JPH01199485A - Manufacture of optical semiconductor element - Google Patents

Abstract

PURPOSE:To enable a semi-insulating semiconductor to grow stably and simply as it is in a buried state by a method wherein an element which forms a deep impurity level or its chemical compound is formed on the surface of an optical waveguide, and the above element is introduced at a process that a high resistive semiconductor is buried into a part or the whole of the side face of the optical waveguide layer. CONSTITUTION:Optical waveguide layers composed of an optical waveguide layer 3 and other waveguide layers formed of clad layers 2 and 4 whose refractive indexes are smaller than that of the waveguide layer 3 are provided, where at least the optical waveguide layer 3 out of the waveguide layers is formed into a mesa shape, and when an optical semiconductor element is manufactured through a process that a high resistive semiconductor is buried into the side face of the mesa-shaped optical waveguide layer 3, an element 12 which forms a deep impurity level or its chemical compound is formed on the face of the above optical waveguide layer 3 and the high resistive semiconductor 6 is buried into a part or the whole of the side face of the waveguide layer 3 by introducing the element 12 into a semiconductor of non-high resistance at a process that the high resistive semiconductor 6 is buried into a part or the whole of the side face of the waveguide layer 3. For instance, an element such as the element which forms a deep impurity level is iron.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a method for manufacturing an optical semiconductor element having a buried structure using a high-resistance semiconductor.

(Conventional technology and its problems) Optical fiber communication technology has progressed by taking advantage of the ultra-low loss properties of optical fibers and the ultra-broadband properties that light inherently has, and has enabled transmission of increasingly longer distances and larger capacities. Research is underway worldwide. Nowadays, the loss of optical fibers has reached its theoretical limit, and research into increasing transmission speed and capacity has become particularly important.

Currently, as a technique for rapidly turning on and off optical signals, a method of directly modulating a semiconductor laser is generally used, and modulation of several G)Iz or more is becoming easy to perform. However, in high-speed direct modulation of a semiconductor laser, the current of the semiconductor laser, which is the oscillation element, changes rapidly, so the oscillation wavelength fluctuates greatly over time, and as a result, the oscillation spectral width becomes abnormal compared to the spectral width of the modulation band. It will spread greatly. Therefore, long-distance or high-speed transmission is greatly affected by the wavelength dispersion of the optical fiber, and the received optical pulses are distorted, making it impossible to obtain good transmission characteristics. In order to avoid such problems, a method has recently been considered in which the output of the semiconductor laser is held constant and high-speed modulation is performed using an external optical modulation element.

Such semiconductor lasers and external light modulation devices will become important optical semiconductor devices in the field of future optical transmission technology, and a modulation band of several GHz to 10 GHz or more will be required. In order to achieve such a wide modulation band, it is necessary to limit the parasitic capacitance of the device to an extremely low level, and in recent years, research and development of buried-structure optical semiconductor devices using high-resistance semiconductors has been underway.

FIG. 1 is a schematic diagram of an example of a conventional light modulation element. On the n-type InP substrate 1, there is an n-type 1nP layer which becomes the n-type cladding layer.
A layer 2, an InGaAsP modulation waveguide layer 3 serving as an optical waveguide layer, a p-type 1nP layer 4 serving as a p-type rad layer, and a p-type 1nGaAsP cap layer 5 are stacked, and these layers form a mesa layer. The periphery of the mesa is filled with semi-insulating 1nP6. Here, the refractive index of the n-type 1nP layer 2 and the p-type 1nP layer 4 is smaller than the refractive index of the InGaAsP modulation waveguide layer 3, and this InGaAsP modulation waveguide layer 3 basically constitutes an optical waveguide layer. . Then, the p-type electrode 101 and the n-type electrode 102 are each p
It is formed so as to be in contact with the type 1 nGaAsP cap layer 5 and the n type 1nP substrate 1. Reference numeral 103 indicates a pad portion for the p-type electrode 101 for performing wire bonding to the p-type electrode.

