U.S. patent application number 14/678414 was filed with the patent office on 2016-09-22 for vertical cavity surface emmiting laser.
The applicant listed for this patent is SAE Magnetics (H.K.) Ltd.. Invention is credited to Babu Dayal PADULLAPARTHI.
Application Number | 20160276805 14/678414 |
Document ID | / |
Family ID | 56878310 |
Filed Date | 2016-09-22 |
United States Patent
Application |
20160276805 |
Kind Code |
A1 |
PADULLAPARTHI; Babu Dayal |
September 22, 2016 |
VERTICAL CAVITY SURFACE EMMITING LASER
Abstract
A VCSEL according to the invention, configured to emit a light
having about 850 nm wavelength, comprises an active region which
comprises one or more In.sub.xGa.sub.1-xAs quantum wells; two or
more GaAs.sub.1-yP.sub.y barriers bonding to the one or more
quantum wells; and x ranges from 0.05 to 0.1, and y ranges from 0.2
to 0.29. The VCSEL has increased optical confinement and high
transmission speed, good reliability characteristics,
high-temperature performance, and long life time.
Inventors: |
PADULLAPARTHI; Babu Dayal;
(Hong Kong, CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SAE Magnetics (H.K.) Ltd. |
Hong Kong |
|
CN |
|
|
Family ID: |
56878310 |
Appl. No.: |
14/678414 |
Filed: |
April 3, 2015 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01S 5/3407 20130101;
H01S 5/187 20130101; H01S 5/18361 20130101; H01S 5/34386 20130101;
H01S 5/34313 20130101; H01S 5/3434 20130101; H01S 5/18311 20130101;
H01S 5/18347 20130101 |
International
Class: |
H01S 5/187 20060101
H01S005/187; H01S 5/34 20060101 H01S005/34; H01S 5/183 20060101
H01S005/183; H01S 5/343 20060101 H01S005/343 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 20, 2015 |
CN |
201510124564.0 |
Claims
1. A vertical cavity surface emitting laser (VCSEL), configured to
emit a light having about 850 nm wavelength, comprising: an active
region which comprises: one or more In.sub.xGa.sub.1-xAs quantum
wells; and two or more GaAs.sub.1-yP.sub.y barriers bonding to the
one or more quantum wells; first and second phase matching layers;
and two reflecting mirror stacks sandwiching the active region;
wherein x ranges from 0.05 to 0.1, and y ranges from 0.2 to 0.29;
and wherein at least one of the reflecting mirror stacks includes
an annular or polygonal oxide layer providing a current confinement
structure sandwiched between the first and second phase matching
layers.
2. The VCSEL according to claim 1, wherein the active region
further comprises one or more separate confinement heterostructure
layers formed adjacent to the barriers, and the separate
confinement heterostructure layers are made of AlGaAs.
3. The VCSEL according to claim 2, wherein the separate confinement
heterostructure layer is formed as a continuous ramp.
4. The VCSEL according to claim 1, wherein the quantum well(s) and
the barriers have a thickness ranging from 3 nm to 5 nm.
5. The VCSEL according to claim 1, wherein the quantum well(s) and
the barriers are grown on a substrate of un-doped GaAs or
p-/n-doped with silicon.
6. The VCSEL according to claim 1, further comprising a mesa
structure and a passivation layer made by a low dielectric constant
oxide or polymer or both covered on an outer surface of the mesa
structure.
7. (canceled)
8. The VCSEL according to claim 1, wherein at least one of the
reflecting mirror stacks includes an annular oxide layer providing
the current confinement structure.
9. (canceled)
10. The VCSEL according to claim 1, wherein the at least one
reflecting mirror stack that includes the annular or polygonal
oxide layer is made by wet thermal oxidation, and the current
confinement structure is in an oxide window.
11. The VCSEL according to claim 1, wherein the barriers are
tensile-strained and the one or more quantum wells is/are
compressively strained so that the net strain is nearly zero and
act as a strain compensated double structure (DHS) system.
12. A vertical cavity surface emitting laser (VCSEL), comprising:
an active region which comprises: one or more In.sub.xGa.sub.1-xAs
quantum wells; and two or more GaAs.sub.1-yP.sub.y barriers bonding
to the one or more quantum wells; first and second phase matching
layers; and two reflecting mirror stacks sandwiching the active
region; wherein there is a lack of transitional layers between the
one or more quantum wells and the barriers; wherein at least one of
the reflecting mirror stacks includes an annular or polygonal oxide
layer providing a current confinement structure sandwiched between
the first and second phase matching layers; wherein x ranges from
0.05 to 0.1, and y ranges from 0.2 to 0.29; and wherein the VCSEL
is configured to emit a light having about 850 nm wavelength.
