JPH03795B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to improvements in edge-embedded semiconductor laser devices.

[Technical background of the invention and its problems]

Semiconductor lasers are expected to find wide application in light sources for optical communications, light sources for optical disks, and the like. but,
Semiconductor lasers are generally extremely susceptible to overcurrent, and it is known that even a pulsed overcurrent can lead to destruction of the device. This property is caused by the current dependence of the optical output of the semiconductor laser and is unavoidable. That is, in a 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 optical output increases greatly with a slight increase in the drive current. The oscillation threshold current I _th of a semiconductor laser is normally several tens of milliamperes (mA), but the optical output generated by an overcurrent several times that amount will cause irreparable damage to the end face of the active region of the semiconductor laser. This is sufficient to cause destruction of the device. This phenomenon is particularly noticeable in GaAlAs-based semiconductor lasers, and it is known that the device is destroyed when the optical output density at the end face of the active region reaches about 10 ⁶ [W/cm ² ].

This characteristic of semiconductor lasers, which is easily destroyed by overcurrent, is extremely inconvenient when handling semiconductor lasers, and has been a major problem in putting semiconductor lasers into practical use.

[Purpose of the invention]

An object of the present invention is to provide a semiconductor laser device that is resistant to breakage due to overcurrent.

[Summary of the invention]

In order to solve the above-mentioned problems in semiconductor lasers, 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, since the optical output of a semiconductor laser increases extremely steeply as the injected current increases, simply increasing the optical output that causes optical damage to the laser resonator end face will not cause the semiconductor laser to generate enough current to cause destruction. The increase in value is small and the effect is weak. In order to obtain a sufficient effect, it is sufficient to make the end face of the active region a buried type and to provide characteristics such that the optical output is saturated with respect to the injected current at an optical output level smaller than the optical damage output.

The present invention focuses on these points, and in a semiconductor laser device having a double heterojunction structure in which an active layer is sandwiched between cladding layers on a semiconductor substrate, the end face of the active region including the active layer is prohibited from the active layer. an auxiliary cladding layer buried deeper than the end face of the laser resonator by a burying layer with a large band width and having a forbidden band width larger than the active layer and smaller than the main cladding layer, at least on one side between the active layer and the cladding layer; It was designed to be formed as follows.

The main cause of optical damage to the semiconductor laser end face is that laser light is reabsorbed at the active region end face, thereby promoting heat generation and chemical reactions with oxygen or moisture present in the atmosphere. Therefore, the end face buried structure as in the present invention is advantageous because there is no absorption of laser light at the resonator end face and the active region is not affected by oxygen, moisture, etc. in the atmosphere. This is extremely advantageous in increasing damage output. In fact, by using an end-embedded structure, it is possible to increase the optical damage output by about one order of magnitude.

In addition, in a normal double heterojunction laser, the difference in forbidden band width between the active layer and the main cladding layer sandwiching it is
Eg is about 0.4 [eV], and the injected carriers are almost completely confined in the active layer due to the potential barrier at the heterojunction interface caused by this. In the present invention, an auxiliary cladding layer is formed between the active layer and the main cladding layer to reduce the difference in forbidden band width Eg' between the active layer and the auxiliary cladding layer.
The overflow of the injection carriers into the auxiliary cladding layer allows the optical output to be saturated at high injection levels. In other words, the difference in forbidden band width
When the injection current is increased while Eg' is small, a part of the carriers injected into the active layer will overflow to the outside of the active layer beyond the potential barrier, and the increase in the injection current will cause an increase in the light emission output. will no longer contribute. Therefore, the relationship between the optical output and the injected current exhibits a saturation characteristic as shown in FIG. The magnitude of the optical output at which this saturation characteristic appears is determined by the difference in the forbidden band width between the active layer and the auxiliary cladding layer.
It depends on the magnitude of Eg' and the magnitude of laser loss determined by the structure of the semiconductor laser.

Here, if the magnitude of the saturated optical output is made smaller than the optical damage output of the semiconductor laser, the limit of destruction of the semiconductor laser due to overcurrent can be raised to the limit where the laser is destroyed by heat generation due to the resistance component. can. In the case of an end-embedded structure, the optical output level at which optical damage occurs is about one order of magnitude higher than that of a normal semiconductor laser, so the above-mentioned saturation output is sufficient for high output requirements such as optical disk writing. It can be a value of

〔Effect of the invention〕

According to the present invention, it is possible to raise the destruction limit of a semiconductor laser due to overcurrent from the destruction limit due to optical damage to the thermal destruction limit. Therefore, the resistance of the semiconductor laser device to overcurrent can be significantly improved. In addition, since the breakdown limit is thermal, it is extremely resistant to breakage against pulsed overcurrents, which occur most often in practice.