In such a light modulation element, the incident light can be modulated by inputting light into the 1 nGaAs P modulation waveguide layer 3 and applying a negative voltage to the p-type electrode 101 and a positive voltage to the n-type electrode 102. For example, if the photon energy of the incident light is designed to be approximately 30 to 60 m e V smaller than the energy bandgap of the InGaAsP modulated waveguide layer 3, the incident light will pass through the InGaAsP modulated waveguide layer 3 when no voltage is applied. In layer 3, almost no light is absorbed and it passes through as is. However, when a voltage is applied, most of the incident light is absorbed. Therefore, the incident light is intensity modulated. Also, the photon energy of the incident light is I
If designed to be sufficiently smaller than the energy bandgap of the nGaAs P modulation waveguide layer 3, the phase of the incident light can be varied while keeping the intensity of the incident light constant.

The configuration shown in FIG. 1 has been described above as a light modulation element, but
By supplying a positive power to the p-type electrode 101 and a negative power to the n-type electrode 102, it is also possible to use it as a light emitting element.

When manufacturing an optical semiconductor device as shown in FIG.
AsP modulation waveguide layer 3, p-type InP layer 4, and p-type 1
After epitaxially growing the nGaAsP cap layer 5, the region where semi-insulating InP6 is to be buried is selectively etched to form a mesa-shaped optical waveguide layer, and high-resistance semi-insulating 1nP6 is epitaxially grown on the etched portion. . Epitaxial growth of semi-insulating InP6 is performed by hydride vapor phase epitaxy or organometallic vapor phase epitaxy, and iron is mainly used as an impurity dopant during growth. However, in the technique of growing semi-insulating InF3 by hydride vapor phase epitaxy or organometallic vapor phase epitaxy, control of the introduced gas is complicated and difficult because it is introduced into the growth apparatus as an unstable iron compound gas as a dopant. Moreover, it can seriously contaminate the growth equipment. Therefore, if you grow semi-insulating 1nP6 in this way, normal nP6 will grow
Crystal growth of the type InP layer 2 and the p-type 1nP layer 4 is impossible (or a new growth apparatus exclusively for iron dopants is required).

As described above, in the conventional manufacturing method of an optical semiconductor device that involves buried growth of a semi-insulating semiconductor 6, not only is it complicated and difficult to achieve good buried growth of a semi-insulating semiconductor 6, but also the growth equipment is significantly contaminated. there were.

(Objects and Features of the Invention) The present invention has been made to solve the problems of the prior art described above, and is to manufacture an optical semiconductor device that can stably and easily perform embedded growth of a semi-insulating semiconductor. The purpose is to provide a method.

A feature of the present invention is that in an optical semiconductor waveguide formed from an optical waveguide layer and a plurality of cladding layers having a lower refractive index than the optical waveguide layer, after forming at least the optical waveguide layer into a mesa shape, A method for manufacturing an optical semiconductor device including a step of burying a side surface of the optical waveguide layer formed in a mesa shape with a high-resistance semiconductor, wherein an element that forms a deep impurity level or a compound of the element is applied to the surface of the optical waveguide. By forming the element so that it is incorporated into a semiconductor that does not have high resistance during the step of forming and embedding the high resistance semiconductor in a part or all of the side surface of the optical waveguide layer, the side surface of the optical waveguide layer is The reason lies in that a portion or the entirety thereof is embedded with the high-resistance semiconductor.

(Structure and operation of the invention) Hereinafter, the present invention will be explained in detail using the drawings.

(Example 1) FIGS. 2(a) to 2(e) show a first example of the present invention, and are process diagrams for manufacturing using the light modulation element shown in FIG. 1. Description will be made below according to the drawing numbers.

(a) First, as shown in Fig. 2(a), 1
n-type 1nP layer 2 forming an optical semiconductor waveguide, InGa
AsP modulation waveguide layer 3, P type 1nP layer 4 and p type 1n
The GaAsP camp layer 5 is epitaxially grown in sequence by a vapor phase growth method, a liquid phase growth method, or the like.

