JPH077217A - Semiconductor laser and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide a window structure wherein light absorption is hard to occur at an emitting edge part by forming a barrier layer of AlGaInP, ordering a stripe part wherein a current is injected, and disordering the light emitting edge part. CONSTITUTION:Barrier layers 41 and 45 are ordered at a stripe-shaped mesa part, and the other part including an emitting edge part is disordered. Therefore, the other region including the emitting edge part becomes wider by several tens of meV in comparison with the region of the stripe-shaped mesa part at the band gap of the barrier layers 41 and 45. Thus, the band gap of a quantum well layer 43 becomes wider by several meV in the same region. Namely, the band gap of the quantum well layer 43 is slightly broadened at the emitting edge, and light absorption at this part is hard to occur. Thus, the window structure where the light absorption is hard to occur can be formed at the emitting edge part. Even if a high output-power semiconductor laser is constituted, heating caused by the light absorption is suppressed, and the high reliability can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a 1 .mu.m band semiconductor laser having an active layer of GaInP or GaAs, which is suitable for pumping an optical fiber amplifier, and more particularly to a semiconductor laser capable of obtaining a high output. It is about.

[0002]

2. Description of the Related Art In order to obtain a high-power semiconductor laser, it is necessary to suppress heat generation due to light absorption at the emitting end face. Therefore, a material having a wide bandgap is generally used in that portion so that light is not absorbed in the vicinity of the emission end face, and this structure is generally called a window.

As a method of forming a window structure on the emission end face, a high resistance A having a wide bandgap is formed on the emission end face after cleaving the chip.
There is a method of growing lGaAs by OMVPE (metal organic chemical vapor deposition). Further, in a semiconductor laser using GaInP as an active layer, a method has been reported in which the GaInP active layer is ordered and epitaxially grown, and thereafter, the vicinity of the emitting end face is disordered to widen the bandgap in that portion (Japanese Patent Laid-Open No. 4-41). 14277).

[0004]

However, the former method is a very expensive process and is not desirable from a commercial point of view. Also, the latter method is currently used for GaIn
It can be used only for a semiconductor laser having a P active layer.

An object of the present invention is GaInAs or Ga.
A semiconductor laser having an active layer of As is provided with a new and easy-to-fabricate window structure, and a method of manufacturing the same.

[0006]

The semiconductor laser of the present invention has been made to achieve this object.
The active layer has a quantum well structure in which a quantum well layer is sandwiched between barrier layers using aAs as a substrate.
In a semiconductor laser made of As or GaInAs, a barrier layer is made of AlGaInP (including a case where Al composition is zero), a stripe portion into which a current is injected is ordered, and a light emitting end face portion is disordered. It is what Furthermore, it is even better if both sides of the stripe part are disordered.
The width of the well should be 40 Å or less.

According to the method of manufacturing a semiconductor laser of the present invention, an n-side clad layer, a quantum well structure active layer, and a p-side clad layer are sequentially formed on a GaAs substrate by epitaxial growth, and then the p-side clad layer is formed. Etching is done to leave a stripe-shaped mesa, and the upper part of this mesa and G
In a method for manufacturing a semiconductor laser in which an electrode is formed on the back surface of an aAs substrate, when the quantum well structure active layer is formed, A
A barrier layer of 1GaInP (including a case where the Al composition is zero) is grown by ordering, and then impurities are diffused into the emission end face portion of the barrier layer and disordering is performed.

[0008]

In the barrier layer, the disordered portion of AlGaInP (including the case where the Al composition is zero) has a larger band gap than the ordered portion. On the other hand, the bandgap of the quantum well layer is affected by the change in the bandgap of the barrier layer. For example, when the band gap of the barrier layer increases by several tens of meV, the band gap of the quantum well layer increases by the order of several meV. That is, in the semiconductor laser of the present invention, the band gap of the quantum well layer is widened due to the influence of the barrier layer that is disordered at the emission end face portion, and it is difficult to absorb light. Ordering here means [11
An atomic layer is sequentially formed for each element on the [1] plane, and disordering means a state in which two or more elements are mixed in the atomic layer on the [111] plane.

