ArticlePDF Available

Temperature dependence of the energy gap of zinc-blende CdSe and Cd[sub 1 - x]Zn[sub x]Se epitaxial layers

Authors:

Abstract and Figures

The temperature dependence of the energy gap of zinc-blende CdSe and Cd 1x Zn x Se has been determined over the entire range of composition from optical transmission and reflection measurements at temperatures between 5 and 300 K. The experimental results can be expressed by the following modified empirical Varshni formula, whose parameters are functions of the composition x: E g (x,T) E g (x,0) (x)T 2 /T (x). E g (x,0) exhibits a nonlinear dependence on composition, according to E g E g (0,0)(1 x) E g (1,0)x ax(1 x). The parameters (x) and (x) can be expressed by (x)(0)(1x)(1)xbx(1x) and x01x1x.
Content may be subject to copyright.
Temperature dependence of the energy gap of zincblende CdSe and
Cd1−xZnxSe epitaxial layers
U. Lunz, J. Kuhn, F. Goschenhofer, U. Schüssler, S. Einfeldt et al.
Citation: J. Appl. Phys. 80, 6861 (1996); doi: 10.1063/1.363753
View online: http://dx.doi.org/10.1063/1.363753
View Table of Contents: http://jap.aip.org/resource/1/JAPIAU/v80/i12
Published by the AIP Publishing LLC.
Additional information on J. Appl. Phys.
Journal Homepage: http://jap.aip.org/
Journal Information: http://jap.aip.org/about/about_the_journal
Top downloads: http://jap.aip.org/features/most_downloaded
Information for Authors: http://jap.aip.org/authors
Downloaded 17 Sep 2013 to 130.95.240.83. This article is copyrighted as indicated in the abstract. Reuse of AIP content is subject to the terms at: http://jap.aip.org/about/rights_and_permissions
Temperature dependence of the energy gap of zinc-blende CdSe
and Cd
1
2
x
Zn
x
Se epitaxial layers
U. Lunz,a) J. Kuhn, and F. Goschenhofer
Physikalisches Institut der Universita
¨tWu
¨
rzburg, Am Hubland, 97074 Wu
¨rzburg, Germany
U. Schu
¨ssler
Mineralogisches Institut der Universita
¨tWu
¨
rzburg, Am Hubland, 97074 Wu
¨rzburg, Germany
S. Einfeldt
Institut fu
¨r Festko
¨rperphysik, Universita
¨t Bremen, Kufsteiner Street, 28359 Bremen, Germany
C. R. Becker and G. Landwehr
Physikalisches Institut der Universita
¨tWu
¨
rzburg, Am Hubland, 97074 Wu
¨rzburg, Germany
~Received 24 June 1996; accepted for publication 17 September 1996!
The temperature dependence of the energy gap of zinc-blende CdSe and Cd12xZnxSe has been
determined over the entire range of composition from optical transmission and reflection
measurements at temperatures between 5 and 300 K. The experimental results can be expressed by
the following modified empirical Varshni formula, whose parameters are functions of the
composition x:Eg(x,T)5Eg(x,0) 2
b
(x)T2/@T1
g
(x)#.Eg(x,0) exhibits a nonlinear dependence
oncomposition,accordingtoEg5Eg(0,0)(12x)1Eg(1,0)x2ax(12x).Theparameters
b
(x) and
g
(x) can be expressed by
b
(x)5
b
(0)(12x)1
b
(1)x1bx(12x) and
g
~x!5
g
~0!~12x!1
g
~1!x.
