U.S. patent application number 11/322804 was filed with the patent office on 2006-07-27 for distributed bragg's reflector of digital-alloy multinary compound semiconductor.
Invention is credited to Won Jun Choi, Jung Il Lee, Jin Dong Song.
Application Number | 20060165148 11/322804 |
Document ID | / |
Family ID | 36677846 |
Filed Date | 2006-07-27 |
United States Patent
Application |
20060165148 |
Kind Code |
A1 |
Song; Jin Dong ; et
al. |
July 27, 2006 |
Distributed Bragg's reflector of digital-alloy multinary compound
semiconductor
Abstract
There is provided a distributed Bragg's reflector (DBR)
comprising a substrate and an unit distributed Bragg's reflector
(DBR) layer, wherein a multi-layer is laminated on the substrate.
The unit DBR layer is composed of a multi-layer laminated structure
of unit digital-alloy multinary compound semiconductor
layer/multinary compound semiconductor layer or unit digital-alloy
multinary compound semiconductor layer/unit digital-alloy multinary
compound semiconductor layer. The unit digital-alloy multinary
compound semiconductor layer is composed of the multi-layer
laminated structure of the first layer of multinary compound
semiconductor and the second layer of a different multinary
compound semiconductor on said first layer. The digital-alloy
distributed Bragg's reflector of the present invention has a
uniform quality on the substance area and the filter and reflector
having uniformly high quality can be mass produced by using the
reflector.
Inventors: |
Song; Jin Dong; (Seoul,
KR) ; Choi; Won Jun; (Seoul, KR) ; Lee; Jung
Il; (Seoul, KR) |
Correspondence
Address: |
JONES DAY
222 EAST 41ST ST
NEW YORK
NY
10017
US
|
Family ID: |
36677846 |
Appl. No.: |
11/322804 |
Filed: |
December 30, 2005 |
Current U.S.
Class: |
372/99 ;
257/E33.069 |
Current CPC
Class: |
H01S 2304/02 20130101;
H01S 5/183 20130101; H01S 2304/00 20130101; H01L 33/105
20130101 |
Class at
Publication: |
372/099 |
International
Class: |
H01S 3/08 20060101
H01S003/08 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 13, 2005 |
KR |
10-2005-0003089 |
Claims
1. A distributed Bragg's reflector (DBR) comprising a substrate and
a unit distributed Bragg's reflector (DBR) layer formed by
laminating a plurality of layers, on the substrate, and wherein
said unit DBR layer comprises one or more of a multi-layer
laminated structure of unit digital-alloy multinary compound
semiconductor layer/multinary compound semiconductor layer and a
first unit digital-alloy multinary compound semiconductor layer/a
second unit digital-alloy multinary compound semiconductor layer,
and wherein said unit digital-alloy multinary compound
semiconductor layer is composed of the multi-layer laminated
structure of a first layer of multinary compound semiconductor and
a second layer of a different multinary compound semiconductor on
said first layer.
2. The distributed Bragg's reflector according to claim 1, wherein
a thickness of each layer constituting the unit digital-alloy
multinary compound semiconductor layer is smaller than a wavelength
of light inside the digital-alloy multinary compound semiconductor
layer.
3. The distributed Bragg's reflector according to claim 1, wherein
the multinary compound semiconductor layer constituting said unit
DBR layer is a separate digital-alloy multinary compound
semiconductor layer having a different composition from a
digital-alloy multinary compound semiconductor layer that underlies
the separate digital-alloy multinary compound semiconductor
layer.
4. The distributed Bragg's reflector according to claim 1, wherein
the unit DBR layer comprises the multi-layer laminated structure of
AlGaAs digital-alloy multinary compound semiconductor layer/GaAs
layer.
5. The distributed Bragg's reflector according to claim 4, wherein
the AlGaAs digital-alloy multinary compound semiconductor layer
comprises a AlAs layer and the GaAs layer on a AlAs layer.