Ordered AlGaInP (Al
It is known that when an impurity such as Zn is diffused, it causes disordering (including the case where the composition is zero). By utilizing this action, impurities are partially diffused in the emission end face portion of the barrier layer, so that the emission end face portion is partially disordered.
Widen the bandgap on the emission end face of the quantum well layer. If both sides of the stripe portion are also disordered, carriers, especially electrons, are slightly confined in the stripe portion. The change in effective bandgap due to barrier disordering is greater when the well width is narrower, and the effect of the present invention is greater. The well width should be 40Å or less. The narrower the wavelength, the shorter the wavelength and the more carriers easily overflow from the well.
The effect of the present invention is enhanced by arranging many thin wells having a molecular layer (about 3Å). However, if it is too thin, it is difficult to manufacture it with good controllability, so it is preferable from the viewpoint of manufacturing that the well is thick as long as the window structure has some effect.

[0010]

FIG. 1 is a perspective view showing a semiconductor laser which is an embodiment of the present invention, and FIG. 2 is a sectional view schematically showing a laminated structure of an epitaxial wafer used for manufacturing this semiconductor laser. is there. Further, FIG. 3 shows the thickness, material, Al (Al + G) of each epitaxial layer of the epitaxial wafer.
a), a list of impurities and their concentrations.

To manufacture this semiconductor laser, first,
The GaAs layer 9 to be the p-side electrode contact layer is formed by low pressure MOVPE (metal organic chemical vapor deposition) at about 60 Torr.
An epitaxial wafer is stacked. Ga
GaAs buffer layer 2, n-type AlG on As substrate 1
aInP clad layer 3, active layer 4, p-type AlGaInP
Cladding layer 5, GaInP etch stop layer 6, p-type A
The lGaInP clad layer 7, the p-type GaInAsP auxiliary clad layer 8, and the GaAs contact layer 9 are formed by epitaxial growth. The active layer 4 has a quantum well structure and includes a GaInP layer 41 and a GaInAsP layer 4.
2, a GaInAs layer 43, a GaInAsP layer 44 and a GaInP layer 45. In this active layer 4, the GaInAs layer 43 is a quantum well layer and the GaInP layer 4 is
1 and 45 are barrier layers, and GaInP barrier layer 4
1 and 45 are ordered. GaInAsP
Layers 42 and 44 are from barrier layer 41 to quantum well layer 4
3 and a buffer layer for preventing disturbance of the interface when switching from the quantum well layer 43 to the barrier layer 45.

In the production of this epitaxial wafer, it is desirable to grow AlGaInP at a high temperature.
Low temperature growth is desirable for s. Further, in order to order GaInP for the barrier layers 41 and 45, low temperature growth is required. Therefore, the n-type buffer layer 3 is grown at a high temperature of about 740 ° C., the active layer 4 is grown at a low temperature of about 650 ° C., and the p-type buffer layer 5 and the subsequent layers are grown at a high temperature of about 740 ° C. When the growth temperature is switched from 740 ° C. to 650 ° C., the epitaxial growth is temporarily suspended, but if this is performed with the surface having a high concentration of Al, which is a Group III element, exposed, the crystallinity tends to deteriorate. Therefore, here, the GaInP barrier layer 41 is slightly grown at 740 ° C., the growth is interrupted, the atmospheric temperature is lowered to 650 ° C., and then the growth of the GaInP barrier layer 41 is restarted. In this example, the GaInP barrier layer 4
When 1 becomes d = 0.005 μm, the growth is stopped. Although not shown in the figure, the growth temperature is gradually lowered immediately before the end of the growth of the AlGaInP layer 7, and the GaInAs
The P layer 8 and the GaAs layer 9 are preferably grown at about 650 ° C.