©1996 American Institute of Physics. @S0021-8979~96!09524-2#
I. INTRODUCTION
Cd12xZnxSe is commonly used as quantum well mate-
rial in ZnSe-based laser diodes.1Bulk Cd12xZnxSe crystal-
lizes either in the cubic zinc-blende structure ~x.0.7!,inthe
hexagonal wurtzite structure ~x,0.5!or in mixture of these
two for 0.5<x<0.7.2However, growth of Cd12xZnxSe on
GaAs~100!substrates with molecular beam epitaxy ~MBE!
results in films of the zinc-blende structure over the entire
range of composition. Literature values for the energy gap of
zinc-blende CdSe at 300 K vary from 1.66 to 1.74 eV. Spec-
troscopic ellipsometric measurements result in a value of
1.74 eV3,4 as well as a value of 1.66 eV.5Reflection
spectroscopy6and photomodulation spectroscopy7also yield
a value of 1.66 eV at 300 K. The energy gap of Cd12xZnxSe
alloys has been determined at 300 K by reflection
spectroscopy8and spectroscopic ellipsometry.5In these in-
vestigations we have grown Cd12xZnxSe films on GaAs with
0<x<1 and measured their energy gap Egusing optical
transmission and reflection in the temperature range from 5
to 300 K.
II. EXPERIMENT
Growth of ternary Cd12xZnxSe films with a typical
thickness of 1
m
mon~100!GaAs was carried out in a Riber
2300 molecular beam epitaxy ~MBE!system. Cd~6N!,
Zn~6N!, and Se~6N!, were used as source materials. The
growth of zinc-blende alloys was monitored by means of
reflection high-energy electron diffraction ~RHEED!. The
composition of the alloys were determined by electron probe
microanalysis ~EPMA!with an experimental uncertainty of
<1.0%. Optical transmission and reflection measurements
were carried out with a Fourier transform spectrometer,
Bruker IFS 88, in the 1.2–3.2 eV energy range in order to
obtain the energy gap Eg. For the transmission measure-
ments, the absorbing GaAs substrates had to be removed as
described elsewhere.9
III. RESULTS AND DISCUSSION
The energy gap Egof these alloys was determined from
optical transmission. From the transmission data, the absorp-
tion coefficient was calculated in the region of strong absorp-
tion using the formula according to Swanepoel:10
a
51
dln A
Twith A516n2s
~n11!3~n1s2!,~1!
where Tis the transmission. The refractive index of glass s
and the refractive index of the layer nwere assumed to be
constant in the region of strong absorption. The refractive
index nand the thickness dof the layer were estimated from
the reflection spectra. Assuming parabolic band structure, the
absorption coefficient
a
is proportional to ~E2Eg!0.5 and an
extrapolation to
a
250 yields a good approximation of the
energy gap Eg. Figure 1 shows the transmission and reflec-
tion spectra and the squared absorption coefficient of a
Cd0.47Zn0.53Se layer at 300 K. The energy gap is indicated by
an arrow. The variation of the band-gap energy with compo-
sition at temperature Tis conventionally described by the
quadratic equation:
Eg~x,T!5Eg~0,T!~12x!1Eg~1,T!x2ax~12x!,~2!
where Eg(0,T) and Eg(1,T) are the energy gaps of CdSe and
ZnSe at temperature Tand the deviation from linearity is
given by a. In Fig. 2 the energy gaps of the alloys over the
entire range of composition at 5 and 300 K are shown. In our
measurements we obtained a value of Eg~CdSe!51.66 eV at
room temperature and a value of Eg~ZnSe!52.68 eV. The
a!Electronic mail: lunz@physik.uni-wuerzburg.de
6861J. Appl. Phys. 80 (12), 15 December 1996 0021-8979/96/80(12)/6861/3/$10.00 © 1996 American Institute of Physics
Downloaded 17 Sep 2013 to 130.95.240.83. This article is copyrighted as indicated in the abstract. Reuse of AIP content is subject to the terms at: http://jap.aip.org/about/rights_and_permissions
observed nonlinearity can be described by a50.48 and 0.42
at 5 and 300 K, respectively. Kim et al.5carried out ellipso-
metric measurements at room temperature on zinc-blende
CdSe and Cd12xZnxSe films. This resulted in the following
equation for the energy gap Egas a function of the compo-
sition x:Eg(x)51.6610.73x10.30x2, which corresponds to
a value of a50.30 at 300 K. Their values for the binaries
agree well with our data, but the energy gap of the ternaries
are slightly larger than our values, i.e., DEg<35 meV. The
deviation of the results of Kim et al. from our measurements
are probably due to the different methods used in determin-
ing the composition x. Kim et al. determined the composi-
tion from the lattice constant, assuming a linear dependence
~Vegard’s law!, however, they made no statement concern-
ing their experimental error. We have found, that the large
lattice mismatch of Cd12xZnxSe to the GaAs substrate leads
to a broadening of the rocking curves and thus an error in the
composition, which is larger than the error in measurements
by EPMA, a method independent of lattice mismatch and
sample quality. The full width at half maximum ~FWHM!of
the ~004!rocking curves of the Cd12xZnxSe layers on GaAs
is between 250 and 900 arcsec. The maximum deviation in
the composition xbetween XRD and EPMA is, in our case,
about 5% absolute, which could easily account for the dis-
crepancy between their results and ours.