13. The VCSEL according to claim 12, wherein the active region
further comprises one or more separate confinement heterostructure
layers formed adjacent to the barriers, and the separate
confinement heterostructure layers are made of AlGaAs.
14. The VCSEL according to claim 13, wherein the separate
confinement heterostructure layer is formed as a continuous
ramp.
15-16. (canceled)
17. The VCSEL according to claim 12, wherein the at least one
reflecting mirror stack that includes the annular or polygonal
oxide layer is made by wet thermal oxidation, and the current
confinement structure is in an oxide window.
18. The VCSEL according to claim 12, wherein the barriers are
tensile-strained and the one or more quantum wells is/are
compressively strained so that the net strain is nearly zero and
act as a strain compensated double structure (DHS) system.
19. A vertical cavity surface emitting laser (VCSEL) for an optical
module used in data communications, comprising: an active region
which comprises: one or more In.sub.xGa.sub.1-xAs quantum wells;
and two or more GaAs.sub.1-yP.sub.y barriers bonding to the one or
more quantum wells, the barriers being tensile-strained; first and
second phase matching layers; and two reflecting mirror stacks
sandwiching the active region; wherein at least one of the
reflecting mirror stacks includes an annular or polygonal oxide
layer providing a current confinement structure sandwiched between
the first and second phase matching layers; wherein the active
region further comprises one or more separate confinement
heterostructure layers formed adjacent to the barriers, the
separate confinement heterostructure layer(s) being made of AlGaAs
and being formed as a continuous ramp with no other transitional
layers existing there-along; wherein x ranges from 0.05 to 0.1, and
y ranges from 0.2 to 0.29; and wherein the VCSEL is configured to
emit a light having about 850 nm wavelength.
20. (canceled)
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a vertical cavity surface
emitting laser (VCSEL), and more particularly to a VCSEL emitting a
light having a wavelength of 850 nm with quantum wells and barriers
with improved reliability.
BACKGROUND OF THE INVENTION
[0002] A VCSEL is a semiconductor laser that emits light in a
vertical direction with respect to a substrate. In general VCSEL
has an active region with a large gain, a low threshold current,
high optical power, reliability, and adequately controlled
polarization. Since the VCSEL does not require a cleavage process,
it allows to be integrated into two-dimensional arrays for on-wafer
testing. It is suitably used in various consumer applications such
as the light source of an image forming apparatus, the light source
of an optical pickup device, the optical communication data
transmitter of optical interconnections and optical modules,
etc.
[0003] The active region of the VCSEL arranged between two
semiconductor multilayer reflector (DBR: Distributed Bragg
Reflector, for example) mirrors is the region in which electrons
and holes combine to generate light. The active region includes a
quantum-well structure provides the photonic device with a lower
threshold current, a high efficiency and a greater flexibility in
choice of emission wavelength.
[0004] A quantum-well structure is composed of at least one (n)
quantum-well layer interleaved with a corresponding number (n+1) of
barrier layers. Each of the quantum well layers has a thickness in
the range from about one nanometer to about ten nanometers. The
barrier layers are typically thicker than the quantum well layers.
The semiconductor materials of the layers of the quantum-well
structure depend on the desired emission wavelength of the photonic
device. The semiconductor material of the barrier layers differs
from that of the quantum-well layer, and has larger bandgap energy
and a lower refractive index than that of the quantum well
layer.
[0005] A quantum-well structure composed of gallium arsenide (GaAs)
quantum well layers and aluminum gallium arsenide (AlGaAs) barrier
layers has been proposed for the active region of a conventional
VCSEL to generate light with a wavelength of 850 nm. FIG. 1a is an
energy-band diagram of an exemplary active region 10 incorporating
such a quantum-well structure. Band energy is plotted as ordinate
and distance from the substrate is plotted as abscissa. As shown,
the active region 10 includes a first cladding layer 121, a first
barrier layer 141 made of AlGaAs, a quantum-well layer 16 made of
GaAs, a second barrier layer 142 made of AlGaAs, and the second
cladding layer 121. The energy-band diagram of FIG. 1a shows the
energies of the conduction band 101 and valence band 102 of the
semiconductor material of each of the layers just described.
