JPH04144297A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To obtain a highly reliable semiconductor laser device capable of an ultra high-speed modulation, by reducing junction capacitances inside the semiconductor laser, and by making the resistance values of the regions other than the current paths leading to an activated layer high, and further, by concentrating effectively high-frequency currents on the activated layer. CONSTITUTION:On an inverse mesa protruding part 20 formed on a substrate 1 of n-InP, laminated are in succession a buffer layer 2 of n-InP, an activated layer 3 of InGaAsP, and a clad layer 4 of p-InP. Further, a first high resistance layer 5 of InP, a stop layer 6 of InGaAsP, and a second high resistance layer 7 of InP are so formed in succession as to cover the inverse mesa protruding part 20. At this time, the stop layer 6 of InGaAsP is so formed as to be at the higher position than the activated layer 3 of InGaAsP, when using the substrate 1 of n-InP as a reference. Therefore, since the surroundings of the activated layer 3 of InGaAsP are the semiconductor layers of high resistance values, most of the currents implanted from a p-side electrode 10 flow into the activated layer 3 of InGaAsP, and an excellent structure in a high-frequency response speed is obtained.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a semiconductor laser device [Prior Art] Conventionally, this type of semiconductor laser device has been designed to reduce parasitic capacitance existing in areas other than the active layer, which is the light emitting region. In order to suppress the leakage of high-frequency signals, an insulating film such as SiO2 with a relatively low dielectric constant is formed on the semiconductor surface layer directly above the active layer.
It enabled high-speed modulation on the order of Gb/s.

[Problem to be solved by the invention]

The high-performance embedded semiconductor laser device conventionally used as a light source for optical communications mentioned above uses a p-n reverse bias junction as a current confinement structure, so it has a large p-n junction capacitance and cannot handle high-frequency signal currents. leaks to regions other than the active layer via this pn junction and the resistance of the semiconductor layer. Therefore, it has been difficult to obtain an ultrahigh-speed semiconductor laser device simply by forming an insulating film such as SiO2 on the surface of the semiconductor layer.

In addition, SiO2 itself has a capacitance. For example, if a SiO2 film with a thickness of about 3000 A is formed on an area about the size of a normal semiconductor laser element (300 x 250 μm2), the S
The capacitance of i02 itself is about 10pF, and 5G
The magnitude was not negligible for high frequency modulation of Hz or higher. Furthermore, since the thermal expansion coefficients of 5i02 and the semiconductor differ by about one order of magnitude, distortion remains inside the semiconductor after 5i02 is formed, which affects the reliability of the semiconductor laser.

The purpose of the present invention is to reduce the junction capacitance inside the semiconductor laser and increase the resistance of areas other than the current path leading to the active layer, thereby effectively concentrating high frequency current in the active layer.
The object of the present invention is to provide a highly reliable semiconductor laser device capable of ultra-high-speed modulation.

[Means to solve the problem]

In the semiconductor laser device of the present invention, when a mesa-shaped protrusion including a conductive buffer layer, an active layer, and a conductive cladding layer formed on a conductive semiconductor substrate is based on the conductive semiconductor substrate, An impurity diffusion layer is buried with high resistance layers sandwiching a diffusion stop layer formed at a higher position than the active layer, and is formed up to the conductive type cladding layer.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a cross-sectional view showing the structure of an embodiment of the present invention, and FIG. 2 is a cross-sectional view showing the manufacturing process of the embodiment of the present invention.

In FIG. 1, an n-InP buffer layer 2. InGa
AsP active layer 3. The first InP cladding layer 4 is sequentially laminated so as to cover the protrusion 20 of the inverted mesa.
P high resistance layer 5°I nGaAsP stop layer 6. A second InP high resistance layer 7 is sequentially formed. At this time I n
The GaAsP stop layer 6 is formed at a higher position than the InGaAsP active layer 3 with respect to the n-1nP substrate 1.

The depth of impurity diffusion is generally controlled by the diffusion time, but controllability is not good because it is difficult to control the temperature profile of the diffusion furnace and the vapor pressure of the diffusion atmosphere. Therefore, the InGaAsP layer 71 is provided to prevent the diffusion front from reaching the n-InP buffer layer 2 or the InGaAsP active As due to variations in the diffusion depth. I
The difference in diffusion rate between nP and InGaAsP, that is, In
This takes advantage of the fact that GaAsP has a slower diffusion rate than InP.6 Since the InGaAsP active layer 3 is surrounded by a high-resistance semiconductor layer, the p-side electric potential g! Most of the signal current injected from 10 flows into the InGaAsP active layer 3, resulting in a structure with excellent high frequency response speed.