In contrast to the value of 1.66 eV for the energy gap of
CdSe at 300 K in this investigation and by other groups,
Janowitz et al.4and Ninomiya et al.3obtained a value of
1.74 eV. However, according to Janowitz et al. experimental
difficulties occur in the analysis of the second derivative
spectra due to the presence of interference fringes, which
results from the finite thickness of the samples and the low
absorption of CdSe in this energy range.
The temperature dependence of Cd12xZnxSe can be ex-
pressed by the empirical Varshni11 formula, where the pa-
rameters
b
and
g
are functions of the composition x:
Eg~x,T!5Eg~x,0!2
b
~x!T2
T1
g
~x!~3!
and Eg(x,0) can be described by Eq. ~2!. The parameters
b
(x) and
g
(x) can be expressed by the following relations:
b
~x!5
b
~0!~12x!1
b
~1!x1bx~12x!,~4!
g
~x!5
g
~0!~12x!1
g
~1!x.~5!
For the binaries, the results from a least square fit to the
Varshni formula are
ZnSe: Eg~1,0!52.82 eV,
b
~1!55.7331024eV/K,
g
~1!565 K.
CdSe: Eg~0,0!51.74 eV,
b
~0!54.7731024eV/K,
g
~0!5295 K.
The values of the nonlinearity parameters aand bare
a50.47 eV,
b521.1431024eV/K,
where aand bresult from a fit over all experimental data.
Figure 3 shows the temperature dependence of the energy
gap Egof several alloys with different compositions. The
curves represent the temperature dependence of the energy
gap for the compositions according to Eqs. ~3!~5!. The de-
viation of the experimental values from this empirical rela-
tionship corresponds to the experimental uncertainty in the
composition. We have estimated, that the experimental un-
certainty in Egis <620 meV. Our value of 1.66 eV for the
energy gap of CdSe at room temperature agrees well with the
data of Kim et al.,5Shan et al.,7and Samarth et al.6At low
temperatures, we obtained a value of 1.74 eV for Eg~CdSe!,
which is smaller by '25 meV than that of Shan et al. as
determined by photomodulation spectroscopy. A possible ex-
FIG. 1. Transmission ~solid line!and reflection ~dotted line!spectra at 300
KofaCd
12x
ZnxSe layer with x553% ~left axis!and the squared absorption
coefficient
a
2~dashed line, right axis!. An extrapolation to
a
250 leads to an
estimation of the energy gap Eg, which is indicated by the arrow.
FIG. 2. Dependence of the energy gap of Cd12xZnxSe for different tempera-
tures. The curves are least-squares fits according to Eq. ~2!. The experimen-
tal error in the energy gap is 0.02 eV.
6862 J. Appl. Phys., Vol. 80, No. 12, 15 December 1996 Lunz
et al.
Downloaded 17 Sep 2013 to 130.95.240.83. This article is copyrighted as indicated in the abstract. Reuse of AIP content is subject to the terms at: http://jap.aip.org/about/rights_and_permissions
planation of this slight discrepancy is the following: Shan
et al. employed a ZnTe buffer layer before the growth of the
CdSe layer, which reduces the effect of strain due to the
lattice mismatch between CdSe and ZnTe. They also argue,
that the different thermal expansion coefficients can be ne-
glected, provided the CdSe is thick enough. If this is the
case, their optical measurements yield the properties of un-
perturbed bulk CdSe. In our case, the transmission spectra of
CdSe at low temperatures exhibit no excitonic absorption
due to the relatively poor structural quality as a consequence
of the large lattice mismatch between CdSe and GaAs or a
consequence of the different thermal expansion coefficients
of CdSe and the glass holder or the glue. Our somewhat
smaller value for Eg~CdSe!at low temperatures may be
caused by strain, which results for either of the above rea-
sons.
