The absorption maximum near 0.17 ev found in $p$-type InAs at 300°K shifts to lower energies at lower temperatures, and to a stationary value of 0.19 ev above 420°K. The peak absorption coefficient has a minimum value near 370°K and increases with increasing and decreasing temperatures. The observed absorption agrees with theoretical expectation provided a term linear in wave vector is included in the energy near the center of the Brillouin zone. Analysis of the data suggests that the energy maximum of the valence band lies 0.003±0.003 ev above the energy at the center of the zone, that the spin-orbit splitting is 0.43 ev, and that the density-of-states effective mass of the heavy-hole band is approximately $0.41m$ at energies well below the top of the band. The temperature coefficient of the intrinsic energy gap above room temperature is about -0.00033 ev/°K for an absorption coefficient of 40 ${\mathrm{cm}}^{-1\mathrm{}}$.

• Received 31 March 1958

DOI:https://doi.org/10.1103/PhysRev.111.472