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Identification of deep radiative levels in VPE ZnSe
Journal of Luminescence 31 & 32(1984)433-435 North-Holland, Amsterdam
433
IDENTIFICATION OF DEEP RADIATIVE LEVELS IN VPE ZnSe
K. A. CHRISTIANSON and B. N. WESSELS Department of Materials Science and Engineering and Materials Research Center, Northweatern University, Evanaton, Illinois 60201.
The defect centera responsible for both the shallow and deep level emiaaions commonly seen in the photoluminescence spectra of high purity vapor phase epitsxially grown ZnSe have been investigated. The donor-acceptor pair emission at 2.681 eV has been associated with hole traps at 90 and 13D meV shove the valence band edge as measured by optical transient capacitance spectroscopy. From the analysis of low temperature photoluminescence the traps are attributed to sodium. Photoluminescence emission at 1.94 eV has been correlated with s deep level at Ec~ 2.25 eV as observed by steady state photocspscitsnce spectroscopy. Electron irradiation of the ZnSe thin films support the association of the defect centers responsible for 1.94 eV emission with the self-sctivsted complex.
1.
INTRODUCTION In this paper we report the characterization of defects in high purity
heteroepitaxially grown ZnSe by the complimentary techniques of photoluminescence, steady state photocapacitance, and deep level transient capacitance spectroscopy.
In support of the defect characterization studies on
es-grown ZnSe, electron irradiated samples have been examined to determine the role of native defects,
2
EXPERIMENTAL The heteroepitaxial layers examined in this study were grown by vapor
phase epitaxy (VPE) using ZnSe as the source material and palladium dif1. The ZnSe layers were grown at 700°C fused hydrogen as the carrier gas on n-type GaAs substrates, and were typically 1 to 10 p.m thick. Photoluminescence measurements were made at 8 and 77K under illumination.
4 nsW/cm2 of 3650~
Electrical measurements were made using Au Schottky diodes
fabricated on the layer.
The characterization techniques of steady state
photocapacitance and deep level transient capacitance spectroscopy have been described elsewhere24.
3.
RESULTS AND DISCUSSION The photoluminescence spectrum at BK of an es-grown ZnSe layer selec-
ted for its prominent donor acceptor pair (DAP) emission at 2.681 eV is shown in Figure 1.
There are also deeper, less intense photoluminescence
0022—2313/84/$03.00© Elaevicr Science Publishers By. (North-Holland Physics Publishing Division)
K .1. (itrsi/atttott, /1. II
434
bands
at
1.94
preduminates
truscepy shown
cv.
and 2.24 twu
hole
traps
/)ti o tot/sit/cc Iris/s Jo I II /tiSt
lit su/t
Fur samples whose hAP end ssion
at
are
transient
seen
hr optical
(ODLTI) at 0.09 and 0.13 eT above
in Figure
2.
From
the
anatys is
us
deep
level
cite valence
the
2. bhl eV
band edge,
loss temperature phototusu 5. The concentration of
the traps were attributed to sodium two hole traps has been measured to be as large as 2x1015
nesceuce
these though
spec-
as is —
,
the typical background concentration is
addition
to
the
sodium
related
+ 0.71 eV is occasionally
hole seen
traps,
in
the
cm
a copper as-grown
related
hole
al-
~,
tess than 1013 cm3.
In
trap
at
material.
II
75
1.
/
“S’
mr4i FIGURE 1
FIGUWF i
Fl. spectrum of Znle thin film showing
large
2.681
ODLTS spectrum of Na rich sample
eT omission
The deep FL emission mc 1.94 cv has been correlated with the appearance of an electronic photocmpacitmnce.
level at ~c
-
2.25 cv as observed by steady state
Figure 3 illustrates
a typical
trum for an as-grown Au-Role lchottky diode. level its
has not been observed using
small capture
cross
tional transitions, he
-
2.65 eV.
(mc Ec
sponsible
spec-
2.25 cv
transient capacicsnce techniques
due to
indicative of deep levels mc E -
1.1, 8 1.4, and c c 1.1 eV hss previously been observed
mc 6c
2.65 eV
-
for the OULTS
while
is presumably due to the same acceptor re-
spectrum as shown
in Figure 2.
electron irradiation mc 1.5 Hey of the ms-grown
mc doses to 6xlD17 c/cm2
has been found to give incremsed intensity
to the 1.94 mnd 2.24 eV phocoluminescence emission,
lineate
-
Also seen in Figure 3 sre several addi-
The deep level at 8c
Room temperature
trates.
cite Ge
1.2 cv) by Bmwolek and Nessels6 in semi-insulating Znle,
-
the deep level
layer
section.
photocapacicance
Note that
mm Figure 4 illus-
This spectrum was measured mc 77K in order to more clemrly dethe chmnges
in the deep emission.
