JP3238971B2 - Semiconductor laser device and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AlGaInP semiconductor laser device and a method of manufacturing the same.

[0002]

FIG. 6 shows a conventional gain-guided AlGaInP.
FIG. 4 is a cross-sectional view illustrating a manufacturing process of a semiconductor laser device.

[0003] First, as shown in FIG.
An n-type GaInP buffer layer 52, n
Mold (Al _u Ga _1-u ) _0.5 In _0.5 P cladding layer 53, undoped (Al _v Ga _1-v ) _0.5 In _0.5 P (u> v ≧ 0)
The active layer 54, the p-type (Al _u Ga _1-u ) _0.5 In _0.5 P cladding layer 55, and the n-type GaAs current blocking layer 56 are formed by MOCV.
Continuous growth is performed by the D method (metal organic chemical vapor deposition) (first crystal growth).

[0006] Next, as shown in FIG. 6 (b), the n-type GaAs current blocking layer 56 is etched and removed in a stripe shape to form a p-type (Al _u Ga _1-u ) _0.5 In _0.5 P cladding layer 5.
Expose 5

[0005] Thereafter, as shown in FIG.
P-type (Al _u) on the p-type GaAs current blocking layer 56 and exposed.
Ga _1-u ) _0.5 In _0.5 P clad layer 55 on p-type GaAs
An s cap layer 57 is grown by MOCVD (second
Times crystal growth). Thereafter, electrodes and the like (not shown) are formed to complete the process.

Other than such a semiconductor laser element, a p-type (Al _u Ga _1-u ) _0.5 In _0.5 P cladding layer having a stripe-shaped ridge portion is disclosed in, for example, the 38th Association of Applied Physics. Proceedings of lectures, 30p-D-10, 1
001. This laser element is also formed by crystal growth twice using the MOCVD method as in the above-described element.

Incidentally, Zn (zinc) is generally used as a dopant in the p-type cladding layer of the semiconductor laser device.

[0008]

As described above, when a semiconductor laser device is formed by the MOCVD method, it is necessary to lower the temperature at the time of crystal growth to about room temperature after crystal growth. Conventionally, the temperature was lowered while flowing AsH ₃ (arsine) in order to prevent As from evaporating from the upper GaAs cap layer or GaAlAs cap layer.

However, in order to inactivate the Zn dopant of the hydrogen produced by the decomposition of AsH ₃ is p-type _{(Al u Ga 1-u)} 0 .5 In 0.5 P cladding layer, a high p-
It was difficult to obtain a carrier concentration (hole concentration). When the carrier concentration of the p-type cladding layer is low, there is a problem that electrons easily overflow from the active layer to the p-type cladding layer, and the threshold current increases.

Conventionally, two crystal growth steps and a step of etching a clad layer or a layer serving as a current blocking layer in order to form a current blocking layer are required, which complicates the manufacturing process. Since the layer exposed to the air is oxidized between the first and second crystal growths, there is a problem in the reliability of the device.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an AlGaInP-based semiconductor laser device having a low threshold current, high reliability, and easy manufacture, and a method of manufacturing the same. Aim.

[0012]

A semiconductor laser device according to the present invention comprises an n-type semiconductor substrate and an n-type Al formed on the substrate.
A GaInP cladding layer, an active layer formed on the n-type AlGaInP cladding layer, and a p-type AlGaInP first cladding layer formed on the active layer.
Doped Zn is activated on InP first cladding layer
A second p-type AlGaInP cladding layer,
The doped Zn located on both sides of the cladding layer is active.
N-type AlGaInP current blocking layer not formed
It is characterized by having been done.

The method of manufacturing a semiconductor laser device according to the present invention
An n-type AlGaInP cladding layer, an active layer, a p-type AlGaInP cladding layer, a Zn-doped n-type AlGaInP layer, and a p-type cap layer are continuously grown on the n-type semiconductor substrate in this order by metal organic chemical vapor deposition. Process and
A step of forming an AsH ₃ atmosphere during cooling, a step of forming a mask having a striped window on the p-type cap layer and impermeable to hydrogen, and a step of performing heat treatment through the mask. It is characterized by the following. In particular, the heat treatment temperature is 450 to 550 ° C.

[0014]

The Zn-doped n-type AlGa formed by the MOCVD method (including a step of lowering the temperature in an AsH ₃ atmosphere).
InP layer, the hydrogen produced by the decomposition of the AsH ₃ is n
Although the Zn is inactivated by being taken in the AlGaInP layer, hydrogen is converted to nGaAlInP by heat treatment.
Since Zn is activated by being removed from the P layer, its conductivity type can be converted to p-type. Then, heat treatment is performed by covering a mask that has a stripe-shaped window on the Zn-doped n-type AlGaInP layer and does not allow hydrogen to pass therethrough, so that the portion covered by the mask has the same conductivity type as the n-type, but the mask is covered. The portion which is not used can be converted from a conductive type to a p-type.

