HK1022213A - Process for manufacturing an infrared-emitting luminescent diode - Google Patents

Description

Method for manufacturing infrared emission light emitting diode

The invention relates to a method for producing an infrared-emitting light-emitting diode, comprising a semiconductor substrate, preferably made of GaAs, which is coated with an active layer sequence that emits an Infrared (IR) -beam when the light-emitting diode is in operation, said sequence consisting of a first AlGaAs cladding layer, an active layer containing GaAs and/or AlGaAs, and a second AlGaAs cladding layer.

Light-emitting diodes, i.e. light-emitting diodes (LEDs), are used as emitting elements, in particular in the field of optical communication technology. The use of different semiconductor systems according to the desired wavelength of the emitted light also leads to different manufacturing methods for their respective underlying semiconductor materials due to their respective technical problems. The use of an AlGaInP alloy system in the visible spectral range with a wavelength of about 400 to 800nm, by adjusting its aluminum content, makes it possible to determine the desired wavelength of light in a relatively broad spectral range. In contrast to light-emitting diodes, which have longer wavelengths operating in the infrared range and are generally based on an AlGaAs system, the upper limit of the wavelength of the emitted light can be about 800nm by adjusting the aluminum content thereof in the typical range of about 10% to 30%. The invention is based on the production of an infrared light-emitting diode based on an AlGaAs system. In the case of the infrared light-emitting diodes to date, all layer sequences applied to GaAs substrates have been produced by the LPE (liquid phase epitaxy) method. In this way, a supersaturated solution of the desired additive material is brought into contact with the GaAs substrate crystal at a certain temperature in order to form an epitaxial layer, and an epitaxial layer of GaAs and AlGaAs is formed on the substrate crystal during a subsequent cooling process. In this way, single-crystal layers of different compositions can be grown corresponding to the phase curve. Liquid phase epitaxy has a relatively large growth rate and is therefore also suitable for producing relatively thick epitaxial layers. This is considered a disadvantage when producing the layer sequence of the infrared light-emitting diodes of the AlGaAs systems of interest here, the relatively thick AlGaAs LPE layers deposited by the methods described to date being subjected to mechanical stress and thus causing the epitaxial wafer to be subjected to bending, which are difficult to process in later steps. For this reason, the methods used so far for manufacturing infrared-emitting light-emitting diodes on semiconductor substrates with wafer combinations of a maximum wafer diameter of two inches have been limited.

In a further configuration of the invention, the infrared-emitting light-emitting diode has a so-called coupling layer to improve the optical coupling efficiency of the light emitted by the light-emitting diode. The optical coupling efficiency is determined here above all to a large extent by the layer structure of the base semiconductor material. If the actual light generation is carried out on a thin, so-called layer which is integrated into the active layer, and for example comprises a so-called active region in a light-emitting diode with a double-hetero-layer structure or a light-generating region formed around a pn transition region in a homogeneous pn-light-emitting diode, a covering layer with a low absorption on both sides can significantly improve the coupling efficiency for the emitted wavelength. Furthermore, the layer structure must be produced by applying a relatively thicker semiconductor layer with a greater bandwidth than in the light-generating region (active layer). Currently, such structures are produced only by Liquid Phase Epitaxy (LPE) or by a combination of various vapor phase epitaxy methods, the latter photogenerated structures generally being produced by MOVPE and the thick coupling layer by VPE. One disadvantage of using the MOVPE method for producing LED structures with such thick coupling layers is the relatively low deposition rate. In order to produce a relatively thick window layer with a thickness of more than about 10nm and a coupling layer, preferably of GaAs, which can increase the coupling efficiency very well, a combination of the MOVPE method and the VPE method has been used. According to the invention, a novel assembly method is also to be provided, with which an LED structure with a thick coupling layer can be produced. However, there is a difficulty, among others, that not only the composition of the coupling layer but also the production conditions of the coupling layer will influence the surface efficiency, since the degree of damage of the sensitive layer structure (double-hetero-layer of an active region, and pn-transition region) is determined by the given parameters.

