and a Si film 18 are sequentially formed.
[0033]
Next, a resist pattern (not shown) that covers the surface of the Si film 18 in a region excluding the n-side electrode formation region is formed by lithography.
Next, the opening 21 is formed by etching the Si film 18 and the insulating film 17 using this resist pattern as a mask.
[0034]
Next, a Ti film, a Pt film, and an Au film are sequentially formed on the entire surface of the substrate with the resist pattern remaining, for example, by vacuum deposition, and then the resist pattern is formed on the Ti film, the Pt film, and the Au formed thereon. Remove with film (lift-off). As a result, the n-side electrode 22 that is in contact with the n-type GaN contact layer 4 through the opening 21 of the insulating film 17 and the Si film 18 is formed. Next, the alloy process for making the n side electrode 22 ohmic-contact is performed.
[0035]
Next, in the same process, the Si film 18 and the insulating film 17 on the ridge are removed by etching to form an opening 19, and then the p-type AlGaInN layer is formed through the opening 19 in the same manner as the n-side electrode 22. A p-side electrode 20 having a Pd / Pt / Au structure in contact with 14 is formed.
[0036]
After that, the substrate on which the laser structure is formed as described above is processed into a bar shape by cleaving or the like to form both resonator end faces, and after applying end face coating to these resonator end faces, A chip is formed by cleavage. Here, the resonator length is, for example, L = 600 μm, and the rear end face reflectance is, for example, R. _r = 0.95, the front end surface reflectance is, for example, R _f = 0.1.
As described above, the GaN-based semiconductor laser having the target ridge structure and SCH structure is manufactured.
[0037]
Next, the operation of this GaN semiconductor laser will be described. FIG. 3 shows a simplified energy band diagram during operation of the GaN-based semiconductor laser. In FIG. 3, E _c Is the energy at the bottom of the conduction band, E _v Is the energy at the top of the valence band, E _F Indicates Fermi energy.
[0038]
Consider the operation of the GaN-based semiconductor laser with reference to FIG. The energy of the holes when the n-type AlGaInN layer 13 is not inserted into the contact portion of the p-side electrode 20 is qV ₁ On the other hand, the energy of holes when the n-type AlGaInN layer 13 is inserted into the contact portion of the p-side electrode 20 as in the first embodiment is qV. ₂ It is. However, q shows the electric charge of a hole. A forward voltage is applied between the p-side electrode 20 and the n-side electrode 22, and V is applied between the p-type AlGaInN layer 14 and the n-type AlGaInN layer 13. ₁ When the n-type AlGaInN layer 13 is inserted into the contact portion of the p-side electrode 20 as in the first embodiment, the p-type AlGaInN layer 14 is injected from the p-side electrode 20. When the holes reach the n-type AlGaInN layer 13, qV ₂ -QV ₁ = Q (V ₂ -V ₁ ) = Energy increases by qΔV. The holes that have reached the n-type AlGaInN layer 13 pass through the n-type AlGaInN layer 13 at a high speed by the tunnel effect while being retained, and are injected into the p-type AlGaN / GaN superlattice cladding layer 12. That is, compared with the case where the n-type AlGaInN layer 13 is not inserted, the energy of holes injected into the p-type AlGaN / GaN superlattice cladding layer 12 is increased by qΔV, and thus the p-type AlGaN / GaN superlattice cladding layer is increased. The tunneling probability of holes passing through 12 by the tunnel effect is greatly increased. In other words, V V is between the p-type AlGaInN layer 14 and the n-type AlGaInN layer 13. ₁ When the voltage of ₁ + ΔV = V ₂ This means that an effect equivalent to that of the above-described voltage can be obtained, and the operating voltage can be reduced by ΔV.
[0039]
According to the first embodiment, the following various advantages can be obtained. That is, since the pnp structure including the p-type AlGaInN layer 14, the n-type AlGaInN layer 13, and the p-type AlGaN / GaN superlattice cladding layer 12 is formed in the contact portion of the p-side electrode 20, the operation is performed as described above. The voltage can be reduced.
[0040]
In addition, according to the first embodiment, the p-side cladding layer has an undoped AlGaN cladding layer 9 having a thickness of, for example, 105 nm and a p-type AlGaN / GaN superlattice cladding layer having a thickness of, for example, 400 nm in order from the active layer 7 side. 12, the operating voltage of the GaN-based semiconductor laser is, for example, about 0 compared to the case where the entire p-side cladding layer is composed of the p-type AlGaN / GaN superlattice cladding layer 12 having the total thickness. .16V can also be reduced. Further, since the total thickness of the p-side cladding layer is about 500 nm and is sufficiently large, the p-side light can be sufficiently confined, and a good far-field image (Far Field Pattern, FFP) can be obtained. That is, the thickness of the p-type AlGaN / GaN superlattice cladding layer 12 having a high specific resistance that causes an increase in operating voltage while ensuring the thickness of the p-side cladding layer necessary for obtaining good optical characteristics. The operating voltage can be reduced by reducing the thickness by about 100 nm.
