Luminescence Spectroscopy of Semiconductor Surfaces and Interfaces

Low energy cathodoluminescence spectroscopy (CLS) employing incident electron energies in the range of a few kV or less enable measurement of electronic structure near semiconductor surfaces and interfaces. Coupled with photoluminescence spectroscopy (PL), the CLS technique has been extended to characterize electronic structure tens of nanometers below the free surface at metal-semiconductor and semiconductor-semiconductor junctions. CLS has revealed discrete, deep electronic states for clean and metallized semiconductor surfaces as a function of atomic ordering as well as vicinal surfaces as a function of misorientation. A combination of CLS and PL reveals deep level features associated with strain relaxation and dislocations at heterojunction interfaces as well as variations in epilayer growth conditions. Such observations demonstrate the existence of discrete, deep levels in the semiconductor band gap and their sensitivity to chemical and atomic structure near surfaces and interfaces. Furthermore, the energies and densities of such deep levels provide a consistent picture of Fermi level stabilization and band bending at semiconductor contacts. Finally, our results indicate that deep level CLS/PL measurements are an effective, in-situ probe of surface and interface quality

Growth of nanostructures by cluster deposition : a review

This paper presents a comprehensive analysis of simple models useful to analyze the growth of nanostructures obtained by cluster deposition. After detailing the potential interest of nanostructures, I extensively study the first stages of growth (the submonolayer regime) by kinetic Monte-Carlo simulations. These simulations are performed in a wide variety of experimental situations : complete condensation, growth with reevaporation, nucleation on defects, total or null cluster-cluster coalescence... The main scope of the paper is to help experimentalists analyzing their data to deduce which of those processes are important and to quantify them. A software including all these simulation programs is available at no cost on request to the author. I carefully discuss experiments of growth from cluster beams and show how the mobility of the clusters on the surface can be measured : surprisingly high values are found. An important issue for future technological applications of cluster deposition is the relation between the size of the incident clusters and the size of the islands obtained on the substrate. An approximate formula which gives the ratio of the two sizes as a function of the melting temperature of the material deposited is given. Finally, I study the atomic mechanisms which can explain the diffusion of the clusters on a substrate and the result of their mutual interaction (simple juxtaposition, partial or total coalescence...)Comment: To be published Rev Mod Phys, Oct 99, RevTeX, 37 figure

Photoelectrochemical Processes at n GaAs 100 Aqueous HCl Electrolyte Interface A Synchrotron Photoemission Spectroscopy Study of Emersed Electrodes

High-resolution synchrotron photoemission spectroscopy has been applied to detail the electrochemical and photoelectrochemical corrosion reactions at the liquid junction n‑GaAs(100)/1 M aqueous HCl solution. Under anodic polarization of 1.8 eV, the main process initiated by the presence of holes in the Ga−As bonding states of the valence band is the formation of soluble gallium chloride complexes and insoluble elemental arsenic on the surface. In addition, arsenic hydroxide forms, which reacts further to soluble HAsO2. In toto, the As/Ga atomic ratio increases, which is accompanied by an increase of the work function. The anodic decomposition reaction is enhanced by illumination as more holes reach the n-semiconductor/electrolyte junction. Under cathodic polarization of 1.5 eV, only minor changes are observed in Ga and As core-level spectra, giving no indication of corrosion, but specific adsorption of hydrated HCl molecules and/or Cl −ions considerably modifies valence bandspectra