JPH10200154A - Optical semiconductor element and fabrication thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance emission efficiency and light receiving sensitivity by forming the active layers at the light emitting part and the light receiving part in a multilayer structure of a III-V compound semiconductor containing nitrogen as a group V element thereby integrating the light emitting part and the light receiving part on the same substrate. SOLUTION: When a transmitting part A is formed circularly and a receiving part B is formed annularly, scattering light from a plastic fiber 30 can be coupled effectively with the receiving part B while coupling the plastic fiber 30 well with the transmitting part A. Since the light emitting part of the transmitting part A and the photosensitive part of the receiving part B can be formed on the same plane, mutual interference can be minimized. When a III-V compound semiconductor containing nitrogen as a group V element, i.e., GaInN, in an active layer, an emission wavelength in the range of 450-600nm can be obtained in the plastic fiber 30 at the transmitting part A while suppressing attenuation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical semiconductor device for a signal transmission device, and more particularly to an optical semiconductor device having a light emitting portion and a light receiving portion formed on the same substrate.

[0002]

2. Description of the Related Art A signal transmission device using an optical fiber has less attenuation even at the time of transmitting a high-speed modulated signal than signal transmission using a coaxial cable. In particular, this difference is remarkable in the case where the diameter of the signal cable is limited between devices or wiring in a panel. However, general quartz-based fiber and GaInAs
A transmission device combining a light-emitting element having a light-emitting layer of P, AlGaAs, or the like is not suitable for fine wiring because the device cost is high and the bending radius of the fiber is large.

In order to solve these inconveniences, some devices using acrylic plastic fibers instead of quartz fibers have been used. However, the plastic fiber has a disadvantage that when a conventionally used semiconductor light emitting device is used as a light source, transmission loss due to light absorption is large.

FIG. 6 shows the wavelength dependence of light absorption loss of a typical plastic fiber. Although absorption loss is large in the long wavelength region used for silica-based fibers,
Absorption is relatively low in the wavelength region around 50 nm.
As a light source in this wavelength range, a GaAlAs-based LED and an AlGaInP-based laser or LED can be used, but these light sources do not always have sufficient operating life for transmission.

In plastic fibers, the diameter is 1
There is a problem in bundling and using a plurality of fibers because they are as thick as about mm, and a bidirectional function capable of transmitting and receiving with a single fiber has been required. For this purpose, an optical semiconductor element in which the light emitting unit and the light receiving unit are integrated on the same substrate is required. However, it is extremely difficult to form devices having different material compositions and film thicknesses on the same substrate. Even when a light-emitting element and a light-receiving element having the same material composition and film thickness are formed on the same substrate, the material composition and the film thickness required for high-efficiency light emission and high-sensitivity light reception are generally different. Performance was not satisfactory.

[0006]

As described above, conventionally, in order to perform transmission and reception using a single plastic fiber, it is necessary to integrate a light emitting unit and a light receiving unit on the same substrate.
In such a configuration, there are problems that manufacturing is extremely difficult and that the performance required for the light emitting unit and the light receiving unit cannot both be satisfied.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above circumstances, and has as its object to easily integrate a light emitting unit and a light receiving unit on the same substrate and to improve luminous efficiency. Another object of the present invention is to provide an optical semiconductor device capable of improving light receiving sensitivity.

[0008]

[Means for Solving the Problems]

(Structure) In order to solve the above problem, the present invention employs the following structure. That is, the present invention is an optical semiconductor device in which a light emitting portion and a light receiving portion are formed on the same substrate, wherein the light emitting portion and the light receiving portion are formed in the same laminated structure using a III-V compound semiconductor, In addition, at least the active layers of the light emitting portion and the light receiving portion are formed of a III-V compound semiconductor containing nitrogen as a group V element.

