Xiancun Cao

Radiative recombination characteristics in GaAs multilayer n+−i interfaces

In this communication, we have carried out a detailed investigation of radiative recombination in n-GaAs homojunction far-infrared detector structures with multilayer emitter (n(+))-intrinsic (i) interfaces by temperature-dependent steady-state photoluminescence measurements. The observation of the emitter-layer luminescence structures has been identified from their luminescence characteristics, in combination with high density theoretical calculation. A photogenerated carrier transferring model has been proposed, which can well explain the dependencies of the luminescence intensities on the laser excitation intensity and temperature. Furthermore, the obtained radiative recombination behavior helps us to offer a proposal to improve the operating temperature of the detector

The effect of low-temperature annealing on ferromagnetic Ga1−xMnxAs thin films studied by photoemission spectroscopy

A systematic photoemission and variable temperature resistivity measurements are carried out on Ga0.946Mn0.054As ferromagnetic semiconductors. It is showed that the Mn 3d valence band and the As 3d core-level spectrum are modified by the annealing treatment. Correlating these modifications with the observed changes in the resistivity and Curie temperatures, we have identified that the low-temperature annealing most likely induces three changes: interstitial Mn out-diffusion, slight increase of the substitution Mn components, and reduction of excess As.

Systematic study of anisotropic magnetoresistance effect in (311)A GaMnAs films

Anisotropic magnetoresistance effect has been studied systematically in (311)A-oriented as-grown and annealed GaMnAs films at different temperatures. Besides a uniaxial term, the measured angular dependence of longitudinal and transverse magnetoresistivities contains higher order terms arising from the crystal symmetry of GaMnAs. A third order crystalline term accounts for the observed antisymmetric planar Hall effect which is intrinsic to (311)A-oriented GaMnAs films. The uniaxial term persists above the Curie temperature, while the higher order terms can only be observed below the Curie temperature, with their magnitudes increasing with decreasing temperatures. It is revealed that the higher order crystalline terms originate from the long range ferromagnetic (FM) phase and the uniaxial one from isolated magnetic polarons (MPs) as well as the FM phase. With decreasing temperatures, the dominant contribution to the uniaxial term changes from isolated MPs to the FM phase. In addition, low temperature annea...

Threading dislocations related persistent photoconductivity effect in hydride vapor phase epitaxy grown GaN epilayers

Deep-level defect-related properties of as-grown and annealed GaN epilayers grown by hydride vapor phase epitaxy (HVPE) are investigated using persistent photoconductivity (PPC) and photoluminescence (PL) measurements. PPC phenomena are seen in these HVPE-GaN epilayers which do not contain the yellow-luminescence (YL) band, suggesting that PPC and YL phenomena are not related. The PPC decay kinetics indicates that the characteristic of the defects which are responsible for the PPC phenomenon would be different from the point defects. The structural qualities of these HVPE-GaN epilayers were characterized by X-ray diffraction. As the densities of threading dislocations decrease, a decrease of photocurrent was clearly observed. The results suggest that the negatively charged threading dislocations are the candidate for PPC effect in our HVPE-GaN epilayers.

Interface dipole formation between GaMnAs and organic material

The interface band alignment between GaMnAs and organic material was investigated by current transport measurement in hole only devices with GaMnAs/NPB/Al structure. The current density – voltage (J-V) curves were measured and numerical simulations performed on this device structure yielded the hole injection barrier between GaMnAs and NPB to be 0.77 eV. A vacuum level shift at GaMnAs/NPB interface was deduced as 0.54 eV, indicating a dipole layer across the interface. We attributed the vacuum level shift to the charge transfer across the interface.

Study of the transport properties of annealed (Ga,Mn)As by x-ray absorption spectroscopy

A systematic Mn L-edge x-ray absorption is carried out on carefully prepared Ga0.946Mn0.054As ferromagnetic semiconductors with varying As2∕Ga flux ratio. It is found that the L3 peak of the absorption spectroscopy is enhanced after low temperature (LT) annealing. Furthermore it is shown that a more localized electronic structure nearly like the d5 high-spin state is obtained. It can be attributed to breaking the MnS–MnI pairs during the annealing process. Furthermore the authors present a direct evidence for a slightly increase of the Mn substitutional concentration due to LT annealing.