6. The distributed Bragg's reflector according to claim 1, wherein
the unit digital-alloy multinary compound semiconductor layer is
selected from a group consisting of InGa(Al)As/In(Ga)AlAs,
InGaAsP/InGaAsP, InGaP/InAlP, (1n)GaAlAsSb/(In)GaAlAsSb,
InGaAlAs(N)/InGaAlAs(N) and SiO.sub.x/TiO.sub.x.
7. A vertical resonator surface light-emitting laser diode
comprising the distributed Bragg's reflector according to claim
1.
8. A vertical resonance light-emitting diode comprising the
distributed Bragg's reflector according to claim 1.
9. A photodetector comprising the distributed Bragg's reflector
according to claim 1.
10. A resonator comprising a substrate and at least one distributed
Bragg's reflector (DBR) layer formed by laminating one or more
layers on the substrate, and wherein said DBR layer comprises at
least one layer of a digital-alloy multinary compound semiconductor
layer, wherein the digital-alloy multinary compound semiconductor
layer is formed by deposition of a plurality of layers that
together form the multinary compound semiconductor layer.
11. The resonator according to claim 10, wherein a thickness of
each layer constituting the digital-alloy multinary compound
semiconductor layer is smaller than a wavelength of light inside
the digital-alloy multinary compound semiconductor layer.
12. The resonator according to claim 10, wherein the multinary
compound semiconductor layer constituting said DBR layer is a
separate digital-alloy multinary compound semiconductor layer
having a different composition from an underlying digital-alloy
multinary compound semiconductor layer.
13. The resonator according to claim 10, wherein the DBR layer
comprises the multi-layer laminated structure of AlGaAs
digital-alloy multinary compound semiconductor layer/GaAs
layer.
14. The resonator according to claim 13, wherein the AlGaAs
digital-alloy multinary compound semiconductor layer comprises a
AlAs layer and a GaAs layer on the AlAs layer.
15. The resonator according to claim 10, wherein the digital-alloy
multinary compound semiconductor layer is selected from a group
consisting of InGa(Al)As/In(Ga)AlAs, InGaAsP/InGaAsP, InGaP/InAlP,
(In)GaAlAsSb/(In)GaAlAsSb, InGaAlAs(N)/InGaAlAs(N) and
SiO.sub.x/TiO.sub.x.
16. A method of making a resonator, the method comprising: forming
a distributed Bragg's reflector (DBR) layer by laminating on a
substrate a plurality layers comprising at least one digital-alloy
multinary compound semiconductor layer, wherein laminating the at
least one digital-alloy multinary compound semiconductor layer
includes the steps of depositing a plurality of layers that
together form the multinary compound semiconductor layer.
17. The method of claim 16 further comprising the step of forming
in the DBR layer at least one multi-layer laminated structure of
AlGaAs digital-alloy multinary compound semiconductor layer/GaAs
layer by laminating a AlAs layer on a AlAs layer.
18. The method of claim 16, wherein a thickness of each layer
constituting the digital-alloy multinary compound semiconductor
layer is smaller than a wavelength of light inside the
digital-alloy multinary compound semiconductor layer.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a distributed Bragg's
reflector of a digital-alloy multinary compound semiconductor.
BACKGROUND OF THE INVENTION
[0002] When forming materials each having a different refractive
index, it is inevitable that there is a change of reflectivity
within a certain wavelength range (FIG. 1). The structure formed in
such a manner is referred to as a distributed Bragg's reflector
(DBR).
[0003] In particular, the DBR technique can make the reflectivity
to be 100% or 0% in a desired wavelength according to the
refractive index difference and the thickness of each layer. Thus,
the technique has been introduced to mainly fabricate filters and
reflectors used in current optical devices such as camera lenses. A
device, which is manufactured by applying the DBR technique to
fabricate a semiconductor laser resonator, is referred to as a
vertical resonator surface-emitting device (see H. Li, K. Iga,
"Vertical Cavity Surface-Emitting Laser Devices," Springer, Berlin,
2002). The device emits a light in a direction perpendicular to a
plane forming the semiconductor active layer. Such device has been
often utilized as a light source in connection with small optical
communication and optical recording apparatuses due to its low
production costs, as well as its low optical spreading and optical
coupling.