[0015]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.

In FIG. 1, reference numeral 1 denotes an n-type GaAs substrate. On one main surface of the substrate 1, an n-type (Al _0.7 Ga _0.3 ) _0.5 layer having a thickness of 0.8 μm to which Si (silicon) is added as a donor is added.
An In _{0 .5} P cladding layer 2, the layer thickness 0.3μm where the layer thickness 0.08μm undoped _{(Al 0.3 Ga 0.7) 0.5 In} 0.5 P active layer 3, as an acceptor Zn (zinc) was added
The first p-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P first cladding layer 4 is formed in this order.

On the p-type first cladding layer 4, Si as a donor and Zn as an acceptor (donor concentration <
(Acceptor concentration) added width 5 μm, layer thickness 0.8
μm stripe-shaped ridge structure p-type (Al _0.7 Ga
_0.3 ) _0.5 In _0.5 P second cladding layer 5 and the p-type second cladding layer 5
0.8 μm thick n-type (Al _0.7 Ga _0.3 ) _0.5 I doped with Si as a donor and Zn as an acceptor (donor concentration> acceptor concentration) on both sides of the cladding layer 5
The n _0.5 P current blocking layers 6 are formed.

On the p-type second cladding layer 5 and the n-type current blocking layers 6 and 6, a p-type GaAs cap layer 7 having a thickness of 0.3 μm and containing Zn as an acceptor is formed. On the cap layer 7 and on the other main surface of the n-type GaAs substrate 1, p-type and n-type ohmic electrodes (not shown) are formed, respectively.

A method for manufacturing such a semiconductor laser device will be described with reference to FIG.

First, as shown in FIG.
An n-type cladding layer 2, an active layer 3, a p-type first cladding layer 4 doped with Zn (zinc) as an acceptor, Si as a donor and Zn as an acceptor on an aAs substrate 1.
Doped n-type (Al _0.7 Ga _0.3 ) with a layer thickness of 0.8 μm
_0.5 In _0.5 P layer 10 and p-type cap layer 7
After continuous growth by the OCVD method, the laminated substrate 11 is formed by lowering the temperature to about room temperature while flowing AsH ₃ at least within the temperature at which As in the p-type cap layer 7 evaporates. In this embodiment, the supply amount of Zn during the crystal growth of the p-type first cladding layer 4 is Zn / III (molar ratio).
= 0.6, and the p-carrier concentration (= acceptor concentration−donor concentration) of the p-type first cladding layer 4 is 3 × 10 ¹⁷
cm ^-3 . Also, n-type (Al _0.7 Ga _0.3 ) _0.5 In
_0.5 supply amount of Zn and Si during crystal growth of the P layer 10 are each Zn / III (molar ratio) = 0.6, Si / III (molar ratio) =
1.5 × 10 ^-3 and n-type (Al _0.7 Ga _0.3 ) _0.5
The In _0.5 P layer 10 has a donor concentration of 6 × 10 ¹⁷ cm ⁻³ and an acceptor concentration of 3 × 10 ¹⁷ cm ^−3.
- carrier concentration (= donor concentration - acceptor concentration) becomes 3 × 10 ¹⁷ cm ^-3.

Next, as shown in FIG. 2B, a mask having a stripe-shaped window of 5 μm width on the p-type cap layer 7 and impermeable to hydrogen, for example, 0.3 μm-thick SiO ₂
Thermal mask (thermal chemical vapor deposition)
Alternatively, it is formed by an EB evaporation method (electron beam evaporation method) or the like.

