Search

InGaAs epitaxial layers lattice-matched to InP substrates are studied by photoluminescence measurements modulated by far-infrared radiation under the condition of cyclotron resonance or impurity cyclotron resonance. Based on the experimental results, the ionization energy of shallow donors is estimated to be 2.3 meV, which is lower than the value of 3.0 meV obtained from the effective mass approximation. In order to explain the difference between the two values, we propose a model of the existence of a Ga-rich region in samples. In addition to electron cyclotron resonance, hole cyclotron resonance is observed. The effective masses of electron and light hole are estimated to be 0.041m0and 0.051m0, respectively.

We have investigated nanoscale ErP islands formed on InP(001) during Er exposure in organometallic vapor-phase epitaxial growth by means of atomic force microscopy and scanning tunneling microscopy. Different features of surface morphologies are observed depending on the growth temperature and the ErP coverage. The generation of misfit dislocation arrays along the [1\bar0] direction leads to anisotropic strain relaxation that originates from the anisotropy of the atomic bonds at the interface. The residual strain of partially relaxed islands is ?2% for growth at 530°C, which corresponds to the minimum of total areal energy of the strained film. Current imaging tunneling spectroscopy shows a high tunnel current at dislocations and ErP island edges suggesting the existence of high-density surface states near the Fermi level and the decrease in tunneling barrier height.

The surface structure of 80 K-phase BiSrCaCuO single crystals with and without Li doping has been studied using low-energy electron diffraction (LEED) at elevated temperatures. Although the superconducting critical temperature rises slightly with Li doping, the cleaved surface becomes amorphous in vacuum at temperature ?100 degrees lower than that of the undoped sample (600°C).

Room-temperature photoreflectance (PR) measurements were successfully used to investigate electric fields at the surface and interface of doped GaAs/semi-insulating GaAs structures grown by molecular beam expitaxy (MBE). Fast Fourier transform (FFT) was applied to the PR spectra measured using a He-Ne laser as the pump light. The transformed spectra exhibited two well-resolved peaks, while two different Franz-Keldysh oscillation periods could not be distinguished in the original PR spectra. Using an Ar+laser as the pump light, the FFT PR spectra showed only one peak. Because of the difference in the penetration depth of these two pump beams, the PR spectra taken with the He-Ne laser had contributions from the surface and the interface, while those taken with the Ar+laser had only contributions from the surface. The measured electric fields at the surface and interface in GaAs with different doping levels were discussed in relation to the calculated electric fields.