JPS6320396B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in semiconductor laser devices used as light sources for optical fiber communications or optical information processing.

Semiconductor laser elements are small in size, have high power efficiency, have a long lifespan, and are easy to maintain, which are unmatched by other lasers, so in recent years their use as light sources for optical fiber communications and optical information processing has been increasingly widespread. However, semiconductor lasers have the characteristic that their oscillation threshold changes with changes in ambient temperature, and therefore their optical output varies. For this reason, conventional semiconductor laser devices are used together with a photodiode to monitor variations in optical output, and a bias current adjustment circuit is added to keep the optical output constant. A semiconductor laser device with a built-in monitor is also known, which monolithically integrates a photodiode with a semiconductor laser device to reduce the number of steps required to assemble the device and to downsize the device as a whole.

However, in the conventional semiconductor laser device with a built-in monitor, a monitor photodiode is formed in a cascade with the laser in the direction of the optical output beam of the laser. For this reason, in the prior art, the laser was constructed with an etched mirror surface whose characteristics were inferior to that of the cleavage plane of the crystal, and a photodiode was constructed separate from the laser. A mirror surface with poor characteristics causes deterioration of laser operation, and a photodiode's light absorption section, which is shared with the active layer of the laser operating section, has the drawback of becoming an obstacle to improving the photodiode's characteristics. Ta.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks and to provide a semiconductor laser device with a built-in monitor that has a built-in highly sensitive monitor and does not cause deterioration of laser operating characteristics.

According to the present invention, in a current injection type semiconductor laser device having a semiconductor multilayer structure including a semiconductor heterojunction, a base region formed of a collector electrode and a light absorption layer separated from a current injection electrode is provided. A semiconductor laser device with a built-in monitor is obtained, which is characterized in that a phototransistor structure including the above is integrated.

Next, the present invention will be explained in detail with reference to the drawings.
The drawing is a cross-sectional view perpendicular to the laser light output beam direction of one embodiment of the present invention. This embodiment includes an active region 11 formed on an n-type semiconductor substrate 10 and having a buried structure, a cladding region 12 made of a p-type semiconductor, a light absorption layer 13 on the cladding region 12, and an n-side electrode 19. It is composed of a current injection electrode 17 and a collector electrode 18. During crystal growth, the light absorption layer 13 is formed of an n-type conductivity type opposite to that of the cladding region 12, and then a collector region 14 is formed by thermal diffusion of p-type impurities.
and a current injection stripe region 15 connected to the cladding region 12. Note that the current injection electrode 17 and the collector electrode 18 are the insulating film 1.
6. To describe the composition and dimensions of each main part, the semiconductor substrate 10 is made of InP single crystal with a plane orientation of (100) and has a thickness of about 70 μm, and the active region 11 has a stripe shape extending in the <011> direction and has a width of 2 μm.
m, thickness 0.15μm, equivalent to oscillation wavelength 1.3μm
In _0.74 Ga _0.26 As _0.56 P _0.44 , the cladding region 12 is Zn-doped InP with a thickness of about 2 μm above the active region 11, and the light absorption layer 13 is In _0.72 Ga with a thickness of about 1.5 μm, corresponding to an absorption edge wavelength of 1.35 μm. _0.28 As _0.62 P _0.38 , the current injection stripe region 15 has a p
The collector region 14 has a width of about 5 μm centered on the active region 11 and is inverted to a p-type by Zn diffusion to a depth of 1 μm, and is spaced apart from the current injection stripe region 15 by about 10 μm. The insulating film 16 has a stripe shape with a width of about 20 μm and a thickness of 0.2 μm.
m SiO ₂ , current injection electrode 17 and collector electrode 18 are Au-Zn alloy with a thickness of about 0.3 μm, n-side electrode 1
9 is an Au-Sn alloy with a thickness of about 0.3 μm. The device is cut out by cleavage in a direction perpendicular to the stripe direction of the active region 11, and its cavity length is approximately
It is 250 μm.

Now, by applying a positive voltage to the current injection electrode 17 and a negative electrode to the n-side electrode 19, a current injection stripe region 15 and a cladding region 12 are applied to the active region 1.
When a current is injected into 1, laser oscillation starts at a point where a current of 30 to 40 mA or more is injected. Collector electrode 1
8 is applied with a negative voltage. A portion of the laser light output scattered by optical imperfections at the interface between active region 11 and cladding region 12 is absorbed by base region 13a, generating a photoexcitation current. This photoexcitation current is amplified by the high current amplification factor of the heterojunction pnp type phototransistor structure constituted by the cladding region 12, the base region 13a, and the collector region 14, and is taken out from the collector electrode 18. In conventional integrated photodiodes, the light absorption layer of the photodiode was often the same as the active layer of the laser, resulting in low light receiving efficiency and only a small monitor current. In this embodiment, since the composition of the light absorption layer 13 can be optimized independently of the composition of the active region 11, high light receiving efficiency can be obtained, and furthermore, since the light is amplified by the high amplification factor of the phototransistor structure, slight scattering can be achieved. Sufficient monitor current can be obtained just by using light. Further, in this embodiment, since the monitor section is arranged in parallel with the laser section, there is an advantage that a resonator can be formed by cleaving the crystal, as in the conventional semiconductor laser device.

By the way, in the above embodiment, the cladding region 12 does not have a current blocking structure, but a current blocking layer made of an n-type semiconductor may be added. Further, the structure of the current injection type semiconductor laser device is not limited to the above-mentioned structure, but may be any other buried structure, or may be a non-buried structure in which the active layer has a planar extent. Semiconductor materials are not necessarily InP/
The material is not limited to InGaAsP, but may be any material such as GaAs/GaAlAs that can form a semiconductor laser device.

Finally, to summarize the advantages of the present invention, by incorporating a highly sensitive monitor into a high-performance semiconductor laser device that uses cleavage planes, a semiconductor laser device with a built-in monitor that is convenient for stabilizing optical output can be obtained. It is something that can be done.

[Brief explanation of the drawing]

The drawing is a cross-sectional view of one embodiment. In the figure, 10...semiconductor substrate, 11... active region, 12... cladding region, 13... light absorption layer,
13a...Base area, 14...Collector area,
15... Current injection stripe region, 16... Insulating film, 17... Current injection electrode, 18... Collector electrode, 19... N-side electrode.

Claims (1)

[Scope of Claims] 1. In a current injection type semiconductor laser device having a semiconductor multilayer structure including a semiconductor heterojunction, a cladding layer formed above an active region of the semiconductor laser device is used as an emitter region and A base region and a collector region are included in a light absorption layer formed on the cladding layer and have a smaller band gap than the semiconductor constituting the active region and a conductivity type opposite to that of the cladding layer. A semiconductor laser device with a built-in monitor, characterized in that a phototransistor structure having a structure electrically isolated from a current injection part by introducing an impurity into the light absorption layer is integrated. 2. The current injection type semiconductor laser device according to claim 1, wherein the current injection type semiconductor laser device has a buried structure active region, and the base region is provided at a position apart from above the active region. Semiconductor laser element with built-in monitor.