JPH0682888B2 - Method of manufacturing semiconductor laser device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor laser device, and more particularly to a method for manufacturing an end face buried type semiconductor laser device in which an end face of an active region is buried inside an end face of a laser resonator.

[0002]

2. Description of the Related Art A semiconductor laser is expected to be widely applied to a light source for optical communication, a light source for optical discs and the like. But,
It is known that semiconductor lasers are generally extremely vulnerable to overcurrent, and even if they are pulse-like, they lead to device destruction. This property is difficult to avoid because it depends on the current dependency of the optical output of the semiconductor laser.
That is, in the semiconductor laser, as shown in FIG. 1, in the current region larger than the oscillation threshold current I _th , that is, in the oscillation state, the light output greatly increases with a slight increase in the drive current. The oscillation threshold current I _th of a semiconductor laser is usually several tens.
The optical output generated by an overcurrent of about several times that of mA is sufficient to cause irreparable damage to the end face of the active region of the semiconductor laser, which leads to device breakdown. This phenomenon is particularly remarkable in the GaAlAs semiconductor laser, and the optical output density at the end face of the active region is 10 ⁶ W / cm ² It is known that destruction of the device occurs at a certain level. The characteristic of the semiconductor laser that it is easily destroyed by an overcurrent is extremely inconvenient in handling the semiconductor laser, and has been a serious problem in putting the semiconductor laser to practical use.

[0003]

As described above, in the conventional semiconductor laser device, there has been a problem that the end surface of the active region is broken due to the overcurrent. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for manufacturing a semiconductor laser device that is not easily broken by an overcurrent.

[0004]

As a solution to the above-mentioned problems in a semiconductor laser, an end face buried type laser in which the end face of the active region is buried with a buried layer has been developed. However, the optical output of the semiconductor laser increases extremely sharply with the increase of the injection current. Therefore, even if the optical output of the laser cavity end face is simply increased, the current that causes the semiconductor laser to break down. The increase in value is small and the effect is small. In order to obtain a sufficient effect, the end face of the active region may be of a buried type and have a characteristic that the optical output is saturated with respect to the injection current at the optical output level smaller than the optical damage output.

The present invention has been made paying attention to such a point, and in an end face buried type semiconductor laser device manufacturing method, an active layer is sandwiched between a main cladding layer and a main cladding layer on a semiconductor substrate. A double heterojunction structure is sandwiched between at least one of the clad layers and an auxiliary clad layer having a forbidden band width larger than the active layer and smaller than the main clad layer, and then the double heterojunction structure is selectively etched to form stripes. -Shaped mesa is formed, and then a buried layer having a band gap larger than that of the active layer is formed on the end face of the mesa so that the end face of the double heterojunction structure is buried inside the laser cavity end face. Is.

According to the present invention, in the method of manufacturing a semiconductor laser device having the above structure, an active layer is sandwiched between main cladding layers on a semiconductor substrate, and at least one of the active layer and the main cladding layer is covered with the active layer. A double heterojunction structure is sandwiched between auxiliary clad layers having a band gap that is larger than the main clad layer, and then a stripe-shaped mask is formed on the double heterojunction structure. The structure is selectively etched to the depth of the substrate to form a stripe-shaped mesa, and then a buried layer with a larger forbidden band width than the active layer is selectively grown in a portion not covered with a mask, and a double hetero structure is formed. This is a method in which the side surface of the junction structure portion is embedded and the end face of the double hetero junction structure portion is embedded inside the laser resonator end face.

[0007]

The main cause of the optical damage on the end face of the semiconductor laser is that the laser beam is re-absorbed by the end face of the active region, thereby promoting heat generation and chemical reaction with oxygen or moisture present in the atmosphere. Is. Therefore, since the end face buried structure as in the present invention does not absorb the laser light at the end face of the resonator, and the active region is not affected by oxygen and moisture in the atmosphere at all, the optical damage output is obtained. It is extremely advantageous in increasing the size. In fact, the optical damage output can be increased by about one digit by adopting the end face buried structure.

