Zha Gangqiang

Atomic and Electronic Structures of Cd0.96Zn0.04Te(110) Surface

X-Ray diffraction is used to analyse the lattice structure of Cd0.96Zn0.04Te (CZT), and the lattice constant is measured to be 0.647 nm. The atomic structure of the clean CZT(110) surface obtained by Ar+ etching in vacuum is observed by low-energy electron diffraction, where no surface reconstruction is discovered. Angle-resolved photoemission spectroscopy was used to characterize the surface state of the clean CZT (110) surface, by which we find a 1.5-eV-wide surface band with the peak at 0.9 eV below the Fermi energy containing about 6.9×1014 electrons/cm2, approximately one electron per surface atom.

In-Situ SRPES Study on the Band Alignment of (0001)CdS/CdTe Heterojunction

The band alignment of a (0001)CdS/CdTe heterojunction is in situ studied by synchrotron radiation photoemission spectroscopy (SRPES). The heterojunction is formed through stepwise deposition of a CdTe film on a wurtzite (0001)CdS single crystalline substrate via molecular beam epitaxy. CdS shows an upward band bending of 0.55 eV, the valence band offset ΔEV is calculated to be 0.65 eV and the conduction band offset ΔEC is 0.31 eV. The interfacial band alignment is sketched to display type-I band alignment.

Effect of de-trapping on carrier transport process in semi-insulating CdZnTe*

The effect of de-trapping on the carrier transport process in the CdZnTe detector is studied by laser beam-induced transient current (LBIC) measurement. Trapping time, de-trapping time, and mobility for electrons are determined directly from transient waveforms under various bias voltages. The results suggest that an electric field strengthens the capture and emission effects in trap center, which is associated with field-assisted capture and the Poole–Frenkel effect, respectively. The electron mobility is calculated to be 950 cm2/Vs and the corresponding electron mobility-lifetime product is found to be 1.32×10−3 cm2/V by a modified Hecht equation with considering the surface recombination effect. It is concluded that the trapping time and de-trapping time obtained from LBIC measurement provide direct information concerning the transport process.

Electronic structure and optical properties of monoclinic HfO2 with oxygen vacancy

Abstract The electronic structure and optical properties of monoclinic HfO 2 ( m -HfO 2 ) with the consideration of oxygen vacancy were calculated using the plane-wave ultrasoft pseudopotential method based on the first-principles density functional theory (DFT). The results reveal that a new defect level at the conduction band edge is introduced for the defective m -HfO 2 , and the 5d states of Hf atoms nearest to the oxygen vacancy make significant contribution to it. Furthermore, the dielectric functions and absorption coefficients of the perfect and defective m -HfO 2 were calculated and analyzed by means of the electronic structures, which were related to the defect levels. The calculated absorption coefficient shows that m -HfO 2 with oxygen vacancy exhibits an absorption band in the ultraviolet region.

XAFS and XRD Studies of the Cd1-xZnxTe Crystal Fine Structure

Cd1−xZnxTe crystal is a new kind of room temperature semiconductor radiation detector material developed in recent years. Cd1−xZnxTe is zinc-blende structure, which is similar to CdTe, but the fine structure of Cd1−xZnxTe ternary compound semiconductor is different from CdTe and ZnTe binary compound semiconductors. In this contribution, the fine structure of Cd1−xZnxTe has been studied by the synchrotron radiation X-ray absorption fine structure (XAFS) technology and X-ray diffraction (XRD) technology. The K-edges XAFS spectra of cadmium, zinc and tellurium in Cd1−xZnxTe have been obtained, and the differences between the structures of binary and ternary compound crystals have also been analyzed. The Fourier transform of the k2-weighted absorption spectra prove that Zn atoms occupy the position of the Cd atoms. The bond lengths of Cd1−xZnxTe have also been obtained by extended X-ray absorption fine structure (EXAFS), and the results imply that the local atomic structure of Cd1−xZnxTe is distorted. The doping of Zn in the structure contributes to the distortion, which should be responsible for the different properties in Cd1−xZnxTe. Normalized X-ray absorption near-edge structure (XANES) spectra on Cd K-edge, Zn K-edge and Te K-edge in CdTe, Cd0.96Zn0.04Te, Cd0.9Zn0.1Te and ZnTe are also shown.

Charge transport performance of high resistivity CdZnTe crystals doped with In/Al

To evaluate the charge transport properties of as-grown high resistivity CdZnTe crystals doped with In/Al, the α particle spectroscopic response was measured using an un-collimated 241Am (5.48 MeV) radioactive source at room temperature. The electron mobility lifetime products (μτ)e of the CdZnTe crystals were predicted by fitting plots of photo-peak position versus electrical field strength using the single carrier Hecht equation. A TOF technique was employed to evaluate the electron mobility for CdZnTe crystals. The mobility was obtained by fitting the electron drift velocities as a function of the electrical field strengths, where the drift velocities were achieved by analyzing the rise-time distributions of the voltage pulses formed by a preamplifier. A fabricated CdZnTe planar detector based on a low In concentration doped CdZnTe crystal with (μτ)e = 2.3 × 10−3 cm2/V and μe = 1000 cm2/(V s), respectively, exhibits an excellent γ-ray spectral resolution of 6.4% (FWHM = 3.8 keV) for an un-collimated 241Am @ 59.54 keV isotope.