[0006] The active region 10 composed of the barrier layers 141 and
142 of AlGaAs and the quantum-well layer 16 of GaAs has a Type I
heterostructure. In this heterostructure, the energy of the valence
band of GaAs of the quantum-well layer 16 is greater than the
energy of the valence band of the AlGaAs of the barrier layers 141
and 142, but the energy of the conduction band of GaAs of the
quantum-well layer 16 is less than the energy of the valence band
of the AlGaAs of the barrier layers 141 and 142.
[0007] The line-up of the band energies in a quantum-well structure
having a Type I heterostructure confines electrons 156 to the
conduction band 101 of the quantum-well structure 16 and confines
holes 158 to the valence band 102 of the quantum-well structure 16.
As a result, the electron-hole recombination process takes place
between carriers confined in the same layer.
[0008] However, the conduction band and valence band
discontinuities (.DELTA.Ec and .DELTA.Ev) between GaAs quantum well
and AlGaAs barrier layers are small due to their fixed bandgap
values, thus carrier leakage will happen in the quantum well layers
16 from the quantum well layer across the barrier layers as shown
in FIG. 1b which brings a reduced performance, such as the optical
confinement in the region layer is low, the high temperature
performance is reduced, and the reliability characteristics of the
VCSELs causes a degraded life time due to internal self heating
effect. Besides above, in the moisture/humidity ambient the element
Al in the barrier layer can easily be oxidized and can form defects
or dislocations causing further reduction of the life time of
VCSELs.
[0009] U.S. Pat. No. 8,837,547 B2, US Publication No. 2014/0198817
A1, and US Publication No. 2012/0236891 disclose 850 nm wavelength
VCSEL respectively, but all of them has the drawbacks mentioned
above more or less.
[0010] Thus, it is desired to provide an improved VCSEL structure
with increased optical confinement and increased speed, good high
temperature and reliability characteristics and long life time to
overcome the above-mentioned drawbacks.
SUMMARY OF THE INVENTION
[0011] One objective of the present invention is to provide
vertical cavity surface emitting laser (VCSEL) which has increased
optical confinement and high transmission speed, good reliability
characteristics, high-temperature performance, and long life
time.
[0012] To achieve above objective, a VCSEL according to the
invention, configured to emit a light having about 850 nm
wavelength, comprises an active region which comprises one or more
compressively strained In.sub.xGa.sub.1-xAs quantum wells; two or
more tensile strained GaAs.sub.1-yP.sub.y barriers bonding to the
one or more quantum wells; and x ranges from 0.05 to 0.1, and y
ranges from 0.2 to 0.29.
[0013] As an embodiment, the active region further comprises one or
more separate confinement heterostructure layers formed adjacent to
the barriers, and the separate confinement heterostructure layers
are made of AlGaAs.
[0014] Preferably, the separate confinement heterostructure layer
is formed as a continuous ramp.
[0015] Preferably, the quantum wells and the barriers have a
thickness ranging from 3 to 5 nm.
[0016] As another embodiment, the conduction band and valence band
discontinuities (.DELTA.Ec and .DELTA.Ev) of disclosed 850 nm VCSEL
structure have at least few meV larger than the conventional 850 nm
VCSEL with GaAs Quantum wells and AlGaAs barriers.
[0017] Preferably, a bandgap discontinuities .DELTA.Ec and
.DELTA.Ev between two energy bands is in a range of 5.about.50 meV
and 5.about.20 meV respectively larger than .DELTA.Ec and .DELTA.Ev
of GaAs Quantum wells and AlGaAs barriers.
[0018] Preferably, the quantum wells and the barriers are grown on
a substrate of un-doped GaAs or p-/n-doped with silicon.
[0019] Preferably, the VCESEL further includes a mesa structure and
a passivation layer made by a low dielectric constant oxide
material such as SiO.sub.XN or polymer (polyimide or BCB) or both
covered on an outer surface of the mesa structure.
[0020] Preferably, further comprises two reflecting mirror stacks
sandwiching the active region, more preferably the reflecting
mirror stacks are distributed Bragg reflectors (DBRs).
