We describe a 750-keV, 5–10×1012 cm−2 dose, 40Ar implant pretreatment for semi-insulating (SI) GaAs substrates allowing generation of 28Si implanted n layers with higher mobility and/or activation efficiency. This effect was observed in Bridgman Cr-doped, Bridgman Cr-O-doped, liquid encapsulated Czochralski (LEC) Cr-doped, and LEC undoped substrates. Pretreated and control samples were studied by carrier profiling, van der Pauw measurements, and secondary ion mass spectrometry (SIMS). The compensation ratio (ϑ = NA/ND) of n layers in pretreated substrates was lower than in controls. Probable mechanisms of improvement in ϑ are (1) reduced surface Cr concentration due to pretreatment, (2) preferential incorporation of 28Si on Ga sites due to pretreatment-created stoichiometry imbalance, and (3) a combination thereof.
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Liu et al. (1982) studied this question.
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