The geometrical structure of GaN (0001) surfaces supercell of GaN was optimized by using the ultra-soft
pseudopotential method of total-energy plane wave based on the density functional theory (DFT) .Electronic structure,
Density of states , band structure and optical properties were calculated and discussed in detail.Geometry optimization
indicates that largest atomic relaxation occurs to metal atoms(Ga) in surface layers where all atoms are displaced
inward,and the interlayer distances vary large, total polarization strength is strong. The band gap of GaN (0001) surface
is obviously narrower than that of GaN, the luminescence spectra shift red.The two aspects go against making high
efficiency white-light LED.This paper provides theoretical foundation of GaN (0001) surface and the direction fo making
high efficiency white-light LED form first-principles calculation.
Light can emit from light emitting transistor of III-V materials. The pn-n+ structure of light emitting
transistor, which has an additional n-n+ heterojunction between the base and electron emitter, is suggested.
The base voltage can control the light output effectively. The functional principle of light emitting transistor is
illuminated. A model about the abrupt isotype heterojunction in the base has been utilized to describe
thermionic electron transport, current density and potential barrier in such a device. The model is used to
explain the underlying mechanisms of the present devices.
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