Optical and Magnetooptical Absorption in Pure HgTe

Infrared absorption in pure, n‐type HgTe has been studied in the wavelength range 3.5 to 35 μm. At ≈ 12 °K, the absorption continues to decrease with decreasing photon energy showing that the energy gap is < 40 meV. The absorption at 300 °K rises with decreasing photon energy after passing a minimum at ≈ 55 meV, due to effect of free carriers. Under an applied magnetic field, up to 30 kG, the absorption at a fixed wavelength shows oscillatory variation with the field strength. These oscillations give a determination of the effective mass and the g‐factor of conduction electrons, and show that the energy gap is close to zero.