Further, according to the present invention, there is provided a method for manufacturing an optical semiconductor device having the above-mentioned structure, wherein a III-V compound semiconductor having a laminated structure of a III-V compound semiconductor on a substrate and at least an active layer containing nitrogen as a group V element. Forming a laminated structure using a compound semiconductor, and forming an electrode on the laminated structure,
Separating the laminated structure and the electrode into a light emitting portion and a light receiving portion by etching.

Here, preferred embodiments of the present invention include the following. (1) The substrate is a single-crystal insulating substrate, for example, a sapphire substrate. (2) A recess is formed on the back surface of the substrate, and an optical fiber is installed in the recess. (3) The light emitting portion is formed in a circular shape, the light receiving portion is formed in a ring shape around the light emitting portion and coaxially with the light emitting portion, and the axis of the transmitting and receiving optical fiber is aligned with the center of the light emitting portion. thing. (4) Use plastic fibers as optical fibers. (5) The light emitting part and light receiving part are optically coupled through the substrate. (6) The peak wavelength of the light from the light emitting section is 450 to 600 nm. (7) The thickness of the active layer (the light emitting layer in the light emitting section and the light receiving layer in the light receiving section) is 10 to 100 nm. (8) the active _{layer, Al x Ga y In 1-} xy N (x + y =
1,0 ≦ x, y ≦ 1). (9) A high-concentration (5 × 10 ¹⁸ cm ⁻³ or more) donor impurity is added to the active layer. (10) The donor impurity is one of Se, S, C, and O. (11) The concentration of the acceptor impurity contained in the active layer is not more than 1/3 of the donor impurity. (12) All layers of the laminated structure contain nitrogen as a group V element
III-V compound semiconductor. (Function) In the present invention, a III-V compound semiconductor containing nitrogen as a group V element, particularly a semiconductor made of an AlGaInN-based mixed crystal, is used as an active layer (a light emitting layer in a light emitting portion and a light receiving layer in a light receiving portion). The present invention realizes high-efficiency and high-speed optical transmission and reception in a wavelength region where the absorption loss of a plastic fiber is low.

In order to use the same material as the light emitting layer and the light receiving layer, it is necessary to narrow the forbidden band width of the light receiving layer in order to shift the light receiving wavelength to a longer wavelength side. The use of the Stark effect can be considered. AlGa
Since the absorption coefficient in the shorter wavelength region than the absorption edge of the InN-based material is much larger than that of a general III-V material, the thickness of the light-receiving layer can be reduced. For this reason, AlGa
By using an InN-based material, it is expected that the absorption edge of the light-receiving part can be sufficiently elongated at the same applied voltage of about 3 V as that of the light-emitting part.

By forming the light emitting portion in a circular shape and the light receiving portion in a ring shape, scattered light from the optical fiber can be effectively coupled to the light receiving portion in a state where the optical fiber and the light emitting portion are well coupled. . Therefore, bidirectional optical transmission using a single optical fiber can be efficiently performed.

In order to set the emission wavelength between 450 and 600 nm, which is the absorption window of the acrylic plastic fiber, it is necessary to increase the In composition of the emission layer to 20% or more. In this case, since the effective mass of electrons and holes is large, the binding energy of excitons is large and the stability is relatively stable even at room temperature. The lattice constant of InN is significantly different from AlN and GaN, and the fluctuation of the mixed crystal tends to be large. In addition, the localization extends the light emission life and slows the response speed. Therefore, in the present invention, a donor impurity is added to the light emitting layer at a high concentration (5.
(× 10 ¹⁸ cm ⁻³ or more), thereby shortening the exciton lifetime by shielding the electrostatic force acting between electrons and holes constituting the excitons.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the illustrated embodiments. (First Embodiment) FIGS. 1A and 1B show a schematic structure of an optical semiconductor device according to a first embodiment of the present invention. FIG. 1A is a plan view, and FIG. It is -A 'sectional drawing.
In this embodiment, a receiving pin diode (light receiving unit)
2 shows an example in which a transmission LED (light emitting unit) is integrated on the same substrate, and further shows a positional relationship with a plastic fiber combined therewith. The light receiving section can respond at high speed by applying a voltage opposite to that of the light emitting section.

