Diffusion and Solubility of Copper in Extrinsic and Intrinsic Germanium, Silicon, and Gallium Arsenide

Abstract

The solubilities of substitutional and interstitial copper (Cus and Cui) have been measured in intrinsic and extrinsic n- and p-type Ge, Si, and GaAs, using Cu64. These measurements show that Cus is a triple acceptor in both Ge and Si, and that Cui is a single donor in all three semiconductors. Charge compensation experiments show that Cus is a double acceptor in GaAs. In intrinsic semiconductor near 700°C the ratios of substitutional to interstitial solubilities are 6, ∼10−4, and 30, respectively. Electrically active donors due to Cui have been observed in Si by Hall-effect measurements. Pairing between Cus and donors is pronounced in n-type Ge but relatively unimportant above 600°C in Si. There is no evidence for pairing between Cui and acceptors in any of these semiconductors. The interstitial diffusion coefficient Di is independent of doping in extrinsic p-type material. At 500°C, Di=2.8, 0.76, and 1.0×10−5 cm2/sec with activation energies of 0.33, 0.43, and 0.53 (±10% in each case) eV, respectively. Di and the single positive charge of Cui in p-type GaAs have been confirmed by drift experiments. The decrease in energy gap with acceptor doping is 0.28 eV in Ge and 0.14 eV in Si at 4×1020 cm−3 acceptors, as deduced from Cui solubility data. KCN solutions remove Cu effectively from surfaces and from liquid Ga. Ga is much more effective than molten KCN in extracting Cu from the interior of semiconductors. KCN contains Cu and may actually introduce Cu instead of removing it.