[0004] The key components of the vertical resonator device are
DBRs, which are formed relative to the semiconductor active layer.
DBRs are generally fabricated by laminating dielectric materials
each having a different refractive index or by laminating compound
semiconductors, which are lattice-matched to a substrate and have
differing compositions.
[0005] For example, in case of a commercially available vertical
resonator surface-emitting device having a mean wavelength of 0.98
.mu.m, DBR is prepared by laminating a pair of AlGaAs/GaAs. Also,
DBR can be prepared by laminating a pair of InGaAlAs/InGaAlAs in
case of 1.3 to 1.55 .mu.m broadband vertical resonator
surface-emitting device, wherein the former InGaAlAs and the latter
InGaAlAs have differing compositions. However, the mean reflection
wavelength of DBR changes too easily, even when there is a slight
change in the composition and thickness.
[0006] In a large area semiconductor, the composition of materials
is subjected to DBR changes due to an unequal heating of the
substrate, thereby decreasing uniformity. Furthermore, since the
composition and thickness must be controlled each time DBR is
fabricated, there is needed a substantial effort to maintain the
conditions of apparatus for fabricating the same, which obviously
decreases productivity.
SUMMARY OF THE INVENTION
[0007] Therefore, it is an object of the present invention to
provide a Bragg's reflector of a digital-alloy multinary compound
semiconductor, which is capable of obtaining uniformity in mass
production while displaying uniformity in fabricating a large area
reflector.
[0008] Thus, the present invention relates to a Bragg's reflector
of a digital-alloy multinary compound semiconductor, which has such
excellent properties.
[0009] More specifically, the distributed Bragg's reflector of the
present invention comprises a substrate and an unit distributed
Bragg's reflector (DBR) layer, as well as a multi-layer laminated
on the substrate. Said unit DBR layer is composed of a multi-layer
laminated structure of unit digital-alloy multinary compound
semiconductor layer/multinary compound semiconductor layer or unit
digital-alloy multinary compound semiconductor layer/unit
digital-alloy multinary compound semiconductor layer. Said unit
digital-alloy multinary compound semiconductor layer is composed of
the multi-layer laminated structure of the first layer of multinary
compound semiconductor and the second layer of a different
multinary compound semiconductor on said first layer.
[0010] In said distributed Bragg's reflector of the present
invention, the thickness of each layer constituting the unit
digital-alloy multinary compound semiconductor layer may be smaller
than the wavelength of the light inside the digital-alloy multinary
compound semiconductor layer.
[0011] Furthermore, the multinary compound semiconductor layer
constituting said unit DBR layer can be composed of a separate
digital-alloy multinary compound semiconductor layer, which has a
different composition from the digital-alloy multinary compound
semiconductor layer that underlies the separate digital-alloy
multinary compound semiconductor layer.
[0012] This and other objects and advantages of the present
invention will be clarified in the following detailed description
of the invention provided below.
BRIEF DESCRIPTION OF DRAWINGS
[0013] The above and other objects and features of the present
invention will become apparent from the following description of
the preferred examples given in conjunction with the accompanying
drawings:
[0014] FIG. 1 shows a general structure of a distributed Bragg's
reflector and a graph showing the relationship of wavelength vs.
reflectivity, which is determined from the structure.
[0015] FIG. 2a shows a structure of a conventional multinary
compound semiconductor.
[0016] FIG. 2b shows a digital-alloy multinary compound
semiconductor according to the present invention.
[0017] FIG. 3 shows an exemplified method of fabricating a
conventional multinary compound semiconductor (a), as well as that
of fabricating a digital-alloy multinary compound semiconductor
according to the present invention (b).
[0018] FIG. 4 shows a laminated structure of 17
Al.sub.0.9Ga.sub.0.1As/GaAs-paired layers in a conventional
distributed Bragg's reflector.