Further, in the usual double heterojunction laser, the difference Eg in the forbidden band width between the active layer and the main cladding layer sandwiching the active layer is about 0.4 eV, and the potential barrier at the heterojunction interface causes the injection. The generated carriers are almost completely confined in the active layer. In the present invention, the auxiliary clad layer is formed between the active layer and the main clad layer, and the forbidden band difference Eg ′ between the active layer and the auxiliary clad layer is formed.
Is smaller, it is possible to saturate the optical output at a high injection level due to the overflow of injected carriers into the auxiliary cladding layer.

That is, when the injection current is increased with the forbidden band difference Eg 'being made small, a part of the carriers injected into the active layer overflows the potential barrier to the outside of the active layer. Therefore, the increase in injection current does not contribute to the light emission output. Therefore, the relationship between the optical output and the injection current has a saturation characteristic as shown in FIG. The magnitude of the optical output at which this saturation characteristic appears depends on the magnitude of the difference Eg ′ in the forbidden band width between the active layer and the auxiliary cladding layer and the magnitude of the loss as a laser determined by the structure of the semiconductor laser.

Therefore, by setting the magnitude of the saturated light output smaller than the light damage output of the semiconductor laser, the limit of destruction of the semiconductor laser due to overcurrent is increased to the limit of destruction of the semiconductor laser due to heat generated by the resistance component. You can In the case of the end face buried structure, the level of the optical output that causes optical damage is about one digit higher than that of a normal semiconductor laser. Therefore, the above-mentioned saturation output is sufficient even for a high output demand such as optical disk writing. Can be any value.

[0011]

The details of the present invention will be described below with reference to the illustrated embodiments.

FIG. 3 shows a schematic structure of an end face buried type semiconductor laser device according to an embodiment of the present invention.
Is a perspective view, and (b) is a cross-sectional view taken along the line AA of (a).
In the figure, 1 is an n-GaAs substrate (semiconductor substrate), and on this substrate 1, an n-Ga _0.65 Al _0.35 As layer (main cladding layer) 2 n-Ga _0.75 Al _0.25 As layer (auxiliary cladding layer) 3 p-GaAs layer (active layer) 4 p-Ga _0.75 Al _0.25 As layer (auxiliary cladding layer) 5 p-Ga _0.65 Al _0.35 As layer (main cladding layer) 6 p-GaAs layer (ohmic contact layer) 7

A mesa stripe portion is formed by stacking the above in the order described above. The side surface and the end surface of the mesa stripe portion are filled with a Ga _0.65 Al _0.35 As layer (embedding layer) 8. In the figure, 9 indicates a Si ₃ N ₄ film (insulating film) for current constriction, and 10 and 11 indicate electrodes, respectively.

Next, a method of manufacturing the device of the above embodiment will be described. First, as shown in FIG. 4A, the main clad layer 2, the auxiliary clad layer 3, the active layer 4, the auxiliary clad layer 5, the main clad layer 6 and the ohmic contact layer 7 are epitaxially grown on the substrate 1 in the above order. .

Next, as shown in FIG. 4B, a striped Si ₃ N ₄ film (mask) 12 is deposited on the ohmic contact layer 7, and H ₃ PO ₄ : H ₂ O: CH ₃ is deposited.
Using the etching solution of OH = 1: 1: 3, the above Si ₃ N
_{4 Using the} film 12 as a mask, the layers 2 to 7 are mesa-etched to a depth reaching the substrate 1.

Next, using the Si ₃ N ₄ film 12 as a mask again, as shown in FIG. 4C, the buried layer 8 is selectively grown by the LPE method to form the mesa region in the buried layer 8.
Embed by. After that, after removing the Si ₃ N ₄ film 12, the insulating film 9 is formed only on the embedded layer 8,
Subsequently, the metal electrodes 10 and 11 are formed by vapor deposition to obtain the semiconductor laser device having the structure shown in FIG.

