Xu Peng-Shou

Electronic structure of ZnO and its defects

The electronic structure of ZnO and its native point defects has been calculated using full potential linear Muffin-tin orbital ( FP-LMTO) method for the first time. The results show that Zn3d electrons play an important role in the bonding of ZnO. Vacant Zn (Vzn) and interstitial O (Oi) produce the shallow acceptor levels at 0.3 eV and 0.4 eV above the top of the valence band (VB), while interstitial Zn (Zni) produces a shallow donor level at 0.5 eV bellow the bottom of the conduction band (CB). However, Vacant O (Vo) produces a deep donor level at 1.3 eV below the bottom of CB. On the basis of these results, we confirm that Zni is the main factor to induce the native n-type conductivity in ZnO

Native Point Defect States in ZnO

The native point defect states in ZnO have been calculated by using a full-potential linear muffin-tin orbital method. The results show that Zn vacancy and O interstitial produce the shallow acceptor levels above the valence band. The O vacancy produces a deep donor level, while Zn interstitial produces a shallow donor level, both below the conduction band. The Zn interstitial is the main factor which induces the native n-type conductivity in ZnO.

A FP–LMTO study on the native shallow donor in ZnO

Abstract First-principle calculations are performed on ZnO:V O , ZnO:V Zn and ZnO:Zn I using a FP–LMTO (full potential linear muffin-tin orbital) method. The results prove that the Zn I is the dominant donor in ZnO, and V Zn , a shallow acceptor, while V O is a deep donor.

In situ high temperature X-ray diffraction studies of ZnO thin film ∗

An epitaxial ZnO thin film was entirely fabricated by pulsed laser deposition. Both the orientation and the size of the crystallites were studied. The X-ray diffraction (XRD) patterns of the film show strong c-axis oriented crystal structure with preferred (002) orientation. The Phi-scan XRD pattern confirms that the epitaxial ZnO exhibits a single-domain wurtzite structure with hexagonal symmetry. In situ high-temperature XRD studies of ZnO thin film show that the crystallite size increases with increasing temperature, and (002) peaks shift systematically toward lower 2θ values due to the change of lattice parameters. The lattice parameters show linear increase in their values with increasing temperature.

Epitaxial Growth of Graphene on 6H-SiC (0001) by Thermal Annealing

An epitaxial graphene (EG) layer is successfully grown on a Si-terminated 6H-SiC (0001) substrate by the method of thermal annealing in an ultrahigh vacuum molecular beam epitaxy chamber. The structure and morphology of the EG sample are characterized by reflection high energy diffraction (RHEED), Raman spectroscopy and atomic force microscopy (AFM). Graphene diffraction streaks can be seen in RHEED. The G and 2D peaks of graphene are clearly observed in the Raman spectrum. The AFM results show that the graphene nominal thickness is about 4−10 layers.

Growth of Few-Layer Graphene on Sapphire Substrates by Directly Depositing Carbon Atoms

Few-layer graphene (FLG) is successfully grown on sapphire substrates by directly depositing carbon atoms at the substrate temperature of 1300°C in a molecular beam epitaxy chamber. The reflection high energy diffraction, Raman spectroscopy and near-edge x-ray absorption fine structure are used to characterize the sample, which confirm the formation of graphene layers. The mean domain size of FLG is around 29.2 nm and the layer number is about 2–3. The results demonstrate that the grown FLG displays a turbostratic stacking structure similar to that of the FLG produced by annealing C-terminated α-SiC surface.

Graphene films grown on sapphire substrates via solid source molecular beam epitaxy

A method for growing graphene on a sapphire substrate by depositing an SiC buffer layer and then annealing at high temperature in solid source molecular beam epitaxy (SSMBE) equipment was presented. The structural and electronic properties of the samples were characterized by reflection high energy diffraction (RHEED), X-ray diffraction Φ scans, Raman spectroscopy, and near edge X-ray absorption fine structure (NEXAFS) spectroscopy. The results of the RHEED and Φ scan, as well as the Raman spectra, showed that an epitaxial hexagonal α-SiC layer was grown on the sapphire substrate. The results of the Raman and NEXAFS spectra revealed that the graphene films with the AB Bernal stacking structure were formed on the sapphire substrate after annealing. The layer number of the graphene was between four and five, and the thickness of the unreacted SiC layer was about 1–1.5 nm.

A novel sulfur-passivation method and magnetic overlayers on passivated III–V semiconductor surface

Abstract A sulfur passivation method for GaAs, CH3CSNH2 treatment has been developed. It is quite effective for removing the surface oxide layer and forming the sulfide passivation layer on GaAs surface, with sulfur atoms bound with Ga and As atoms. After being annealed, a stable sulfur passivation layer is formed. The enhancement of PL intensity reveals the reduction of surface non-radiative recombination and the density of surface states. Moreover, the investigation has been made for the role of S-passivation on interfacial interaction between magnetic overlayer and GaAs. The interdiffusion of As, Ga into overlayer is effectively inhibited, and the magnetization of Fe overlayers is enhanced. In addition, a relationship has been found between the surface chemical structure of the substrates and the magnetic property of overlayers.

PHOTOEMISSION-STUDIES OF K-PROMOTED NITRIDATION OF INP(100) SURFACE USING SYNCHROTRON-RADIATION

The effect of molecular nitrogen exposure on the surfaces of InP(100) modified by potassium overlayers is investigated by core-level and valence-band photoemission spectroscopy using Synchrotron radiation. In comparison with InP(110) surface, we found the promotion is much stronger for InP(100) surface due to the central role of surface defects in the promotion; furthermore, in contrast with K-promoted oxidation of InP(100) where the bonding is observed between indium and oxygen, indium atoms did not react directly with nitrogen atoms during the K-promoted nitridation of InP(100).

Effect of Growth Temperature on the Band Lineup of Ge/CdTe(111) Polar Interfaces

By using synchrotron radiation photoelectron spectroscopy, the band lineup of Ge/CdTe(111) interfaces grown at different temperatures have been measured. Experimental studies show that the valence band offset of Ge/CdTe(111) interface grown at room temperature is 0.88?0.1 eV, which agrees well with previously reported value. While as for the interface grown at 280?C, an obvious reduction of valence band offsets is observed and attributed to the effect of different interface dipole.