[0041]
Further, the distance between the active layer 7 and the p-type layer doped with Mg, that is, the p-type AlGaN electron blocking layer 11, the p-type AlGaN / GaN superlattice cladding layer 12, and the p-type AlGaInN layer 14 is the undoped InGaN optical Since the total thickness of the wave layer 8, the undoped AlGaN cladding layer 9 and the undoped InGaN layer 10 is, for example, 30 nm + 100 nm + 5 nm = 135 nm, Mg in the p-type layer diffuses into the active layer 7 during crystal growth or aging. Can be effectively suppressed, whereby deterioration of the active layer 7 due to Mg diffusion can be prevented, aging degradation rate of the GaN-based semiconductor laser can be reduced, and reliability and yield can be improved. Can be planned.
[0042]
Further, since there is an undoped AlGaN cladding layer 9 which is a lattice strained layer between the active layer 7 and the p-type layer doped with Mg, this also prevents the Mg in the p-type layer from diffusing into the active layer 7. It is possible to suppress the deterioration of the active layer 7 more effectively.
[0043]
In addition, the p-type layer doped with Mg generally has lower crystallinity than the n-type layer and is likely to absorb light. Therefore, when the p-type layer is in the vicinity of the active layer 7, the light absorption coefficient α increases. However, since the active layer 7 and the p-type layer are separated by 135 nm as described above, α in the vicinity of the active layer 7 can be suppressed sufficiently low. As a result, the threshold current density J of the GaN-based semiconductor laser _th Therefore, the threshold current I _th Can be reduced, and the slope efficiency can be improved. Furthermore, since the p-type layer doped with Mg having poor crystallinity is sufficiently separated from the vicinity of the active layer 7 having a high light density as described above, the crystal near the active layer 7 is hardly deteriorated by light. The lifetime and reliability of the GaN-based semiconductor laser can be improved.
[0044]
Further, there is a large lattice constant difference between the p-type AlGaN electron blocking layer 11 having a large Al composition ratio of 0.18 and the active layer 7 made of InGaN, but they are separated by 135 nm as described above. Therefore, the strain generated in the active layer 7 due to this lattice constant difference can be relaxed, and the luminous efficiency can be improved. Therefore, the threshold current density J _th Therefore, the threshold current I _th Can be reduced, and the slope efficiency can be improved.
[0045]
In addition, since the undoped InGaN layer 10 having substantially the same lattice constant as that of the active layer 7 is provided between the undoped AlGaN cladding layer 9 and the p-type AlGaN electron blocking layer 11, the active layer 7 and the p-type AlGaN electron blocking layer 11 are provided. And the p-type AlGaN / GaN superlattice cladding layer 12, the p-type AlGaN electron blocking layer 11 and the p-type AlGaN / GaN superlattice cladding layer 12 cause the active layer 7 to have a large lattice constant difference. Distortion can be relaxed. Therefore, the threshold current density J of the GaN-based semiconductor laser _th Therefore, the threshold current I _th Can be reduced, and the slope efficiency can be improved.
[0046]
Further, the above threshold current I _th By reducing this, it is possible to improve the noise characteristics of the GaN-based semiconductor laser.
[0047]
When electrons injected into the active layer 7 pass through the active layer 7 and reach the undoped AlGaN cladding layer 9, the energy difference ΔE of the conduction band between the undoped InGaN optical waveguide layer 8 and the undoped AlGaN cladding layer 9. _C When electrons having a larger energy jump over the undoped AlGaN cladding layer 9, ΔE _C Energy is reduced by that amount. On the other hand, ΔE _C Electrons having less energy cannot jump over the undoped AlGaN cladding layer 9 and remain in the undoped InGaN optical waveguide layer 8. Thus, the energy efficiency and the number of electrons that attempt to jump over the undoped AlGaN cladding layer 9 can be reduced, thereby improving the slope efficiency of the GaN-based semiconductor laser. In addition, it is possible to prevent the GaN-based semiconductor laser from overflowing electrons when driven at a high temperature and high output, and to reduce the operating current of the GaN-based semiconductor laser.