(b) Next, on the surface of the p-type 1nGaAsP cap layer 5, a silicon nitride film 11 and an element or a compound of the element that forms a deep impurity level in the semiconductor, such as iron or chromium, which is a feature of the present invention, are applied. Form.

In this embodiment, the thin film 12 made of iron will be explained as an example, but a compound such as iron oxide may also be used.

(c) InGaAs which becomes at least an optical semiconductor waveguide
The P modulation waveguide layer 3 is etched into a mesa shape.

Here, a part of the n-type 1nP layer 2 and the p-type 1nP layer 4 are also mesa-etched in the same way.

(d) InP epitaxial growth is performed using hydride vapor phase epitaxy or organometallic vapor phase epitaxy. At this time, in the present invention, the iron of the iron thin film 12 formed on the surface of the optical semiconductor waveguide is incorporated into the buried semiconductor InF3, and the epitaxially grown semiconductor layer 6 becomes semi-insulating.

(e) Finally, as shown in (e) of the same figure, the silicon nitride film 11
After removing the iron thin film 12 by etching, a p-type electrode 101 and an n-type electrode 102 are formed by vacuum evaporation.

In this way, in the present invention, the impurity dopant for making the semiconductor semi-insulating is naturally supplied from the iron thin film I2 formed on the surface of the optical semiconductor waveguide. No need to flush. Therefore, the manufacturing process is greatly simplified and the growth equipment is not contaminated.

(Example 2) FIGS. 3(a) to 3(f) show a second example according to the present invention, and are process diagrams for manufacturing using the light modulation element shown in FIG. 1 as in Example 1. be.

(a) First, an n-type 1nP layer 2, an InGaAs P modulation waveguide layer 3, a p-type 1nP layer 4, and a p-type 1nGaAs P can 1 layer 5, which form an optical semiconductor waveguide, are placed on an n-type 1nP substrate 1. Epitaxial growth is performed sequentially using a phase growth method, a liquid phase growth method, or the like.

(b) Next, on the surface of the p-type 1 nCyaAs P can 1 layer 5, a silicon nitride film 11 and an element or a compound of the element that forms a deep impurity level in the semiconductor, such as iron or chromium, which is a feature of the present invention, are added. form.

In this embodiment, the thin film 12 made of iron will be explained as an example, but a compound such as iron oxide may also be used.

(C) At least the InGaAsP modulation waveguide layer 3, which will become an optical waveguide, is etched into a mesa shape. Here, a part of the n-type 1nP layer 2 and the p-type 1nP layer 4 are also mesa-etched in the same way. The steps up to this point are the same as in the first embodiment.

(d) Further, as a feature of the second embodiment, as shown in FIG. 3(c), only the InGaAs P modulation waveguide layer 3, which is an optical waveguide layer, is selectively etched.

(e) Perform jnP epitaxial growth using hydride vapor phase epitaxy or organometallic vapor phase epitaxy. However, in this example, the etched grooves were not completely filled, and the etching stopped when rnP6 grew in the etched portion in the step (d). At this time, the iron of the iron thin film 12 formed on the surface of the optical semiconductor waveguide is incorporated into the InP layer 6, which is a buried semiconductor, and the epitaxially grown semiconductor layer 6 becomes semi-insulating.

(f) After filling the trench with polyimide 13, the silicon nitride film 11 is removed by etching, and the p-type electrode 101 is etched.
and n-type electrode 102 are formed by vacuum evaporation.

In Example 2, the groove portion is filled with polyimide, which is an insulator with a lower dielectric constant than the InP layer 6, so that the parasitic capacitance is further reduced and the high frequency characteristics are improved. Further, since the buried growth time is shortened, the manufacturing process can be further simplified.

