Fermi level unpinning in ex situ Schottky contacts on n-GaAs capped with low-temperature-grown GaAs

Abstract

The Schottky barrier behavior of a GaAs layer structure consisting of a thick n-GaAs layer, capped by a thin (3.5 nm) layer of as-grown unintentionally or Be-doped low-temperature-grown GaAs (LTG:GaAs), both grown by molecular beam epitaxy, has been studied. Nonalloyed, ex situ Schottky contacts using three different metals were fabricated on the LTG:GaAs-capped layers and on n-GaAs control samples, in order to study the interface barrier height (φb) versus the metal work function (φm). High frequency capacitance–voltage measurements, along with simulations that incorporate a complete description of the defect states in LTG:GaAs, were used to extract the φb values. The variation in φb with the metal work function is nearly six times greater in the LTG:GaAs capped contacts than in uncapped n-GaAs samples. This direct observation of Fermi level unpinning is consistent with earlier measurements that indicated the inhibited oxidation of LTG:GaAs layers in comparable structures for short air exposure times.