Ohmic Contacts to Photoconducting CdS Single Crystal Samples Using Pure Indium

Abstract

We have prepared ohmic contacts to photoconducting CdS samples by either soldering or diffusing high purity indium into the samples. The electric field distribution was measured along the samples with an electric field measuring equipment of 40 μ resolution. From these measurements we found that spikes or contact fields appear at the ends of the sample when the contacts were made by soldering indium to the sample. These contact fields can be large enough to nucleate high electric field domains at the contacts which strongly influence the development of the electric field in the rest of the sample. Such contact fields were absent when high purity indium was diffused into the sample for times longer than 30 min, at 600 °C in He atmosphere. On the other hand, for diffusion times shorter than 30 min, same as in the case of the soldered indium contacts, contact fields were observed at the ends of the sample. Furthermore, for diffusion times longer than 30 min, the electric field distribution indicated the existence of heavily doped layers at the ends of the sample; the thickness of these layers being typically of the order of 100 μ. These layers changed distinctly with time since after three months the thickness of these layers has been reduced by about 50 μ. The reduction of the thickness of these layers is probably caused by the recapture of some of the electrons by the donors, since atomic diffusion in solids at room temperatures is known to be extremely slow.