Orientation Of CdTe Research Articles

Study of Structural, Electrical and Optical Properties of (200)-Oriented CdTe Thin Films Depending on the Post-deposition Low Temperature

Cadmium telluride nanoparticles (CdTe NPs) have been synthesized by a sonochemical technique, deposited on glass and quartz glass at 100°C and 2.7 × 10−6 kPa and then studied by analyzing the x-ray diffraction (XRD), ultraviolet–visible spectroscopy (UV–Vis), current–voltage test (I–V) and scanning electron microscopy (SEM). The XRD results indicated the formation of a strong preferential (200) orientation of CdTe with a cubic zinc-blende structure on both substrates. In order to show the effect of heating on the structure and optical properties of the prepared thin films, they were annealed at temperatures of 50°C, 70°C and 100°C for 1 h. It was found that the grain size in this orientation increases with the increase of the temperature. In addition, the obtained optical band gap energies by UV–Vis measurements were in the range of 1.46–1.53 eV. The electrical properties of the prepared films were observed to increase with annealing using I–V measurements. The thin films were also found to be uniform with a small particle size, as revealed by SEM.

Specific features of the growth of A II B VI films on (0001)Al2O3 substrates

The structure and orientation of CdTe and ZnO films on sapphire have been investigated for different techniques of pregrowth substrate treatment. Polycrystalline CdTe films are found to grow of substrates unannealed or annealed in vacuum at a residual pressure P < 0.13 Pa. Epitaxial CdTe films with the sphalerite cubic structure, oriented parallel to the substrate by the (111) plane, grow on substrates annealed in air at a temperature of 1000°C or more and having a system of smooth terraces and steps on the surface. For ZnO films with a wurtzite hexagonal structure obtained by magnetron sputtering, a similar correlation between the structural quality and the regime of treatment of sapphire substrates is observed. It is shown that thermal annealing of (0001) sapphire plates in air is the optimal way of substrate preparation for growing epitaxial ZnO films with the base orientation. The obtained epitaxial CdTe films contain a certain amount of structural defects (mosaicity and twins), while the epitaixal ZnO films treated in the same way are close to perfect.

Metalorganic Vapor-Phase Epitaxial Growth of (211)B CdTe on (211) Si Using Ge Interfacial Layer

We have achieved metalorganic vapor-phase epitaxial growth of (211)B CdTe on Si without the requirement of a pregrowth high-temperature oxide desorption step. This was achieved by growing a thin Ge film on the starting (211) Si substrates. To get (211)B CdTe orientation, the Ge surface was exposed to As prior to the start of CdTe growth. A thin ZnTe interlayer between Ge and CdTe has been shown to improve the CdTe surface morphology.

X-Ray photoelectron spectroscopy study of CdTe oxide films grown by rf sputtering with an Ar–NH 3 plasma

CdTe oxide films were prepared on glass substrates using the rf-sputtering technique and a controlled plasma of Ar–NH 3. Films were studied by X-ray photoelectron spectroscopy and X-ray diffraction. The changes in chemical composition as a function of NH 3 partial pressure during deposition indicate that oxygen incorporates in the films up to approximately 62 at.%, while the Cd and Te contents decrease from ∼43 to 19 at.%. At NH 3 partial pressure of 1.3×10 −2 Pa, the Te–Cd bonds are strongly reduced and the Te in the films is mainly bonded to oxygen. The Cd MNN X-ray Auger feature shows a shift in energy of approximately 0.8 eV as a function of NH 3 partial pressure. This shift appears to be related to the change in Cd bonding from Cd–Te to Cd–O. Films prepared at NH 3 partial pressure of 4×10 −4 Pa present crystallinity with a [111] cubic CdTe orientation, while those prepared at higher NH 3 partial pressure show an amorphous structure. The amorphous material formed at NH 3 partial pressure saturation appears to be mainly amorphous CdTeO 3.

Effect of growth temperature on the orientation of CdTe on GaAs prepared by molecular beam epitaxy

CdTe films were grown on (211) A GaAs and (211)B GaAs substrates by molecular beam epitaxy in a wide range of growth temperature. X-ray double crystal rocking curves were used to analyze the quality and orientation of the epitaxial films. Our experiments provethat the growth temperature has a great effect on the quality and orientation of the epitaxial CdTe films: T sub < 280 °C, CdTe(133)‖GaAs(211)A; T sub > 280 °C, CdTe(211)‖GaAs(211) A. For (211) B GaAs, the orientation of CdTe changes at 295 °C. An explanation is given of this result by considering the lattice mismatch and interface energy.

Mechanism of different orientation of CdTe on GaAs by molecular beam epitaxy

CdTe films have been grown on (001) GaAs substrates by molecular beam epitaxy in a wide range of growth temperature. X-ray double crystal rocking curve has been used to analyze the quality and orientation of the epitaxial films. Our experiments prove that the growth temperature has a great effect on the quality and orientation of the epitaxial CdTe films: Tsub&amp;lt;300 °C, CdTe (111)∥GaAs (001); Tsub≳300 °C, CdTe (001)∥GaAs (001). An explanation is given for this result by considering the lattice mismatch and interface energy.

CdTe/GaAs/Si substrates for HgCdTe photovoltaic detectors

CdTe epitaxial films have been grown on GaAs on (100) silicon by congruent evaporation on CdTe in ultrahigh vacuum. The (100)CdTe orientation is strongly preferred in growth on (100)GaAs/Si, in contrast with the (111)CdTe preference on (100)GaAs substrates. Growth of the (111) orientation requires special processing. The (100)GaAs epilayer grows on misoriented (100)Si with a lattice tilt of ∼0.04° (back toward normal) for each degree of silicon misorientation. A similar lattice tilt in CdTe growth, in combination with the variable misorientation of the three-dimensional as-grown GaAs epilayer, is probably responsible for a mosaic structure in CdTe epilayers on GaAs/Si. In (111)CdTe layers, rotational twinning can occur on unpolished GaAs/Si. With increasing GaAs/Si misorientations, increasing numbers of (100) twin inclusions can also be found. Chemical polishing prior to CdTe growth eliminates the mosaic and twinning problems in most cases.

Epitaxial growth of II–VI compounds on sapphire substrates

CdTe has been grown on sapphire and used as a hybrid substrate material for the epitaxial growth of Cd x Hg 1− x Te using an exclusively MOVPE process. A relationship was established between the CdTe orientation with respect to that of the sapphire substrate, with the extent of the CdTe rotation being related to the degree of sapphire misorientation. The crystal quality of the epitaxial CdTe films were found to be dependant upon growth parameters with optimum improvements occurring at higher pre-bake and growth temperatures. Best FWHM values found in this study were 1.6 arc min. The CdTe layer could be deposited in either the (111)A or (111)B orientation with the (111)A material exhibiting the better FWHM values. CMT can be grown onto the CdTe/sapphire material in the same growth run as the CdTe layer. Some preliminary data is reported upon the characteristics of this material.

(100) and (111) oriented superlattices of (Cd,Mn)Te on (100)GaAs

Previously reported (111) oriented superlattices of the (Cd,Mn)Te system on (100)GaAs have exhibited unusual exciton properties speculated to be related to characteristics of the (111) heterointerface. The epitaxial growth of both (111) oriented and (100) oriented CdTe on (100)GaAs provides an opportunity to investigate effects of orientation on the optical properties of these (Cd,Mn)Te superlattices. Techniques for the growth of (100) oriented superlattices on (100)GaAs by three different growth methods for the selection of the (100) orientation of CdTe are described. Significant differences in the optical properties of superlattices grown with the two orientations are shown, with emphasis on photoluminescence and excitation spectra.