JPS6249999B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention uses GaAsP as a substrate.
The purpose is to reduce the threshold current of a semiconductor laser device that has a double heterostructure formed by epitaxially growing InGaPAs.

Conventionally, a double-hetero type semiconductor laser that emits visible light has been reported, which uses a vapor-phase grown GaAsP crystal as a substrate and grows InGaPAs in a liquid phase on this substrate. For example, using GaAs _1-y P _y (y=0.3) as a substrate, layers are sequentially deposited on this substrate by liquid phase growth.
The first of In _1-x Ga _x As _1-y P _y (x=0.66, y〓0.01)
Clad layer, followed by x=0.84~0.86, y=0.38~
In _1-x Ga _x As _1-y P _y active layer of 0.42;
A double heterostructure consisting of a second cladding layer having the same composition as the first cladding layer is realized. (R,
CHIN et,al, IEEE.Journal of Quantum
electronics vol QE―14 No.10, October1978).

After forming stripe electrodes and attaching ohmic electrodes on a double heteroepitaxial wafer with such a structure, when a forward current is applied, a laser beam with an oscillation wavelength of 6280 Å reaches a threshold current of about 100 mA at 77㎓. It can be obtained with However, continuous oscillation at room temperature was not possible, and the above report states that when a current approximately 10 times that of 77〓 was applied as a pulse, an oscillation wavelength of 6580 Å was obtained.

In addition, for a semiconductor laser with the same structure as in the above report, with a first cladding layer of 1 μm, an active layer of 0.2 μm, a second cladding layer of 4 μm, and a stripe electrode of 25 μm width, the oscillation wavelength and threshold at 77㎓ were determined. As a result of examining the value current, they are 6278Å and 6278Å, respectively.
A value of I _Th =98 mA was obtained.

However, after examining epitaxial wafers with the same structure in more detail, the inventor came to the knowledge that this threshold propagation largely depends on the striped pattern (hereinafter referred to as crosshatch) on the vapor-grown GaAsP. . FIG. 1 shows the striped pattern on this substrate. The GaAsP growth layer grown in vapor phase on the GaAs (100) plane is oriented in the <110> direction.
A lattice-like striped pattern (called a crosshatch) made up of unevenness that is perpendicular to each other is seen, and as shown in the figure, there are many horizontal stripes and few vertical stripes. When double heteroepitaxial growth is performed on such a substrate using the liquid phase method using the above-mentioned composition, the cross section A-B (cleavage plane) in Fig. 1 becomes extremely uneven as shown in Fig. 2. It became a fierce aspect. 1 in the diagram is
A GaAsP substrate, 2 is a first cladding layer, 3 is an active layer, and 4 is a second cladding layer. (GaAs crystals are omitted). However, the CD cross section in FIG. 1 was a very flat growth surface as shown in FIG. The present inventors have discovered the fact that when forming stripe electrodes on such an epitaxial wafer, the threshold current is significantly reduced by forming the stripe electrodes in the longitudinal direction parallel to the CD direction. I found out that there is.
This will be explained below by giving examples.

<Example 1> Using a general slide board for liquid phase growth,
n- _{In 1 -x} Ga _x P _1-z As _z (x
= 0.66, z = 0.01 Se doped), active layer: In _1-x Ga _x P _1-z As _z (x = 0.84, z = 0.4 non-doped), second cladding layer: p-
In _1-x Ga _x P _1-z As _z (x = 0.84, z = 0.01 Zn doped) was grown sequentially.

The size of the board was 1 cm x 1 cm, and it was placed in the boat so that the sliding direction was in the direction of AB in FIG. 1 of the board.

Electrodes were attached to such a double heteroepitaxial wafer as shown in FIG. Note that the stripes are attached in the CD direction shown in FIG.

In Fig. 4, 5 is the GaAsP substrate layer, 6 is the first layer.
The composition of the cladding layer is as above, 7 is an active layer, 8 is a second cladding layer, 9 is an Al ₂ O ₃ oxide film, and 10 is an alloy of Au and Cr to form an ohmic electrode, and then Au. It is a 25 μm wide stripe electrode with vapor deposited. 11 is an ohmic electrode made of an alloy of Au and Sn. The size of the sample is 200 μm x 300 μm and the thickness is 100 μm.