2.24 cv band to 2.28 e\t upon irrmdimtlon.
There
is also a shift of the
Whether or nut this shift is
KA. Christianson, B. W. Weasels
/ Deep radiative lerelm in
Znse K lOB
2,5* k4~
.6
2416
LEE ZnSe
2.0
22
24
26
2.1
~
U
Phstsn Enersy eV)
‘no,,,
U
K
K
c,,,, mm)
FIGURE 3 Fhotocmpmcitmnce spectrum of mm-grown Au-RoSe Schottky diode
FIGURE 4 FL spectrum of ZnSe thin film (m) mm-grown, £b)sfter irradiation to 16e/cm~ 5xlO cmused by the introduction of a new center is currently being investigated. The deep level observed by photocapacitance at Ec
-
2.25 eV has also been
noted to increase in concentration following room temperature electron irradiation.
These results are consistent with the identification of the
1.94 eV PL emission and associated photocapacitance transition mc Ec -2.25 eV with the self-activated Woods2.
In contrast,
center,
as suggested recently
by Qidwai mnd
the DAP emission at 2.6Bl eV and related
traps undergo no change upon electron
irradiation,
consistent
ODLTS hole with their
identification as being Na related. This work was supported by the Department
of Energy, under contract
DE-ACO279EE1O39O. REFERENCES 1)
P. Besomi and B. N. Wessels,
J. Cryst.
Growth 55 (l9Bl) 477.
2)
A. A. Qidwsi and 3. Woods, 3. Phys. C: Solid State Phys.
3)
D. V. Lang, 3. Appl.
4)
K. A. Christianson
5)
K. N, Bhargava, R. .3. Seymour, B. 3. Fitzpatrick, and S. P. Herko, Fhys. Rev. B2O (1979) 2407.
6)
E. 3. Bawolek and B. N. Wessels, Thin Solid Films 102 (l9B3) 251.
16
(l9B3)67B9.
Phys. 45 (1974) 3023.
and B. N. Wessels,
3. Appl. Phys. 54 (19B3) 4205.
435
433
IDENTIFICATION OF DEEP RADIATIVE LEVELS IN VPE ZnSe
K. A. CHRISTIANSON and B. N. WESSELS Department of Materials Science and Engineering and Materials Research Center, Northweatern University, Evanaton, Illinois 60201.
The defect centera responsible for both the shallow and deep level emiaaions commonly seen in the photoluminescence spectra of high purity vapor phase epitsxially grown ZnSe have been investigated. The donor-acceptor pair emission at 2.681 eV has been associated with hole traps at 90 and 13D meV shove the valence band edge as measured by optical transient capacitance spectroscopy. From the analysis of low temperature photoluminescence the traps are attributed to sodium. Photoluminescence emission at 1.94 eV has been correlated with s deep level at Ec~ 2.25 eV as observed by steady state photocspscitsnce spectroscopy. Electron irradiation of the ZnSe thin films support the association of the defect centers responsible for 1.94 eV emission with the self-sctivsted complex.
1.
INTRODUCTION In this paper we report the characterization of defects in high purity
heteroepitaxially grown ZnSe by the complimentary techniques of photoluminescence, steady state photocapacitance, and deep level transient capacitance spectroscopy.
In support of the defect characterization studies on
es-grown ZnSe, electron irradiated samples have been examined to determine the role of native defects,
2
EXPERIMENTAL The heteroepitaxial layers examined in this study were grown by vapor
phase epitaxy (VPE) using ZnSe as the source material and palladium dif1. The ZnSe layers were grown at 700°C fused hydrogen as the carrier gas on n-type GaAs substrates, and were typically 1 to 10 p.m thick. Photoluminescence measurements were made at 8 and 77K under illumination.
4 nsW/cm2 of 3650~
Electrical measurements were made using Au Schottky diodes
fabricated on the layer.
The characterization techniques of steady state
photocapacitance and deep level transient capacitance spectroscopy have been described elsewhere24.
3.
RESULTS AND DISCUSSION The photoluminescence spectrum at BK of an es-grown ZnSe layer selec-
ted for its prominent donor acceptor pair (DAP) emission at 2.681 eV is shown in Figure 1.
