Abstract
Measurements have been made of the effect of hydrostatic pressure upon the intrinsic infrared absorption of germanium, silicon, and tellurium in the pressure range 1-2000 atmospheres. In germanium the variation with pressure of the lowest lying conduction band minimum, (111), is found to be (7.3\ifmmode\pm\else\textpm\fi{}1.5)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}6}$ ev/atmos. It is suggested that the variation with pressure of the next highest conduction band edge, (000), has a value of (11\ifmmode\pm\else\textpm\fi{}3)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}6}$ ev/atmos. The shift of the infrared absorption edge with pressure in silicon is small and is toward smaller energy, amounting to about -2\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}6}$ ev/atmos between 1 and 2020 atmospheres. The sign and magnitude of the pressure coefficient in this material are in agreement with the results of Warschauer, Paul, and Brooks. For tellurium both ${E}_{g\ensuremath{\perp}}$, the energy gap corresponding to light polarized perpendicular to the $c$-axis of the crystal, and ${E}_{g\mathrm{II}}$, the energy gap for polarization parallel to the $c$-axis, decrease as the pressure is increased. It appears that ${E}_{g\ensuremath{\perp}}$ decreases more rapidly with pressure than ${E}_{g\mathrm{II}}$. The mean pressure coefficient of ${E}_{g\ensuremath{\perp}}$ is - (2.2\ifmmode\pm\else\textpm\fi{}0.4)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}5}$ ev/atmos. For ${E}_{g\mathrm{II}}$ the mean pressure coefficient is - (1.8\ifmmode\pm\else\textpm\fi{}0.3)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}5}$ ev/atmos. The measured pressure coefficients are used to calculate the thermal dilation term in the equation for the change of the energy gap with temperature for each material. The electron-lattice interaction term appearing in this equation is then deduced. In silicon these two terms are of opposite sign with the electron-lattice term dominant. In germanium the electron-lattice interaction effect accounts for 75% of the effect of temperature on the energy gap. For tellurium the two effects are almost equal in magnitude but of opposite sign.
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