Pan Shi-Hong

Photoreflectance spectra from the surface and GaAs/GaAs interfaces of doped MBE GaAs films

The authors report on photoreflectance (PR) measurements of the electric fields at the surface and GaAs/GaAs interface of doped GaAs films prepared by molecular beam epitaxy (MBE). By using He-Ne and He-Cd lasers alternately as the pump light, PR signals from the surface and interface of the films can be effectively separated because of the difference in the penetration depths of these two pump beams. Electric fields at the surface and interface were evaluated from PR spectra. Film interference effects on modulation spectroscopy have been studied. The origin of the electric field at interfaces has also been discussed.

FRANZ-KELDYSH OSCILLATION FROM THE SPACE CHARGE REGION OF MBE GaAs FILMS

We have investigated doped MBE GaAs films using photoreflectance (PR) spectroscopy. Special spectral structures have been observed in the vicinity of the fundamental band gap, which are quite different from the Franz-Keldysh oscillation (FKO) from uniform electric fields under flatband modulations. Numerical analysis has been performed for FKO from electric fields in the space charge region under non-flatband modulations. Some typical FKO line shapes are illustrated. For moderately doped samples the calculated line shapes are basically consistent with experiments. The surface electric field and the Fermi level pinning have also been deduced from experiments.

Modulation Spectroscopy of GaAs Covered by InAs Quantum Dots

Contactless: electroreflectance has been employed at room temperature to study the Fermi level pinning at undoped-n(+) GaAs surfaces covered by 1.6 and 1.8 monolayer (ML) InAs quantum dots (QDs). It is shown that the 1.8 ML InAs QD moves the Fermi level at GaAs surface to the valence band maximum by about 70 meV compared to bare GaAs, whereas 1.6 ML InAs on GaAs does not modify the Fermi level, It is confirmed that the modification of the 1.8 ML InAs deposition on the Fermi level at GaAs surface is due to the QDs, which are surrounded by some oxidized InAs facets, rather than the wetting layer.

Photodiffractive effects in semiconductor microstructures

We have investigated the photodiffractive effect induced by resonant excitations in semi-conductor microstructures by means of the multiple wave coupling method. We have derived a set of multiple wave coupling equations for photodiffractions in the case of coexistence of refraction and absorption gratings. Numerical results of the equations for a few typical cases have been analysed in detail, and their physical significance is also discussed.

Multiple wave coupling theory of the photodiffractive effect in semiconductor microstructures

We have investigated the photodiffractive effect induced by resonant excitations in semiconductor microstructures by means of the multiple wave coupling method. We have derived a set of multiple wave coupling equations for photodiffraction in the case of coexistence of refraction and absorption gratings. Numerical results of the equations for a few typical cases have been analysed in detail. The results show that the absorption grating does not contribute to the two-wave-mixing effect, but it does contribute to the photodiffractive effect. The negative absorption grating (that is, a phase shift of pi to the interference fringe) is more effective for photodiffraction than is the positive absorption grating. The combination of the refraction grating with the absorption grating may enhance the photodiffractive effect.

Optical processes of a single-atom model in the phonon field

The optical processes of a single-atom model in the phonon field have been studied. To deal with the quantum electrodynamics phenomena in condensed matter microcavities, the influence of electron-phonon interactions has to be taken into account. As a clear picture, the effect of the lattices oscillation on the optical transition in condensed matter microcavities is reduced to a model of a single atom in a phonon field. We deduce that in the case with a phonon participating, the Bloch equation is still satisfied. In the process of spontaneous emission for an electron interacting with a phonon, we derive the Rabi oscillation for the simple atom in the phonon field.

An improved defect model for Schottky barrier formation on III-V compounds

An improved defect model has been proposed by combination of the defect model with the Bardeen model. The predictions based on this model can qualitatively explain the experimental results of the Schottky barrier formation on GaAs(110).