[0048]
Further, in the growth from the undoped InGaN optical waveguide layer 6 to the p-type AlGaN electron block layer 11, the carrier gas atmosphere is changed to N. ₂ The atmosphere is H and the carrier gas atmosphere is H ₂ In particular, since the desorption of In from the active layer 7 can be suppressed, deterioration thereof can be prevented, and the reliability and lifetime of the GaN-based semiconductor laser can be improved.
[0049]
As described above, it is possible to realize a GaN-based semiconductor laser having a low operating voltage and a threshold current, good temperature characteristics, a long lifetime, and high reliability.
The GaN-based semiconductor laser according to the first embodiment can reduce the operating current and operating voltage when driving at high temperature and high output, and has a long life. It is suitable for use.
[0050]
Next explained is a GaN compound semiconductor laser according to the second embodiment of the invention. FIG. 4 is an enlarged view of the vicinity of the ridge portion of the GaN-based semiconductor laser.
As shown in FIG. 4, in the GaN-based semiconductor laser according to the second embodiment, a p-type GaInNAs layer 23 is provided instead of the p-type AlGaInN layer 14 in the GaN-based semiconductor laser according to the first embodiment. Yes. The thickness of the p-type GaInNAs layer 23 is, for example, 5 nm. The p-type GaInNAs layer 23, the n-type AlGaInN layer 13, and the p-type AlGaN / GaN superlattice cladding layer 12 form a pnp structure of the contact portion of the p-side electrode. Here, the p-type GaInNAs layer 23 has a large lattice constant difference with AlGaInN. However, since the thickness is as thin as 5 nm, uniform film formation is possible, even if film formation is uneven. Even if irregularities occur on the surface, there is almost no problem.
[0051]
Since other configurations are the same as those of the GaN-based semiconductor laser according to the first embodiment, description thereof is omitted.
The method for manufacturing the GaN-based semiconductor laser is the same as the method for manufacturing the GaN-based semiconductor laser according to the first embodiment, and thus description thereof is omitted.
According to the second embodiment, the same advantages as those of the first embodiment can be obtained.
[0052]
Next explained is a GaN compound semiconductor laser according to the third embodiment of the invention. FIG. 5 is an enlarged view of the vicinity of the ridge portion of the GaN-based semiconductor laser.
As shown in FIG. 5, in the GaN-based semiconductor laser according to the third embodiment, p-type InGaAs is used instead of the p-type AlGaInN layer 14 and the n-type AlGaInN layer 13 in the GaN-based semiconductor laser according to the first embodiment. A layer 24 and an n-type GaSbAs layer 25 are provided. The thickness of the p-type InGaAs layer 24 is 5 nm, for example, and the thickness of the n-type GaSbAs layer 25 is also 5 nm, for example. The p-type InGaAs layer 24, the n-type GaSbAs layer 25, and the p-type AlGaN / GaN superlattice cladding layer 12 form a pnp structure of the contact portion of the p-side electrode. Here, the p-type InGaAs layer 24 and the n-type GaSbAs layer 25 have a large lattice constant difference between them and AlGaInN. However, since the thickness is as thin as 5 nm, uniform film formation is possible. Even if unevenness occurs and irregularities are generated on the surface, there is almost no problem.
[0053]
Since other configurations are the same as those of the GaN-based semiconductor laser according to the first embodiment, description thereof is omitted.
The method for manufacturing the GaN-based semiconductor laser is the same as the method for manufacturing the GaN-based semiconductor laser according to the first embodiment, and thus description thereof is omitted.
According to the third embodiment, the same advantages as those of the first embodiment can be obtained.
[0054]
As mentioned above, although embodiment of this invention was described concretely, this invention is not limited to the above-mentioned embodiment, The various deformation | transformation based on the technical idea of this invention is possible.
[0055]
For example, the numerical values, structures, shapes, substrates, raw materials, processes and the like given in the first to third embodiments are merely examples, and if necessary, numerical values, structures, shapes, substrates, Raw materials, processes, etc. may be used.
[0056]
Specifically, for example, in the above-described first to third embodiments, an n-type layer for forming a laser structure is first laminated on a substrate, and a p-type layer is laminated thereon, This may be reversed to the stacking order, and a p-type layer is first stacked on the substrate, and an n-type layer is stacked thereon.
[0057]
In the first to third embodiments described above, the undoped InGaN optical waveguide layer 6 as the n-side optical waveguide layer and the undoped InGaN optical waveguide layer 8 as the p-side optical waveguide layer have the same composition. The composition of the undoped InGaN optical waveguide layer 6 and the undoped InGaN optical waveguide layer 8 may be different from each other as long as good optical characteristics can be obtained. It may be lower than the layer 6. Furthermore, if necessary, a material having a composition different from that of InGaN, such as GaN, may be used as the material for the n-side optical waveguide layer and the p-side optical waveguide layer.
