There currently exists a wide range of powerful techniques for probing surfaces, mainly involving the use of electron or ion beams under high- or ultra-high-vacuum conditions. Recently there have been major efforts to develop surface sensitive optical probes that have the inherent advantage that they can be applied in more challenging environments such as in high pressures or under liquids and in real time. The most powerful of these techniques to emerge ( years ago) is reflection anisotropy spectroscopy (RAS), which early on demonstrated its ability to distinguish different reconstructions of GaAs(001) and to detect monolayer-growth-related oscillations similar to those routinely obtained using reflection high-energy electron diffraction. This article describes some aspects of the development of the RAS technique since that time, focusing on our own theoretical and experimental studies concerning the (001) surfaces of cubic semiconductors which have been prepared by molecular beam epitaxy. These studies demonstrate that in surface chemistry, structure and electronic properties RAS has made powerful contributions to the study of such surfaces.

We have performed photoluminescence (PL) measurements on chemically etched single-crystal p-CdTe. In addition, x-ray photoemission measurements have been used as a guide to surface stoichiometry for each chemical treatment. The relative intensities of the 0.875±0.005 eV and 1.125±0.005 eV PL bands are seen to be linked to the preferential depletion of either Cd or Te from the CdTe surface. Furthermore, the energies of these deep level transitions measured at T=4 K show remarkable agreement with the two values of Schottky barrier, Φb=0.72±0.02 eV and Φb=0.93±0.02 eV, normally obtained at room temperature for Au and Sb contacts to n-CdTe.

Reflectance anisotropy spectroscopy ͑RAS͒ has been employed in situ to investigate the overlayer growth of GaAs onto submonolayer to one monolayer coverages of Si ␦ layers deposited on the GaAs(001)-c(4ϫ4) surface. The intensity of RAS features, thought to arise from the linear electro-optic ͑LEO͒ effect, is found to vary with both the number of atoms in the Si ␦ layer and the position of the ␦ plane from the GaAs surface. Self-consistent solutions to Poisson's equation are made to calculate the electric field in the near-surface region of the samples. The results show a direct correlation between the LEO intensity and the surface field averaged over the penetration depth of the incident radiation, in confirmation of the LEO model. ͓S0163-1829͑97͒00648-6͔

A series of investigations are presented which address various aspects of the growth, by molecular beam epitaxy, of n-type (Si doped) on-axis GaAs/GaAs(11 l)B. In situ characterization by reflection high-energy electron diffraction has identified four surface phases on the static (zero growth rate) surface, and three reconstructions which occur, depending upon the substrate temperature, during growth. The n-type doping properties of GaAs/GaAs(1ll)B epilayers have been compared with n-GaAs/GaAs(100) structures. Hall effect and low-temperature photoluminescence measurements have demonstrated that it is possible to dope GaAs/GaAs(11 l)B with Si in the 6X 10" to lo'* cm-3 range. A variable growth temperature study is also presented which examines the surface structural, electrical, optical, and surface morphological properties of n-GaAs/GaAs(111) B grown in the 400 to 650 "C! temperature range. The onset of electrical conduction, and optically active material, was found to be directly related to changes in the dynamic surface structure. The variable growth temperature study also revealed a temperature regime within which it was possible to significantly improve the surface morphology of on-axis GaAs/GaAs (111) B structures whilst retaining good electrical and optical properties.

Optical and structural properties of strained InAlAs/InAs x P 1−x multi-quantum wells grown by solid source molecular beam epitaxy Line-of-sight mass spectrometric study of As/Sb exchange on Sb-terminated and Ga-terminated GaSb (001) during molecular beam epitaxy Processes of quantum dot formation in the InAs on GaAs(001) system: A reflectance anisotropy spectroscopy study J.