The Intrinsic Absorption Edge of Heavily Doped N- and P-type Germanium

Abstract

Measurements of the infrared absorption spectrum of heavily doped p- and n-type germanium in the free carrier concentration range of 4×1017∼9×1019 cm-3 are reported. Both the indirect and the direct absorption edge in the impure samples of both types differ strongly from that in pure germanium. The shift of the indirect absorption edge is larger than the shift of the direct absorption edge in both types. The shift of the direct absorption edge is almost the same value in both cases but the shift of indirect absorption edge in n-type is about twice as large as that in p-type. The absorption due to indirect transitions rises more rapidly with photon energy in the impure samples of both types than in pure germanium. The highest absorption value in the direct absorption region is less than that in the pure sample.