[0058]
In the first to third embodiments described above, the c-plane sapphire substrate 1 is used. If necessary, a SiC substrate, a Si substrate, a spinel substrate, a substrate made of a thick n-type GaN layer, or the like is used. It may be used. Further, instead of the GaN buffer layer 2, an AlN buffer layer or an AlGaN buffer layer may be used.
[0059]
In the first to third embodiments described above, the present invention has been described for the case where the present invention is applied to a GaN-based semiconductor laser having an SCH structure. However, the present invention is, for example, a GaN-based semiconductor having a DH (Double Heterostructure) structure. Of course, it may be applied to a GaN-based light emitting diode.
[0060]
Further, in the above-described first to third embodiments, in the p-type AlGaN / GaN superlattice cladding layer 12, the AlGaN layer is not doped with Mg. Alternatively, Mg may not be doped into the GaN layer, and Mg may be doped only into the AlGaN layer.
[0061]
【The invention's effect】
As described above, according to the present invention, the contact portion of the electrode on the first conductivity type side includes the first layer of the first conductivity type, the second layer of the second conductivity type, and the second layer in this order from the electrode side. With the stacked structure including the first conductivity type third layer, the operating voltage can be reduced.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a GaN-based semiconductor laser according to a first embodiment of the invention.
FIG. 2 is an enlarged cross-sectional view of a main part of a GaN-based semiconductor laser according to the first embodiment of the invention.
FIG. 3 is a schematic diagram showing an energy band structure for explaining the operation of the GaN-based semiconductor laser according to the first embodiment of the invention.
FIG. 4 is an enlarged cross-sectional view of a main part of a GaN-based semiconductor laser according to a second embodiment of the present invention.
FIG. 5 is an enlarged cross-sectional view of a main part of a GaN-based semiconductor laser according to a third embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... c-plane sapphire substrate, 4 ... n-type GaN contact layer, 5 ... n-type AlGaN clad layer, 6 ... Undoped InGaN optical waveguide layer, 7 ... Active layer, 8 ... Undoped InGaN optical waveguide layer, 9 ... undoped AlGaN cladding layer, 10 ... undoped InGaN layer, 11 ... p-type AlGaN electron blocking layer, 12 ... p-type AlGaN / GaN superlattice cladding layer, 13. .... n-type AlGaInN layer, 14 ... p-type AlGaInN layer, 17 ... insulating film, 18 ... Si film, 20 ... p-side electrode, 22 ... n-side electrode, 23 ... p-type GaInNAs layer, 24... p-type InGaAs layer, 25... n-type GaSbAs layer

Claims (3)

a p-type AlGaN / GaN superlattice cladding layer;
Si as an n-type impurity on the p-type AlGaN / GaN superlattice cladding layer is 1 × 10 ¹⁸ cm ^-3 N-type Al doped to the above concentration and having a thickness of 10 nm or less _x Ga _1-x-z In _z N layer (however, 0 ≦ x ≦ 1, 0 ≦ z ≦ 1),
N-type Al _x Ga _1-x-z In _z P-type Al on N layer _x Ga _1-x-z In _z N layer (however, 0 ≦ x ≦ 1, 0 ≦ z ≦ 1) or p-type Ga _p In _1-p N _q As _1-q A layer (where 0 ≦ p ≦ 1, 0 ≦ q ≦ 1),
P-type Al _x Ga _1-x-z In _z N layer or p-type Ga _p In _1-p N _q As _1-q A p-side electrode in contact with the layer,
P-type Al _x Ga _1-x-z In _z N layer or p-type Ga _p In _1-p N _q As _1-q Layer and the above n-type Al _x Ga _1-x-z In _z A GaN-based semiconductor light-emitting device in which the band gap of the N layer is smaller than the band gap of the p-type AlGaN / GaN superlattice cladding layer. The p-type AlGaN / GaN superlattice cladding layer and the p-type Al _x Ga _1-x-z In _z N layer or p-type Ga _p In _1-p N _q As _1-q 1 × 10 Mg as p-type impurity in the layer ¹⁸ cm ^-3 The GaN-based semiconductor light-emitting device according to claim 1 doped at the above concentration. The GaN-based semiconductor light-emitting device according to claim 2, wherein the GaN-based semiconductor light-emitting device is a GaN-based semiconductor laser or a GaN-based light-emitting diode.

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