[0019] FIG. 5 shows a laminated structure of 17 digital-alloy
Al.sub.0.9Ga.sub.0.1As/GaAs-paired layers in a digital-alloy
distributed Bragg's reflector of the present invention.
[0020] FIG. 6 is a graph showing a relationship between
reflectivity and wavelength in the Bragg's reflector shown in FIGS.
4 and 5.
[0021] FIG. 7 shows a structure of a digital-alloy distributed
Bragg's reflector vertical resonator, which utilizes a
digital-alloy Al.sub.0.9Ga.sub.0.1As/GaAs structure shown in FIG.
5.
[0022] FIG. 8 is a graph showing a relationship between
reflectivity, wavelength and large area (3 inches) uniformity in a
digital-alloy distributed Bragg's reflector vertical resonator of
the present invention.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
[0023] According to one embodiment of the present invention, a one
unit DBR layer comprises a multi-layer laminated structure of
AlGaAs digital-alloy multinary compound semiconductor layer/GaAs
layer, wherein said AlGaAs digital-alloy multinary compound
semiconductor layer comprises an AlAs layer and a GaAs layer on the
AlAs layer.
[0024] Further, the unit digital-alloy multinary compound
semiconductor layer of the present invention can be selected from a
group consisting of InGa(Al)As/In(Ga)AlAs, InGaAsP/InGaAsP,
InGaP/InAlP, Si/(Si)Ge, (In)GaAlAsSb/(In)GaAlAsSb,
InGaAlAs(N)/InGaAlAs(N) and SiO.sub.x/TiO.sub.x.
[0025] Moreover, the present invention provides a vertical
resonator surface light-emitting laser diode, a vertical resonance
light-emitting diode (LED) and a photodetector including the
distributed Bragg's reflector of the present invention.
[0026] The term "digital-alloy," as used herein, means a material
prepared by multi-layer laminating each of the unit composition
materials (in case of AlGaAs, AlAs and GaAs) in an uniform
thickness (e.g., 1 to 2 nm thickness in fabricating multinary
compound semiconductor, ternary compound semiconductor such as
AlGaAs, or quaternary compound semiconductor such as InGaAlAs. The
digital-alloy is used for discriminating against an ordinary
multinary compound semiconductor (J. D. Song, D. C. Heo, I. K. H,
J. M. Kim, Y. T. Lee, S. H. Park, "Parametric study on optical
properties of digital-alloy In(Gal-zAlz)As/InP grown by
molecular-beam epitaxy," Appl. phys. lett. 84, pp. 873 (2004)).
[0027] FIG. 2a shows the structure of a conventional multinary
compound semiconductor. FIG. 2b shows the structure of a
digital-alloy multinary compound semiconductor
Al.sub.0.5Ga.sub.0.5As of the present invention. The composition of
Al.sub.0.5Ga.sub.0.5As digital-alloy of the present invention
depends on the ratio of thickness of each unit composition
material. FIG. 3 illustrates a method of fabricating the
conventional multinary compound semiconductor (a), as well as that
of the digital-alloy multinary compound semiconductor
Al.sub.0.5Ga.sub.0.5As according to the present invention (b).
There is illustrated a specific action of a shutter for fabricating
the conventional multinary compound semiconductor and the
digital-alloy multinary compound semiconductor of the present
invention by using the representative compound semiconductor growth
method, that is, molecular beam epitaxy. From FIG. 3, it can be
noted that it is possible to grow the structure of FIG. 2a by (a)
of FIG. 3 as well as the structure of FIG. 2b by (b) of FIG. 3.
[0028] The features and effects of the present invention will now
be described in detail while presenting as one embodiment the
distributed Bragg's reflector fabricated by laminating the
Al.sub.0.9Ga.sub.0.1As/GaAs-paired layer seventeen (17) times.
