JPH0646667B2 - Manufacturing method of AlGaInP semiconductor laser - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of use) The present invention introduces a mesa structure to perform lateral mode control of AlGaIn.
The present invention relates to a method of manufacturing P.

(Prior Art) AlGaIn that introduces a mesa structure in FIG. 4 to perform transverse mode control
An example of a method for producing P will be shown. Figure 4 (a) shows the formation of DH wafers by metalorganic vapor phase epitaxy (MOVPE and abbreviated below), (b)
Shows the completion of the laser structure by mesa etching and (c) the buried growth.

(Problems to be Solved by the Invention) The yield of a semiconductor laser manufactured by following this type of process is most affected by the yield of the mesa etching process of (b), and this process is the most difficult to control. Clad layer 50 and clad layer
When 40 is made of AlGaInP having the same composition, the mesa etching controls the etching time, and the thickness of the clad layer 40 to be left varies depending on the execution, which affects the laser characteristics. Clad layer 50 is Al _0.5 In _0.5 P and clad layer 40
Is (Al _0.4 Ga _0.6 ) _0.5 In _0.5 P, the mesa etching is very easy and can be completely stopped at the surface of the cladding layer 40 by selective etching. However, in order to reduce the vertical divergence angle of the laser emission beam, it is necessary to use AlGaInP for the cladding layer 50 to reduce the Al composition.
At this time, the effect of selective etching is greatly reduced and the etching yield is reduced. For the selective etching effect, the difference between the Al composition of the crystal to be etched and the Al composition of the crystal for which etching should be stopped must be large. For that purpose, it is sufficient to introduce a low composition etching stopper layer as shown in FIG. 3, but increasing the Al composition difference by making the Al composition very close to the active layer composition increases the light absorption loss. I can't because I'm doing it. For the same reason, it cannot be thickened. Therefore, the selective etching method cannot be used sufficiently, and the yield cannot be improved sufficiently.

An object of the present invention is to solve the above problems and provide a method capable of introducing an etching stopper layer having the same composition as that of the active layer and sufficiently exhibiting the effect of selective etching.

(Means for Solving Problems) In the present invention, the formation of the active layer and the etching stopper layer formed by the MOVPE method is performed at a growth temperature, V /
Under the condition of III ratio, the etching stopper layer is characterized in that it is performed under the conditions of growth temperature and V / III ratio which give high band gap energy in the same Al composition.

(Operation) FIG. 1 shows an example of an AlGaInP semiconductor laser to which the manufacturing method of the present invention is applied. A clad layer 40 and an etching stopper layer 20 are stacked on the active layer 10, and a mesa-shaped AlGaInP clad layer 50 is placed on the clad layer 40 and the etching stopper layer 20. The current blocking layer 70 is a mesa-shaped clad layer so that a current flows only through the clad layer 50 on the mesa and the transverse mode is stabilized.
It is laminated on 50 side surfaces, and the cap layer 60 is arranged thereon.

The manufacturing method of this semiconductor laser is shown in FIG. 3. In FIG. 3, the etching stopper layer is introduced to the conventional method as described above. At this time, the active layer is (Al _x Ga _1-x )
_0.5 In _0.5 P, clad layer 40 is (Al _y Ga _1-y ) _0.5 In _0.5 P, clad layer 50 is (Al _z Ga _1-z ) _0.5 In _0.5 P, etching stopper layer 20 is (Al _q Ga _{1 -y} ). _q ) In the case of _0.5 In _0.5 P, the relationship of x <y, x <z, x ≦ q <z is satisfied due to the requirement of selective etching with the semiconductor laser. If the difference between q and z is not sufficient, the selective etching method cannot be used. Actually the difference between q and z is
When z is 1.0 to 0.8, 0.4 or more, and when z is 0.8 to 0.6 or 0.6 or more, the etching step of FIG. 3 (b) can be performed very easily. That is, it is necessary that the etching stopper layer and the active layer have almost the same Al composition. On the other hand MOVPE
It was found that the band gap energy of AlGaInP prepared by the method differs depending on the growth conditions even if the composition is the same. Figure 2 shows the relationship between the bandgap energy growth temperature and the V / III ratio in the case of GaInP. Growth temperature and V
The bandgap energy differs by more than 50 meV depending on the / III ratio. By using a low bandgap energy condition for forming the active layer and using a high bandgap energy condition on the etching stopper layer, the etching stopper layer 20 disposed close to the active layer 10 as shown in FIG. Even if the composition of the active layer 10 is the same as that of the active layer 10, the light absorption is small and the laser characteristics are not deteriorated. This makes it possible to match the Al composition of the etching stopper with the Al composition of the active layer.
The Al composition ratio z of the cladding layer 50 can be set to a value that allows selective etching. As a result, the controllability of the process of FIG. 3 (b) can be improved.

