The effects
of
laser illumination and high energy electrons on
molecular-beam epitaxial growth
of
CdTe
Y.
S.
WU,a)
C.
R.
Seeker,
A.
Waag,
R.
N. Sieknell-Tassius, and
G.
Landwehr
Physikalisches lnstitut der Universitat wurzburg. D-8700 WUrzburg. Germany
(Received
25
May 1990; accepted for publication
21
August 1990)
We report the results
of
a detailed investigation on the Te-stabilized
(2X
1) and the Cd-
stabilized
c(2
X
2)
surfaces
of
(100) CdTe substrates. The investigation demonstrates for the
first time that both laser illumination and, to a greater extent, high-energy electron irradiation
increase the Te desorption and reduce the Cd desorption from
(100)
CdTe surfaces. Thus it
is
possible by choosing the proper growth temperature and photon
or
electron fluxes to change
the surface reconstruction from the normally Te-stabilized to a Cd-stabilized phase.
J.
INTRODUCTION
The use
of
light to improve the quality
of
molecular-
beam epitaxially (MBE) grown II-VI materials and to en-
hance substitutional doping
is
one
of
the recent exciting de-
velopments in the growth
of
compound semiconductors.
Bicknell et al. and Hwang et al.
I
-
3
have grown high-quality
CdTe with this photoassisted molecular-beam epitaxy
(PAMBE)
method. Their best undoped n-type CdTe had a
mobility
of
6600 cm
2
;V
s and their In-doped CdTe
(n
= 2 X
10
16
cm - 3 at 300
K)
had a mobility
of
2380
cm
2
;V
s.
This
is
in contrast to conventional MBE-grown
CdTe which
is
semi-insulating.
4
Due to the availability
of
high-quality conducting epilayers
of
CdTe, all thin-film
CdTe electronic devices have been recently produced, i.e.,
p-
n junctions and metal-semiconductor field-effect transis-
tors.
5
,6
Photoassisted molecular-beam epitaxy has also been
applied to the growth
of
highly conducting, dilute magnetic
semiconductor epitaxiallayers and superlattices.
7
Recently,
this new technique has been applied to the growth
of
mer-
cury-based U-VI materials. Koestner et al. have grown
(lOO)
and
(211)
HgCdTe epitaxiallayers using
PAMBE
which exhibited a low dislocation density,
1-2
X
IOS
and
3-
5 X 10
4
cm -
2,
respectively, over a wider range
of
growth
conditions than
is
possible by conventional MBE.
8
Similarly
Myers et al. have grown some
of
the best epitaxial HgCdTe
to date with extremely narrow x-ray double-crystal rocking
curves and very high carrier mobility.9 They reported dislo-
cation line densities for
(211)
HgCdTe as low as 5 X 10
4
cm -
2.
Their reported electron mobilities
of
the
(100)
HgCdTe epilayer are as high as
8.5
X
lOS
cm
2
;V
s for sam-
ples with
13%
Cd, and are 4 X 10
5
cm
2
IV
s for a sample with
20%
Cd.
The above results may be summarized in general by stat-
ing that photoillumination during MBE growth greatly im-
proves the structural properties as well as the electrical prop-
erties
of
the epitaxial layers that are grown using the
photoassisted MBE technique. Therefore, detailed investi-
gations into the mechanisms
of
how light affects the growing
surface
is
of
utmost importance.
If
the mechanism
of
the
photoassisted MBE process
is
understood
in
detail it should
a)
Permanent address: Institute
of
Physics, Chinese Academy
of
Sciences,
Bcijing. People's Republic
of
China.
be easier to optimize the technique for
anyone
material and
easier to apply it to other materials systems. In fact, it has
been recently reported that UV light illumination can en-
hance the migration
of
adsorbates
of
dissociated adatoms on
GaAs surfaces and thereby improve the GaAs quality grown
by molecular layer
epitaxy.lO.11
To date, only a limited number
of
investigations have
been carried out that give insight into the microscopic mech-
anisms
of
the P AMBE process. Benson et al. have shown
that laser illumination enhances Te desorption and produces
more sites for
Sb
incorporation.