[Embodiments of the invention]

FIG. 3a is a perspective view showing a schematic structure of an end-face buried semiconductor laser device according to an embodiment of the present invention, and FIG. 3b is a sectional view taken along the arrow AA in FIG. 3a. In the figure, 1 is an N-GaAs substrate (semiconductor substrate), and on this substrate 1 are an N-Ga _0.65 Al _0.35 As layer (main cladding layer) 2 and an 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
A mesa stripe portion is provided in which layers (ohmic contact layers) 7 are laminated in the above order. The side and end surfaces of the mesa stripe section are
Ga _0.65 Al _0.35 As layer (buried by buried layer 8. In FIG. 3, 9 indicates a Si ₃ N ₄ insulating film for current confinement, and 10 and 11 indicate electrodes, respectively.

Next, a method of manufacturing the device of the above embodiment will be explained. First, as shown in FIG. 4a, a main cladding layer 2, an auxiliary cladding layer 3, an active layer 4, an auxiliary cladding layer 5, a main cladding layer 6, and an 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 (mask) 12 is deposited on the ohmic contact layer 7, and H ₃ PO ₄ :H ₂ O:CH ₃ OH=
Using a 1:1:3 etching solution and using the Si ₃ N ₄ film 12 as a mask, the layers 2, -, 7 are etched onto the substrate 1.
Mesa etching to a depth of . Thereafter, using the Si ₃ N ₄ film 12 as a mask again, the mesa region is buried with the buried layer 8 by the LEP method as shown in FIG. 4c. Next, after removing the Si ₃ N ₄ film 12, the insulating film 9 is formed only on the buried layer 8, and then the metal electrodes 10 and 11 are formed by vapor deposition to form the structure shown in FIGS. 3a and 3b. A semiconductor laser device is obtained.

The thus obtained semiconductor laser device had far greater resistance to overcurrent than the conventional double heterojunction semiconductor laser device in which the auxiliary cladding layers 3 and 5 were not formed.

Note that the present invention is not limited to the embodiments described above, and can be implemented with various modifications without departing from the gist thereof. For example, the auxiliary cladding 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. Furthermore, the forbidden band width of the auxiliary cladding layer may be determined as appropriate in a range that is greater than that of the active layer and smaller than that of the main cladding layer, depending on the desired saturation output, etc. Further, in the embodiment, the side surfaces of the active region are also buried with a buried layer, but the side surfaces of the active region do not necessarily have to be buried. Furthermore, the semiconductor material to be used is not limited to GaAlAs-GaAs type, but InGaAsP-InP type and other various semiconductors can be used.

[Brief explanation of drawings]

FIG. 1 is a characteristic diagram showing the relationship between drive current and optical output in the conventional device, FIG. 2 is a characteristic diagram showing the relationship between drive current and optical output in the device of the present invention, and FIG.
Figure a is a perspective view showing a schematic configuration of an edge-embedded semiconductor device according to an embodiment of the present invention, Figure 3 b is a sectional view taken along arrow A-A in Figure a, and Figures 4 a to c are the above-described implementations. FIG. 3 is a cross-sectional view showing the manufacturing process of the example device. 1...Na-GAs 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), 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 (auxiliary cladding layer). Microcontact layer), 8...Ga _0.65 Al _0.35 As layer (buried layer), 9... Si ₃ N ₄ film (insulating film), 10, 11
...Electrode, 12...Si ₃ N ₄ film (mask).

Claims (1)

[Claims] 1. In a semiconductor laser device having a double heterojunction structure in which an active layer is sandwiched between main cladding layers on a semiconductor substrate, the end face of the active region including the active layer is formed by a buried layer having a wider forbidden band width than the active layer. An auxiliary cladding layer buried deeper than the end face of the laser resonator and having a forbidden band width larger than the active layer and smaller than the main cladding layer is formed at least on one side between the active layer and the main cladding layer. Features of the semiconductor laser device.