[0029] The apparatus used for fabricating the structure of FIG. 4
and FIG. 5 is a molecular beam growth apparatus, V80 manufactured
by VG Semicon (UK). The apparatus used an ion pump for performing a
vacuum formation, wherein the vacuum before growth was
2.5.times.10.sup.-11 torr and the vacuum during the growth was
2.times.10.sup.-7 torr or less. The apparatus is equipped with two
Ga sources, one Al source and one As source. The respective growth
rate of AlAs and GaAs are 2 .ANG./s and 2.4 .ANG./s. In growing
AlGaAs, the GaAs growth rates of two Ga sources were set at 2.4
.ANG./s and 0.22 .ANG./s, respectively, so that all structures can
be grown without any growth stoppage. The pressure ratio of As/Ga
was about 10:1. GaAs substrate was heated at a temperature of
600.degree. C. to remove the oxidizing film of the substrate
surface. The temperature was then decreased to 580.degree. C. so
that GaAs, which has a thickness of about 100 nm, may be grown as a
buffer. Thereafter, the structures of FIG. 4 and FIG. 5 were grown
at 580.degree..
[0030] The conventional multinary compound semiconductor, as shown
in FIG. 4, was fabricated by laminating the GaAs (thickness: 95.2
nm)/Al.sub.0.9Ga.sub.0.1As (thickness: 109.9 nm)-paired layer on
the GaAs substrate seventeen (17) times. That is, as exemplified in
(a) of FIG. 3, in fabricating Al.sub.0.9Ga.sub.0.1As, the As source
shutter is always opened (As supply state). The Al source shutter
set to 2 .ANG./s of the growth rate in growing AlAs, as well as the
Ga source shutter set to 0.22 .ANG./s of the growth rate in growing
GaAs, are opened at once. At this time, the growth rate of
Al.sub.0.9Ga.sub.0.1As is 2.22 .ANG./s and thus, the desired
Al.sub.0.9Ga.sub.0.1As of 109.9 nm can be obtained during growth of
about 495.0 seconds. In fabricating the GaAs layer having 95.2 nm
thickness, another Ga source is used, wherein said source is set to
the growth rate of 2.4 .ANG./s in growing GaAs (the growth period
of about 396.6 seconds). Therefore, a total of two Ga sources are
necessary for fabricating all structures without any interruption
of growth. The entire structure is completely fabricated by
laminating the Al.sub.0.9Ga.sub.0.1As/GaAs-paired layer seventeen
(17) times.
[0031] The digital-alloy of the present invention was fabricated by
multi-layer laminating on the GaAs substrate a pair of GaAs having
the thickness of 95.2 nm and the digital-alloy
Al.sub.0.9Ga.sub.0.1As as shown in FIG. 5. Herein, the
digital-alloy Al.sub.0.9Ga.sub.0.1As was fabricated by laminating
GaAs (thickness: 0.283 nm)/AlAs (thickness: 2.547 nm)-paired layer
thirty-nine (39) times. The thickness ratio of each unit
composition material (GaAs:AlAs) is 1:9, on which the composition
of Al.sub.0.9Ga.sub.0.1As digital-alloy depends. The
Al.sub.0.9Ga.sub.0.1As digital-alloy was manufactured as in shown
in (b) of FIG. 3. The shutter of As source was always opened (As
supply state), wherein the Al source shutter set to 2 .ANG./s of
the growth rate in growing AlAs and the Ga source shutter set to
2.4 .ANG./s of the growth rate in growing GaAs were opened
successively. That is, the Ga source shutter was opened for 1.2
seconds, thereby growing GaAs having the thickness of 0.283 nm.
Thereafter, the Al source shutter was opened for 12.7 seconds to
grow AlAs having a thickness of 2.547 nm. It does not matter
whether GaAs or AlAs is grown first. Rather, it is important that
the shutters of Ga and Al sources are not opened at once. That is,
the shutter of Ga source and the shutter of Al source should be
repetitively opened in a successive manner. When laminating such
grown GaAs and AlAs thirty-nine (39) times, it results in the
formation of the Al.sub.0.9Ga.sub.0.1As digital-alloy. The GaAs
layer having a thickness of 95.2 nm is made by using the Ga source,
which is previously set to 2.4 .ANG./s of the growth rate in
growing GaAs (growth period of about 396.6 seconds). Therefore,
only one Ga source is required for fabricating all structures
without any interruption of growth. The entire structure was
fabricated by laminating the Al.sub.0.9Ga.sub.0.1As
digital-alloy/GaAs-paired layer seventeen (17) times.