121t
has also been shown that
the use
of
an excess cadmium
flux
during the MBE growth
of
CdTe has a similar effect to that obtained
by
the PAMBE
technique.
13
.
14
An attempt to explain the effects
of
illumina-
tion on compound semiconductor surfaces during epitaxial
growth has been made by Farrell et al. who have proposed a
model to describe the mechanisms by which light interacts
with surface species during thin-film growth using MBE or
other related techniques.
IS
Normally the region within the MBE system that
is
di-
rectly involved
in
the growth process can be divided into
three distinct parts: the crystalline phase, the gaseous phase,
and the interface
or
the transition layer between these two.
The crystalline epitaxial layer exhibits long-range order
in
the spatial distribution
of
the constituent atoms. In contrast,
the gaseous phase near the substrate surface consisting
of
molecular and atomic beams
is
characterized
by
a complete
lack oflong-range spatial order. The interface between these
two phases where all processes leading to epitaxy occur
is
obviously the most important part
of
the growth system. Its
geometrical form and the processes occurring there depend
strongly on the growth conditions chosen. Therefore, it
is
critical for the growth
of
ideal films to recognize and to prop-
erly adjust the structure and compositions
of
this interface
layer.
To
our
knowledge no publication has reported on laser-
induced effects on the CdTe growing surface except for the
studies
of
the static CdTe surface by Benson et al.
12
•
16
In
addition, only a
few
studies
of
the effect
of
high-energy elec-
trons
(HEE)
on the surface chemistry have appeared in the
literature, even though one
of
the most widely used
in
situ
surface analysis techniques
is
reflection high-energy electron
diffraction
(RHEED).
In fact, irradiation
of
the CdTe sur-
face during growth by high-energy electrons strongly in-
268 J. Appl. Phys. 69 (1), 1 January 1991
0021-8979/91/010268-05$03.00
© 1991 American Institute
of
PhySiCS
268
fluences the surface stoichiometry and therefore the ob-
served surface reconstruction. Thus, this brings into
question the applicability
of
RHEED
and
other such tech-
niques to the investigation
ofCdTe
surfaces.
In
this paper we
present observations
of
the effects
of
laser illumination
and
HEE
irradiation on the growing surface
of
CdTe epitaxial
layers.
The experiments that are reported in this paper should
be contrasted with the recent investigations
of
the effects
of
post-growth electron irradiation
of
CdTe surfaces
that
showed that such irradiation produces deep level defects in
the sample. 17 In the present experiments we have illuminat-
ed the CdTe at a glancing incidence angle
(::::::
n,
which
is
typical
of
those used in
RHEED
studies.
At
such low inci-
dence angles the penetration depth
of
the electrons into the
sample surface
is
limited to the first
few
atomic layers.
Due
to this very shallow penetration the effects
of
the electron
illumination
is
limited to the growth interface.
11.
EXPERIMENTAL DETAILS
Epitaxial growth was carried out in a four-chamber
RIBER
2300 MBE system. The
MBE
system has been modi-
fied
to permit illumination
of
the substrate during the film
growth process. Two MBE sources were employed in the
surface phase diagram studies.
One contained high-purity
polycrystalline CdTe and the other contained high-purity
cadmium.
It
should be noted that while the
Cd
source was
of
conventional "open-tube" design, as
is
available from sever-
al commerical suppliers, the CdTe source was
of
Knudsen
cell design. The orifice
of
the CdTe cell was 3
mm
in diame-
ter, and should help to ensure
that
near-equilibrium condi-
tions exist within the effusion cell.
In
the present work, typi-
cal operating temperatures
of
the CdTe and
Cd
sources were
750 and 150
cC,
respectively.
The
vacuum in the CdTe
growth chamber was better than 6 X
10-
to
Torr.