IV. SUMMARY
In conclusion zinc-blende CdSe and Cd12xZnxSe alloys
have been grown and their energy gap has been determined
as a function of temperature. An empirical formula Eg(x,T),
which describes the energy gap as a function of composition
and temperature has been derived. A small deviation from
a previously published empirical formula can probably be
ascribed to a different method of determining the composi-
tion x.
ACKNOWLEDGMENTS
The authors would like to thank P. Wolf-Mu
¨ller and T.
Schuhmann for sample preparation. The support of the
Bundesministerium fu
¨r Bildung und Forschung ~BMBF!is
gratefully acknowledged.
1M. A. Haase, J. Qiu, J. M. DePuydt, and H. Cheng, Appl. Phys. Lett. 59,
1272 ~1991!.
2A. S. Nasibov, Yu V. Korostelin, P. V. Shapkin, L. G. Suslina, D. L.
Fedorov, and L. S. Markov, Solid State Commun. 71, 867 ~1989!.
3S. Ninomiya and S. Adachi, J. Appl. Phys. 78, 4681 ~1995!.
4C. Janowitz, O. Gu
¨nther, G. Jungk, R. L. Johnson, P. V. Santos, M.
Cardona, W. Faschinger, and H. Sitter, Phys. Rev. B 50, 2181 ~1994!.
5Y. D. Kim, M. V. Klein, S. F. Ren, Y. C. Chang, H. Luo, N. Samarth, and
J. K. Furdyna, Phys. Rev. B 49, 7262 ~1994!.
6N. Samarth, H. Luo, J. K. Furdyna, S. B. Qadri, Y. R. Lee, A. K. Ramdas,
and N. Otsuka, Appl. Phys. Lett. 54, 2680 ~1989!.
7W. Shan, J. J. Song, H. Luo, and J. K. Furdyna, Phys. Rev. B 50, 8012
~1994!.
8N. Samarth, H. Luo, J. K. Furdyna, R. G. Alonso, Y. R. Lee, A. K.
Ramdas, S. B. Qadri, and N. Otsuka, Appl. Phys. Lett. 56, 1163 ~1990!.
9U. Lunz, B. Jobst, S. Einfeldt, C. R. Becker, D. Hommel, and G. Land-
wehr, J. Appl. Phys. 77, 5377 ~1995!.
10R. Swanepoel, J. Phys. E 16, 1214 ~1983!.
11Y. P. Varshni, Physica 34, 149 ~1967!.
FIG. 3. Temperature dependence of the energy gap of several alloys. The
lines represent fits of the experimental data using the Varshni formula.
6863J. Appl. Phys., Vol. 80, No. 12, 15 December 1996 Lunz
et al.
Downloaded 17 Sep 2013 to 130.95.240.83. This article is copyrighted as indicated in the abstract. Reuse of AIP content is subject to the terms at: http://jap.aip.org/about/rights_and_permissions
... When comparing temperature dependence of maximum emission energy for NBP:CdSe/ZnS(0.3) and NBP:CdTe composites with bandgap energy of bulk CdSe [19] and CdTe [20] (Figure 5), it can be noticed that in the case of both QD-doped materials it changes with increasing temperature faster than bandgap energy of a bulk semiconductor. It indicates that the emission originates from a quantum structure rather than from a solid material, that would be created if the QDs had melted into the glass matrix. ...
... Combining QDs with metallic nanoparticles exhibiting plasmonic properties could lead to strong PL enhancement [25,26] or lasing. [27,28] Additionally, as the NPDD method can allow the use of particles of different shapes, asymmetric nanoparticles exhibiting multiple [19] and CdTe. [20] The slopes of calculated linear regression are more steep for QD-doped composite materials. ...