There are also deeper, less intense photoluminescence
0022—2313/84/$03.00© Elaevicr Science Publishers By. (North-Holland Physics Publishing Division)
K .1. (itrsi/atttott, /1. II
434
bands
at
1.94
preduminates
truscepy shown
cv.
and 2.24 twu
hole
traps
/)ti o tot/sit/cc Iris/s Jo I II /tiSt
lit su/t
Fur samples whose hAP end ssion
at
are
transient
seen
hr optical
(ODLTI) at 0.09 and 0.13 eT above
in Figure
2.
From
the
anatys is
us
deep
level
cite valence
the
2. bhl eV
band edge,
loss temperature phototusu 5. The concentration of
the traps were attributed to sodium two hole traps has been measured to be as large as 2x1015
nesceuce
these though
spec-
as is —
,
the typical background concentration is
addition
to
the
sodium
related
+ 0.71 eV is occasionally
hole seen
traps,
in
the
cm
a copper as-grown
related
hole
al-
~,
tess than 1013 cm3.
In
trap
at
material.
II
75
1.
/
“S’
mr4i FIGURE 1
FIGUWF i
Fl. spectrum of Znle thin film showing
large
2.681
ODLTS spectrum of Na rich sample
eT omission
The deep FL emission mc 1.94 cv has been correlated with the appearance of an electronic photocmpacitmnce.
level at ~c
-
2.25 cv as observed by steady state
Figure 3 illustrates
a typical
trum for an as-grown Au-Role lchottky diode. level its
has not been observed using
small capture
cross
tional transitions, he
-
2.65 eV.
(mc Ec
sponsible
spec-
2.25 cv
transient capacicsnce techniques
due to
indicative of deep levels mc E -
1.1, 8 1.4, and c c 1.1 eV hss previously been observed
mc 6c
2.65 eV
-
for the OULTS
while
is presumably due to the same acceptor re-
spectrum as shown
in Figure 2.
electron irradiation mc 1.5 Hey of the ms-grown
mc doses to 6xlD17 c/cm2
has been found to give incremsed intensity
to the 1.94 mnd 2.24 eV phocoluminescence emission,
lineate
-
Also seen in Figure 3 sre several addi-
The deep level at 8c
Room temperature
trates.
cite Ge
1.2 cv) by Bmwolek and Nessels6 in semi-insulating Znle,
-
the deep level
layer
section.
photocapacicance
Note that
mm Figure 4 illus-
This spectrum was measured mc 77K in order to more clemrly dethe chmnges
in the deep emission.
2.24 cv band to 2.28 e\t upon irrmdimtlon.
There
is also a shift of the
Whether or nut this shift is
KA. Christianson, B. W. Weasels
/ Deep radiative lerelm in
Znse K lOB
2,5* k4~
.6
2416
LEE ZnSe
2.0
22
24
26
2.1
~
U
Phstsn Enersy eV)
‘no,,,
U
K
K
c,,,, mm)
FIGURE 3 Fhotocmpmcitmnce spectrum of mm-grown Au-RoSe Schottky diode
FIGURE 4 FL spectrum of ZnSe thin film (m) mm-grown, £b)sfter irradiation to 16e/cm~ 5xlO cmused by the introduction of a new center is currently being investigated. The deep level observed by photocapacitance at Ec
-
2.25 eV has also been
noted to increase in concentration following room temperature electron irradiation.
These results are consistent with the identification of the
1.94 eV PL emission and associated photocapacitance transition mc Ec -2.25 eV with the self-activated Woods2.
In contrast,
center,
as suggested recently
by Qidwai mnd
the DAP emission at 2.6Bl eV and related
traps undergo no change upon electron
irradiation,
consistent
ODLTS hole with their
identification as being Na related. This work was supported by the Department
of Energy, under contract
DE-ACO279EE1O39O. REFERENCES 1)
P. Besomi and B. N. Wessels,
J. Cryst.
Growth 55 (l9Bl) 477.
2)
A. A. Qidwsi and 3. Woods, 3. Phys. C: Solid State Phys.
3)
D. V. Lang, 3. Appl.
4)
K. A. Christianson
5)
K. N, Bhargava, R. .3. Seymour, B. 3. Fitzpatrick, and S. P. Herko, Fhys. Rev. B2O (1979) 2407.
6)
E. 3. Bawolek and B. N. Wessels, Thin Solid Films 102 (l9B3) 251.
16
(l9B3)67B9.
Phys. 45 (1974) 3023.
and B. N. Wessels,
3. Appl. Phys. 54 (19B3) 4205.
435