JPS5941317B2 - Manufacturing method of semiconductor laser device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a semiconductor laser device having a low threshold current and good temperature characteristics of the threshold current.

It is extremely desirable to reduce the threshold current that causes laser oscillation in a semiconductor laser device, and for this purpose, several structures are known, but a TJS type laser device that can achieve single mode oscillation is particularly excellent.

Figure 1 is a perspective view showing the basic structure of a conventional TJS laser device.
) Substrates 2, 3, 4, 5, and 6 are each GaAs
N-type GaAs layers, p-type aluminum, gallium, and
Arsenic (AIGaAs) layer, N-type AlGaAs layer, N-type G
an aAs active layer and an N-type AlGaAs layer.

7 is a P-type AlGaAs layer, and 8 is Ga from this P-type AlGaAs layer.
9 is a P-type layer formed by diffusing P-type impurities into the As substrate 1 and epitaxial layers 2 to 6;
This is an active region formed by diffusing type impurities.

Further, 10 and 11 are N-side and P-side electrodes, respectively.
2A to 2D are cross-sectional views of each step of this conventional TJS laser device to show the manufacturing method, but since the outline is clear from the device configuration in FIG. Avoid this and stick to the general outline.

First, layers 2 to 6 are epitaxially grown on a P-type GaAs substrate 1 by a liquid phase epitaxial method (see Fig. 2A).
). Then, silicon nitride (
A mask 15 such as Si3N4) film is formed (Fig. 2B).
). After etching the portion where the Si3N4 film 15 is not formed until it reaches the GaAs substrate 1 by chemical etching or pre-epitaxial melt etching to form the groove 16 (FIG. 2C), the P-type AlGaAs layer 7 is etched into the structural portion 1.
Epitaxial growth is selectively performed only on 6.

Further, a P-type AlGaAs layer 7 is grown, and a P-type impurity is diffused into the GaAs substrate 1 and epitaxial layers 2 to 6 during the growth to form a P-type layer 8 there (FIG. 2D).

Thereafter, the Si3N4 film 15 is removed, N-side and P-side electrodes are formed, and the device is divided into chip shapes to complete the device. However, in the manufacturing process of the conventional apparatus, as shown in FIG. 2B, the selective growth mask 15 is required in the selective growth process.

This mask 15 normally uses a Si3N4 film, but since the Si3N4 film has a thermal expansion coefficient different from that of the underlying AlGaAs or GaAs layer, stress is applied to the epitaxially grown layer. In particular, stress is concentrated at the boundary between the portions with and without the Si3N4 film, causing defects in the epitaxial layer during the selective growth process. These defects invaded the GaAs active region 9, shortening the life of the laser diode and causing problems such as deterioration of reverse characteristics. Further, in the conventional device described above, the P-N junction is exposed on the chip surface J, and therefore the N-side electrode 10 can be formed in only one groove on the chip surface. Therefore, assembly can only be carried out by the so-called upside-up method in which the active region 9, which generates heat during laser oscillation, is located above the chip. In the upside-down method, the heat generated in the active region 9 must be diffused through the thick substrate 1. For this reason, in conventional semiconductor laser devices,
There were problems in that not only the threshold current increased, but also characteristics deteriorated quickly due to heat generation. Furthermore, in the above-mentioned four conventional device manufacturing methods, in order to perform selective growth, the process of processing the wafer once epitaxially grown is unavoidable. As a result, the epitaxial wafer may be distorted or contaminated during handling such as forming the mask pattern 15 for selective growth, which may adversely affect the characteristics of the semiconductor laser device. In addition, in the selective growth process,
Since the wafer that has been epitaxially grown is once again exposed to a high-temperature atmosphere, there have been problems such as thermal decomposition or oxidation of the surface of the wafer on which epitaxial growth was first performed, which adversely affects the characteristics of the semiconductor laser device. This invention was made in view of the above-mentioned points, and does not use any mask such as Si3N4 film that causes stress to the epitaxial layer, and also has a P-N junction on the surface of the chip. Therefore, it is possible to attach electrodes to the entire surface of the semiconductor laser device, and to provide a method for manufacturing a semiconductor laser device in which an active region can be formed in one epitaxial growth. FIG. 3 is a perspective view showing the structure of an example of a semiconductor laser device according to the present invention.

12 is an N-type GaAs substrate with a step, 4 is an N-type AlG
aAs layer, 5 is N-type GaAs active layer, 6 is N-type AlGa
As layer, 3 is P-type AlGaAs layer, 2 is N-type GaAs layer, 7 is P-type AlGaAs layer, 13 is P-type GaAs layer.
This is the contact layer.

Further, 8 is the epitaxial layer 4 from the P-type AlGaAs layer 7.
, 5, 6, 3, and 2 are P-type layers in which P-type impurities are diffused. 14 is P-type GaAs formed on the GaAs substrate 12.
It is a layer.

Reference numeral 9 denotes an active region formed in a part of the GaAs active layer 5 by diffusion of P-type impurities.

Further, 10 and 11 are N-side and P-side electrodes, respectively.
Here, the P-type GaAs layer 14 and the P-type AlGaAs layer 3 form an N-P-N structure in which each side is sandwiched between N-type layers, and during laser operation, the current is reverse biased and no current flows, causing the active region 9 to It has a structure that effectively concentrates current. FIGS. 4A to 4D are cross-sectional views at each stage for explaining an embodiment of the manufacturing method according to the present invention.

