JPH02292884A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To effectively concentrate a high frequency current on an active layer to enable a semiconductor laser device of this design to execute a super- high speed modulation by a method wherein a part other than the vicinity of a light emitting region is covered with a high resistance semiconductor layer or the like. CONSTITUTION:An InP high resistance layer 9 is laminated on an N-InP substrate 1, the InP high resistance layer 9 is removed leaving a part of it unremoved so as to expose the N-InP substrate 1 for the formation of an inverted mesa-shaped step. An N-InP buffer layer 2, an InGaAsP active layer 3, a P-InP clad layer 4, and a P-InAsGaP contact layer 5 are successively laminated on the P-InP substrate 1 bringing the ends of them into contact with the inverted mesa-shaped step. The other ends of the InGaAsP active layer 3, the P-InP clad layer 4, and the P-InGaAsP contact layer 5 are etched to form a continuous reverse mesa-shaped step. As the InGaAsP active layer 3 is surrounded with a high resistance semiconductor layer or air, nearly all the signal current injected from a P-side electrode 7 is made to flow through the InGaAsP active layer, and consequently a semiconductor laser device of this design has a structure excellent in response characteristic to high frequency.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a semiconductor laser device.

[Conventional technology]

Optical semiconductor devices such as light emitting diodes and photodiodes using m-v group compounds are used as key devices for optical fiber communications and optical information processing. In particular, semiconductor lasers are the most important element in the development and practical implementation of long-distance, high-capacity optical fiber communication systems, and efforts have been made in recent years to improve their speed.

In order to increase the speed of semiconductor lasers, it is important to reduce the extra capacitance (parasitic capacitance) that exists outside the active layer region, which is the light emitting region, in order to reduce leakage of high-frequency signals. This point is pointed out by Kobayashi et al. in paper number 918 of the ``Collection of Lectures at the 1980 Spring National Conference of the Institute of Electronics and Communication Engineers.'' In order to reduce the parasitic capacitance, is it possible to place an insulating film such as Si02 with a high dielectric constant on the area other than the semiconductor surface layer directly above the active layer? By completely forming such an insulating film, the semiconductor laser can achieve 2Gb
It is possible to perform modulation at high speeds of about /s.

[Problem that the invention seeks to solve]

By the way, in high-performance buried semiconductor lasers used as light sources for optical communications, p-
n reverse bias junction is used. For this reason, the pn junction capacitance is large (high-frequency signal current leaks to regions other than the active layer through this pn junction and the resistor metal of the semiconductor layer).

As a result, it is not possible to obtain an ultrahigh-speed semiconductor laser simply by completely forming an insulating film such as 8102 on the surface of the semiconductor layer.

In addition, S10■ itself has a large capacitance, and for example, the area is about the size of a normal semiconductor laser element (300 x 250 μm).
When a Sin2 film with a thickness of about 3000 mm is completely formed on the 810cm1), the capacitance of 810■ itself is about 10 pF, which cannot be said to be a small capacitance for high frequency modulation of 5 GHz or higher. Furthermore, is the coefficient of thermal expansion of Si02 and semiconductor about one digit? Therefore, distortion remains inside the semiconductor after the SiO2 is formed, which adversely affects the reliability of the semiconductor laser.

The purpose of the present invention is to effectively concentrate high frequency current in the active layer,
An object of the present invention is to provide a highly reliable semiconductor laser device that is capable of ultra-high-speed modulation.

[Means for solving problems]

In the semiconductor laser device of the present invention, a first conductive type semiconductor substrate on which a high resistance semiconductor layer is laminated is removed so that a part of the first conductive type semiconductor substrate is exposed to provide a stepped portion, and the active layer is formed with a stepped portion. The first layer is in contact with the high resistance semiconductor layer of the
Semiconductor layers including a conductive type semiconductor layer, an active layer, a second conductive type semiconductor layer, and a contact layer are stacked, and the contact layer,
The second conductivity type semiconductor layer and the active layer are formed by etching the entire active layer in stripes.

[For production]

By configuring the present invention as described above, the active layer, which is the light emitting region, is surrounded by a high resistance semiconductor layer and air.
There is very little so-called parasitic capacitance. Therefore, almost all of the signal current flowing within the semiconductor is supplied to the active layer up to the high frequency range, resulting in a semiconductor laser device with excellent high frequency characteristics.

〔Example〕

Next, the present invention will be explained by examples.

Referring to FIG. 1, an InP high resistance layer 9 is laminated on an n-InP substrate 1 until the n-nP substrate 1 is exposed, leaving a part of the InP high resistance layer 9 (i-InP substrate 1). 1), thereby forming an inverted mesa-like stepped portion. On the n-InP substrate 1, there is n-In
P buffer layer end (left end)'f. A nGaA sP active layer 3, a p-type nP cladding layer 4. The other end (right end) of the p-nGaAsP contact layer 5 is etched to form a continuous inverted mesa-like step. This step is formed when the electrode is formed, and the flat surface on the right side of the step (hereinafter referred to as the bottom surface of the step) and the flat surface on the left side of the step (hereinafter referred to as the top surface of the step) (p-side electrode) are completely electrically connected. This is because it is necessary to separate the electrodes into two, and as will be described later, if the entire shadow of this inverted mesa surface is utilized, the electrodes can be completely separated using only the vapor deposition process.