In
order to
ensure that Cd or CdTe fluxes escaping around the effusion
cell shutters did not effect the experimental results, a second
shutter close to the substrate was also used.
The
substrate
temperature was measured with an accuracy
of
± 2
cC
by
means of a thermocouple which was in actual physical con-
tact with the molybdenum substrate holder.
The
thermocou-
ple was carefully calibrated
at
the melting points
of
indium
and tin.
The substrates were
(100) CdTe wafers which were
chemomechanically polished for several minutes, degreased
using standard solvents, etched in a weak bromine/meth-
anol solution, and rinsed in methanol. Immediately prior
to
loading the substrates into the MBE system, they were
rinsed in
de··ionized water, briefly dipped in hydrochloric
acid, and then rinsed
in
de-ionized water so as
to
remove any
remaining oxide and carbon on the substrate surface.
The CdTe substrates were preheated
at
100
cC
for
15
min and then the temperature was slowly raised up to
300-
400
cC
depending on the substrate surface which was moni-
tored with reflection high-energy electron diffraction
(RHEED).
The use
of
in
situ x-ray photoelectron spectros-
copy (XPS) helped to ensure that only optimally cleaned
surfaces were used in the following investigations.
18, 19
A
RIBER
model
CER
606 electron gun with model
269
J, AppL Phys" Vot. 69, No. 1,1 January 1991
ACE
1010 controlling electronics was used as a source
of
high-energy electrons both for
the
RHEED
patterns
and
in
the
investigations
of
the effects
of
high-energy electrons on
the epitaxial growth surfaces.
In
the present experiments,
the acceleration voltage
of
the electron gun was about 9 kV,
the
electron
current
was about 20 j1A, and the beam was
focused as small as possible. A Coherent Inova
90-6 Argon-
ion laser (514.5
nm)
was used to produce the photons
that
were employed in
the
PAMBE
experiments. This laser al-
lowed the entire growth surface to be uniformly illuminated
with powet densities
up
to 500 mW
/cm
2
,
The
power densi-
ties incident on the surface were determined using a Coher-
ent 210 power meter.
In
the present work power densities
of
up
to
320 m W
/cm
2
were employed.
At
these power densities
the rise in
the
substrate surface temperature
is
expected to be
smaller than 1
cc.
4,20
Ill. RESULTS AND DISCUSSION
In
general, the Te-stabilized surface
is
smooth
and
its
RHEED
pattern in the [011] azimuth displays half-order
reconstruction
(HOR).2J
The
Cd-stabilized surface
is
rougher and the corresponding
RHEED
patterns in the
[010] and [001] azimuths also display HOR. There
is
a
mixed region in which
HOR
appears in the [011], [010],
and [001] azimuths.
In
particular,
HOR
in the [011] azi-
muth
always appears even though the CdTe surface
is
under
a Cd-rich environment, i.e., excess
Cd
flux. Therefore, in this
work we have used the appearance
of
a very weak
HOR
in
the [010] azimuth as a limit for determining
the
desorption
time
of
excess Te on the surface. In other words, the first
appearance
of
excess Cd on the surface denotes the desorp-
tion
of
excess Te.
A.
Static CdTe surfaces
Figure 1 shows the effect
oflaser
illumination and
HEE
on the "static"
CdTe
surface, i.e., without cadmium, telluri-
um,
or
CdTe fluxes impinging on the surface.
In
these ex-
periments the
CdTe
flux (3 X 10
-7
Torr)
was stopped after
10'
~~----~------~----
__
----~
U
III
(I)
W
10
3
:I:
H
I-
Z
o
~
10
2
CL
~
o
UJ
w
o
1.7 1.8
1.9
2.0
lOOO/T
(l/K
)
FI
G. I, Desorption time
of
excess Te on the static surface with
(a)
neither
laser nor high-energy electron
(HEE)
irradiation,
(b)
laser illumination,
(c)
HEE
irradiation, and
(d)
both the laser illumination and the
HEE
irra-
diation. The laser intensity was
45
± 5 mW/cm2,
Wu eta/.