It is known from U.S. Pat. No. 8, 5,233,204 and from K.H. Huang, et.al.appl.Phys.Lett.61(9), 31.8.1992, page 1045-1047 to produce light-emitting diodes in the visible spectral range with a wavelength of 555 to 620nm, based on an AlGaInP alloy system. The light-emitting diode comprises a layer sequence consisting of a GaAs substrate, a first AlGaInP cladding layer of n-type, an active region of n-type AlGaInP and a second AlGaInP cladding layer of p-type. The two capping layers each have a thickness of about 800nm and the active region has a thickness of about 500 nm. The first AlGaInP cladding layer, the active region, and the second AlGaInP cladding layer are fabricated by a MOCVD (metal-organic chemical vapor deposition) process. It is also known that the second AlGaInP cladding layer is formed by a light-transmitting coupling layer of GaP, AlGaAs and GaAsP with a thickness of at least 15 μm, which is manufactured by a VPE (vapor phase epitaxy) method. The coupling layer here increases the effective light radiation of the light-emitting diode by reducing the amount of light emitted laterally and by reducing the amount of light absorbed by the light-absorbing substrate. For this purpose, the coupling layer has a thickness of at least 0.06 × the width of the light-emitting diode. The optical refractive index of the coupling layer is then selected such that the portion of light absorbed in the light-emitting diode is reduced, as determined by the angle of total reflection.

The object underlying the invention is to provide a method for producing an infrared-emitting light-emitting diode from a GaAs semiconductor substrate and an AlGaAs-based layer sequence, in which the mechanical stresses that occur can be reduced even when AlGaAs layers are deposited to a relatively large thickness, and which is therefore also suitable for the problem-free mass production of light-emitting diodes with wafer assemblies having a diameter of more than 2 inches.

This object is achieved by the method stated in claim 1.

Advantageous further developments and embodiments of the method according to the invention are the subject matter of the dependent claims 2 to 9.

The content of the invention is as follows: the first AlGaAs-cladding layer and the active region are produced by a MOVPE (metal vapor phase epitaxy) -method and the second AlGaAs-cladding layer is produced by an LPE (liquid phase epitaxy) -method. The combined method of MOVPE and LPE according to the invention has the following advantages in the production of an AlGaAs system-based infrared-emitting light-emitting diode compared with the methods used hitherto:

in order to obtain an optimum optical structure match, which is important for good discharge carrier mobility and long service life of the epitaxial layers, the first AlGaAs-cladding layer and the active layer, which are particularly dangerous for mechanical stress, are manufactured by an MOVPE method, in which the metal used is transported in a low vapor pressure gas phase, preferably using trichlorogallium as the gas phase carrier. The deposition then takes place well below the melting point of the GaAs crystals, so that the penetration of impurities from the epi-system is clearly prevented. The deposition rate provided by MOVPE-methods is still sufficiently high when the total thickness of the active layer structure consisting of the cover layer and the active region is typically about 10 μm. The LPE method is selected for the production of the second AlGaAs cladding layer, is relatively simple and inexpensive and provides a high deposition rate, and is therefore particularly suitable for use when the layer thickness is relatively large. The epitaxial wafers produced in this way have a very small curvature compared to the epitaxial wafers produced according to the methods known to date.

In order to produce a relatively thick window layer with a thickness of more than about 10 μm and a coupling layer or even a self-supporting coupling layer with a thickness of more than about 70 μm on the second cladding layer, the invention principle proposes that a novel method for producing the desired ir-emitting light-emitting diode is provided by means of a combination of MO-vapor phase epitaxy for the first cladding layer and the active layer and liquid phase epitaxy for the second cladding layer and the coupling layer, in which case a LPE modification method is used in particular for the liquid phase deposition, which method brings about the smallest possible thermal load on the light-generating layer structure, i.e. for example a temperature difference-LPE method. This is achieved by subsequent etching and dissolution of the GaAs-absorbed substrate, and the IP-light-emitting diode produced in this way has a particularly high coupling efficiency.

Further features, advantages and objects of the invention will be described below with the aid of construction examples of the drawings. Such as:

FIG. 1 is a schematic cross-sectional view of an IR-LED in accordance with a first embodiment of the invention;

FIG. 2 is a schematic cross-sectional view of an IR-LED in accordance with a second embodiment of the invention; and

fig. 3 is a schematic cross-sectional view of an IR-led according to a third embodiment of the present invention.

