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We report the far-infrared photoconductivity spectroscopy (FIRPCS) of the high purity n-GaAs grown by molecular beam epitaxial (MBE) technique. The current-voltage (I-V) measurement and FIRPCS under different electric field strength have been performed on high purity n-GaAs at 4.2 K. Except for photothermal ionization process, a new far-infrared photoconductivity (FIRPC) mechanism is observed. This photo ionization process is assisted by impact ionization and depends on external electric field. This new mechanism originates from photo-field ionization.

The electron effective masses, scattering time and mobilities near the Fermi level for the lowest two subbands of the two-dimensional electron gases in a pseudomorphic In0.80Ga0.20As/In0.53Ga0.47As/In0.52Al0.48AsHEMT structure are determined by fitting the cyclotron resonance spectra. The significant enhancement of the electron effective masses, resulting from the conduction band nonparabolicity and the wave function penetration, is observed. The evident subband dependencies of the electron scattering time and mobilities dominated by the alloy scattering and ionized impurities scattering are also discussed.

The resonant subband-Landau-level coupling(RSLC) between the N=1 Landau level of the lowest subband and the N＝0 Landau level of the subbands with quantum index up to i＝5 of two-dimensional electron gases in GaAs/AlGaAs heterojunction was observed under relatively low magnetic field.Several intersubband energies were accurately determined. The experimental results were in good agreement with the self-consistent calculations including the depolarization shift and exciton-like effect corrections.The quantum index dependence of the level splitting due to the RSLC was discussed.

The ultrathin molecular organized films of hemicyanine dyes were prepared by langmuir-Blod-gett technique. The films show ferroelectric hysteresis loop and pyroelectric effect. The pyroelectric coefficient measured by the method of integrated charges is 12μC·m-2·K-1 at 300 K, and the relationship between the orientaton of DAEP in the films and temperature was studied by polarized FTIR spectroscopy. The microscopic mechanism of pyroelectricity in the films was discussed.

Photoconductivity (PC) spectra of impurities in n type GaAs under magnetic field are presented. The resonant interaction between high excited states of bound electrons and LO phonons under relatively low magnetic field was observed. The magnetic field dependency of PC response of resonant polaron and the physical origin of the PC peak stuck on the energy position of LO phonon are discussed.

The 2p± and 3p± excited lines of P donors in Si0.92Ge0.08 epitaxial layer have been observed using photothermal ionization spectroscopy.The ionization energy of P in Si0.92Ge0.08 is 45.51meV according to effective mass approach.The spectral lines of P in Si1-xGex compared with those in pure Si apparently broaden due to alloy disorder effect.

We report direct experimental determination of the wavefunction mixture and composition for hybridized Zeeman states of P in Si. The intensity evolution of the Zeeman transitions nearby anti-crossing region for the isolated P donors in high pure Si bas been measured quantitatively by use of high sensitive and high resolution photothermal ionization spectroscopy (PTIS); The wavefunction compositions and their evolutions upon magnetic field for the hybridized Zeeman states of bounded electrons of impurities have been deduced from the measurement. A variational calculation under the frame of effective mass approach has been performed to estimate theoretically the wavefunction composition. The results are campare with experimental ones.

The transmission spectra of p-PbTe have been measured by the strip-line technique with different far infrared laser wavelengths at different anhgles of the direction of maqnetic field relative to the crystal axis at low temperature of 1.5 k. A strong influence of mode coupling on strip-line transmission spectra has been observed and analyzed. The final results extracted from experimental spectra by numerical simulation are in good agreement with the six band k·p model calculation.

The luminescence lines of the neutral donor bound exciton (D 0 X) are investigated in magnetic fields up to 10 T. From the observed Zeeman-splitting and shifting, we deduce to our knowledge for the first time the values of the g -factors and the diamagnetic shifts of the electrons and the hole in this complex.