The photoluminescence (PL) spectra of Mg-doped GaN on sapphire have been measured at 12K. The residual strain induced by the mismatch of the lattice constants and thermal expansion between GaN epilayers and substrates have been investigated by micro-Raman scattering and x-ray diffraction. Redshifts of the ultraviolet PL bands were observed in Mg-doped GaN after annealing in nitrogen ambient, which may be related to the carrier concentration and the strain in the epilayers. For heavily Mg-doped GaN films, the hole concentration in GaN, which shifts the PL peaks, is the dominant influence, whereas the strain is comparatively secondary.
A novel characteristic of the junction current drift effect in the Cu/porous silicon (Cu/PS) device prepared by electrodeposition in which Cu ions were deposited on porous silicon is reported. The junction current increases with time and gradually approaches to a saturated value when a certain forward bias is applied on the Cu/PS device. Moreover, after the bias was withdrawn for a period, a different drift process was observed when the same bias was applied again. The drifttime constant and the initial current of latter drift process depend on cut-off time. Such an effect is explained in terms of the model that only part of electrons from porous silicon contributes to the junction current while other electrons are captured by the traps in the interface between Cu and porous silicon in the Cu/PS device.* Supported by the National Natural Science Foundation of China under Grant No. 59372108.@by the Chinese physical societyNo. 2 WANG Guan-zhong et al.
Two kinds of Cu substrates were used to grow diamond films,one of them being 99.99% polycrystalline Cu foil and the other 99.95% phosphorus deoxidized Cu foil.Large-area,free-standing polycrystalline diamond films were obtained by hot filament CVD on both substrates.The diamond films on the two kinds of Cu substrates were comparatively investigated by high resolution optical microscopy,scanning electron microscopy,Raman spectroscopy,and X-ray diffraction.The quality of films on deoxidized Cu are not worse than that on polycrystalline Cu,while the nucleation densities ,growth rate and stress in film on deoxidized Cu is higher than those on polycrystalline Cu.It is indicated that the annealing process and optimized growth conditions must be used to obtain large-area continuous diamond films.
Synchrotron radiation photoelectron spectroscopy is used to measure the valence-band offsets for Si/ZnS(111) and (100) heterojunctions. The valence band discontinuities obtained from the measurements are both (1.9±0.1)eV for Si/ZnS(111) and Si/ZnS(100) interfaces,which is in excellent agreement with the theoretical predictions but considerably different from the experimental- result of ZnS/Si(111) reported by Maierhofer et al. This suggests that the commutativity rule of- band offset may not be valid for Si/ZnS polar interface and the reason is discussed.
The scattering of phonons as main factors infuencing the thermal conductivity were analized theoretically. The thermal conductivity of diamond films was measured by means of the photothermal deflection method with an error of 5%. The effects of methane concentration and grain orientation on thermal conductivity of diamond films were studied. The results showed that (100) oriented diamond-films deposited by microwave plasma chemical vapour deposition method under low methane concentration have higher thermal conductivity.
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