Next, the epitaxial wafer thus formed is subjected to mesa etching as shown in FIG. First, a silicon nitride film is deposited to a thickness of 0.1 μm on the entire surface of the epitaxial wafer shown in FIG. 2, and then a stripe pattern is left by using a lithography technique to remove other portions. Next, using the silicon nitride film 41 as a mask, the GaAs layer 9 and GaInAs are formed.
The P layer 8 is removed. The etchant at this time is phosphoric acid:
Hydrogen peroxide: water = 5: 1: 40 is used. Then Al
GaInP is etched, but GaAs, GaInA
sP and GaInP are not etched Etched with concentrated sulfuric acid at 60 ° C. until the color of the wafer surface changes. The part where the color of the wafer is changed is where the GaInP layer 6 is exposed. FIG. 4 is a diagram showing a cross section at this time.

Next, Si is ^added to a concentration of about 1 × 10 ¹⁸ cm ^-3.
Regrows GaAs doped with. As a result, Zn is diffused from the AlGaInP cladding layer 5 to the active layer 4 in the portion where the GaAs is regrown, that is, in the portion other than the stripe-shaped mesa portion, and the barrier layers 41 and 44 which have been ordered are removed. Ordered. After that, the regrown GaAs is entirely removed by etching with the above-mentioned etchant of phosphoric acid: hydrogen peroxide: water = 5: 1: 40.

Then, the silicon nitride film 41 is formed with hydrofluoric acid: water =
Etch 1: 1. Then, electrodes are formed and cut out to obtain the semiconductor laser shown in FIG. 5 is a cross-sectional view taken along the line VV of FIG. 1. The p-side electrode 52 is formed by vapor deposition through the silicon nitride film 51 from which the upper portion of the mesa portion is removed, and the n-side electrode 53 is the GaAs substrate 1. Is formed by vapor deposition after shaving from the back surface to a thickness of about 100 μm. When the chip is cut out, the cleavage is performed outside the end of the mesa portion by a predetermined distance e such as several tens of μm. As a result, the Ga
The InP barrier layer can be left on the emission end face. In addition,
Regarding the size of the mesa portion of this embodiment, the length L in the longitudinal direction is 11
It is 60 μm and the width W is 4 μm.

In the semiconductor laser manufactured as described above, the barrier layers 41 and 45 are ordered in the stripe-shaped mesa portion, and are disordered in the other portion including the emission end face portion. Therefore, the band gaps of the barrier layers 41 and 45 are several tens of meV wider in the other regions including the emission end face portion than in the stripe mesa region. As a result, the band gap of the quantum well layer 43 is increased by several meV in the same region.
That is, the bandgap of the quantum well layer 43 widens at the emission end face portion, although it is small, and it becomes difficult for light absorption to occur here. Further, since the bandgap of the quantum well layer 43 is slightly widened on both sides of the stripe portion, carriers are likely to accumulate in the stripe portion having a relatively narrow bandgap, and lateral current confinement can be achieved.

As the quantum well layer 43 becomes thinner,
The increase in the bandgap of the quantum well layer with respect to the increase in the bandgap of the barrier layer is large. For example, in the case of a semiconductor laser having a laser oscillation wavelength of 980 nm, the effective band gap of the barrier layer increases from 1.85 eV to 1.90 eV.
If the meV is increased, if the quantum well layer is 40 angstroms, an effective bandgap increase of about 4 meV is obtained. Then, further increase the thickness of the quantum well layer to 25 Å
If so, an effective bandgap increase of about 10 meV can be obtained.

Although the barrier layer of this embodiment is GaInP, partial disordering can be performed in the same manner by using AlGaInP. When it is desired to increase the band gap of the barrier layer, AlGaInP may be used, or GaInP having a large Ga composition may be used. With this composition, the strain is opposite to that of GaInAs of the active layer 43, and thus dislocation is hard to enter into the crystal. Conversely, when it is desired to reduce the band gap of the barrier layer, GaI with a large In composition is used.
Although nP can be used, in this case, since the strain direction is the same as that of GaInAs of the active layer 43, the film thickness cannot be made too thick. It is necessary to confirm what kind of strain and thickness are allowed by experiments by referring to the already known data.

