CdTe ZnTe Research Articles

InSbZn xCd 1−xTe photosensitive thin-film mis-structures

The results of C- V and G- V measurements of InSb-based thin-filmstructures on high resistivity ZnTeCdTe are presented. It was shown that the density of surface states N ss is within the range of (1.5–3)×10 9 cm −2 eV −1 at 4.2 K. A photomemory effects is seen, resulting from the device capacitance under illumination.

Optical absorption study of MOCVD grown CdTeZnTe superlattices

The absorption spectra of MOCVD grown CdTeZnTe superlattices were studied at different temperatures in the range of 300 to 15 K. Superlattices with periods varying between 30 and 80 Å and CdTe well thicknesses between 12 and 46 Å were measured. The lowest absorption band detected is assigned to a transition to the first confined state. A second distinct absorption line assigned to a transition to the second confined energy level can be seen for samples with a well width exceeding 25 Å. The experimental results are found to be reasonably well fitted to the energies calculated using the Kronig-Penney model, disregarding strain.

Growth and characterisation of ZnTe and ZnTeCdTe superlattices on GaAs substrates

Epitaxial layers of ZnTe and CdTeZnTe superlattices have been grown by atmospheric pressure MOVPE on {;100}; GaAs substrates and characterised by RHEED, SEM and TEM. Although they are of high crystal quality, the ZnTe layers exhibit a characteristic ridged morphology due to anisotropic facetting. These layers are found by TEM to contain a high density of misfit dislocations extending throughout a 2 μm thick layer. In contrast, CdTeZnTe superlattices grown under the same conditions are shown to have a much improved surface morphology but with a characteristic assymetric rectangular network of slip traces and cracks. These are attributed to the thickness of the CdTe layers and the high growth temperature causing the strain in the system to be largely relieved.

Observations of structural deviations in MBE grown II–VI superlattices

X-ray diffraction analyses of HgTeCdTe and CdTeZnTe superlattices (SL's) have revealed a few exceptional samples possessing complex satellite structures that cannot be attributed to a single modulation period of one specific average composition. All of the examined SL's were grown, by molecular beam epitaxy (MBE), to have one well-defined period. Four of these unique SL's are reviewed and the observed deviations with respect to a single period SL model are illustrated. The SL samples are characterized by several diffraction techniques. Extended x-ray ω − 2θ scans were performed with the scattering vector along the SL growth direction. These scans were complemented by ω scans to assess the lateral coherence of the diffracting planes. The complex diffraction spectra suggest that several SL regions coexist within one macroscopic sample. Differences in the period and average composition distinguish each domain by observing the satellite spacing and central peak position, respectively.

Calculation of the valence band offsets of common-anion semiconductor heterojunctions from core levels: The role of cation d orbitals

The valence band offsets of the common-anion CdTe–HgTe, CdTe–ZnTe, ZnTe–HgTe, and GaAs–AlAs semiconductor pairs are calculated from the core level energies. The good agreement obtained with experiment for lattice-matched systems and a simple electrostatic model analysis suggest interface dipoles to have only a small effect. Furthermore, the microscopic origin of the failure of the common-anion rule in lattice-matched systems is identified: it is found that participation of cation d orbitals (neglected by tight-binding and pseudopotential approaches alike) in the valence band maxima is responsible for much of the band offset in these systems.

Trap Depth at the Interface of CdTe–ZnTe Heterojunctions

A study of the spectroscopy of deep levels has been made through measurements of complex admittance and also by the thermally-stimulated capacitance (TSCAP) method at the interface of CdTe–ZnTe heterojunctions in which epitaxial layers of ZnTe were grown on the Cd and Te planes of n-CdTe single crystals. The complex admittance measurements show that right from the shallow levels of about 0.12 eV, as many as four trapped levels exist, with the deepest level being around 1 eV. Also, the TSCAP measurements show the existence of two levels at 0.28 eV and 0.6 eV. These values agree well with the admittance spectroscopy results. The mechanisms and causes of the experimental results are discussed in this paper.

Reflectivity Spectra and Band Structure of the ZnTe–CdTe System

AbstractThe reflectivity spectra of ZnTe:Cs, ZnTe:Ga2O3, and ZnxCd1−xTe crystals (x = 0.0, 0.2, 0.4, 0.5, 0.6, 0.7, 0.8, 1.0) in the range 1 to 12.5 eV at 293 K and in the range 1 to 5.5 eV at 90 K are investigated. The experimental results obtained prove the hypothesis about a great detailed similarity of ZnxCd1−xTe band structures in a wide energy range and the existence of a straightline dependences of interband transition energies on molar composition. A strong effect of fresh cleavage and impurities on the reflectivity spectra is detected.

Thermodynamics and Calculation of the Liquidus-Solidus Gap in Homogeneous, Monotonic Alloy Systems

A general expression for the thermodynamic relationship between liquidus and solidus equilibrium compositions is derived for systems which are nonideal but homogeneous and monotonic. For a number of typical systems, the nonideal term in this expression is found to be very small, thus indicating that the ideal form of the general expression can be used to calculate one of the boundaries of the two-phase field when the other one and the enthalpies of fusion of the pure components are known. For many of the systems examined (InAs–GaAs, InSb–InAs, InSb–GaSb, GaSb–AlSb, InSb–AlSb, CdTe–ZnTe, CdTe–CdSe, HgTe–CdTe, GeTe–MnTe, PbBr2–PbCl2), the solidus curves calculated by this method are in good to excellent agreement with the published experimental values; for the Ag–Au, InAs–InP, SnTe–PbTe, and PbTe–PbSe systems they confirm the results of the more recent and more dependable investigations; for the Cu–Ni, Ge–Si and HgTe–HgSe systems however, they suggest the need for a critical reevaluation of the presently available data. In the absence of pertinent experimental data, calculated solidus and liquidus curves, respectively, are also presented for the ZnTe–ZnSe and HgTe–ZnTe systems.

On the absorption spectra of the sulphides of zinc, cadmium, and mercury from λ 7000-1900, and the heat of dissociation of sulphur

The sulphides of zinc, cadmium, and mercury form part of the following series of diatomic compounds:- ZnO CdO HgO ZnS CdS HgS ZnSe CdSe HgSe ZnTe CdTe HgTe which are all chemically similar. One of the constituents of these substances has a positive and the other a negative electrovalency of two:- positive electrovalency of two- Zn, Cd, Hg. negative electrovalency of two-O, S, Se, Te.