269
growing a thin CdTe layer by conventional MBE for
15
min
prior to every measurement. Under these conditions the
CdTe surfaces show
HOR
in the [011] azimuth. After clos-
ing the shutter to stop the CdTe growth the transition layer
changes gradually with time. Curve(a) in Fig. 1 displays the
desorption time
of
excess Te atoms on the surface as deter-
mined by the substrate temperature at which
HOR
in the
[010] azimuth appeared. The substrate surface was not irra-
diated by
HEE
or
photons. The time spent on checking
RHEED
patterns was as short as possible to minimize the
effects
of
illumination
by
high-energy electrons. Normally
about 2-3 s were needed to observe the
RHEED
pattern.
This was achieved using a switch to change the
x-y
deviation
voltages
of
the electron gun.
At
230·C
no
HOR
in the
[OIOJ
azimuth could be found
even after 100 min. Curves
(b),
(c),
and
(d)
were obtained
under laser illumination,
HEE
irradiation, and both, respec-
tively.
It
is obvious from Fig. 1 that both laser illumination
and
HEE
irradiation
of
the substrate accelerated the desorp-
tion
of
Te, whereby the effect
of
the
HEE
irradiation was
appreciably larger. The fact that laser-illumination induces
tellurium desorption from CdTe surfaces
is
consistent with
the experimental results
of
Benson et al. 12
B.
Dynamic CdTe growth surfaces
Laser illumination and
HEE
irradiation also affect the
CdTe surface during growth. Table I lists the substrate tem-
perature ranges over which half-order reconstruction in the
[OIOJ
azimuth occurs for various growth conditions. The
CdTe flux was 1.67 X
10
- 7
Torr
and the incident laser inten-
sity was 200 mW
/cm
2
•
Corresponding to this CdTe flux, the
growth rate at
320·C
was 0.4
A/s,
which was measured in
situ using
RHEED
oscillations. The appearance
of
the
HOR
in
the [010] azimuth was determined with the naked eye. No
evidence for
HOR
in the [010] azimuth was found outside
the indicated temperature ranging during growth with the
indicated growth conditions (i.e., laser illumination.
HEE
irradiation, etc). As shown in Table
I,
HOR
in
the [010]
azimuth could be observed only in a very narrow tempera-
ture range between 350 and
356·C
when conventional MBE
growth techniques were employed. This means that outside
this small temperature range the surface
is
tellurium stabi-
lized. This is due to a combination
of
several factors: the Cd-
to-Te flux ratio
of
our
CdTe Knudsen source, the Cd and Te
sticking coefficients, and the reevaporation rates from the
surface.
TABLE
I. Temperature ranges over which half-orders reconstruction
along the [010] azimuth occur under various growth conditions.
Conditions
Neither laser nor high-
energy electrons
Laser
High-energy electrons
Laser and high-energy
electrons
Temperature range
CC)
Lower temperature
350
338
316
310
Upper temperature
356
364
374
386
270
J. Appl. Phys., Vol. 69, No. 1, 1 January 1991
Irradiating the CdTe growing surface with photons,
HEE
or
both greatly increased the temperature range over
which
HOR
in the [010] azimuth appeared, as indicated
in
Table
I.
Therefore, the conclusion can
be
drawn that laser
illumination and
HEE
irradiation increase the Cd content
on the surface and extend the temperature range over which
HOR
in the [010] azimuth can
be
observed.
The effect
of
laser illumination on the CdTe growing
surface
is
dependent on the incident laser intensity, as shown
in Fig.
2.
In the following experiment the CdTe
flux
was
5 X
10
- 8 Torr, which corresponds to a growth rate
of
ap-
proximately 2 monolayers per minute.