[0021] Preferably, at least one of the reflecting mirror stacks
includes a high Al (>98%) containing III-V semiconductor thin
layer in the form as annular oxide layer providing a current
confinement structure.
[0022] In comparison with the prior art, as the active region of
the present invention applies the strained quantum wells of
In.sub.xGa.sub.1-xAs, and the strained barriers of
GaAs.sub.1-yP.sub.y, instead of the conventional barrier of GaAs,
the barriers of GaAs.sub.1-yP.sub.y according to the present
invention provide a higher band gap to prevent carriers leakage or
overflow, so as to bring improved optical confinement and improved
communication speed. Further the barrier of GaAs.sub.1-yP.sub.y is
good for resisting high temperature, and obtains a long life time
for the semiconductor device.
[0023] Other aspects, features, and advantages of this invention
will become apparent from the following detailed description when
taken in conjunction with the accompanying drawings, which are a
part of this disclosure and which illustrate, by way of example,
principles of this invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] The accompanying drawings facilitate an understanding of the
various embodiments of this invention. In such drawings:
[0025] FIG. 1a is an energy-band diagram of an active region of a
conventional VCSEL;
[0026] FIG. 1b shows carrier leakage in the conventional active
region of FIG. 1a;
[0027] FIG. 2 is cross section of a VCSEL according to an
embodiment of the present invention;
[0028] FIG. 3 is a simplified profile of the active region
according to the present invention;
[0029] FIG. 4 is an energy-band comparison diagram between the
VCSEL according to the present invention and the conventional
VCSEL;
[0030] FIG. 5a shows an the calculated full VCSEL F-P dip
wavelength according to the present invention; and
[0031] FIG. 5b shows an experimental epitaxially/MOCVD grown full
VCSEL F-P dip wavelength.
DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS
[0032] Various preferred embodiments of the invention will now be
described with reference to the figures, wherein like reference
numerals designate similar parts throughout the various views. As
indicated above, the invention is directed to a VCSEL which has
increased optical confinement and high transmission speed, good
reliability characteristics, high-temperature performance, and long
life time.
[0033] It should be noted that, the VCSEL of the present invention
is directed to emit light with about 850 nm wavelength, with
photoluminescence emission at 840 nm and full VCSEL Fabry-Perot
(FP) dip at 846 nm.
[0034] FIG. 2 is a cross-sectional view of a VCSEL device according
to a first embodiment of the present invention. The VCSEL device
200 includes a substrate 201, a bottom DBR 202 and a top DBR 204
formed on the substrate 201, an active region 203 sandwiched
between the bottom DBR 202 and top DBR 204 to generate laser light.
A top electrode layer 206 is formed on and electrically connected
with the top DBR 204, and a bottom electrode layer 207 is formed
beneath the substrate 201, which are adapted for applying current
to the active region 203 to generate laser light. A first window 29
is opened in the top electrode layer 206, so as to expose a part of
the top DBR 204.
[0035] The substrate 201 may be n-type GaAs doped with silicon,
p-type GaAs doped with silicon, or an undoped/semi-insulating GaAs.
In the present embodiment, the substrate 201 is an un-doped
(semi-insulating) GaAs. In this case the bottom electrode layer 207
(207a, 207b) is made to present on the top side. The bottom
electrode layer 207 forms an Ohmic contact to the substrate 201 and
is typically made of electrically conductive metal. In this case,
bottom electrode layer 207 can also be made present at the bottom
of the substrate 201 as shown in FIG. 2.
[0036] Concretely, the bottom DBR 202 can be n-type reflector or
p-type reflector, and the top DBR 204 has the opposite polarity. In
the present embodiment, the bottom DBR 202 is an n-type reflector
and the top DBR 204 is a p-type reflector. Generally, the bottom
and top DBRs 202, and 204 respectively are stacks of III-V group
semiconductor layers in different refractive index layers
alternately arranged, which are made with materials such as AlAs,
GaAs, or AlGaAs having different mole fractions of Aluminum and
Gallium. In actual implementations, each of DBR 202 or 204 may
includes many layers such as twenty or thirty pairs of layers, or
more. Preferably, for the emission wavelength around 850 nm, the
bottom DBR 202 is optimized to include stacks of
Al.sub.0.12Ga.sub.0.88As and Al.sub.0.9Ga.sub.0.1As, and
Al.sub.0.12Ga.sub.0.88As and AlAs.
