ZnTe Epitaxial Films Research Articles

Improved growth quality of epitaxial ZnTe thin films on Si (111) wafer with ZnSe buffer layer

To achieve high-quality and low-cost ZnTe epitaxial films, a low-temperature (LT, 200 °C) ZnSe buffer layer with a thickness of 5 nm was grown on Si (111) wafers prior to the epitaxy of ZnTe layers by molecular beam epitaxy. Reflection high-energy electron diffraction patterns reveal that ZnTe epilayers grown at 335 °C with a thickness of 100 nm on the LT-ZnSe buffer layer present a completely two-dimensional growth mode. Film surfaces present smooth and flat morphology with the lowest surface roughness of ∼2.2 nm at a Te/Zn beam equivalent pressure ratio of 1.6. X-ray diffraction θ-2θ scanning indicates that the out-of-plane structure of ZnTe films is highly preferred with the (111) growth orientation of ZnSe/Si. X-ray diffraction φ scanning further confirms that the in-plane structure of ZnTe epilayer is also a single-crystal orientation growth. Thus, high-quality ZnTe (111) single-crystal epilayer with the lowest full-width at half-maximum of ∼200 arc sec and the smallest dislocation density of ∼1.12 × 108 cm−2 was grown on Si (111) wafers. In addition, the ZnSe buffer layer could alleviate the residual stress effectively for the heteroepitaxy of Si wafers. The most balanced residual stress for ZnTe/ZnSe/Si with σx of ∼96.5 MPa and σy of ∼94.2 MPa was obtained, which is essential for achieving high-performance and good mechanical properties of ZnTe-based devices.

Observation of ultra-broadband terahertz emission from ZnTe films grown by metaloganic vapor epitaxy

ZnTe films were grown on (0001) sapphire substrates by the metalorganic vapor phase epitaxy (MOVPE) method. Single crystalline (111) ZnTe epitaxial layers were confirmed by x-ray diffraction, reflection high-energy electron diffraction, and cathodoluminescence measurements. Emission of THz radiation with a spectral distribution up to 40 THz was clearly observed from the ZnTe film with a thickness of 10 μm. The results show that MOVPE is a promising growth method for obtaining high-quality ZnTe epitaxial films on sapphire substrates, which paves the way for obtaining thinner ZnTe films to provide a flatter frequency response in THz device applications.

Optical properties of ZnTe films prepared by molecular beam epitaxy

In this paper, the optical properties of ZnTe epitaxial thin films prepared by molecular beam epitaxy (MBE) onto GaAs single crystal substrates are studied using the combined optical method employing a simultaneous interpretation of experimental data obtained by means of variable angle spectroscopic ellipsometry (VASE) and near-normal spectroscopic reflectometry (NNSR). The spectral dependences of both the optical constants, i.e. the refractive index and extinction coefficient, characterizing these films are presented within the spectral region 230–850 nm. It is shown that the optical properties of the ZnTe epitaxial films depend on the values of their thickness. This conclusion was found using the model of the optical constants exhibiting a profile across these films. A roughness of the upper boundaries of the ZnTe films and the existence of a very thin native oxide layer (NOL) on these boundaries are taken into account within the optical analysis.

Effect of a ZnSe buffer layer on the surface, structural, and optical properties of the ZnTe/ZnSe/GaAs heterostructures

Lattice-mismatched ZnTe epilayers on GaAs (1 0 0) substrates with and without ZnSe buffer layers were grown by using molecular beam epitaxy. AFM, XRD, and TEM measurements were performed to investigate the surface and structural properties of the ZnTe thin films. Photoluminescence, Raman scattering, and TEM measurements showed that the crystallinity of a ZnTe epilayer grown on a GaAs substrate was remarkably improved by using a ZnSe buffer layer. Photoreflectance measurements showed that the strain of the ZnTe layer with the ZnSe buffer layer was smaller than that without the ZnSe buffer layer. These results indicate that ZnTe epitaxial films grown on GaAs substrates with ZnSe buffer layers hold promise for potential applications in optoelectronic devices operating in the blue–green spectral region.