Next, the manufacturing process will be explained with reference to FIG. n-
MO-C for stacking semiconductor layers on the InP substrate 1
Using a VD device, as shown in FIG. 2(A), n-In
P buffer layer 2 has a thickness of 3 μm.

InGaAsP active layer 3 is O,llzm, P-InP
A multilayer semiconductor 20 is formed by sequentially growing the cladding layer 4 to a thickness of 1 μm.

Next, as shown in FIG. 2(B), using the silicon nitride film 20 having a width of 2.5 μm as a mask, a protrusion on the inverted mesa is formed approximately at the center of the multilayer semiconductor layer 20 using an etching method. The etching depth is, for example, approximately 2 μm until reaching the n-InP buffer layer 2. At this time, the direction of the mask stripe is the <100> direction, and the etching solution is
Using a bromine methyl solution (a mixed solution of 0.2 cc of bromine and 100 cc of methyl alcohol), an inverted mesa-shaped protrusion is formed as shown in FIG. 2(B).

Next, as shown in FIG. 2(C), a first InP high resistance layer 5 of 1,51 tm and InGaA
An sP strike 71 layer 6 is formed to a thickness of 0.471 m. At this time, since the silicon nitride film 20 remains formed on the inverted mesa-shaped protrusion, the semiconductor layer does not grow. silicon nitride 1
After removing the IK20 using buffered hydrofluoric acid, the second InP high resistance layer 7 is formed to have a thickness of 1 μm, and the p-I nGaAsP cap layer 9 is formed to a thickness of 0 μm using the MO-CVD apparatus again.
．． Sequentially formed to have a thickness of 5 μm.

Next, impurity diffusion is performed over the entire surface in FIG.
Due to the sP stop layer 6, diffusion progresses slowly except outside the four p-InP cladding layers, so the diffusion front is
Since the current does not reach the P buffer layer 2 or the InGaAsP active layer 3, a current path in the low resistance layer is not formed around the InGaAsP active layer N3.

Thereafter, Cr and Au are sequentially vapor-deposited as vapor-deposited metals on the p-1n GaAsP cab 1 layer 9 side by a resistance heating vacuum vapor deposition method to form an electrode. After further heat treatment for 5 minutes in a hydrogen atmosphere at 380° C., the n-InP substrate 1 side is mirror-polished to a thickness of 150 μm. Subsequently, Au.Qe7''Ni was sequentially deposited on the n-InP substrate 1 side as an n-side electrode, and then heat-treated for 5 minutes in a hydrogen atmosphere at 380°C.

Finally, the p-side electrode as a protective electrode] Ti/Pt/' on the 0 side
Au and T i 7' Au are deposited on the n-side electrode 11 side using a sputtering device to complete the manufacturing process.

The cavity length of this semiconductor laser is 300 μm.
The semiconductor was cleaved so that A value of 10 GHz or more was obtained. This 3 db band can be expected to be further improved by increasing the photon density by shortening the cavity, decreasing the photon lifetime, cooling, etc.

Although the InGaAsP semiconductor laser has been described above, it is also applicable to semiconductor lasers made of other materials, such as GaAlAs. This structure also has a distributed feedback structure (
DFB-LD) and distributed Bragg reflection structure (DBR-L)
D) can be easily applied, ultra-high-speed modulation is possible, and
A semiconductor laser device that oscillates in a single-axis mode can be easily obtained.

〔Effect of the invention〕

As explained above, according to the present invention, a structure in which a portion other than the vicinity of the light emitting region is covered with a high-resistance semiconductor layer and parasitic capacitance inside a semiconductor laser can be removed can be easily obtained with good reproducibility. Furthermore, since a dielectric film such as 5i02 is not used, reliability is improved.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a structure of an embodiment of the present invention, and FIG. 2 is a sectional view showing a structure of a manufacturing process of an embodiment of the invention. 1 ・-n-1n P substrate, 2- n -I r+ P
Buff layer, 3-InGaAsP active layer, 4-p-In
P cladding layer, 5... first I n F' high resistance layer,
6... InGaAsP stop layer, 7... Second In
P high resistance layer, 8...diffusion layer, 9-p-T nGaA
sP cap layer, 10...p-side electrode, 11...n@electrode, 20...inverted mesa protrusion.

Claims (1)

[Claims] A mesa-shaped protrusion including a conductive buffer layer, an active layer, and a conductive cladding layer formed on a conductive semiconductor substrate is
When the conductive type semiconductor substrate is used as a reference, an impurity diffusion layer is buried with a high resistance layer sandwiching a diffusion stop layer formed at a higher position than the active layer, and is formed until reaching the conductive type cladding layer. A semiconductor laser device characterized by: