Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal
Reexamination Certificate
1998-07-23
2001-10-23
Le, Vu A. (Department: 2824)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
C438S037000, C438S046000
Reexamination Certificate
active
06306672
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a Group III-V complex vertical cavity surface emitting laser (hereinafter refer to VCSEL) diode manufactured using GaN-system III-V nitride and a manufacturing method thereof.
2. Description of the Related Art
In general, a VCSEL manufactured of GaN-system III-V nitride can emit near ultraviolet light of 400 nm wavelength and blue light, so it can be used in a high-capacity information storage apparatus. Also, the surface emitting laser oscillates in a single longitudinal mode as opposed to an edge emitting laser.
Such a surface emitting laser diode, as shown in
FIG. 1
, usually includes a cavity
10
and Distributed Bragg Reflectors DBR
20
and
30
of reflectance of 99.9% or greater, respectively provided on the lower and upper surfaces of the cavity
10
. The cavity
10
has an active layer
11
formed of InGaN multi quantum wells, and n-AlGaN and p-AlGaN carrier restrictive layers
12
and
13
respectively formed on the lower and upper surfaces of the active layer
11
. The DBRs are generally one of two types. One type uses semiconductor materials which have similar lattice constants and are capable of epitaxial growth, such as GaAs and AlAs, and the other type uses a dielectric material such as SiO
2
, Al
2
O
3
, TiO
2
, or ZnO
2
. In the former case, current can be injected via semiconductor, and the quality of the thin film is excellent. Here, a usable DBR has a greater bandgap energy than that of a light of wavelength self-stimulating in the active layer
11
, and the self-stimulating light must not be absorbed in the DBR. It is preferable that the difference in the refractive index between two layered OBR materials is great. In the GaN-system VSCEL diode as shown in
FIG. 1
, the DBRs
20
and
30
can be formed of a semiconductor material such as alternating layers of GaN
22
and
32
and AlN or AlGaN
21
and
31
. Among them, AlGaN and AlN
21
and
31
, containing at least 30% Al, have significantly high bandgap energy. Accordingly, when current is injected via the DBRs composed of the AlGaN and AIN
21
and
31
, a voltage for driving them significantly increases, so that problems due to generation of heat may be created. Furthermore, when the DBR is comprised of the GaN
22
and
32
and AlN
21
and
31
having the greatest difference in refractive index, at least
20
pairs of layers must be stacked to obtain a desired high reflectance. Furthermore, a very narrow wavelength width in a high reflectance region makes it difficult to design a VSCEL diode. A slight deviation from the thickness of the cavity
10
or a small change in the composition of the active layer
11
can ruin self-stimulating conditions.
FIGS. 2A and 3A
show reflectance of DBRs formed by stacking GaN and AlN with a thickness of &lgr;/4n (&lgr; is a wavelength, and n is refractive index) to 15 pairs and to 30 pairs, respectively. Here, the refractive indices of GaN and layers are set to 2.67 and 2.15, respectively, and a central wavelength is set to 430 nm. From
FIG. 2B
being an extended graph of
FIG. 2A
, we can see that sufficient reflectance cannot be obtained by the 15-pair DBR and that the width of a spectrum indicating high reflectance is very narrow. From
FIG. 3B
being an extended graph of
FIG. 3A
, we can recognize that sufficient reflectance can be obtained by the 30-pair DBR but that the width of the spectrum indicating high reflectance is still too narrow. However, a more serious technical problem is that manufacture of the DBR with so many pairs is difficult due to slow and difficult crystal growth of GaN/AlN in contrast with the DBR manufactured of GaAs/AlAs.
A dielectric DBR can be utilized in order to overcome such defects, but it can be applied to only an upper DBR. A lower DBR must be manufactured by the crystal growth method in order to grow the cavity.
SUMMARY OF THE INVENTION
To solve the above problems, it is an objective of the present invention to provide a vertical cavity surface emitting laser (VCSEL) diode comprising a DBR having a high reflectance by growing a small number of layers using a crystal growth technique, and a manufacturing method thereof.
Accordingly, to achieve the above objective, there is provided a Group III-V complex vertical cavity surface emitting laser (VCSEL) diode including a lower distributed bragg reflector (DBR), a cavity and an upper DBR, wherein each of the lower and upper DBRs is formed by stacking pairs of a relatively high refractive index GaN layer and a relatively low refractive index air layer to 2 or more (e.g., 3 to 15) pairs of stacked layers, each layer having a thickness of &lgr;/4n, when &lgr; is the wavelength of produced light and n is the refractive index of a DBR constituent material.
In the Group III-V complex VCSEL diode, the lower and upper DBRs are comprised of pairs of an air layer and an AlGaN layer having Al of a predetermined amount or less. The cavity comprises: an active layer formed of InGaN multi quantum wells; and an n-AlGaN first carrier restrictive layer and a p-AlGaN second carrier restrictive layer, formed respectively on the lower and upper surfaces of the active layer, for restricting carriers. The cavity further comprises a first n-GaN contact layer and a second p-GaN contact layer for connecting electrodes, formed on one surface of the first n-AlGaN carrier restrictive layer and one surface of the second pAlGaN carrier restrictive layer, respectively. The cavity further comprises an n-AlN layer formed as a current passage in the mid portion of the n-AlGaN first carrier restrictive layer or the first n-GaN contact layer, and a current blocking layer formed of oxidized n-AlN or air in the vicinity of the n-AlN layer, or further comprises a p-AlN layer formed as a current passage in the mid portion of the second p-AlGaN carrier restrictive layer or the first p-GaN contact layer, and a current blocking layer formed of oxidized p-AlN or air in the vicinity of the p-AlN layer.
An electrode is formed on the upper edges of the first n-GaN contact layer and second pGaN contact layer, to be isolated from the upper DBR and the cavity. It is preferable that the lower DBR layer, the cavity and the upper DBR layer are formed in the shape of a cylinder having a large diameter in the stacking sequence, and supporters for supporting the cylindrical lower DBR layer, cavity layer and upper DBR layer are formed on the outer side of the cylindrical structure in a body of each layer.
To achieve the above objective, there is also provided a method of manufacturing a Group III-V complex surface emitting laser diode, comprising the steps of: (a) sequentially growing a preliminary lower DBR layer, a preliminary cavity layer and a preliminary upper DBR layer on a semiconductor substrate and patterning the preliminary upper DBR layer using a first dry etch method; (b) forming an upper DBR layer by removing an AlN layer from the patterned preliminary upper DBR layer using a selective wet etch method and forming an air layer having a relatively low refractive index; (c) forming a cavity by etching the
The step of forming a buffer layer by growing AlN or GaN directly on the semiconductor substrate using metal organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE) is further comprised before the step (a), In the step (a), when &lgr; is the wavelength of light and n is the refractive index of a constituent material of a DBR, the upper and lower DBR layers are formed by alternately stacking GaN and AlN, or AlGaN with a relatively small amount of Al and AlGaN with a relatively great amount of Al, each of the four materials having a thickness of &lgr;/4n. Pairs of GaN and AlN, or pairs of AlGaN with a relatively small amount of Al and AlGaN with a relatively great amount of Al, are stacked to 2 or more (e.g., 3 to 15) pairs of stacked layers. In the step (a), forming the preliminary cavity layer comprises the substeps of forming an n-AlGaN carrier restrictive layer for restricting carriers, on the preliminary lower DBR lay
Burns Doane , Swecker, Mathis LLP
Le Vu A.
Samsung Electronics Co,. Ltd.
Smith Bradley K
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