Tellurium - modified surface states of GaAs(001) and InAs(001)

Abstract

We i n vestigate the stability and electronic structure of 1 2 and 2 2 GaAs 001 :Te and InAs 001 :Te surfaces with di erent degrees of tellurium coverage T e= 1 4 ; 1 2 ; 3 4 ; 1 , by means of rst-principles pseudopotential calculations within density-functional theory. The adsorption stability decreases as the tellurium coverage increases. The adsorption on InAs 001 is more stable than on GaAs 001 . As-Ga or As-In bonds for the uppermost As atoms are s 2 p 2 -like nearly planar , while the Te bonds at the surfaces are sp 3 -like. The hetero-dimers in T e= 1 2 modify the character of GaAs 001 :Te and InAs 001 :Te surfaces resulting in a semiconductor structure. I IntroductionThere are observation 1 of the surfactant action of Te in the heteroepitaxial growth of large mismatch systems such as InAs GaAs by addition of Te o ver GaAs 001 . In ref. 2 the authors propose that the 2D growth is stabilized by half a monolayer of Te atoms that remain on the interface. This model is supported by the experimental indication that only the excess of half a monolayer of Te atoms oats at the InAs surface 3 and by a total energy calculation showing a reduction of the GaAs InAs interface strain energy by a T e interlayer 4 . Our previous theoretical calculations with adsorbed atoms at bridge positions 5, 6 determined a pattern of atomic relaxation with dimerization in -110 direction in agreement with experimental results 7 , indicating that the GaAs 001 :Te-2 2 Te = 1 surface has two dimers geometries at the lowest con guration. Also, for the concentration Te = 1 2 T e atoms prefers to be adsorbed on the sites o -chain, indicating a monoatomic adsorption. We report an investigation of stability and electronic structure of 1 2 and 2 2 GaAs 001 :Te, Ga terminated, and InAs 001 :Te, In terminated surfaces, covered by T e and As atoms with concentration Te = 1 4 ; 1 2 ; 3 4 and 1. II CalculationOur calculations to simulate the systems are based on density-functional theory within the local-density approximation DFT-LDA . We consider an arti cial periodic slab geometry along the 001 direction. The unit cell includes an atomic slab with six atomic GaAs 001 , or InAs 001 layers for Ga or In terminated surfaces, covered by T e or As adlayer and a vacuum region equivalent in thickness to a six layers. The dangling bonds on the back-side of the slab As surface were satured H atoms. The tree uppermost layers and surface are allowed to relax. The eletric eld resulting from the inequivalence of the two surfaces is corrected by a dipole calculated self-consistently 8 . The electron-ion interaction is treated by using fully separable, norm-conserving pseudopotentials 9 . For the electron-electron interaction we employ the exchange correlation potential of Ceperlay-Alder 10 as parameterized by P erdew and Zunger 11 . Single particle orbitals are expanded into plane waves up to a cuto energy of 12 Ry.k-space integrations are replaced by a sum over eight 1 2 cells or four 2 2 cells special points in the irreducible part of the surface Brillouin zo...