Free-carrier absorption at low temperatures in uniaxially stressed n-type Ge, Si and GaAs

Abstract

The effect of uniaxial compressive stress of up to 6*109 dyn cm-2 on free-carrier absorption in various doped Ge, Si and GaAs crystals has been investigated. Absorption measurements were made at 18.5K and 79K over the wavelength range 8 mu m to 24 mu m with radiation polarized parallel or perpendicular to stress. The latter was applied along (111), (110) or (100) directions in Ge, (110) or (100) directions in GaAs but (100) directions only in Si. Changes in absorption produced in all but one of the germanium crystals are explained by a simple electron-transfer model in which the total electron concentration in the conduction band remains constant and electrons merely transfer between the (111) multivalley states as they are split by stress. For the other germanium crystal, the behaviour under (111) stress was similar to that found in silicon under (100) stress.