At
the beginning
we
grew CdTe at
345
·C on the prepared (100) CdTe substrate
and slowly lowered the substrate temperature until
HOR
in
the [010] azimuth disappeared. Then
we
increased the laser
power until
HOR
in the (010] azimuth appeared. In this
way
we
found that
HOR
in
the [010] azimuth cannot be
found if the substrate temperature was less than about
340·C
and
if
a laser intensity less than
45
m W
/cm
2
was
employed.
The other points in Fig. 2 with the exception
of
points A
and B indicate that
HOR
in the [010] azimuth appeared at
the indicated substrate temperature when a laser intensity
laser than the value indicated by the point was employed.
To
summarize,
HOR
in the [010] azimuth, which
is
indicative
of
a Cd-stabilized surface, was observed
in
region
II
and was not observed in region
I.
In contrast,
HOR
in the
[011] azimuth was visible at all temperatures and laser in-
tensities investigated.
From
the curves
in
Fig. 2
we
can make the following
statements: Firstly, there
is
a laser power threshold, i.e.,
HOR
in the [010] azimuth cannot be found if the illumina-
tion power density
is
less than a limiting value. Secondly,
laser intensities ranging from 50 to 160 m W
/cm
2
can induce
large changes in the substrate temperature region over
which
HOR
in the
[OIOJ
azimuth can be observed. Lastly,
below a certain temperature
HOR
in the (010] azimuth can-
not
be
observed independent
of
the illumination intensity
employed. These observations are consistent with the work
N
~
320
,
3:
E
240
>-
I-
H
Ul
z
160
w
I-
Z
H
~
80
W
Ul
Cl:
CdTe
flux:
5 x
10-
8
Torr
II
A
•
-.J
OL...._L--_>-----I.---~---~----J
280
300
320
340
TEMPERATURE
(OC)
FIG.
2.
Laser intensity
vs
substrate temperatures. Region I: no HOR
in
the
[010] azimuth appeared. Region lI:
HOR
in
the [010] azimuth appeared.
Points A and B were obtained
in
HEE
irradiation and corresponding laser
illumination.
Wu
et
al.
270
of
Bicknell-Tassius et al., which indicated that to optimize
the photoluminescence spectra from CdTe epilayers grown
by
photoassisted MBE there was a resonance in the power
density employed during the PAMBE process.
22
In the above experiments the effects
of
illumination by
high-energy electrons was also noted.
If
during these experi-
ments the
RHEED
pattern was observed for more than
about
10
s,
HOR
in the [010] azimuth was much more clear-
ly
apparent unless the substrate temperature was smaller
than the temperatures defined by points A and B corre-
sponding to growth with and without laser illumination, re-
spectively. This fact clearly demonstrates again the large
ef-
fect
HEE
irradiation has on the surface. Here the growth
rate was very low, about 2 monolayers per minute, and the
surface was optically smooth.
We
propose that the MBE
system was nearly in equilibrium.
At
this low growth rate we
could observe and maintain these phenomena over a longer
period
of
time.
Laser illumination and
HEE
irradiation has also been
observed to affect the desorption
of
Cd from Cd-stabilized
surfaces. In these experiments a CdTe epilayer was grown at
300
°C
on the prepared (lOO) CdTe substrate for several
minutes, using conventional MBE, photoassisted MBE,
or
HEE
irradiation during the MBE growth process. The re-
sults described below were independent
of
the growth proce-
dure employed. In this way a smooth Te-stabilized surface
showing a (2
Xl)
reconstruction was obtained. The CdTe
source shutter was closed and the
Cd
source shutter was
opened for 1 min. The CdTe and Cd source
Buxes
employed
were 3 X
10-
7 and 7 X
10
- 6 Torr, respectively. After clos-
ing the Cd source shutter the surface exhibited a
c(2X2)
reconstruction, typical
of
a Cd-stabilized surface.