[0037] The active region 203 is typically constructed from one or
more quantum wells and multiple barriers. The active region 203 is
configured to generate light having a predetermined emission
wavelength. The predetermined emission wavelengths of 850 nm is
used for high-speed data-communication in the VCSEL device 200 of
the present invention with the predetermined material described
thereinafter, other emission wavelengths will not be applicable
with the present invention.
[0038] When a drive current is applied to the top and bottom
electrode layers 206, 207, it flows through the active region 203,
and then laser light is generated in the active region 203. The
laser light is amplified while it is reflected at each interface
between layers of top DBR 204 and bottom DBR 202, and is emitted
from the first window 29 of the VCSEL device 200 vertically.
[0039] Referring to FIG. 2, the VCSEL 200 further includes a
heavily p-doped contact layer 208 formed between the top electrode
layer 206 and the top DBR 204. The contact layer 208 is made of
GaAs, AlGaAS or InGaAs.
[0040] As an improved embodiment, an oxide section 310 is formed on
the active region 203, and the oxide section 310 includes at least
two phase matching layers (PML) 311, 312 (in the figures only two
phase matching layers are shown) and a current limiting/confining
layer 313 sandwiched between the two PML layers 311, 312. The
current limiting/confinement layer 313 is made of high Al
molefraction (>98%), for example Al.sub.0.98Ga.sub.0.02As or
AlAs semiconductor layers subjected to wet thermal oxidation
process to create Al containing oxide and is used to direct the
electrical current generally toward the center of the active region
203 through oxide aperture region 314. When used, the current
limiting layer 313 insulates all but a circular or polygon-shaped
window 314 having a diameter being of the order of the diameter of
the first window 29. Because most of the electrical current is
directed toward the center of the active region 203, most of the
light is generated within the center portion of the active region
203. And the phase matching layers 311, 312 are made of AlGaAs
semiconductor with different mole fractions of Al and Ga. For
efficient high speed operation, a VCSEL structure can include at
least one individual oxide section with at least one current
limiting/confining layers because, the addition of additional
current limiting/confining layers decreases mesa capacitance and
hence increases the bandwidth and speed of VCSEL device.
[0041] In a mesa structure (not shown in the figure) of the VCSEL
200, an insulator (not shown) acted as a passivation layer which is
made of silicon oxynitride (SiO.sub.xN) a thickness of 1.0 .mu.m
for example is formed to cover the outer side surface of the mesa
structure, namely cover the exposed side layers of the elements
mentioned above. In addition to the above passivation layer
(SiO.sub.xN), a 5.about.10 .mu.m thick polyimide or BCB coating is
simultaneously applied to further reduce p- and n-electrode pad
capacitances. The insulator is used for protecting the whole layers
of the VCSEL 200.
[0042] With the contemplation of the present invention, the active
region 203 of the VCSEL 200 has one or more quantum wells 280 and
two or more barriers 270, as shown in FIG. 3. The quantum wells 280
and barriers 270 are physically adjacent and connected to each
other. Electrical confining regions can sandwich the active region
203 and provide optical gain efficiency by confining carriers to
the active region 203. Preferably, the quantum wells 280 is made of
In.sub.xGa.sub.1-xAs and the barriers 270 is made of
GaAs.sub.yP.sub.1-y, and the value of x in In.sub.xGa.sub.1-xAs
ranges from 0.05 to 0.1, and the value of y in GaAs.sub.yP.sub.1-y
ranges from 0.2 to 0.29. In the present invention disclosure, a
total of five In.sub.xGa.sub.1-xAs quantum wells layers with value
of x=0.06 and a total of six GaAs.sub.yP.sub.1-y barrier layers
with value of y=0.75 including four inner barriers and two outer
barriers. All the five In.sub.xGa.sub.1-xAs quantum wells layers
and the four inner GaAs.sub.yP.sub.1-y barrier layers have a
thickness of 4.0 nm and 2 outer GaAs.sub.yP.sub.1-y barrier layers
have a thickness of 10.0 nm for a emission wavelength targeted at
840 nm wavelength.