The exemplary embodiment of an infrared-emitting light-emitting diode produced according to the inventive method, which is shown in fig. 1, comprises a GaAs semiconductor substrate, to which an active layer sequence is applied which emits an IR radiation beam when the light-emitting diode is in operation, which is formed from a first layer x =0.35 of AlxGa1-xAs cladding layer 2, an active layer 3 and a second layer x =0.35 of Al of the semiconductor substrate 1_xGa_1-xAs-coating layer 4. The active layer 3 according to the embodiment of fig. 1 shows an AlGaAs-double-hetero structure emitting at a wavelength of about 830nm ir-rays; the active layer 3 can also consist of a homogeneous pn transition region. The layer structure shown in fig. 1 is particularly suitable for producing particularly fast infrared-emitting light-emitting diodes.

First Al_xGa_1-xAs-cladding layer 2 and active layer 3 are made by MOVPE (vapor phase epitaxy of metal structure) method, and the second Al_xGa_1-xThe As-coating 4 is manufactured by an LPE- (liquid phase epitaxy) -process.

In the embodiment shown in FIG. 2, in the second Al_xGa_1-xAn x =0.2-0.4 coating of As-coating 4 is additionally depositedAl_xGa_1-xAs-coupled layer 5 of Al_xGa_1-xThe As-coupled layer 5 is deposited by an LPE- (liquid phase epitaxy) -method and has a total thickness of about 10 to 50 μm. The symbols 6 and 7 are electrically conductive electrode connections, which are omitted in the figure of fig. 1 for the sake of simplicity.

Al in the example of FIG. 3_xGa_1-xThe As-coupling layer 5 is composed of a self-supporting layer having a thickness of at least about 50 μm. And the light-absorbing substrate 1 is dissolved away by etching or a similar dissolution method. The self-supporting coupling layer 5 in this embodiment acts as a light-transmissive substrate supporting the structure consisting of 2, 3, 4 and 6,7 layers.

The embodiments shown in fig. 2 and 3 are particularly suitable for the production of particularly bright infrared-emitting light-emitting diodes.

Symbol table

1 semiconductor substrate

2 first Al_xGa_1-xAs-coating

3 active layer

4 second Al_xGa_1-xAs-coating

5 Al_xGa_1-xAs-coupled layer

6,7 conductive electrode connection

Claims (9)

1. A method for producing an infrared-emitting light-emitting diode, in which an active layer, which emits an infrared radiation when the light-emitting diode is in operation, is applied to a semiconductor substrate (1), which preferably consists of GaAs, and which, proceeding from the semiconductor substrate (1), consists of a first AlGaAs cladding layer (2), an active layer (3) containing GaAs and/or AlGaAs, and a second AlGaAs cladding layer, is characterized in that the first AlGaAs cladding layer (2) and the active layer (3) are produced by a MOYPE (metal vapor phase epitaxy) method and the second AlGaAs cladding layer (4) is produced by an LPE (liquid phase epitaxy) method.

2. Method according to claim 1, characterized in that the Al content of each of the first AlGaAs cladding layer (2) and/or the second AlGaAs cladding layer (4) is about 10% to about 35%.

3. A method according to claim 1 or 2, characterized in that the mass production of wafer-assembled ir-emitting leds is achieved if the diameter of the wafer is larger than 2 inches.

4. A method according to one of claims 1 to 3, characterized in that the second AlGaAs-cladding layer (4) is coated with an electrically conductive coupling layer (5) transparent in the infrared spectral range and having a thickness of at least about 10 μm by an LPE- (liquid phase epitaxy) -method.

5. A method as claimed in claim 4, characterized in that the coupling layer (5) is constructed to be self-supporting and has a thickness of at least approximately 50 μm.

6. A method as claimed in claim 5, characterized in that the semiconductor substrate (1), preferably of GaAs, is removed after the manufacture of the self-supporting coupling layer (5).

7. Method according to claim 5 or 6, characterized in that the coupling layer (5) is made of AlGaAs with an Al-content of preferably about 20% to about 35%.

8. A method according to one of claims 5 to 7, characterized in that the coupling layer (5) is manufactured in a plurality of LPE-single processes.

9. A method according to claims 4 to 8, characterized in that the coupling layer (5) is manufactured by a thermo-LPE-method.