Strain dependence and deformation potential of the E1 and E1+ Δ1 transitions of ZnTe grown on a GaAs (001) substrate

ZnTe epitaxial films grown on GaAs (001) substrates with varying film thicknesses were investigated by spectroscopic ellipsometry (SE). As the epilayer thickness decreases, the interband-transition structures near 3.6 and 4.2 eV due to E 1 and E 1+ Δ 1 edges, respectively, shift gradually to higher energies and their energy splitting Δ 1 increases, indicating the increase in lattice-mismatch-induced strain with decreasing film thickness. The exact energies of the E 1 and E 1+ Δ 1 edges are obtained by a line-shape analysis of numerical second derivative spectra of the dielectric functions. From the strain dependences of the E 1 and E 1+ Δ 1 energies, the deformation potentials (DP), D 1 1 and D 3 3, at the L point of the Brillouin zone (BZ) are estimated.

Temperature dependence of exciton peak energies in ZnS, ZnSe, and ZnTe epitaxial films

High-quality ZnS, ZnSe, and ZnTe epitaxial films were grown on (001)-GaAs-substrates by molecular beam epitaxy. The 1s-exciton peak energy positions have been determined by absorption measurements from 2 K up to about room temperature. For ZnS and ZnSe additional high-temperature 1s-exciton energy data were obtained by reflectance measurements performed from 300 up to about 550 K. These complete E1s(T) data sets are fitted using a recently developed analytical model. The high-temperature slopes of the individual E1s(T) curves and the effective phonon temperatures of ZnS, ZnSe, and ZnTe are found to scale almost linearly with the corresponding zero-temperature energy gaps and the Debye temperatures, respectively. Various ad hoc formulas of Varshni type, which have been invoked in recent articles for numerical simulations of restricted E1s(T) data sets for cubic ZnS, are discussed.

On the nature of the luminescence centers in epitaxial films of zinc telluride

The luminescence properties of zinc telluride films are studied experimentally. The chemical nature of the luminescence centers of ZnTe epitaxial films is established.

XPS analysis of chemically etched II–VI semiconductor surfaces

X-ray photoelectron spectroscopy (XPS) was used to investigate the modification of the surfaces of ZnSe and ZnTe epitaxial films caused by HCl and NaOH cleaning. It was found that the HCl treatment successfully removed surface oxides but that the NaOH treatment did not. It was further found that the HCl treatment reduced the groupII/VI atomic ratios and promoted the formation of a group VI-rich surface.

Growth of ZnTe films by ionized cluster beam epitaxy at low temperature

Lattice-mismatched ZnTe(100) epilayers and highly (111)-oriented ZnTe film were grown on GaAs(100), Si(100), and glass substrates, respectively, by ionized cluster beam epitaxy at a growth rate of up to 1.2 nm s −1. From the analysis of X-ray diffraction and reflection high-energy electron diffraction, the grown layers were shown to be ZnTe epitaxial films. It was found that the crystalline quality of the epilayers depended on the substrate temperature. At a low substrate temperature of 300 °C, the optimum films on GaAs, Si and glass exhibit full width at half maximum (FWHM) values of X-ray rocking curves to be 110, 148 and 1417 arc sec, respectively.

Interfacial stages of the ZnTe/GaAs strained heterostructures grown by temperature-gradient vapor transport deposition at low temperature

A lattice-mismatched ZnTe epilayer on a GaAs (100) substrate was grown by the simple method of temperature-gradient vapor deposition. From the x-ray diffraction analysis, the grown layers were found to be ZnTe epitaxial films. The stoichiometry of the ZnTe films was investigated by Auger electron spectroscopy. Transmission electron microscopy measurements showed that there was a large lattice mismatch between the ZnTe epitaxial layer and the GaAs substrate. These results indicate that ZnTe epitaxial films grown on GaAs substrates at 320 °C have no significant interdiffusion problems, and that pseudomorphic, fully strained ZnTe layers are observed for deposits after ten molecular layers.

Preparation of ZnTe Epitaxial Films on CdS by Vapor Transport Method

Preparation of ZnTe Epitaxial Films on CdS by Vapor Transport Method