Infrared properties and band gaps of HgTe/CdTe superlattices

Measurement of the optical transmission spectra of four HgTe/CdTe superlattices grown by molecular beam epitaxy has been carried out at 300 and 30 K to determine the absorption coefficients, refractive indexes, and band-gap energies. In all cases the optical absorption coefficients reached high values (near 104 cm−1) at energies above the band gap. The absorption coefficients had an energy dependence of α≊(E−Eg)1/2 which confirms theoretical predictions of a superlattice band structure with a direct gap. Three of the superlattices measured showed little or no temperature dependence for their band gaps while the third, which may be anomalous, showed a temperature-dependent band gap.