The effect of sputter cleaning on Au/GaAs contacts and the role of doping

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Abstract
The effects of Ar-ion sputtering on electrical properties of Au contacts on (100) GaAs and the role of doping concentration have been studied. The n-GaAs was doped with 1017 or 1018 cm−3 Si or with 1018 cm−3 Te and the p-GaAs with 1018 or 1019 cm−3 Zn. After either chemical etching or Ar-ion beam cleaning of the GaAs, Au contacts were formed by evaporation in ultrahigh vacuum (10−9 Torr). Ion bombardment with Ar+ produced clean but nonstoichiometric, damaged GaAs surfaces. Contacts on chemically cleaned GaAs were either (nearly) ohmic or Schottky, depending upon the dopant and concentration. On sputtered GaAs, all the contacts showed soft rectification but did not act as purely Schottky contacts. The type of dopants, i.e., n or p, caused differences in the I-V behavior, but the behavior for different dopants of the same type was very similar. Sputtering increased the depletion depth on all the samples, and the depletion depth became larger as the ion energy increased and/or the dopant concentration decreased. The electrical behavior of the sputtered samples is suggested to result from the creation of a compensated layer with deep defect states. The deep level states are postulated to be related to defects resulting from sputtering.