Effect of alloy fluctuations on the surface states of ternary semiconductor alloys: One-dimensional models

Abstract

States which are localized to a surface or to a defect in a semiconductor alloy should be more sensitive to local fluctuations in site occupation than are the bulk states of the semiconductor valence and conduction bands. To illustrate the effects of alloy fluctuations on surface states and to assess the sensitivity of these effects to the localization of the states, calculations are presented for the local electronic surface densities of states of semi-infinite one-dimensional chains. The chains are used to model ternary semiconductor alloys with randomly occupied cation sites. Results are presented for the surface and adsorbate states of ideal chains with unrelaxed ends and for the surface states of chains with relaxed ends. The embedded cluster approach is employed to incorporate the alloy effects on states localized near a chain end. These results are compared with results obtained using the coherent potential approximation (CPA). For surface states which are well localized, the CPA reproduces the structure in the embedded cluster density of states resulting from fluctuations in the occupation of the two cation sites nearest the chain end and from the broadening due to fluctuations at other cation sites.