Article
Quantum dot (QD)‐based light‐emitting materials are gaining increased attention because of their easily tunable optical properties desired for various applications in biology, optoelectronics, and photonics. However, few methods can be used to manufacture volumetric materials doped with more than one type of QD other than QD‐polymer hybrids, and they often require complicated preparation processes and are prone to luminescence quenching by QD aggregation and separation from the matrix. Here, simultaneous doping of a volumetric glass‐based nanocomposite with two types of QDs is demonstrated for the first time in a single‐step process using the nanoparticle direct doping method. Glass rods doped with CdTe, CdSe/ZnS, or co‐doped with both QDs, are obtained. Photoluminescence and lifetime experiments confirm temperature‐dependent double emission with maxima at 596 and 720 nm with mean lifetimes up to 16 ns, as well as radiative energy transfer from the short wavelength–emitting QDs to the long wavelength–emitting QDs. This approach may enable the simple and cost‐efficient manufacturing of bulk materials that produce multicolor luminescence with cascade excitation pumping. Applications that could benefit from this include broadband optical fiber amplifiers, backlight systems in LCD screens, high‐power LEDs, or down‐converting solar concentrators used to increase the efficiency of solar panels.
... It has been investigated experimentally that the band gap reduces with the increase of temperature for bulk semiconductors [28][29][30]. On the other hand, the temperature dependence of band gap has been experimentally determined as [31][32][33] ...
... For our simulation purposes, we have calculated the band gap energy vs. temperature, E T g( ) , for CdSe and CdS QDs using Eq. (7) and values of E g 0 K°( ) , α, β reported in [28,29] as shown in table 1. Also, for CdTe QD and TiO 2 , ZnO, SnO 2 MOs, we have calculated E T g( ) using the relations reported in [30,[34][35][36][37]. Table 2 shows values of the effective masses of electron and hole, the relative permittivity, and the conduction band edge vs. vacuum, for three QDs and three MOs. ...
Article
Electron transfer rate from quantum dot (QD) to metal oxide (MO) in quantum dot sensitized solar cells (QDSSCs) has an important role in the efficiency. In this work, we analyse the electron transfer rate from CdSe, CdS and CdTe QDs to TiO2, ZnO and SnO2 MOs by extending the related equations with considering various effects, based on the Marcus theory. In this regard, the effects of QD diameter, QD-MO spacing, the crystalline defects, temperature, and the reorganizational energy, on the electron transfer rate are investigated. The results show that, the maximum electron transfer rate is achieved for CdTe QD with the mentioned three MOs. Moreover, in order to direct the designer to reach the appropriate QDs-MOs combinations for obtaining the maximum electron transfer rate, the average electron transfer rate for various combinations is calculated. For the verification of simulation method, a part of work has been compared with the previous experimental and theoretical results, which indicates the correctness of our simulation algorithm.
... The shift magnitude is of about 100 meV for the I X1 band, 57 meV for the I QD band and 50 meV for the I X2 band. The red-shift of the I QD band agrees with CdSe band gap shrinkage [15,16], while the I X1 band shifts to the red much stronger and similarly to the band gap change of bulk CdS [17]. The temperature-dependent increase of the FWHM of the I QD band is apparently determined by the exciton scattering with acoustic and LO phonons [15,18,19]. ...
... The PL spectra in the range of the I X band (solid curves) and their fitting with two Gaussian lines corresponding to the I X1 and I X2 bands (dashed lines) at 83 and 298 K (a), temperature dependences of the PL intensity (b), blue-shift of PL peak position (c) and FWHM (d) for the I QD band (circles), I X1 (open triangles) and I X2 (filled triangles) components of the I X band; λ exc ¼325 nm. The dashed lines in (c) show change of band gap energy with temperature for bulk CdSe[16] and CdS[17]. Room-temperature micro-Raman spectra of bio-conjugated QDs under excitation with different lines of Ar-Kr laser: 514.5 nm (curve 1), 488.0 nm (curve 2) and 457.9 nm (curve 3). ...