To determine the lifetime
of
excess Cd on this surface
the elapsed time for the appearance
of
HOR
in the [031]
azimuth, which
is
18.4°
±
1°
displaced from the [010]
a~i
muth, was measured. The reconstruction along the [031]
azimuth rather than along [010] azimuth was used to deter-
mine the Cd surface lifetime. The reason for this is
that
the
Te-stabilized (2
Xl)
reconstructed surface surface displays
strong
HOR
in
the [011] azimuth and very clear but weaker
HOR
in the [031] azimuth. The Cd-stabilized
c(2X2)
re-
constructed surface surface shows a very strong
HOR
in the
[010] azimuth, a weak
HOR
in the [011]
azim~th,
and no
HOR
in the [031] azimuth. The
HOR
in the [031 J azimuth
appeared when the intensity
of
the
HOR
in the [011] and
[010] azimuths were almost identical. Obviously this indi-
cates that the surface
is
now neither Te nor Cd stabilized,
but
is
at some intermediate
or
mixed stage. The process for the
surface to change from the Cd-stabilized
c(2X2)
phase to
the mixed phase
is
due to the desorption
of
excess Cd.
Ther:-
fore,
we
have chosen the appearance
of
HOR
in the
[03lJ
azimuth as a measure for the desorption time
of
excess Cd on
the Cd-stabilized surface.
In this
way
we
found the persistence time
of
the excess
Cd on the CdTe surface at 300°C was 118,26, and
16
min
with
HEE
irradiation, laser illumination, and neither one,
respectively. Therefore, it
is
apparent that laser illumination
and high-energy electron illumination
of
the surface de-
creases the Cd desorption rate. The surface lifetime
of
excess
271 J. Appl. Phys., Vol. 69, No. 1, 1 January 1991
Cd on the surface under
HEE
irradiation at 300
°C
is
consis-
tent with the data presented in Ref.
16.
Again it
is
apparent
that the effects observed upon illuminating the surface with
high-energy electrons
is
very similar to what
is
observed
when the surface is illuminated with photons.
IV.
CONCLUSIONS
The results
of
this investigation can be summarized as
follows. Firstly, the high-energy photons
of
an Ar-ion laser
increases the desorption
of
Te from (100) CdTe surfaces.
The
opposite is true
of
Cd, i.e., the desorption is decreased
upon illumination with photons. Secondly, both
of
these
above statements are true when the (100) CdTe epitaxial
layer is irradiated with HEE, but to a much larger extent.
Lastly, there is a laser intensity range over which a c( 2 X 2)
Cd-stabilized surface can be observed.
It
is
possible that this
is
related to the optimum laser intensity for the growth
of
high-quality CdTe epitaxiallayers.
The effects observed under high-energy electron illumi-
nation are new and
we
believed very exciting. Effects very
similar to those obtained with photon illumination have
been obtained. Whether highly conducting CdTe epilayers
can be obtained using
HEE
irradiation
is
not known, but if it
is
possible this effect could have many new and interesting
applications. Such an effect would allow the control
of
the
electrical properties in the growth plane by selective illumi-
nation
of
the epilayer surface with the high-energy electrons.
This would be much easier with
HEE
illumination than with
photons since the steering
of
the electron beam is quite tri-
vial. Further studies are under way to investigate the electri-
cal properties
of
the
HEE
illuminated epilayers.
From
a more short-term perspective the results present-
ed in this paper should lead anyone using
RHEED
to char-
acterize growth surfaces to take a careful look to be sure that
they are not changing what they want to look at by irradiat-
ing their surfaces with high energy electrons.
ACKNOWLEDGMENTS
This project was supported by the Bundeministerium
fUr
Forschung und Technologie and the Deutsche Fors-
chungsgemeinschaft (Bonn).
'R. N. Bicknell, N. C. Giles, and J. F. Schetzina, Appl. Phys. Lett. 49,1095
(1986).
'R.
N. Bicknell, N. C. Giles, and J. F. Schetzina, Appl. Phys. Lett. 49,1735
(1986).
-'s.
Hwang, R. L. Harper, K. A. Harris, N. C. Giles, R. N. Bicknell, R. M.
Kolbas, and J. F. Schetzina, J. Vac. Sci. Technol. B
6,
777 (1988).