The semiconductor laser device thus obtained was much more resistant to overcurrent than the conventional double heterojunction semiconductor laser device in which the auxiliary cladding layers 3 and 5 were not formed.

The present invention is not limited to the above-described embodiments, and various modifications can be carried out without departing from the scope of the invention. For example, the auxiliary clad layer does not necessarily have to be on both sides of the active layer, but may be provided on one side of the active layer. Further, the forbidden band width of the auxiliary cladding layer may be appropriately determined within a range larger than that of the active layer and smaller than that of the main cladding layer, depending on a desired saturation output and the like. Further, in the embodiment, the side surface of the active region is also buried in the buried layer, but the side surface of the active region does not necessarily have to be buried. Further, the semiconductor material used is not limited to the GaAlAs / GaAs system, and InGaAsP / InP system and other various semiconductors can be used.

[0019]

As described in detail above, according to the present invention, it is possible to raise the breakdown limit of the semiconductor laser device due to overcurrent from the breakdown limit due to optical damage to the thermal breakdown limit. Therefore, the resistance of the semiconductor laser device to overcurrent can be significantly improved. Further, since the breaking limit is thermal, it is extremely hard to break against the pulse-like overcurrent that is most frequently generated in practice.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing a relationship between a drive current and a light output in a conventional device,

FIG. 2 is a characteristic diagram showing the relationship between drive current and light output in the device of the present invention,

FIG. 3 is a perspective view showing a schematic configuration of an end face buried laser according to an embodiment of the present invention,

FIG. 4 is a cross-sectional view showing a manufacturing process of an edge-embedded laser according to an embodiment of the present invention.

[Explanation of symbols]

1 ... n-GaAs substrate (semiconductor substrate), 2 ... n-Ga _0.65 Al _0.35 As layer (main cladding layer), 3 ... n-Ga _0.75 Al _0.25 As layer (auxiliary cladding layer), 4 ... p-GaAs layer ( Active layer) 4, 5 ... p-Ga _0.75 Al _0.25 As layer (auxiliary cladding layer), 6 ... p-Ga _0.65 Al _0.35 As layer (main cladding layer), 7 ... p-GaAs layer (ohmic contact layer), 8 ... Ga _0.65 Al _0.35 As layer (buried layer), 9 ... Si ₃ N ₄ (insulating film), 10, 11 ... electrode, 12 ... Si ₃ N ₄ film (mask).

Claims (2)

[Claims] 1. An auxiliary clad layer in which an active layer is sandwiched between main clad layers on a semiconductor substrate, and a forbidden band width larger than the active layer and smaller than the main clad layer is provided in at least one of the active layer and the main clad layer. A step of forming a double heterojunction structure part sandwiching the double heterojunction structure part, a step of selectively etching the double heterojunction structure part to form a stripe-shaped mesa, and a bandgap having a band gap larger than that of the active layer on an end face part of the mesa. A step of forming a large semiconductor layer and burying the end face of the double heterojunction structure portion inside the end facet of the laser resonator. 2. An auxiliary clad layer in which an active layer is sandwiched between main clad layers on a semiconductor substrate, and a band gap which is larger than the active layer and smaller than the main clad layer is provided in at least one of the active layer and the main clad layer. A step of forming a double heterojunction structure portion sandwiching the double heterojunction structure portion, a step of forming a stripe-shaped mask on the double heterojunction structure portion, and using the mask, select the double heterostructure portion to a depth reaching the substrate. A step of forming a stripe-shaped mesa by etching, and a buried layer having a larger forbidden band width than the active layer is selectively grown in a portion not covered with the mask, and a side surface of the double heterojunction structure is formed. And embedding the end face of the double heterojunction structure portion inside the end facet of the laser resonator. Law.