Z. Q. Wang

Bond-orientational order in liquid Si

We study bond‐orientational order in liquid Si via Monte Carlo simulation in conjunction with empirical two‐ and three‐body potentials of the form proposed by Stillinger and Weber. Bond‐orientational order (BOO) is described in terms of combinations of spherical harmonic functions. Liquid Si is found to have pronounced short‐range BOO corresponding to l=3, as expected for a structure with local tetrahedral order. No long‐range BOO is found either in the equilibrium or the supercooled liquid. When the three‐body potential is artificially removed, the tetrahedral bond‐orientation order disappears and the liquid assumes a close‐packed structure.

A simple scaling formula and monte carlo study of liquid semiconductor surfaces: application to CdxTe1−x

Crystal growth of semiconductor compounds in a microgravity environment depends on the temperature- and concentration derivatives of surface tension. In such situations, gravity-driven convective forces are suppressed, and the dominant one is the so-called Marangoni connection, which is driven by surface tension gradients parallel to the surface. A particularly interesting material from this point of view is liquid Cd[sub x]Te[sub 1[minus]x]. In its solid phase, only a single stoichiometric compound exists, and this is nearly insoluble in either pure Cd or pure Te. The liquid phase forms a continuous solid solution at all temperatures above the liquidus. The stoichiometric compound is semiconducting, with a very low electrical conductivity of [approximately] 90 [Omega][sup [minus]1] cm[sup [minus]1] at the melting temperature. As a first step in understanding nonstoichiometric Cd[sub x]Te[sub 1[minus]x], the authors describe in this paper Monte Carlo calculations for such alloys using the same potentials as used for x = 0.50. These lead to the apparently anomalous prediction that the surface tension of Cd[sub x]Te[sub 1[minus]x] is a nonmonotonic function of x. While there are no available experimental results for Cd[sub x]Te[sub 1[minus]x] with determined x except at x = 0.5, other semiconductor alloys do exhibit such an anomaly, whichmorexa0» is therefore evidently accounted for by the empirical potentials. In order to shed more light on this anomaly, they also analyze it by means of a scaling formula for the surface tension, which they have briefly introduced in a previous paper. This scaling formula permits them to calculate the surface tension from only two parameters in the potentials. Here, they apply this scaling formula to other elemental and compound liquid semiconductors as well as to off-stoichiometric CdTe. The scaling results are in good agreement with the Monte Carlo results and available experiments.«xa0less

Thermal conductivity and viscosity of liquid CdTe: A theoretical study

Cadmium telluride (CdTe) is a widely used semiconductor, having applications as gamma-ray detector as well as excellent photorefractive and electrooptic characteristics in the infrared. It is also used as a substrate for HgCdTe for the detection of infrared radiation. These applications generally require large high-quality crystals containing minimum quantities of defects such as grain boundaries, dislocations, and residual impurities. In this work, the authors estimate the temperature-dependent thermal conductivity and liquid CdTe, as well as the kinematic viscosity of CdTe and several other liquid semiconductors at melting. Both of these properties are necessary inputs in models of crystal growth. To estimate the viscosity, and the molecular contribution to the thermal conductivity, they use both a hard-sphere model in combination with a transformed Debye formula. The electronic part of thermal conductivity is calculated from the Wiedemann-Franz law.