First, a P-type layer 14 is formed on the surface of an N-type GaAs substrate 12 by diffusion or epitaxial growth, a band-shaped mask such as photoresist is formed, a groove 16 is formed by chemical etching, and then the resist mask is removed. to clean the surface (Figure 4A). Next, epitaxial growth is performed on the entire surface of the substrate in which the groove 16 is provided. First, the GaAs substrate 12
N-type AlGaAs layer 4, N-type GaA
s active layer 5, N-type AlGaAs layer 6, and P-type AlGa
An As layer 3 is provided, and then an N-type GaA layer is formed so as to fill the trench 16.
The s-layer 2 is epitaxially grown (FIG. 4B).

Here, in order to grow along the grooves provided in the GaAs substrate 12, the slow cooling rate during growth should be set to 0.5 de9/Mm or more, and in order to grow so as to fill the grooves, the slow cooling rate during growth should be The cooling rate may be set to 0.3 de9/Mm or less. The epitaxially grown wafer is removed from its surface by melt etching until at least a portion of each epitaxial layer 4, 5, 6, 3, and 2 is reached (FIG. 4C), and then P-type AlGaAs layer 7 and P-type G
An aAs layer 13 is grown. The growth of the P-type AlGaAs layer 7 and the P-type GaAs contact layer 13 is improved by using a P-type impurity such as Zn or Cd which has a high diffusion rate into the crystal as a dopant for the P-type AlGaAs layer 7. A P layer 8 is formed by diffusing into the epitaxial layer. (Figure 4D). Thereafter, P-side and N-side electrodes are attached to the P-type GaAs contact layer 13 and the N-type GaAs substrate 12, respectively, and separated into chips to complete the laser device. In the above embodiment, GaAs-AjG
Although the case using an aAs-based crystal has been described, the present invention can be widely applied to semiconductor laser devices using semiconductor crystals having different forbidden band widths.

Furthermore, it is obvious that the conduction type of each part may be reversed from this embodiment. In addition, the P-type GaAs layer 14 and the P-type AlGa
The As layer 3 is formed to prevent the flow of reactive current, but the resistance of these layers is 10Ω? Even with the above-mentioned high resistivity layer, the effect is exactly the same.

Furthermore, in the above embodiment, the structure of a single heterojunction TJS laser was described, but the P-type AlGaAs layer 7 is
The effects of the present invention are also similar in the case of a homojunction type in which a shape diffusion layer is used. To manufacture a homojunction type TJS laser, after forming the layer shown in FIG. 4B, as shown in FIG. 5, p+ diffusion is performed from the entire surface of the epitaxial growth surface to form a p+ diffusion layer 17. Therefore, a P-type layer may be formed.

Further, in the above embodiment, a case was described in which the active region 9 was formed in a straight line perpendicular to the helical end face, but the P-type GaA
As mentioned above, the active region 9 is made of AlGaA with a small refractive index.
Surrounded by the S layers 4, 6, and 7 and the N-type GaAs layer 5, a strong index guiding structure is formed. Therefore, the active region can have a curvature depending on the strength of the guide, and if it is made circular, it can also be used as a ring laser. As explained above, in the semiconductor laser device and its manufacturing method according to the present invention, a groove is formed in the substrate before epitaxial growth and an active region is formed using the groove, so a mask such as a Si3N4 film is used. is not required, so that the adverse effects caused by the difference in thermal expansion coefficient between the Si3N4 film and the semiconductor layer can be avoided.

Furthermore, in order to efficiently concentrate current in the active region, the structure is such that a reverse bias layer is provided in a portion where reactive current tends to flow. Further, according to the present invention, since the epitaxial growth process can be performed in one growth process, reproducibility is good and there is no contamination during the process. Furthermore, in this structure, since the PN junction does not appear on the surface of the semiconductor chip, electrodes can be formed on the entire surface, and an upside-down mounting method with good heat dissipation is also possible. As described above, according to the present invention, it is possible to manufacture a semiconductor laser device that has a low threshold current during laser oscillation, has good temperature characteristics, and has a long life.

[Brief explanation of the drawing]

Figure 1 is a perspective view showing the basic structure of a conventional TJS type semiconductor laser device, Figures 2A-D are cross-sectional views at each stage showing the manufacturing method of this conventional device, and Figure 3 is the main structure of the conventional TJS type semiconductor laser device. A perspective view showing the structure of an example of a semiconductor laser device according to the invention, FIGS. 4A to 4D are cross-sectional views at each stage for explaining an embodiment of the manufacturing method according to the invention, and FIG. FIG. 3 is a sectional view showing another embodiment of the invention. In the figure, 12 is an N-type GaAs substrate, 16 is a groove, 5 is an active layer, 4 and 6 are 8 N-type AlGaA layers, 14 and 3 are P-type layers for preventing reactive current, 7 is a P-type AlGaAs layer, and 8 is a P-type layer. 9 is an active region.

Claims (1)

[Claims] 1. A step is provided on a part of one main surface of a semiconductor substrate of a first conductivity type, and a first semiconductor layer of a first conductivity type is formed on the main surface of the semiconductor substrate along the step; 1st above
a second semiconductor layer of a first conductivity type having a narrower forbidden band width than the semiconductor layer; and a first semiconductor layer having a wider forbidden band width than the second semiconductor layer.
a third semiconductor layer having a conductivity type of After forming a fifth semiconductor layer having a first conductivity type with a narrower forbidden band width than the first semiconductor layer so as to reduce the step difference on the surface of the layer, from the surface of the fifth semiconductor layer At least a portion of each of the first to fifth layers is exposed by etching, and a second conductivity type determining impurity is introduced to a predetermined depth from the entire exposed surface, and the second semiconductor layer is formed on this surface. A sixth semiconductor layer having a second conductivity type whose forbidden band width is wider than that of the sixth semiconductor layer, and a seventh contact layer having a second conductivity type whose forbidden band width is narrower than that of the sixth semiconductor layer. A method for manufacturing a semiconductor laser device.