Electrical activation of implanted single crystal germanium substrates

We studied the electrical activation of ion implanted dopants in single crystal germanium substrates. Germanium was implanted with arsenic, phosphorus or boron, passivated, and rapid thermal annealed at various temperatures. Several surface passivation processes were explored to understand their influence on the activation process. Sheet resistances was measured by a four-point probe and Hall mobility was used to measure and quantify the activation fraction of dopant in the substrates. A sheet resistance minimum was achieved for all implanted dopants between 450 and 600°C. Variability in the passivation processes had a very large impact in the final sheet resistance values. Secondary Ion Mass Spectrometry demonstrated that there was a loss of dopant and or germanium during the annealing process. For near surface implants, an increase in sheet resistance corresponds to a decrease in activation percentage and an observed dopant loss. Deeper implants are not as susceptible to surface effects. Proper passivation of the germanium surface is critical for achieving low sheet resistance. Acceptable sheet resistances were obtained for the manufacturing of optical devices.