After a comparison of the β-, ϵ-, γ-, and δ-type GaSe crystal structures, the different interlayer interactions are discussed. New values for the intralayer interatomic distances Se–Ga = 2.463 (15) A, Ga–Ga = 2.457 (18) A, and the interlayer distance Se–Se = 3.880 (15) A are proposed. These are mean values for the δ-type determined with a higher accuracy than the previous ones, relevant to the ϵ- and γ-type structure. The influence of the growth method on crystal type and dislocation density are discussed.

Crystal structure and interatomic distances in GaSe

Properties of gallium selenide single crystal

Transport and phototransport properties of crystalline indium monoselenide (InSe) doped with a variety of elements are reported. Measured mobilities, lifetimes, and effective diffusion lengths of photoexcited carriers are used to interpret electrical and photovoltaic properties of several different structures. These include p‐n junctions, bismuth/p‐type InSe, platinum/n‐type InSe, and indium tin oxyde (ITO)/p‐type InSe. External solar efficiencies of the best devices are between 5% and 6%. The influence on the efficiency of the various parameters is evaluated, and ways of improvement are discussed.

/pdf/photoconductivity-and-photovoltaic-effect-in-indium-selenide-3qto981sby.pdf

Photoconductivity and photovoltaic effect in indium selenide

Publisher Summary The chapter presents a discussion on the theoretical aspects of the electron-hole liquid in semiconductors. In an intrinsic semiconductor such as germanium or silicon, there are essentially no free carriers at very low temperatures. However, high densities of positive (hole) and negative (electron) charge carriers can be generated in these crystals by photoexcitation with a photon energy greater than the forbidden gap. In recent years, experiments in Ge and Si have revealed that optically pumped electrons and holes at high densities can undergo a phase transition at liquid helium temperatures into a metallic, liquid state. This condensate represents a state of matter particularly unique in nature because the electrons and holes, by reason of their small masses, are simultaneously in the quantum limit. This chapter presents a discussion on the collective behavior of electrons and holes at low temperatures and high densities. The chapter presents an historical introduction, mentions a few of the important early experiments performed, and presents a comparison of theory and experiment. Semiconductors can be divided into two classes. Those in which the conduction band minimum and valence band maximum occur at the same value of the wavevector are known as direct gap semiconductors, while those in which they are separated in k space are known as indirect gap semiconductors. The chapter discusses the latter.

The Electron-Hole Liquid in Semiconductors: Theoretical Aspects

Reflectivity and wavelength-modulated reflectivity measurements on GaSe and $\mathrm{Ga}{\mathrm{S}}_{x}{\mathrm{Se}}_{1\ensuremath{-}x}$ mixed crystals are presented for energies ranging from 3 to 6 eV. Additional electroreflectance measurements are used to investigate the excitonic character of the structure at 3.4 eV in GaSe. The results are discussed on the basis of a new pseudopotential band-structure calculation for GaSe. The prominent spectral structures of GaSe are identified in terms of location in $\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}}$ space and atomic character of the states involved in the transitions. The main structures in the optical-response function of GaSe are found to result from excitations of the Ga-Ga bond and from atomiclike transitions between nonbonding Se $p$ and $s$ states. These main transitions are located in $\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}}$ space close to symmetry determined "special $\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}}$ points." The observed mixed-crystal spectra can be decomposed into three classes of transitions which exhibit zero, intermediate, and strong energy shifts with anion substitution. Theoretically, the three classes of transitions are found to take place between states with zero or little, intermediate, and large charge concentrations on the anion sites. Thus, the characteristic energy shifts, observed experimentally can directly be related to atomic spectral properties of sulphur and selenium.

I. Zschokke

Papers

GaSe: A layer compound with anomalous valence band anisotropy