JPH02130984A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To reduce the parasitic capacitance inside a semiconductor laser for enhancing the high-frequency characteristics and the reliability by a method wherein the parts excluding the luminescent region are covered with high resistance semiconductor. CONSTITUTION:At InGaAsP active layer 2, a high resistance InP layer 3 and an InGaAsP cap layer 8 are included in an inverse mesa type protrusion part formed in a semiconductor InP substrate 1. A p-InP buried layer 4, an n-InP buried layer 5 are formed respectively on the left and right side of the inverse mesa type protrusion part. In such a structure, the active layer 2 being encircled by the high resistance semiconductor layers 3, almost the whole signal current fed from p side electrode 6 runs into the active layer 2 to reduce the parasitic capacitance. Consequently, the excellent high-frequency response and the reliability of the title semiconductor laser device can be enhanced.

Description

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

[Conventional technology]

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

゛In order to increase the speed of semiconductor radars, it is necessary to reduce leakage of high-frequency signals, and for this purpose, it is important to reduce the extra capacitance (parasitic capacitance) that exists outside the active layer region, which is the light emitting region. There's something.

"Collection of Lectures at the Spring 1981 National Conference of the Institute of Electronics and Communication Engineers"
This was pointed out by Kobayashi et al. in paper number 918. To reduce this parasitic capacitance.

An insulating film such as SiO□ having a relatively large dielectric constant may be formed in a region other than the semiconductor surface layer directly above the active layer.

By doing K like this, the semiconductor radar becomes 2Gb/s.
It is now possible to modulate at relatively high speeds.

[Problem to be solved by the invention]

However, high-performance embedded semiconductor radars used as light sources for optical communications use a pn reverse bias junction as a current confinement mechanism.

This p-n junction has a large p-n junction capacitance and the high-frequency signal current
It leaks to regions other than the active layer via the junction and the resistance of the semiconductor layer. For this reason, it has been difficult to obtain an ultrahigh-speed semiconductor laser simply by forming an insulating film such as 5f02 on the surface of the semiconductor layer. In addition, 5io2 itself has a capacitance2, for example, an area approximately the size of a normal semiconductor laser element (300
When a SiO□ film with a thickness of about 3000X is formed on the
Therefore, the capacity cannot be said to be sufficiently small for high frequency modulation of 5 GHz or higher. Furthermore, St.
The coefficient of thermal expansion between O□ and semiconductor is about one order of magnitude different, so 5i02
After formation, distortion remained inside the semiconductor, which had a negative impact on the reliability of the semiconductor radar.

The purpose of the present invention is to solve these problems.

Reduce the junction capacitance inside the semiconductor radar as much as possible.

By increasing the resistance of areas other than the current path leading to the active layer, high-frequency current can be effectively concentrated in the active layer, thereby providing a highly reliable 'semiconductor radar device that is capable of ultra-high-speed modulation. .

[Means to solve the problem]

In the present invention, a mesa-shaped protrusion is left approximately in the center of a multilayer semiconductor substrate in which an active layer, a high-resistance semiconductor layer, and a cap layer are sequentially stacked on a semi-insulating substrate, so as to include the semi-insulating substrate; One side of this protrusion is filled with a first conductive type semiconductor layer, and the other side is filled with a second conductive type semiconductor layer.

[Effect]

By configuring the present invention as described above, the periphery of the active layer, which is the two light-emitting regions, is covered with a high-resistance semiconductor layer, so that the presence of so-called parasitic capacitance is extremely small. Therefore, almost all of the signal current flowing inside the semiconductor is supplied to the active layer up to the high frequency range, resulting in a semiconductor radar device with excellent high frequency characteristics. Further, since an element with sufficiently excellent high frequency characteristics can be obtained without using an insulating film with a relatively large dielectric constant such as 5i02 as an electrode structure, the f process is easy and the reliability is also excellent.

〔Example〕

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

FIG. 1 schematically shows an embodiment of the present invention.

An InGaAsP active layer 2. High resistance InP layer 3, I
An nGaAsP cap layer 8 is included. On the left side of this inverted mesa protrusion is a p-InP buried layer 4. On the right is n-I
An nP buried layer 5 is formed. In this structure,
Since the InGaAsP active layer 2 is surrounded by a high-resistance semiconductor layer, almost all of the signal current injected from the p-side electrode 6 is InGaAsP active layer 2.
It flows into the GaAsP active layer 2, resulting in a structure with excellent high frequency response characteristics.

FIGS. 2(a) to 2(f) show the manufacturing process of this embodiment.

First, as shown in FIG. 2(a), a semi-insulating InP substrate l
Upper K InGaAsP, active layer 2 is Q, l μ+ffl
, the high resistance InP layer 3 is 2 Am, InGaAsP
A cap layer 8 having a thickness of 0.5 μm is sequentially grown using an MO-CVD apparatus to form a multilayer semiconductor 20.