Although GaInAs is used as the quantum well layer, the present invention can be applied to GaAs instead.

[0020]

As described above, according to the semiconductor laser of the present invention, in the semiconductor laser having GaAs or GaInAs as the active layer, the so-called window structure in which light absorption is unlikely to occur is formed in the emitting end face portion. Therefore, even if a high-power semiconductor laser is configured, heat generation due to light absorption at the emission end face is suppressed, and high reliability can be obtained. Further, according to the manufacturing method of the present invention, the barrier layer of the active layer is partially disordered at the emission end face portion to widen the band gap of the quantum well layer of the active layer at the emission end face portion to form the window structure. This is much simpler than the conventional method in which a material having a wide band gap is grown on the emission end face after the chip cleavage.

[Brief description of drawings]

FIG. 1 is a perspective view showing an appearance of a semiconductor laser which is an embodiment of the present invention.

FIG. 2 is a view schematically showing a sectional structure of an epitaxial wafer used for manufacturing the semiconductor laser.

FIG. 3 is a table showing a list of materials for each layer of the epitaxial wafer.

FIG. 4 is a sectional view showing an intermediate process of the semiconductor laser of this embodiment.

5 is a cross-sectional view taken along the line VV of the semiconductor laser of FIG.

[Explanation of symbols]

1 ... GaAs substrate, 2 ... GaAs buffer layer, 3 ... n-type AlGaInP cladding layer, 4 ... Active layer, 5, 7 ... p-type AlGaInP cladding layer, 41, 45 ... Barrier layer, 4
3 ... Quantum well layer.

Claims (8)

[Claims] 1. In a semiconductor laser having a quantum well structure in which a quantum well layer is sandwiched between barrier layers by using GaAs as a substrate, and the quantum well layer is made of GaAs or GaInAs, the barrier layer is AlGaInP ( The semiconductor laser is characterized in that the stripe portion into which the current is injected is ordered, and the light emitting end face portion is disordered. 2. The semiconductor laser according to claim 1, wherein both sides of the stripe portion of the barrier layer are disordered. 3. The semiconductor laser according to claim 1, wherein the quantum well layer has a thickness of 40 Å or less. 4. An n-side cladding layer, a quantum well structure active layer, and a p-side cladding layer are sequentially formed on a GaAs substrate by epitaxial growth, and then the p-side cladding layer is partially etched to leave a stripe-shaped mesa. 4. The method of manufacturing a semiconductor laser according to claim 1, wherein an electrode is formed on an upper portion of the mesa and a back surface of the GaAs substrate, wherein when the active layer is formed, AlGaInP (when Al composition is zero). Of the barrier layer is grown by ordering, and then impurities are diffused into the emitting end face portion of the barrier layer or both sides of the stripe-shaped mesa to perform the disordering. 5. The method of manufacturing a semiconductor laser according to claim 4, wherein the impurity is Zn. 6. Disordering of the barrier layer comprises:
The method for manufacturing a semiconductor laser according to claim 4, wherein the method is performed by growing an n-type semiconductor layer on a p-type cladding layer on the barrier layer. 7. The method of manufacturing a semiconductor laser according to claim 6, wherein the p-type cladding layer is a Zn-doped cladding layer and the n-type semiconductor layer is a Si-doped semiconductor layer. 8. The n-type cladding layer is formed of AlGaInP and has a lower Al composition than AlGaInP (A
(including the case where the l composition is zero) is formed as a barrier layer, AlGaInP having a low Al composition is continuously and slightly grown on the n-type cladding layer, and then the growth can be interrupted and the growth temperature can be ordered. The method for manufacturing a semiconductor laser according to claim 4, wherein the growth is restarted in a state where the conditions are lowered.