Intriguing properties of pulsed laser beam mixed Au/Te/Au/GaAs ohmic contacts

Abstract

The formation of Au-Te ohmic contacts on GaAs by pulsed laser beam mixing has been studied using I–V measurements, Mössbauer spectroscopy, X-ray diffraction, and Rutherford backscattering spectrometry. For the lowest laser energy fluences used (≃ 0.2 J/cm 2), ohmic contact structures are formed with a very thin intermixed layer. The low-resistive conductivity can, as deduced from Mössbauer and X-ray data, be assigned to the formation of an n +-Ga 2Te 3/GaAs heterojunction. High laser fluence alloying (≃ 0.3–3.0 J/cm 2) results in a strong intermixing of the Au and Te elements with the GaAs substrate. For this intermixing regime, similar low ohmic contact resistances are obtained on as well n-type as p-type GaAs, correlated to the formation of a very high density of Te AsV - Ga defect complexes (tellurium atoms quasi-substitutional on an As site with a Ga vacancy in the first neighbor shell). This result can most consistently be interpreted in the frame of the amorphous heterojunction ohmic contact model.