An n-GaN buffer layer 11 is formed on a sapphire substrate 10, and a n-A
A double heterojunction structure comprising an lGaN cladding layer 12a, a GaInN light emitting layer (active layer) 13a, and a p-AlGaN cladding layer 14a is formed, and p-Ga is formed thereon.
An N contact layer 15a is formed. Here, the light emitting portion A is formed in a columnar shape.

A ring-shaped light receiving section B is provided around the light emitting section A coaxially with the light emitting section A. The light receiving section B is composed of the layers 12b, 13b, 14
b, 15b. The light emitting side electrode 21 is formed on the contact layer 15a of the light emitting part A, the light receiving side electrode 22 is formed on the contact layer 15b of the light receiving part B, and the common electrode 23 is formed on the buffer layer 11. ing.

On the back surface of the sapphire substrate 10, a recess having a diameter of about 500 μm is provided below the light emitting portion A. Then, a plastic fiber 30 is set in the recess, and the light emitting portion A and the light receiving portion B are connected to the fiber 3.
0 is optically coupled.

Next, a method for manufacturing the optical semiconductor device of the present embodiment will be described. First, as shown in FIG.
As the substrate 10, 1 to 1 in the sapphire c-plane or M-plane direction.
Using a substrate tilted by 10 degrees, an n-type GaN buffer layer 11 (1 to
9 × 10 ¹⁸ cm ⁻³ , 1 to 10 μm), n-type Al _0.15 Ga
_0.85 N cladding layer 12 (Si, Se, S concentration 1 × 10 ^18
-3 × 10 ¹⁹ cm ^-3 , 0.1-1.0 μm), Ga _0.6
In _0.4 N (5 × 10 ^{18 to} 5 × 10 ¹⁹ cm ⁻³ , 30 to ³
00 nm) active layer 13, p-type Al _0.15 Ga _0.85 N cladding layer 14 (Mg concentration: 1 × 10 ^{18 to} 3 × 10 ¹⁹ cm ⁻³ ,
0.1-1.0 μm), p-type GaN contact layer 15
(Mg concentration 1 × 10 ^{18 to} 5 × 10 ¹⁹ cm ⁻³ , 0.1 to
1.0 μm), and a p-side electrode 20 is formed thereon.
(Pd 0.05 μm / Pt 0.05 μm / Au 0.1 μm or Ni
0.1 μm).

Next, as shown in FIG. 2B, the p-side electrode 20 is selectively etched by a known lithography process to separate a circular portion 21 having a diameter of 200 μm and a ring-shaped portion 22 surrounding the circular portion 21.

Next, as shown in FIG. 2C, each of the semiconductor layers 15 to 15 between the light emitting portion A and the light receiving portion B, and around the light receiving portion B.
12 is removed by reactive ion etching until the n-type GaN buffer layer 11 is exposed. Thus, the light emitting unit A and the light receiving unit B can be created from the same wafer.

Next, the n-type G exposed outside the light receiving portion B
On the aN buffer layer 11, an n-side electrode 23 (Ti 0.05 μm
/ Pt 0.05 μm / Au 0.1 μm or Al 0.1 μm) so as to surround the light receiving portion B. Then, the back surface of the substrate 10 is etched so as to form a recess having a diameter of about 500 μm corresponding to the light emitting portion A, thereby obtaining the above-described FIG.
The structure shown in FIG.

In this embodiment, the G of the light emitting layer 13a is
The In composition of aInN increases the emission wavelength from 450 nm to 600 nm.
To control in the nm range, 10% to 50% is appropriate. In this case, it is considered that the difference between the energy of light emission and the energy of the absorption edge contributing to carrier conduction is large due to the large fluctuation of the band. (Active layer 13
It is necessary to apply a high electric field of 10 ⁵ V / cm or more to b).