FIG. 5 shows a comparison of characteristics between the above semiconductor laser and a semiconductor laser having the same composition but with striped electrodes oriented in the direction of AB in FIG. 1. Figure 5 shows the 77
This is a comparison of the threshold currents at 〓. Although the two methods only differed in the mounting direction of the stripe electrodes, the threshold current was reduced by about 1/3.3 on average in the case of the present invention in which the stripe electrodes were formed in the longitudinal direction in the C-D direction. ing.

<Example 2> During liquid phase epitaxial growth, the position of the substrate with respect to the boat was placed in the direction where the crosshatch was strong, that is, the CD direction in FIG. 1 was the sliding direction of the boat, and double epitaxial growth was performed. manufactured wafers. When the same electrode as in Example 1 was attached and the change in threshold current depending on the direction of the striped electrode was observed, the threshold current was 20% in the A-B direction and 30% in the C-D direction compared to the case shown in Fig. 5. It was found that the current was improved.

Continuous oscillation was also possible at room temperature when the threshold current was less than 20mA. Note that the threshold current at this time was approximately 230 mA.

<Example 3> The value of y of the vapor-phase grown n-GaAs _1-y P _y substrate was varied in the range of 0.15 to 0.4.

Note that in all of the substrates within this range, crosshatches were observed that were strong in the CD direction and weak in the AB direction, as shown in FIG. Using the above board,
A double heterostructure was grown by matching the lattice constants, and a striped electrode was formed using the method described in Example 1.
-B direction and C-D direction, and the ratio of their threshold currents was investigated. FIG. 6 shows the results, and the horizontal axis shows the P concentration y of the GaAs _1-y P _y substrate. Also, the vertical axis indicates the stripe electrode as the first
Threshold current when installed in direction A-B in the diagram
This shows the ratio of Ith _A - _B to Ith _C - _D in the CD direction, that is, the degree of improvement in the threshold current by attaching the stripes in the CD direction.

As can be seen from the figure, the effect of the present invention is not so significant in the region where the value of y is small, that is, in the case where a substrate with a low P concentration is used. The lower limit value of y at which the effects of the present invention begin to appear was 0.15.
In addition, for samples with a y value of 0.35 or more, a pulse current was applied to examine the threshold current, but no oscillation was observed in samples with a y value of more than 0.4. Therefore, the upper limit of y in this embodiment is effective even up to 0.4. In fact, when we cut open samples with different y values in the direction of A-B in Figure 1 and observed them, we found that some samples with small y values had 3.
As shown in the figure, a good double heterostructure with few irregularities was observed.

In this example, a broad contact type structure was described, but diffused type, embedded type (Appl, Phys. Lett35, 7, P513, 1979), TJS type (IEEE, Journal of Quantum Electronics QE
-11, P42, 1975), a similar effect was obtained, and furthermore, oscillation was observed at low currents.

As described above, the present invention provides at least Ga, P,
In, Ga,
The stripe electrode of a double heterojunction semiconductor laser device, which has at least one epitaxial layer containing at least three types of elements among As and P, is arranged so that its longitudinal direction coincides with the direction of strong crosshatch on the substrate. With this structure, the threshold current can be significantly reduced.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing the appearance of cross hatches on the semiconductor substrate used in the present invention, FIG. 2 is a cross-sectional view taken along the direction A-B in FIG. 1, and FIG. 3 is a cross-sectional view taken along the line C-D in FIG. 4 is a perspective view of a semiconductor device according to an embodiment of the present invention, FIG. 5 is a diagram showing threshold current characteristics, and FIG. 6 is a diagram showing threshold current characteristics.
FIG. 3 is a diagram showing the relationship between the value of GaAs _1-y P _y and the threshold current. DESCRIPTION OF SYMBOLS 1, 5... Semiconductor substrate, 2, 6... First cladding layer, 3, 7... Active layer, 4, 8... Second cladding layer, 10... Stripe electrode.

Claims (1)

[Claims] 1. On a semiconductor substrate containing at least Ga, P, and As and having an approximately (100) plane,
At least one epitaxial layer containing at least three types of elements shown by As and P
In a double heterojunction semiconductor laser device having a layer, <110> appears on the surface of the semiconductor substrate;
Of the two types of striped pattern groups consisting of surface irregularities that have directions and are orthogonal to each other, the denser striped pattern
Alternatively, a semiconductor laser device characterized in that a stripe electrode is provided so that the stripe direction of a group of stripes with large unevenness steps coincides with the longitudinal direction of the stripe electrode. 2. The semiconductor laser device according to claim 1, wherein the semiconductor substrate is made of a GaAs _1-y P _y substrate, and the value of y is 0.15 or more and 0.4 or less.