Subsequently, as shown in FIG. 2C, the laminated substrate 11 is subjected to a heat treatment at 500 ° C. for 15 minutes in a high knee gas (N ₂ / H ₂ = 9/1: volume ratio) atmosphere. In this heat treatment step, the portion of the n-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P layer 10 covered with the mask 12 has a donor concentration of
Although the acceptor concentration is not changed, the donor concentration is not changed in the portion not covered by the mask 12, but the acceptor concentration is set because the heat treatment allows hydrogen to be released from the layer 10 through the stripe-shaped window of the mask 12 and Zn to be activated. It is improved from 3 × 10 ¹⁷ cm ⁻³ to 1 × 10 ¹⁸ cm ⁻³ . Also, the portion of the p-type first cladding layer 4 covered with the mask 12 has the same acceptor concentration, but the portion not covered with the mask 12 has the same acceptor concentration of 3 × 10 ¹⁷ cm ^-3 to 1 ×. It is improved to 10 ¹⁸ cm ^-3 . Therefore, by this heat treatment step, the n-type (Al _0.7 Ga
_0.3 ) _0.5 In _0.5 P layer 10 has an n-carrier concentration of 3 × 1
0 ¹⁷ cm n-type ^{_{-3 (Al 0.7 Ga 0.3) 0.5}} In 0.5 p -type P current blocking layer 6, 6 and p- carrier concentration has a large value 4 × 10 ¹⁷ cm ^-3, as compared with the conventional (Al _0.7 Ga _0.3 ) _0.
5 In _0.5 P becomes the second clad layer 5. The p-type first cladding layer 4 also has a p-carrier concentration of 1 × 10 in the vicinity of the light emitting portion.
It will be improved to ¹⁸ cm ^-3 .

Subsequently, as shown in FIG. 1, the mask 12 made of SiO ₂ is removed with a hydrofluoric acid (HF) solution, and then the p-type cap layer 7 and the other main surface of the n-type GaAs substrate 1 are removed. On the upper side, p-type and n-type side ohmic electrodes (not shown) are formed.

In the above embodiment, a method of manufacturing a single semiconductor laser device has been described for the sake of simplicity. However, since a plurality of devices are usually formed on a single wafer (substrate) as conventionally known, Unlike the manufacturing method described above, the side and end faces of the element are not exposed during the manufacturing.

FIG. 3 shows the IL characteristics at room temperature of the semiconductor laser device of this embodiment and the conventional semiconductor laser device.

From this figure, it can be seen that the semiconductor laser device of this embodiment has a threshold current of 71 mA, and a threshold current of 88 m of the conventional example.
It turns out that it is remarkably reduced compared with A. this is,
Since the p carrier concentration of the first and second cladding layers 4 and 5 of this embodiment is increased at least in the vicinity of the light emitting portion, and the energy barrier between the active layer 3 and the p-type cladding layer is increased. This is because it was possible to suppress the electrons from overflowing into the first and second cladding layers 4 and 5.

FIG. 4 shows the results of reliability tests of the semiconductor laser device of this embodiment and a conventional semiconductor laser device. In this experiment, the device environment temperature was 30 ° C., the light output was 3 mW,
C drive was performed.

From this figure, it can be seen that the semiconductor laser device of the present embodiment operates stably even after 1000 hours or more, while the conventional device deteriorates remarkably in about 500 hours.
This is considered to be due to the fact that the device of the present embodiment can be formed by crystal growth only once, so that crystal oxidation or the like does not occur.

FIG. 5 shows the MOCVD method (AsH
Created by ₃ including flow _{process) (Al x Ga 1-x} ) 0.5
4 shows the relationship between In _0.5 P, the Zn concentration and the acceptor concentration. The supply amount of Zn is Zn / III = 0.6,
The heat treatment was performed at 500 ° C. for 15 minutes in a high knee gas.

As can be seen from this figure, after the formation of Zn-doped (Al _x Ga _{1 -x} ) _0.5 In _0.5 P (as gross)
wn) has a low acceptor concentration because (Al _x Ga _1-x ) _0.5 In _0.5 P has hydrogen incorporated therein and Zn is inactivated, but heat treatment removes hydrogen to activate Zn. Therefore, it can be understood that the acceptor concentration is improved.

Therefore, p of a composition ratio different from that of the above-described embodiment is used.
The second type cladding layer 5 and the n-type current blocking layer 6 can be similarly formed. That is, n-type (Al _x Ga _{1 -x} ) _0.5 In _0.5 P layer 1
Before the heat treatment (as
(grown), the n-type current blocking layer 6 requires n-
The carrier concentration (donor concentration> acceptor concentration) is reached, and after the heat treatment, Zn is activated and the acceptor concentration is improved, so that the p-type second cladding layer requires p.
-The carrier concentration (acceptor concentration> donor concentration) may be set. This heat treatment temperature is 450 ° C ~
The temperature may be in the range of 550 ° C., and the atmosphere gas may be an inert gas such as N ₂ gas or Ar gas instead of the high knee gas. Further, the heat treatment time is preferably about 5 minutes to 1 hour.

In the above description, n-type (Al _x Ga _{1 -x} ) _0.5
Although Si was used as a donor of the In _0.5 P layer 10, Si
May be replaced with Se, for example. As described above, the activation rate of Zn serving as an acceptor differs depending on the presence or absence of a heat treatment step (presence or absence of a hydrogen removal step).
The activation rate of e does not depend on the presence or absence of a heat treatment step.

