Recently, conditions have been defined for the growth of mirror-smooth layers of Ge on either Ge or semi-insulating GaAs by the Gel2 disproportionation reaction. In attempting to dope such layers with p-type impurities under the defined surface-rate-limited growth conditions, it was observed that order-of-magnitude decreases in resistivity occurred on heating the grown layers to temperatures higher than the original growth temperature. This indicated that impurities were initially incorporated in an electrically inactive state. Results are presented which show this behavior to be increasingly pronounced for fast growth rates and low substrate temperatures. and growth conditions to minimize the effect are defined. © 1970, The Electrochemical Society, Inc. All rights reserved.