Donor Concentration at the Surface of a Diffused N‐type Layer on P‐type Germanium

Abstract

Four methods of evaluating the donor concentration at the surface of a diffused N‐type layer on P‐type germanium have been investigated. All methods assumed a complementary error function (erfc) distribution in the diffused layer. The methods required the use of experimental data for junction depth and sheet resistivity, and of published data for diffusion coefficients of group V elements and electron mobilities in germanium. The methods were applied to calculate the donor concentrations at the surfaces of a number of diffused samples. Under diffusion conditions, which were expected to result in an erfc impurity distribution, the actual concentration profile in the vicinity of the junction was shown to deviate from the erfc law. Due to this deviation, one of the methods of calculating the surface concentration was ruled out. With the other three methods, calculated surface concentrations agreed within a factor of 2 or 3. The disagreement is mainly caused by lack of precise information in respect to the electron mobilities in the diffused layer. Therefore, all the methods represent approximations only.