(Embodiment) An explanation will be given as shown in (a) according to the process chart of FIG. Ga
Se-doped (Al _0.4
Ga _0.6 ) _0.5 In _0.5 P 1 μm thick clad layer 30, Ga
_0.5 In _0.5 P, 0.08 μm thick active layer 10, Zn-doped
(Al _0.4 Ga _0.6 ) _0.5 In _0.5 P cladding layer 0.3 μm thick
40, Ga _0.5 In _0.5 P thickness 100 Å etching stopper layer 20, Zn-doped (Al _0.6 Ga _0.4 ) _0.5 In _0.5 P thickness
0.8μm clad layer 50Zn-doped GaAs thickness 0.6μ
m protective layers 80 were sequentially laminated by the MOVPE method. At this time, the growth temperature of the active layer 10 was 700 ° C. V / III ratio was 400, and the growth temperature of the etching stopper layer 20 was 700 ° C. V / III ratio was 60. At this time, the band gap energy of the active layer is 1.
It is 845 eV, and the band gap energy of the etching stopper layer is 1.896 eV. Next, as shown in (b), Si
Mesa etching was performed using the O ₂ film as an etching mask. Etchant for AlGaInP has an etching rate of 0.4 .mu.m / min for HCl and H ₂ O is a mixture of _{(Al 0.6 Ga 0.4) 0.5 In} 0.5 P, with respect to the Ga _0.5 In _0.5 P 50Å / mi
n. Therefore, the etching time was about 2 minutes, and the etching could be completed easily with the etching stopper layer by etching for 3 minutes. At this time, the etching time actually has a tolerance of 2 minutes, and the control is very simple. Next, as shown in (c), the current blocking layer 70 made of Se-doped GaAs is 1.2 μm by the selective MOVPE method.
With a thickness of m, the above-mentioned etching mask was used as a selective mask, and the cladding layer 50 was laminated on both sides. After removing the selective mask, a cap layer 60 made of Zn-doped GaAs was laminated with a thickness of 1 μm.

(Effects of the Invention) As specifically described in Examples, 2 minutes out of 3 minutes of etching is the time actually required for etching.
The minute is set as an allowable time during which etching is almost stopped at the etching stopper layer 20, and it is easy to completely define the mesa shape. In the embodiment, the etching stopper layer 20 is 100 Å, but if the thickness is 200 Å, an allowable time of 4 minutes can be obtained. In the layer structure of the composition shown in the example, the clad layer is formed without the etching stopper layer 20.
The etching cannot be stopped at 40, and the allowable time can hardly be taken unless the composition of the etching stopper layer is GaInP having the same composition as the active layer. As described above, according to the manufacturing method of the present invention, the etching stopper layer having substantially the same composition as that of the active layer can be adopted, and the effect of selective etching can be utilized. In addition, even if a semiconductor laser is formed by actually forming electrodes, the differential charge and output is 0 at an oscillation threshold current of about 50 mA.
It was 5mW / mA, which was comparable to the normal one.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a cross-sectional structure of a laser to which the manufacturing method of the present invention can be applied, FIG. 2 is a diagram showing the MOVPE growth condition dependence of the band gap energy of GaInP, and FIG. 3 is a manufacturing method of the present invention. Fig. 4 is a conventional manufacturing process diagram, 10 is an active layer, 20 is an etching stopper layer, 30, 40,
50 is a clad layer, 60 is a cap layer, 70 is a current blocking layer, 80 is a protective layer, and 100 is a substrate.

Claims (1)

[Claims] 1. An active layer made of (Al _x Ga _1-x ) _0.5 In _0.5 P has a larger bandgap energy than that of the active layer.
In the preparation according to the semiconductor laser metal organic chemical vapor deposition, including double heterostructure sandwiched between cladding layers (MOVPE) method consisting in the active layer, a cladding layer made of _{(Al y Ga 1-y)} 0.5 In 0.5 P, ( Al _q Ga _1-q ) _0.5 In _0.5 P etching stopper layer, mesa processed into stripes (Al _z Ga _1-z ).
Including a step of laminating a cladding layer made of _0.5 In _0.5 P in this order, and making the Al composition ratios of the active layer and the etching stopper layer substantially equal, (xq), and further, crystal growth of the active layer is performed by the etching stopper layer. And the growth temperature and V which have low band gap energy in the same Al composition
A method of manufacturing an AlGaInP semiconductor laser, which is characterized in that it is performed at a ratio of / III.