... Da in dieser Arbeit sehr kleine Strukturen (< 4 nm) betrachtet werden, ist davon auszugehen das sowohl CdSe als auch ZnS in Zinkblendestruktur vorliegen ([36], [37])[39]. betragen E g, ZnS = 3.68 eV [40] und E g, CdSe = 1.66 eV [41]. Werden die Strukturen kleiner und die Materialien entsprechend kombiniert, wie im Falle eines CdSe-oder CdSe/ZnS-Quantenpunktes, kann die Bandlücke signifikant abgesenkt oder angehoben werden, sowie die Exzitonenbindungsenergie durch den Ladungsträgereinschluss erhöht werden. ...
Article
The knowledge of the electronic and optical coupling as well as electron transfer across the internal interfaces of hybrid nanostructures opens possibilities to specifically tailor their microscopic transport and luminescence processes by combining specific properties of different organic and inorganic material systems. In this thesis, two different hybrid systems are studied, ZnO nanowire/CdSe quantum dot structures and nanostructures coated with p-type polymers. First, CdSe quantum dots (QDs) with different organic linker molecules are attached to ZnO nanowires (NWs) to study luminescence dynamics and electron tunneling from the QDs to the nanowires in time-resolved photoluminescence (PL) and photoconductivity measurements. After linking the QDs to the ZnO NW surface, photo-induced electron tunneling from an excited state of the QD into the conduction band of the nanowire becomes visible by a clear decrease of the PL decay time of the QDs. By comparing the PL transients of QDs in solution with those of QDs linked to ZnO NWs, the photo-induced electron transfer (PET) process between excited states of the QD and the nanowire is demonstrated and discussed in the frame of a rate equation model. Efficient electron tunneling is confirmed by a strong enhancement of the photocurrent through the functionalized nanowires. The tunneling rate can be controlled by using different organic linker molecules. Surface functionalization of ZnO nanostructures by QD systems with different QD sizes and surface modifications will lead to hybrid solar cells with high absorption over a wide spectral range, and a high energy conversion efficiency. Secondly, the coating of ZnO nanowires and GaN microrods with p-conductive polymers (polypyrrole, poly(3,4-ethylenedioxythiophene)) is analyzed by scanning electron microscopy, energy dispersive X-ray spectroscopy and photoluminescence spectroscopy. For the fabrication of hybrid ZnO/polymer and GaN/polymer core-shell nanostructures, oxidative chemical vapor deposition (oCVD) is used. oCVD, compared to wet-chemical processes, is a completely solventless, dry process where both, the oxidizing agent and the monomer are provided in the gaseous phase. The thickness and homogeneity of the polymer coating depend on the amount of the oxidizing agent (here FeCl3), the substrate and the substrate temperature. With oCVD deposition a 15nm thin and homogeneous polypyrrole layer on the ZnO nanowire surface is demonstrated, whereas, the primary optical properties of ZnO are not affected. A controlled deposition of the polymer shell with a thickness control in the nanometer range is required to tailor the electronic and optical properties. This offers a huge potential for the realization of efficient light-emitting devices
... La différence de structure induit des différences de propriétés optiques et électroniques. En effet, les écartements de bandes ne sont pas les mêmes pour les deux structures et on peut noter, entre autres, que les largeurs de bandes interdites diffèrent : 1.74 eV [16] en wurtzite et 1.66 eV [16][17][18] en zinc blende. Dans la structure wurtzite, il y a une dégénérescence en k=0 due au champ cristallin, lui-même induit par l'élongation suivant l'axe c. ...
Article
Full-text available
We have determined the local pressure in CdS/ZnS nanocrystals, thanks to the manganese phosphorescence signal. A few dopant atoms per nanoparticle were placed at controlled radial positions in a ZnS shell formed layer by layer. The experimental pressure measurements are in good agreement with a simple spherically symmetric elastic continuum model. Using spherically symmetric elastic continuum model could be used to better understand some structural phenomena observed in these nanocrystals, such as changes in crystalline phases, or cracking of some shells and could be used to design better core/shell nanoparticles. In a second step, we developed the colloidal synthesis of CdSe, CdS and CdTe quantum wells. The thicknesses of these nanoparticles are tuned at the atomic level and they present some new physical properties. We cite, in particular, their emission with a full width half maximum of the order of kT at room temperature. Finally, we show that it is possible to laterally extend these nanoparticles and we used the k.p model applied to quantum wells to determine the real values of nanoplatelets thicknesses and to verify the physical parameters for the three materials.
