Abstract
The absorption spectra of single crystal homogeneous InSb were measured in the spectral range 5 to 10 microns at temperatures of 78°K and 298°K. Primary emphasis was placed on the precise determination of absorption coefficients less than 400 . Absorption spectra were measured in many samples over the following range of impurity concentrations. Net impurity concentrations, expressed in atoms , ranged from 5× to 9.5× in -type samples, and from 2× to 3× in -type samples, as determined from Hall coefficients measured at 78°K.
In general, the spectral range covered included regions where the absorption was dominated by either free-carrier absorption or valence-conduction band transitions. Free-carrier absorption in -type InSb indicates a simple valence-band structure about k=0, consisting of light and heavy hole bands. Free carrier cross sections at 298°K are per hole and per electron (at 9 μ). Whereas the free hole absorption coefficient is roughly independent of wavelength, the free electron absorption varies as and agrees well with the classical Zener-Drude model.
The main absorption edge at both temperatures may be extended to lower absorption coefficients by subtracting the extrapolated free carrier absorption coefficients . The resultant band edge values when plotted against the photoenergy () fits a straight line. The slopes of these band edges increase at the lower temperature and decrease (either at 78° or 298°K) as the acceptor concentration in the optical sample increases. Various models previously proposed are compared with the experimental results.
- Received 11 May 1959
DOI:https://doi.org/10.1103/PhysRev.116.597
©1959 American Physical Society