In the above embodiment, the active layer 3 is made of Al
Although an example of the case of a GaInP layer has been described,
A layer or an active layer having a multiple quantum well structure may be used as appropriate.

Further, as is well known in the art, a clad layer having a larger band gap energy and a smaller refractive index than the active layer (in the case of AlGaInP, the clad layer has a larger Al composition ratio than the active layer) can be used.
Depending on the active layer, (Al _x Ga _{1 -x} ) _0.5 In _0.5 P (x =
1) Needless to say, the cladding layer can be used as the AlGaInP cladding layer of the present invention, and the n-type AlGaInP current blocking layer of the present invention is n-type (Al _x Ga _1-x ).
_0.5 In _0.5 P (x = 1) may be used.

As the cap layer, AlGaAs can be appropriately used instead of GaAs.

[0036]

The semiconductor laser device of the present invention has a p-type Al
Doped Zn is active on the GaInP first cladding layer.
A second p-type AlGaInP cladding layer,
Doped Zn located on both sides of the second cladding layer
Is not activated and the n-type AlGaInP current blocking layer is
Since the structure is formed, a p-type AlGaInP cladding layer having a high p-carrier concentration and an n-type AlGaIn
The P current blocking layer can be obtained by one crystal growth without an etching step for forming the p-type AlGaInP cladding layer and the n-type AlGaInP current blocking layer. Therefore, p-type A
Since the carrier concentration of the 1GaInP cladding layer increases, the threshold current can be reduced. In addition, since it can be manufactured by one crystal growth and the semiconductor layer in the device is not oxidized, the reliability of the device is improved. Further, since it is not necessary to etch the semiconductor layer, the manufacturing can be simplified.

The method for manufacturing a semiconductor laser device of the present invention
After the formation of the semiconductor layer is completed by one crystal growth, a heat treatment is performed on the Zn-doped n-type AlGaInP layer through a mask having a stripe-shaped window. AlGaInP layer is n-type AlG
an aInP current blocking layer and a p-type AlGaInP cladding layer, and at least a p-type AlGaIn
The carrier concentration of the P clad layer can be improved. Therefore, the threshold current can be reduced, the reliability can be improved, and the manufacturing can be simplified.

[Brief description of the drawings]

FIG. 1 is a sectional view of a semiconductor laser device according to an embodiment of the present invention.

FIG. 2 is a sectional view showing a manufacturing process of the semiconductor laser device of the embodiment.

FIG. 3 shows IL of the semiconductor laser devices of the present embodiment and a comparative example.
It is a figure showing a characteristic.

FIG. 4 is a diagram showing the results of a reliability test of the semiconductor laser devices of this example and a comparative example.

FIG. 5 is a diagram showing the relationship between Zn-doped (Al _x Ga _{1 -x} ) InP and acceptor concentration.

FIG. 6 is a cross-sectional view showing a manufacturing process of a conventional semiconductor laser device.

[Explanation of symbols]

 Reference Signs List 1 n-type GaAs substrate 2 n-type AlGaInP cladding layer 3 active layer 4 p-type AlGaInP cladding layer 6 n-type AlGaInP current blocking layer 10 n-type AlGaInP layer 12 mask

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H01S 5/00-5/50

Claims (3)

(57) [Claims] 1. An n-type semiconductor substrate, an n-type AlGaInP cladding layer formed on the substrate, and the n-type AlGaIn
An active layer formed on the P-cladding layer, and a p-type AlGaInP first cladding layer formed on the active layer, wherein a doped Z is formed on the p-type AlGaInP first cladding layer.
n-type activated p-type AlGaInP second cladding layer
And doped on both sides of the second cladding layer and doped
N-type AlGaInP current blocking without activated Zn
The semiconductor laser device characterized Rukoto and the layers are formed. 2. An n-type AlGaInP on an n-type semiconductor substrate.
Cladding layer, active layer, p-type AlGaInP cladding layer,
A step of continuously growing a Zn-doped n-type AlGaInP layer and a p-type cap layer in this order by metal organic chemical vapor deposition, and a step of setting the atmosphere to an AsH ₃ atmosphere during cooling.
A method for manufacturing a semiconductor laser device, comprising: a step of forming a mask having a stripe-shaped window and not allowing hydrogen to pass therethrough on the p-type cap layer; and a step of performing a heat treatment through the mask. . 3. The method according to claim 2, wherein the heat treatment temperature is 450 to 550 ° C.