... As reported by others [18,27], the bandgap shows a nonlinear dependence on composition x, which was fitted by Eg(x) = Eg(CdSe) + (Eg (ZnSe)-Eg(CdSe)-b)x + bx 2 , where b is the bowing parameter. The least square fit yields b = 0.55 eV, which is slightly larger than that of bulk (0.41~0.48 eV), but lower than that obtained by Yoon (0.79 eV) [18,31,35]. As we know, bowing parameter b in a mixed crystal of A x B 1-x C reflects their miscibility between AC and BC [30,36,37]. ...
Article
Full-text available
ZnO/Zn x Cd1-x Se coaxial nanowires (NWs) have been successfully synthesized by combining chemical vapor deposition with a facile alternant physical deposition method. The shell composition x can be precisely tuned in the whole region (0 ≤ x ≤ 1) by adjusting growth time ratio of ZnSe to CdSe. As a result, the effective bandgaps of coaxial nanowires were conveniently modified from 1.85 eV to 2.58 eV, almost covering the entire visible spectrum. It was also found that annealing treatment was in favor of forming the mixed crystal and improving crystal quality. An optimal temperature of 350°C was obtained according to our experimental results. Additionally, time resolved photo-luminescence spectra revealed the longest carrier lifetime in ZnO/CdSe coaxial nanowires. As a result, the ZnO/CdSe nanowire cell acquired the maximal conversion efficiency of 2.01%. This work shall pave a way towards facile synthesis of ternary alloys for photovoltaic applications.
... The technological interest in polycrystalline-based devices is mainly caused by their very low production costs. Different researchers [8][9][10] prepared Cd 1x Zn x Se films by different techniques and studied their structural, optical and photoelectrochemical properties. In the present study we have prepared Cd 1x Zn x Se films by electron beam evaporation technique at 100 o C with various zinc content incorporated with cadmium as x 0.2, 0.4, 0.6 and 0.8 and their structural, optical and surface morphological properties were studied. ...
Article
Full-text available
Cd 1 – x Zn x Se films with different zinc content were deposited by electron beam evaporation technique onto glass substrates for the application of solid-state photovoltaic devices. The structural, surface morphological and optical properties of Cd 1 – x Zn x Se films have been studied in the present work. The host material, Cd 1 – x Zn x Se, have been prepared by the physical vapor deposition method of electron beam evaporation technique (PVD: EBE) under a pressure of 1 10 – 5 mbar. The X-ray diffractogram indicates that these alloy films are polycrystalline in nature, hexagonal structure with strong preferential orientation of the crystallites along (002) direction. Linear variation of lattice constant with composition (x) is observed. The optical properties shows that the band gap (E g) values varies from 2.08 to 2.64 eV as zinc content varies from 0.2 to 0.8. The surface morphological studies show the very small, fine and hardly distinguishable grains smeared all over the surface. It is observed that the grain size is decreasing with increasing zinc content.
... As the cw-spectrum shows the emission shifts by 3 nm to 560 nm. From the temperature induced shift of the bandgap of CdZnSe a temperature rise in the active region by about 20 K is estimated which is identical with the values we obtained for our conventional ZnSe-based laser structures [18,19]. ...
Article
Subject classification: 42.55.Px; 78.55.Et; 81.05.Dz; 85.60.Jb; S8.12 ZnSe-based laser diodes with emission wavelength from 500 to 560 nm are studied. The long wavelength operation of these laser diodes requires careful optimization of the CdZnSSe quantum well material. It is shown that under stoichiometric growth conditions quantum wells with high optical and structural qualtity can be realized. Employed in laser structures room-temperature cw-operation around 560 nm is obtained. In comparison with laser diodes emitting at 505 nm it is found that the high Cd content of the quantum well does not degrade the operational characteris-tics of the devices. In pulsed mode more than 1100 mW output power at 560 nm is achieved.