4R.
N. Bicknell, N. C. Giles,
and
J. F. Schetzina, J. Vac. Sci. Technol. A
5,
3059 (1987).
'D.
L. Dreifus, R. M. Kolbas, K. A. Harris, R. N. Bicknell, R.
L.
Harper,
and
J. F. Schetzina, Appl. Phys. Lett. 51,
931
(1987).
"D. Dreifus,
R.
Kolbas, J. Tassintino, R. Harper, R. Bicknell
and
J. Schet-
zina, J. Vac. Sci. Technol. A
6,
2722 (1988).
7R.
L. Harper, R. N. Bicknell, D. K. Blanks, N. C. Giles, J. Schetzina,
Y.
R.
Lee,
and
A. K. Ramdas, J. Appl. Phys. 65, 624
(1989).
SR.
J. Koestner, H.-Y. Liu, H. Schaake,
and
T. Hanlon,
J.
Vac. Sci. Tech-
nol. A
7,517
(1989).
"T.
Myers, R. Yanka, K. Harris, A. Reisinger, J.
Han,
S.
Hwang, Z. Yang,
N. Giles, J. J. W. Cook, J. Schetzina, R. Green,
and
S.
MeDivitt, J. Vac.
Sci. Technol.
7, 300 (1989).
Wuetal.
271
IOJ.
Nishizawa, H. Abe, T. Kurabayshi,
and
N. Sakurai,
J.
Vac. Sci. Tech-
no!. A
4,706
(1986).
11
J.
Nishizawa, T. Kurabayshi,
and
J. Hoshina, J. Electrochem. Soc. 134,
502 (1987).
12J.
Benson, D. Rajavel,
B.
Wagner, R. Benz
n,
and
C.
J. Summers, J. Cryst.
Growth 95,543 (1989).
13R.
N. Bicknell-Tassius, A. Waag, Y.
S.
Wu, T. A.
Kuhn,
and W. Ossau, J.
Cryst. Growth (in press).
14y'
S.
Wu, A. Waag,
and
R.
Bicknell-Tassius, (unpublished).
"H.
Farrell,
X.
Nahory, and J. Harbison, J. Vac. Sci. Techno!. B
6,
779
(1988).
16J.
Benson.B. Wagner,A.
Torabi,andC.J.
Summers,App!. Phys. Lett. 49,
272
J. Appl. Phys., Vol. 69, No. 1, 1 January 1991
1034 (1986).
17J.
Shaw, L. Brillson,
S.
Sivanathan, and J. Faurie, App!. Phys. Lett.
56,
1266 (1990).
'"A. Waag,
Y.
S.
Wu, R. N. Bicknell-Tassius, and G. Landwehr, App!.
Phys. Lett. 54, 2662 (1989).
19
A. Waag, Y.
S.
Wu, R. N. Bicknell-Tassius,
C.
Gonser-Buntrock, and O.
Lanwehr, J. Appl. Phys. 68, 212 (1990).
20c.
Uzan,
R.
Legros, Y. Marfaing, and R. Triboulet, Appl. Phys. Lett. 45,
879 (1984).
21J.
Singh and J. Arias, J. Vac.
ScL
Technol. A
7,
2562 (1989).
22R.
N. Bicknell-Tassius, T. A. Kuhn, and
W.
Ossau, Appl. Surf.
Sci.
36,
95
( 1989).
Wu
eta!.
272
![TABLE I. Temperature ranges over which half-orders reconstruction along the [010] azimuth occur under various growth conditions.](/figures/table-i-temperature-ranges-over-which-half-orders-1lzzo64e.webp)
![FIG. 2. Laser intensity vs substrate temperatures. Region I: no HOR in the [010] azimuth appeared. Region lI: HOR in the [010] azimuth appeared. Points A and B were obtained in HEE irradiation and corresponding laser illumination.](/figures/fig-2-laser-intensity-vs-substrate-temperatures-region-i-no-2qcbp3xc.webp)