[0032] FIG. 6 is a graph showing the computer simulation results of
reflectivity vs. wavelength in the Bragg's reflector, which is
shown in FIGS. 4 and 5. From FIG. 6, it was noted that two
reflectivity were substantially identical with just a slight
difference. This means that the digital-alloy Bragg's reflector of
the present invention showed a refractive index identical to the
conventional alloy for a light having a wavelength of 1.3 .mu.m.
This also means that the influence by each interface does not occur
since the thickness of the unit composition material in the
digital-alloy is merely 1/150 of the wavelength of light in the
semiconductor (refractive index: .ltoreq.3.5).
[0033] FIG. 7 shows a structure of the digital-alloy distributed
Bragg's reflector vertical resonator, which utilizes the
digital-alloy Al.sub.0.9Ga.sub.0.1As/GaAs structure of the present
invention shown in FIG. 5. FIG. 8 is a graph showing the
relationship of reflectivity, wavelength and large area (3 inches)
uniformity in the digital-alloy distributed Bragg's reflector
vertical resonator, which utilizes the Al.sub.0.9Ga.sub.0.1As/GaAs
structure of the present invention as shown in FIG. 7.
[0034] As shown in FIG. 8, the reflectivity is sharply decreased at
the central position in the determined reflectivity graph. This is
because Fabry-Perot passing phenomenon occurs due to two
reflectors, which are present at the upper and lower positions of
the device. There are many methods of determining the substrate
uniformity. The present invention used a distributed level
[{(determined maximum value+minimum value)-average value}/average
value] as the standard of determining uniformity, which is
ordinarily used in the relevant industry. In other words, as the
distributed level becomes lower, it is generally considered that
the substrate uniformity becomes better. The large area (3 inches)
distributed level of Fabry-Perot passing wavelength is 0.35%. When
considering that the average distributed level of 2 inch-substrate
in the industry is 1% and the area of 3 inch-substrate is almost
twice as large as the 2 inch-substrate, it can be noted that the
example of the present invention shows 6 times higher uniformity
than the conventional DBR.
[0035] Since each unit composition material is grown in a time
interval in the digital-alloy method shown in FIG. 2, only a
composite material (e.g., GaAs or AlAs) grows when grown on the
substrate. That is, the composition change due to the substrate
area and temperature imbalance during the growth period does not
affect such growth of the composition material. Further, since the
growth rate of the elemental compound can be measured in a direct
method during the growth of the compound in the growth apparatus,
the growth rate of each elemental compound can be accurately
identified regardless of the experimental frequency. For these
reasons, the digital-alloy semiconductor achieves both the area and
time uniformity.
[0036] Furthermore, since all multinary compounds are manufactured
by using the elemental compound, the multinary compound having
various compositions can be grown homogenously on one substrate.
For this reason, the structure of the growing apparatus can be
simplified and it is easy to maintain and operate the apparatus,
thereby improving productivity. Therefore, the digital-alloy
distributed Bragg's reflector of the present invention has a
uniform quality on the substance area and the filter and reflector
having uniformly high quality can be mass produced by using the
reflector.
[0037] The group IV semiconductors such as Si/(Si)Ge may be also be
used in the semiconductor layer in some embodiments of the present
invention, although Si/(Si)Ge forms a binary alloy, not a multinary
alloy. Furthermore, while the present invention has been shown and
described with respect to a preferred embodiment, those skilled in
the art will recognize that various changes and modifications may
be made without departing from the scope of the invention as
defined in the appended claims.
* * * * *