Next, as shown in FIG. 2(b), approximately the left half of the multilayer semiconductor layer 20 is etched using the silicon nitride film 11 as a mask. At this time, the etching depth needs to reach at least the semi-insulating InP substrate 1, and in this embodiment, the etching depth is approximately 2.
．． It was 5 μm. At this time, the direction of the mask stripe is (
100) direction, and the etching solution was a bromomethyl solution (0.2cc of bromine and 100% of methyl alcohol).
cc), an inverted mesa-shaped etched surface is formed as shown in FIG. 2(b).

Next, as shown in FIG. 2(c) K, a p-InP buried layer 4 is formed in the etched portion using an MO-CVD apparatus. The growth conditions for crystal growth were selected so that almost no semiconductor layer would grow on the silicon nitride film 11 and the surface of the buried p-InP layer 40 would be flat. At this time, the polycrystalline semiconductor slightly grown on the silicon nitride film 11 can be easily removed during the secondary step of Kutufurd hydrofluoric acid treatment.

Next, as shown in FIG. 2(d), the silicon nitride film 11 is once removed using buffered hydrofluoric acid.

A silicon nitride film is formed again so that about the right half of the semiconductor multilayer film is etched. At this time, in the inverted mesa-shaped protrusion formed almost at the center of the multilayer semiconductor substrate, In
A silicon nitride film was formed so that the width of the GaAsP active layer 2 was approximately 1.2 μm.

Next, as shown in FIG. 2(a), an n-InP buried layer is formed on the etched right half using a MO-CVD apparatus. In this case, as in the case of forming the p-InP buried layer, a flat growth layer could be obtained only in the etched portion.

Next, after removing the silicon nitride film 12 using buffered hydrofluoric acid, a lift-off method using a resist film is performed to remove the parts other than those on the inverted mesa-shaped protrusion including the InGaAsP active layer 2, as shown in FIG. 2(f). A p-side electrode 6 and an n-side electrode 7 were simultaneously formed in the region. As electrode metals, titanium, platinum, and gold were sequentially formed using an E-gun vapor deposition apparatus. In this case, the separation interval between the p-side electrode 6 and the n-side electrode 7 is 20 to 30
It was sufficient to have a thickness of approximately μm, and the electrode could be formed with sufficient reproducibility using the lift-off method.

After heat-treating both the p and n electrodes, the semi-insulating substrate 1 side was mirror polished to a device thickness of about 150 μm.

Titanium and gold, which are fusion metals 9, are sequentially formed on the polished surface side, and the process is completed.

The semiconductor radar of this example is g InGaAsP active layer 2
is surrounded by a high resistance layer. Therefore, since there is almost no extra junction capacitance due to a p-n junction or the like, most of the electrical signals supplied from the electrode metal are supplied to the InGaAsP active layer 2 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 was cleaved so that the cavity length was 300 μm, and the semiconductor laser was assembled by directly fusion bonding onto the strip line, and its small signal frequency characteristics were measured. As a result, a value of 10 GHz or more was obtained as a 3 dB band at a bias current value twice the two-oscillation threshold.

This 3 dB band can be expected to become even higher by increasing the photon density by shortening the resonator, decreasing the photon lifetime, cooling, etc.

In the embodiment shown in FIGS. 1 and 2, InGa
Although an AsP-based semiconductor laser is used, it is also applicable to semiconductor lasers made of other materials such as GaAlAs. Also, this structure is a 9 distributed feedback reflection type structure (DFB-LD).
, it can also be easily applied to distributed Bragg reflection type structures (DBR-LD). In this case, ultra-high-speed modulation is possible,
Moreover, a semiconductor laser device that oscillates in a single-axis mode can be easily obtained.

〔Effect of the invention〕

As explained above, the present invention makes it possible to eliminate the parasitic capacitance inside the semiconductor laser as much as possible by covering the portion other than the vicinity of the two light-emitting regions with a high-resistance semiconductor layer. Moreover, St.
Since a dielectric film such as O□ is not used, reliability is also greatly improved.

In view of the above points, the present invention can easily provide an ultra-high speed semiconductor radar device which has a modulation band of -10 GHz or more and is also excellent in reliability.

InGaAsP active layer, 3 high resistance InP layer, 8 In
GaAsP quad layer, 4 is p-InP buried layer, 5
is an n-InP buried layer, 6 is a p-side electrode, 7Fin-
This is the side electrode.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the structure of an embodiment of the present invention. 2(a) to 2(f) are cross-sectional views sequentially showing the manufacturing process of the embodiment shown in FIG. 1. In the figure, 1 is a semi-insulating InP substrate, and 2 is a semi-insulating InP substrate.

Claims (1)

[Claims] 1. A mesa-shaped protrusion in which an active layer, a high-resistance semiconductor layer, and a cap layer are sequentially laminated on a semi-insulating substrate and extending in a predetermined direction, and the semi-insulating substrate on one side of the protrusion. A semiconductor laser device comprising: a first conductive type semiconductor layer formed on the semi-insulating substrate; and a second conductive type semiconductor layer formed on the semi-insulating substrate on the other side of the protrusion.