[0043] It is one of the objectives of this invention to make strain
compensated optical cavity with Al-free active region for
high-speed data-communication VCSELs with high device performance
described previously. It is to be noted that a strain compensated
data-communication VCSEL at 1060 nm wavelength with five
In.sub.0.29Ga.sub.0.71As compressively strained quantum wells and
six GaAs.sub.0.75P.sub.0.25 tensile strained barrier layers with
thickness different from current invention was reported. The net
strain resulting from compressively strained quantum wells and
tensile strained barrier layers would be carefully optimized to a
nearly zero strain value. But till now, there was no
data-communication VCSEL design with In.sub.xGa.sub.1-xAs
compressively strained quantum wells and GaAs.sub.yP.sub.1-y
tensile strained barrier layers targeted at 850 nm emission
wavelength band with net strain to zero value. Therefore in the
current invention for a fine tuned/optimized 850 nm
data-communication VCSEL, preferably the quantum wells and the
barriers have a thicknesses from 3 nm to 5 nm.
[0044] It is also one of the objectives of this invention to have
same In.sub.xGa.sub.1-xAs compressively strained quantum wells and
GaAs.sub.yP.sub.1-y tensile strained barrier layers double
heterostructure system at both 1060 nm and 850 nm wavelength bands.
At 1060 nm wavelength, standards OM2 (optical multi-mode fiber
standards), OM3, OM4 optical fibers can't be directly used and a
dispersion compensated fiber is needed and this is costlier than
standard OM2, OM3, OM4 fibers. However at 850 nm band, standard
OM2, OM3, OM4 fibers can readily be used for data transmission
without having dispersion compensated fibers. This factor alone has
large commercial benefits by using a high performance and high
speed VCSEL at 850 nm wavelength.
[0045] As shown in FIG. 4, it shows a comparison diagram showing an
energy band of the active region 203 of the present invention and
the conventional 850 nm VCSEL with GaAs quantum wells and AlGaAs
barriers. As shown, in the conduction band, the barriers of AlGaAs
of the conventional 850 nm VCSEL provides an energy level Ec1, the
barriers 270 of GaAs.sub.1-yP.sub.y of the invention provides an
energy level Ec2 which is larger than Ec1, and the difference value
.DELTA.Ec is in a range of 5.about.50 meV or higher; in the valence
band, the barriers of AlGaAs of the conventional 850 nm VCSEL
provides an energy level Ev1, the barriers 270 of
GaAs.sub.1-yP.sub.y of the invention provides an energy level Ev2
which is larger than Ev1, and the difference value .DELTA.Ev is in
a range of 5.about.20 meV or higher.
[0046] As shown in FIG. 3 again, the active region 203 further
includes one or more separate confinement heterostructure (SCH)
layers 261, 262 connected to the barriers 270 respectively, and two
cladding layers 251, 252 sandwiching the quantum wells 280, the
barriers 270, and the SCH layers 261, 262. Specifically, the SCH
layers 261, 262 are made of AlGaAs, and the cladding layers 251,
252 are un-doped with respect to p-DBR and n-DBRs. In this
embodiment, the SCH layers 261, 262 are formed as a continuous
ramp, and no other material or a transition layer exists along the
ramp of graded SCH as disclosed by U.S. Pat. No. 8,837,547 B2.
[0047] FIG. 5a shows the calculated result for light emission
wavelength of the full VCSEL 200 according to the present
invention. As shown, the wavelength of the light in the VCSEL F-P
dip is 846.2 nm. The result is very close to the epi-taxially grown
full VCSEL F-P dip value at 845.5 nm as show in FIG. 5b. This
confirms that, the current disclosed VCSEL 200 with the active
region 203 of the present invention is applicable to emit light of
about 850 nm wavelength.
[0048] In conclusion, as the active region 203 of the present
invention applies the compressively strained quantum wells 280 of
In.sub.xGa.sub.1-xAs, and the tensile strained barriers 270 of
GaAs.sub.1-yP.sub.y, instead of the conventional un-strained
barrier of GaAs, the barriers 270 of GaAs.sub.1-yP.sub.y according
to the present invention provide a higher band gap to prevent
carriers leakage or overflow, so as to bring improved optical
confinement and improved communication speed. Further the barrier
of GaAs.sub.1-yP.sub.y is good for high temperature performance,
and provides a longer life time for the semiconductor laser
device.
[0049] While the invention has been described in connection with
what are presently considered to be the most practical and
preferred embodiments, it is to be understood that the invention is
not to be limited to the disclosed embodiments, but on the
contrary, is intended to cover various modifications and equivalent
arrangements included within the spirit and scope of the
invention.
* * * * *