In this structure, since the InGaAsP active layer 6 is surrounded by a high-resistance semiconductor layer (or air), almost all the signal current injected from the p-side electrode 7 flows into the InGaAsP active layer 5, resulting in a structure with excellent high frequency response characteristics. becomes.

Here, FIGS. 2(a) to 2(d) show the manufacturing process of this embodiment.

First, as shown in FIG. 2(a), an InP high resistance layer 9 of approximately 5 μm thickness is laminated using a silicon nitride film 11 as a mask.
Approximately half of the first-process nP substrate 1 is etched to a depth of about 6 μm. At this time, the etching is in the (100> direction,
Prom methyl solution (prom 0.2C
A mixed bath solution of C and 100 cc of methyl alcohol is used in a tray. Since the prommethyl bath solution is used in this way, the
As shown in a), the etched surface (step part) has an inverted mesa shape.
can be formed.

Next, as shown in FIG. 2(b), using the silicon nitride film 11 as a mask,
n-nP buffer layer 2 with a thickness of 2 μm on one-nP substrate 1;
(1) An nGaAsP active layer 5 of 111 μm, a p--2 nP cladding layer 4 of 2 μm, and a p-InGaAsP contact layer 5't of 1 μm are sequentially laminated using a MOOVD apparatus. Here, since the entire silicon nitride film is used as a mask, polycrystals are not grown on the mask.Furthermore, an inverted mesa-like step is formed, so the growth surface of each layer can be grown relatively flat. .

As shown in FIG. 2(C), after removing the silicon nitride film 11 using buffered 7-hydrochloric acid, a new silicon nitride film 12 is completely formed, and an MO-CVD apparatus is used to form the silicon nitride film 12 using the silicon nitride film 12 as a mask. The formed n-InP buffer yN
2, InGaAsP active layer 5,p
- The nP cladding layer 4 and the P-nGaAsP contact layer 5 are coated with at least an
Etching is performed until the first nP puff layer 2 is exposed. The silicon nitride film 12 serving as a mask is formed so that the width of the nGaAsP active layer 6 is approximately 1 μm after etching.

2-buffered hydrofluoric acid as shown in Figure 2(d)? After the silicon nitride film 12 is completely removed using a p-side electrode Z, a p-side electrode Z is deposited. Here, Cr and Au'f! are used as vapor deposited metals. : Sequentially deposited by resistance heating vacuum evaporation method. In the vacuum evaporation method, the metal to be evaporated advances almost linearly from the evaporation source because the evaporation is performed in a high vacuum. Therefore, if the evaporation source is placed diagonally to the upper left of FIG. 2(d) and the evaporation is performed, the structure shown in FIG. parts) can be separated. After further heat treatment for 5 minutes in a hydrogen atmosphere at 580°C, the n-InP substrate 1 side was mirror-polished to a thickness of approximately 150 μm. The process is then completed with all heat treatments.

The semiconductor laser described above has a nGaAsP active layer 5.
Both sides are covered with a high resistance layer or air. Therefore p
There is almost no extra junction capacitance due to -n junctions, etc., and most of the electrical signals supplied from the electrode metal are supplied to the InGaAsP active layer 6 in the range from direct current to high frequency. Therefore, a semiconductor laser device with excellent high frequency response characteristics is provided.

This semiconductor laser wafer gold was cleaved to a cavity length of 500 μm, fused directly onto the strip line, a semiconductor laser was assembled, and all small signal frequency characteristics were measured. As a result, a value of 10 GHz or more was obtained as a 5 dB band at a bias current value twice the oscillation threshold. This 3dB band is due to the increase in photon density due to the shortened cavity.
By reducing the photon lifetime and applying cooling, etc., the value becomes even higher.

The present invention has been described above with reference to embodiments, and although the InGaAsP-based semiconductor laser has been described in this embodiment, it is also applicable to semiconductor lasers made of other materials, such as GaAIAs-based semiconductor lasers.

〔Effect of the invention〕

As described above, in the present invention, by covering the portion other than the vicinity of the light emitting region with a high-resistance semiconductor layer or the like, it is possible to eliminate the parasitic capacitance inside the semiconductor laser as much as possible. Furthermore, since a dielectric film such as Sin2 is not used, reliability is greatly improved.

As described above, according to the present invention, an ultrahigh-speed semiconductor laser device having a modulation band of 1QGHz or more and excellent reliability can be easily obtained.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the structure of a first embodiment of the present invention, and FIGS. 2(a) to 2(d) are sectional views for explaining the manufacturing process of the embodiment shown in FIG. In the figure, 1 is an n-type nP substrate, 9 is an InP high resistance layer,
2 is an n-nP buffer layer, 6 is an active nGaAsP layer, 4 is a p-InP cladding layer, and 5 is a p-nGaAsP contact layer. Figure 2

Claims (1)

[Claims] 1. A first conductive type semiconductor substrate, a high resistance semiconductor layer formed on the first conductive type semiconductor substrate so that a part of the first conductive type semiconductor substrate is exposed, and the first conductive type semiconductor substrate and a step defined by the high resistance semiconductor layer;
a first conductivity type semiconductor layer formed on the first conductivity type semiconductor substrate with one end in contact with the step; and a first conductivity type semiconductor layer with one end in contact with the step and formed on the first conductivity type semiconductor layer. an active layer formed in a stripe shape along the step surface;
A semiconductor laser device comprising a second conductivity type semiconductor layer and a contact layer, wherein the one end of the active layer is in contact with the high-resistance semiconductor layer.