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The thermal ionization energy ET of DX centers in AlxGa1-xAs and its dependence with the value of x and the pressure are very important for estab- lishing the model of DX centers. The conventional DLTS and Hall methods used to DX center measurement have some ambiguities in theoretical analysis and experiments and the values of ET determined are different with those methods. The new constant temperature transient C-V measurement is based on the fact that at low temperature both electron capture and emission rates of DX centers are very slow. During the transient C-V measurement, change; of bias voltages and capacitance measurements are completed in a time duration much shorter than the electron capture and emission time constants, therefore the electrons occupied on the DX centers are considered to be frozen. The density of DX centers, the distribution profile of electrons on DX centers in the depletion region of a Schottky diode at a constant reverse bias, and the density of free electrons in conduction band in the bulk and their temperature dependence have been measured. 相似文献
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A new electron trap state SD was found by DLTS measurement under light illumination in Si doped A.lxGa1-xAs. This new trap energy level ESD is shallower than the DX center energy in the gap and the concentration of SD is comparable to that of DX centers. The emission activation energy Ec=0.20±0.05eV and capture activation energy Ec= 0.17±0.05eV. The SD DLTS peak has never been detected previously because under dark and thermal equilibrium condition most of the electrons occupy the deeper DX states and most of SD states are empty. However, when the sample is illuminated by light, electrons are excited to the conduction band and then re-captured by SD since the deeper DX states have a slower electron capture rate, thus a new DLTS peak corresponding to SD appears. Constant temperature capacitance transient C-t and transient C-V measurements were also used to further confirm the existence of SD states. 相似文献
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The self-consistent pseudopotential calculation method is used in ab initio calculations of quasiparticle energies for semiconductors with particular attentions paid to GaAs. Although having highly accurate for ground state properties the traditional Density Functional Theory for calculations of many electron systems is not very reliable when applied to excited states. The long standing proble mof underestimations of ab initio calculated energy band gaps for semiconductors and insulators is well known. For Si, Ge and GaAs, e.g., the first principle pssudopotential calculations yield band gaps of 0.52eV, 0.07eV and 0.461eV, respectively, as compared with the experimental measurements of 1.17eV, 0.744eV and 1.51eV. When taking quasiparticle self-energies into account, the excitations (quasiparticle energies) of the many electron systems can be accurately described. The lowest calculated excitation energies above tin highest occupied levels are accurate to within a few percent of experimental band gaps. We have performed ab initio quasiparticle energy calculations for GaAs; our calculated energy band gap Eg= 1.524eV is in excellent agreement with experiments. In Green's function approach GW approximation is utilized, and Generalized Plasma Pole model is used to obtain dynamical dielectric matrix. 相似文献
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A diagram representation method is proposed to interpret the complicated charge pumping(CP) processes. The fast and slow traps in CP measurement are defined.Some phenomena such as CP pulse rise/fall time dependence, frequency dependence,the voltage dependence for the fast and slow traps,and the geometric CP component are clearly illustrated at a glance by the diagram representation.For the slow trap CP measurement,there is a transition stage and a steady stage due to the asymmetry of the electron and hol... 相似文献
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