Optoelectronic properties of metal-Ge Schottky barrier quantum detectors

An experimental study has been made of the electronic properties of rectifying metal-Ge contacts for a range of metals (Au, Cu, Ag, Pb and Ni) and their optoelectronic characteristics under HeNe (6328 Å) laser illumination. For each metal, very Nearly ideal I - V characteristics were obtained with n values from the exponential forward bias region of 1.02 to 1.08 and excellent reverse saturation at 300°K. The dependence of photoresponse on thickness of the various metal electrodes (from 50 Å to more than 1000 Å) was observed. In the case of Au, Cu, Ag and Ni, the Schottky barrier height (φB) was found to be independent of metal thickness (d) whereas Pb - Ge structures show a pronounced decrease in φBwith d. φB´s found from C - V measurements performed on these devices are in close agreement with the values obtained from the I - V characteristics. The dependence of quantum efficiency (Q.E.) upon metal thickness was measured for all metals and these results exhibit the expected decline in Q.E. with d ≤ 100 Å. For d ≥ 100 Å, the Q.E. at zero bias for Au is approximately 52%, for Cu 45%, for Ag 43%, with considerably lower values for Ni and Pb. The Q.E. may be enhanced in most cases by moderate reverse bias (- 1.0 V.) and in this case the Q.E. for Au rises to 66%, Cu to 78%, Ag to 56%. These results may be understood in terms of the contact collection velocity for photogenerated minority carriers. This work represents the first systematic study of the optoelectronic properties of metal-germanium Schottky barriers. The results are of considerable significance for the optimization of Ge Schottky barrier quantum detectors for communication by phosphosilicate fiber optic channel in the wavelength range 1.1 µm < λ < 1.4 µm.