The donor concentration in high-purity bulk crystals was found to be reversibly changed by heat treatment. At levels of between 5 x 1014 and 2 x 1015/cm3, the concentration decreased below 340C and increased above 380C. Far-infrared photoconductivity measurements revealed that shallow donors with a binding energy of about 0.0075eV were caused to disappear and appear by low- and high-temperature treatments, respectively. One probable mechanism was suggested to be that shallow extrinsic donors, attributed to Si, were electrically passivated by some kind of defect such as atomic H and were reactivated by low- and high-temperature treatment, respectively.

Reversible Variation of Donor Concentrations in High-Purity InP by Thermal Treatment E.Kubota, K.Ando, S.Yamada: Journal of Applied Physics, 2000, 87[6], 2885-9