Although the above explanation has been made using an InP-based semiconductor, the present invention can also be applied to GaAs-based semiconductors and other materials. Furthermore, although iron is used as the impurity dopant, other elements that form deep impurity levels, such as chromium and cobalt, and compounds of these elements can also be used.

(Effects of the Invention) As described above in detail, the present invention provides an impurity dopant for making a semiconductor semi-insulating by naturally forming an impurity dopant element or a compound of the element formed on the surface of an optical semiconductor waveguide. Therefore, there is no need to flow an iron compound gas or the like as in the conventional case, and the manufacturing process is greatly simplified and the growth apparatus is not contaminated.

Furthermore, the manufacturing process is simplified by filling all the side surfaces of the optical waveguide layer with a high-resistance semiconductor.

By burying the side surface of the optical waveguide layer near the optical waveguide layer with a high-resistance semiconductor, and burying the side surface of the other optical waveguide layer with an insulator having a lower permittivity than the high-resistance semiconductor, parasitic capacitance can be further reduced. It becomes smaller and the high frequency characteristics are improved. By using iron, chromium, and cobalt as impurity dopants, deep impurity units can be formed.

Therefore, according to the present invention, high-performance optical semiconductor devices such as buried structure semiconductor lasers and optical modulation devices using semi-insulating semiconductors can be easily manufactured, and can be applied as devices for ultra-high-speed optical fiber transmission, etc. The effect is extremely large.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an example of a conventional optical semiconductor device, and FIGS. 2(a) to (e) and 3(a) to (f) show first and second embodiments of the present invention. FIG. 3 is a cross-sectional view for explaining the manufacturing process of the optical semiconductor device. 1 ・n-type InP substrate, 2 ・n-type 1nP layer, 3...
・InGaAs P modulation waveguide layer, 4...p type I
nP layer, 5 ・P type 1nGaAsP camp layer, 6
... Semi-insulating InP layer, 11... Silicon nitride film, 12... Iron thin film, 13... Polyimide, lot... P-type electrode, 102... N-type electrode,
103... Pad for p-electrode. Patent applicant International Telegraph and Telephone Corporation

Claims (8)

[Claims] (1) Of an optical semiconductor waveguide formed from an optical waveguide layer and a plurality of cladding layers having a refractive index lower than that of the optical waveguide layer, after forming at least the optical waveguide layer into a mesa shape,
A method for manufacturing an optical semiconductor device including a step of burying a side surface of the optical waveguide layer formed in a mesa shape with a high-resistance semiconductor, wherein an element that forms a deep impurity level or a compound of the element is added to the surface of the optical waveguide. and embedding the high-resistance semiconductor in a part or all of the side surface of the optical waveguide layer, the element is incorporated into the semiconductor that does not have high resistance, so that the side surface of the optical waveguide layer is A method for manufacturing an optical semiconductor device, characterized in that a part or all of the device is embedded with the high-resistance semiconductor. (2) The method for manufacturing an optical semiconductor device according to claim 1, wherein the entire side surface of the optical waveguide layer is filled with the high-resistance semiconductor. (3) A side surface of the optical waveguide layer near the optical waveguide layer is buried with the high-resistance semiconductor, and another side surface of the optical waveguide layer is buried with an insulator having a dielectric constant lower than that of the high-resistance semiconductor. A method for manufacturing an optical semiconductor device according to claim 1, characterized in that: (4) The method for manufacturing an optical semiconductor device according to claim 1, wherein the element forming the deep impurity level is iron. (5) The method for manufacturing an optical semiconductor device according to claim 1, wherein the element forming the deep impurity level is chromium. (6) The method for manufacturing an optical semiconductor device according to claim 1, wherein the element forming the deep impurity level is cobalt. (7) The method for manufacturing an optical semiconductor device according to claim 1, wherein the compound of the element forming the deep impurity level is iron oxide. (8) The method for manufacturing an optical semiconductor device according to claim 3, wherein the insulator is polyimide.