The light receiving section B is opaque to the emission wavelength and needs to have a maximum absorption coefficient of 10 nm or more in order to detect light with high efficiency. As described above, an electric field strength of 10 ⁵ V / cm or more is required to sufficiently reduce the band gap, and it is necessary to be 10 ⁶ V / cm or less to suppress the leak current sufficiently low. From these requirements, the thickness of the active layer 13 is desirably 30 to 300 nm.

To perform two-way communication using a single optical fiber, some contrivance is required. In this example, by forming the light emitting part A in a circular shape and the light receiving part B in a ring shape, the scattered light from the plastic fiber 30 is transmitted to the light receiving part B in a state where the plastic fiber 30 and the light emitting part A are well coupled. Can be effectively combined. Further, since the light-emitting portion of the light-emitting portion A and the light-sensitive portion of the light-receiving portion B can be on the same plane, mutual interference can be minimized.

As described above, according to the present embodiment, the active layer 1
By using GaInN, which is a III-V compound semiconductor containing nitrogen as a group V element, 450 in the light emitting section A with less attenuation in the plastic fiber 30
An emission wavelength in the range of 600 nm can be obtained. Moreover, the donor impurity concentration of the active layer 13 is set to 5 × 10 ¹⁸ cm ^−3.
Because of the above, the exciton lifetime in the light emitting portion A can be shortened to improve the response speed.

Since GaInN is opaque to the emission wavelength, even if the active layer 13 is thinned, the light receiving portion B
, Sufficient light receiving sensitivity can be obtained. Moreover,
The thinning of the active layer 13 makes it possible to apply a high electric field to the detection part, and the received light wavelength can be shifted to the longer wavelength side by using the Stark effect. Thereby, the light receiving sensitivity can be improved. Further, since the light emitting unit A and the light receiving unit B are formed in a coaxial structure, the coupling efficiency with the fiber 30 can be increased, and the mutual interference can be suppressed.

Since the light emitting section A and the light receiving section B are formed in the same laminated structure, that is, in the same material composition and film thickness,
It is extremely easy to integrate them on the same substrate without requiring complicated processes. Therefore, a highly reliable optical transmission device having both high transmission efficiency and high-speed response can be realized at low cost, and its usefulness is great. (Second Embodiment) FIG. 3 is a sectional view showing a schematic structure of an optical semiconductor device according to a second embodiment of the present invention. The same parts as those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof will be omitted.

In this embodiment, the light receiving portion B is not formed in a ring shape, but is formed in the vicinity of the light emitting portion A. In this case, the n-side electrode is 24
And 25 on the light receiving section B side. Further, the area of the light receiving section B is set larger than that of the light emitting section A so that the scattered light from the fiber 30 can be effectively detected. (Third Embodiment) FIG. 4 is a sectional view showing a schematic structure of an optical semiconductor device according to a third embodiment of the present invention. 1 and 3 are denoted by the same reference numerals, and detailed description thereof will be omitted.

In this embodiment, the light emitting section A and the light receiving section B are provided relatively far apart, and dedicated fibers 31 and 32 are connected to the light emitting section A and the light receiving section B, respectively. In this case, transmission and reception using a single fiber cannot be performed, but the effect is obtained that the performance of each of them can be improved while the light emitting unit A and the light receiving unit B having the same laminated structure are integrated on the same substrate. (Fourth Embodiment) FIG. 5 is a sectional view showing a schematic structure of an optical semiconductor device according to a fourth embodiment of the present invention. 1 and 3 are denoted by the same reference numerals, and detailed description thereof will be omitted.

The present embodiment functions as a photocoupler, and light is transmitted from the light emitting section A to the light receiving section B through the substrate 10 without using an optical fiber. Specifically, on the light emitting unit A side and the light receiving unit B side, the side surface of the substrate 10 is etched to form a 45 ° inclined portion 5.
1 and 52 are provided, and the reflection of light at these inclined portions 51 and 52 is used. Inclined portions 51 and 5 to increase reflection efficiency
2, a reflection film or the like may be formed. Further, an electrode 26 may be provided between the light emitting unit A and the light receiving unit B, and may be used as a common electrode.

