Papers by Author: Y.D. Zheng

Abstract: The Ge mole fraction (x) of Si_1-xGe_x layer was described by the C-V technique for Schottkey contact of single heterojunction Si_1-xGe_x/Si, whose structure profile can be characterized by SEM image and EDS. Then the strained Si cap layer was grown on the Si_1-xGe_x/Si, and C-V technique was used to determine the carrier concentration and structure of double heterojunction Si/Si_1-xGe_x/Si. The change of the structure between Si_1-xGe_x/Si and Si/ Si_1-xGe_x/Si was also observed by this method.

Abstract: The MOCVD-growth and annealing of InN films have been studied in this work. The XRD spectra of InN films grown at 350 °C~500 °C indicate that the diffraction of In increases with increasing the growth temperature to 425 °C and the temperature higher than 425 °C causes the decrease of In diffraction. The corresponding SEM images show that In grains disappear from the surface as the growth temperature is higher than 425 °C. These are attributed to the increase of the desorption of In with the growth temperature. In addition, the SEM images of the annealed InN films also show that the In grains decrease gradually as the annealing temperature is higher than 425 °C. Thus, it is concluded that the desorption of In is the main process as the temperature is higher than 425 °C.

Abstract: In this paper we have characterized the performance of a vertical metalorganic chemical vapor deposition (MOCVD) reactor used for deposition of ZnO thin films. The equations of the mathematical model are solved numerically using a control-volume-based finite difference method. A two-dimensional model is put forward to study the dependence of the growth rate on the inlet flow rate and susceptor temperature. The mass-fraction distribution of the reactants has been studied as a function of the position above the substrate, which shows that gas phase pre-reaction in our reactor is well confined. The simulation results are useful for the practical growth of ZnO.

Abstract: The morphology evolution of ZnO films grown on sapphire (0001) by MOCVD have been studied as a function of buffer growth time and temperature by means of atomic-force microscope (AFM), x-ray diffractions (XRD) and optical microscopy. When the buffer growth temperature decreased to 450°C, the surface became smooth greatly, indicating the transition from typical 3D island growth to quasi-2D growth mode. As the buffer growth time exceeds 5min, the micron-sized pit-like features are formed. It is due to the lack of stabilization of adatoms under the “etching” action of ionized O2/Ar during high temperature buffer annealing

Abstract: The weak-localization of the two-dimensional electron gas (2DEG) in a modulation-doped Al0.22Ga0.78N/GaN single quantum well has been investigated through the magnetoresistance measurements. The elastic scattering time τε, dephasing time τφ and spin-orbit(s-o) scattering time τso at various temperatures are obtained. The fitting parameters indicate that the inelastic scatterings to the 2DEG are mainly due to the piezoelectric field and the alloy disorder in the AlxGa1-xN barrier. When the second subband in the triangular quantum well at the heterointerface is occupied by the 2DEG, the anti-weak localization is observed clearly, which is due to the strong spin-orbit interaction. The spin-orbit effect dominates the quantum correction of the conductivity in the upper subband. The intersubband scattering becomes stronger with increasing temperature.

Abstract: Infrared reflectivity measurements of GaN1-xPx alloys and quantitative fittings using Lorentz model have been carried out. In the GaN1-xPx alloys, two competitive mechanisms that determine the carrier concentration have been put forward. The one is from the effect of the isoelectronic traps which decrease the carrier concentration while the other is from the effect of defects which increase the carrier concentration. The calculated results of imaginary part of the elastivity of GaN and GaN1-xPx alloys show that the longitudinal optical phonon-plasmon (LPP) modes shift to high frequency direction and its linewidth gradually broadens with increasing carrier concentration in GaN1-xPx, indicating that the coupling of LPP modes gradually enhances and the damping of LPP modes gradually augments.