Gaseous Diffusion of Arsenic and Phosphorus into Germanium

Abstract

The diffusion of arsenic and phosphorus from a gaseous ambient into germanium is investigated using capacitance and breakdown measurements of diodes produced by plating indium into indentations of various depths. The diffusion constants found for arsenic in germanium agree well with those published by Bosenberg. On the other hand, the diffusion constant of phosphorus in germanium at 780°C was found to be which differs considerably from data by Dunlop. The surface concentration of arsenic in germanium appears to increase in proportion to the fourth root of the arsenic vapor pressure at 725°, 750°, and 800°C, with no significant differences among these temperatures. In the case of phosphorus a fourth root dependence was found also at 780°C, the only temperature investigated.Presence of germanium arsenide was found at the germanium surface, particularly at arsenic surface concentrations exceeding 1019 at./cc, using electron diffraction techniques. Thermal conversion of the interior of the germanium wafers (which were 15 ohm‐cm N‐type) to P‐type could be suppressed by arsenic surface concentrations exceeding 5.1018 at./cc. This elimination of thermal conversion depends on the surface to volume ratio of the wafer. It is proposed that the thermal conversion level in the bulk of the indiffused material depends on the electric field which arises during diffusion if the impurity concentration exceeds the intrinsic carrier concentration.