The present invention is not limited to the above embodiments. In the embodiment, the AlGaInN-based semiconductor is used as the group III-V compound semiconductor, but the present invention can be applied to a group III-V compound semiconductor containing nitrogen as a group V element. In addition, the substrate is not necessarily limited to a single-crystal insulating substrate such as sapphire, and may be any substrate as long as it can satisfactorily grow a group III-V compound semiconductor. Further, conditions such as the type and concentration of impurities in each layer can be appropriately changed according to specifications. In addition, various modifications can be made without departing from the scope of the present invention.

[0032]

As described in detail above, according to the present invention, a III-V compound semiconductor containing nitrogen as a group V element is used as an active layer, and a light emitting portion and a light receiving portion are formed in the same laminated structure on the same substrate. By forming the optical semiconductor element, an optical semiconductor element capable of two-way communication can be realized in combination with a plastic fiber or the like, and sufficient performance can be exhibited in both the light emitting section and the light receiving section.

[Brief description of the drawings]

FIGS. 1A and 1B are a plan view and a cross-sectional view illustrating a schematic structure of an optical semiconductor device according to a first embodiment.

FIG. 2 is a sectional view showing a manufacturing process of the optical semiconductor device according to the first embodiment.

FIG. 3 is a sectional view showing a schematic structure of an optical semiconductor device according to a second embodiment.

FIG. 4 is a sectional view showing a schematic structure of an optical semiconductor device according to a third embodiment.

FIG. 5 is a sectional view showing a schematic structure of an optical semiconductor device according to a fourth embodiment.

FIG. 6 is a diagram showing the wavelength dependence of optical transmission loss of a typical plastic fiber.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Sapphire substrate 11 ... n-GaN buffer layer 12 ... n-AlGaN cladding layer 13 ... GaInN active layer 14 ... p-AlGaN cladding layer 15 ... p-GaN contact layer 21 ... light emitting part side p electrode 22 ... light receiving part side p Electrodes 23, 26 ... Common n-electrode 24 ... Light-emitting unit side n-electrode 25 ... Light-receiving unit side n-electrode 30, 31, 32 ... Plastic fibers 51, 52 ... Substrate inclined part

Claims (5)

[Claims] 1. A light emitting section and a light receiving section are formed on the same substrate, wherein the light emitting section and the light receiving section are formed in the same laminated structure using a III-V compound semiconductor, and the light emitting section and the light receiving section are formed. At least the active layer contains nitrogen as a group V element III-
An optical semiconductor device comprising a group V compound semiconductor. Wherein said active _{layer, Al x Ga y In 1-} xy N
2. The optical semiconductor device according to claim 1, wherein (x + y = 1, 0 ≦ x, y ≦ 1). 3. The light-emitting portion is formed in a circular shape, and the light-receiving portion is formed in a ring shape around the light-emitting portion and coaxially with the light-emitting portion. An optical semiconductor element characterized in that the axes of are aligned. 4. A step of forming a layered structure of a group III-V compound semiconductor on a substrate and using a layered structure of a group III-V compound semiconductor containing nitrogen as a group V element in at least an active layer; A method for manufacturing an optical semiconductor device, comprising: forming an electrode on a laminated structure; and separating the laminated structure and the electrode into a light emitting portion and a light receiving portion by etching. 5. A step of growing a buffer layer made of a group III-V compound semiconductor on a single crystal substrate, and using a group III-V compound semiconductor containing nitrogen as a group V element as an active layer on the buffer layer. Growing a double heterojunction structure, growing a contact layer made of a III-V compound semiconductor on the double heterojunction structure, forming an electrode on the contact layer, Selectively etching the surface to reach the buffer layer, separating the inner light emitting portion and the outer light receiving portion surrounding the light emitting portion, and removing the outer region of the light receiving portion; Forming a common electrode on the buffer layer exposed in an outer region.