... The technological interest in polycrystalline-based devices is mainly caused by their very low production costs. Different researchers [16][17][18][19] prepared Cd 1−x Zn x Se films by different techniques and studied their structural, optical and photoelectrochemical properties. In the present study we have prepared Cd 1−x Zn x Se films by electron beam evaporation technique at 100 • C with various zinc content incorporated with cadmium as x = 0.2, 0.4, 0.6 and 0.8 and their structural, optical and surface morphological properties were studied. ...
Article
Full-text available
Cd1−xZnxSe films with different zinc content were deposited by electron beam evaporation technique onto glass substrates for the application of solid-state photovoltaic devices. The structural, surface morphological and optical properties of Cd1−xZnxSe films have been studied in the present work. The host material, Cd1−xZnxSe, has been prepared by the physical vapor deposition method of electron beam evaporation technique under the pressure of 1 × 10 −5 mbar. The X-ray diffractogram indicates that these alloy films are polycrystalline in nature, of hexagonal structure with strong preferential orientation of the crystallites along (0 0 2) direction. Linear variation of lattice constant with composition (x) is observed. Surface roughness measured by atomic force microscopy is used to estimate the interface roughness. The optical properties show that the band gap (Eg) values vary from 2.08 to 2.64 eV as zinc content varies from 0.2 to 0.8. The surface morphological studies show the very small, fine and hardly distinguishable grains smeared all over the surface. The material properties would be altered and excellently controlled by adiusting the system composition x.
Article
Full-text available
CdS and CdCO 3 thin films were grown onto glass by chemical bath deposition (CBD). The temperature of the bath (T d) was selected at 80°C and 20°C, respectively. CdCO 3 were annealed in at air atmosphere an normal pressure for 0.5 h. Scanning Electron Spectroscopy (SEM), X-ray diffraction (XRD), optical absorption (OA), measurements were carried out to characterize the layers. Using the SEM grown layers: T d = 80 °C concentration atomic: Cd = 49.10, S = 51.90, for T d = 20 °C, increase of carbon and oxygen: Cd = 12.8, C= 20.0, O = 67.2. CdCO 3 annealing thermal in atmosphere air: Cd = 49.8, O = 50.2. We analyzed the morphological of the films. Patterns XRD show that the layer with T d = 80 °C, CdS in Wurzite (W) phase. T d = 20 °C Peaks at 2 = [23., CdCO 3 which has rhombohedral crystalline. CdCO 3 annealing 120 °C completely disappeared and only peaks of CdO are identified. All of the peaks in this pattern has pure cubic phase of CdO: 2 = [33.1, 38.2, 55.3, 59.9. 69.3]. The average grain size (GS), calculated from the main XRD peak by CdCO 3 reduce of 30.5 nm reaching 12.8 nm respectively, was calculated by employing Scherer's formula. The forbidden band gap energy for: CdS E g = 2.48 eV, CdCO 3 E g = 3.87 eV, and CdCO 3 annealed (CdO) E g = 2.31 eV.
Article
The first laser diodes fabricated from wide‐band‐gap II‐VI semiconductors are demonstrated. These devices emit coherent light at a wavelength of 490 nm from a ZnSe‐based single‐quantum‐well structure under pulsed current injection at 77 K. This is the shortest wavelength ever generated by a semiconductor laser diode.
  • S Ninomiya
  • Adachi
. Ninomiya and S. Adachi, J. Appl. Phys. 78, 4681 1995.
  • D Kim
  • M V Klein
  • S F Ren
  • Y C Chang
  • H Luo
  • N Samarth
  • J K Furdyna
D. Kim, M. V. Klein, S. F. Ren, Y. C. Chang, H. Luo, N. Samarth, and J. K. Furdyna, Phys. Rev. B 49, 7262 1994.
  • S Nasibov
  • Yu V Korostelin
  • P V Shapkin
  • L G Suslina
  • D L Fedorov
  • L S Markov
S. Nasibov, Yu V. Korostelin, P. V. Shapkin, L. G. Suslina, D. L. Fedorov, and L. S. Markov, Solid State Commun. 71, 867 1989.
  • J J Shan
  • H Song
  • J K Luo
  • Furdyna
Shan, J. J. Song, H. Luo, and J. K. Furdyna, Phys. Rev. B 50, 8012 1994.