Infrared absorption in ${\mathrm{Cd}}_{1\mathrm{-}\mathrm{x}}$${\mathrm{Mn}}_{\mathrm{x}}$Te: Bound-magnetic-polaron effects on the photoionization of acceptors

Infrared absorption in semimagnetic ${\mathrm{Cd}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{Mn}}_{\mathrm{x}}$Te has been studied as a function of temperature for compositions 0≤x≤0.60 from the fundamental absorption edge down to the reststrahlen band. Apart from multiphonon absorption in the 400–200-${\mathrm{cm}}^{\mathrm{-}1}$ region, a strongly temperature-dependent absorption is observed in the midinfrared. The absorption spectra, together with data from electrical measurements, show it to be dominated by uncompensated acceptors present in the p-type material. Good quantitative agreement is obtained between the room-temperature spectra and a calculation for the absorption from inter-valence-band transitions by free holes. On the other hand, the absorption originating from photoionization of acceptors at $E_A$=46 meV exhibits unusual temperature-dependent shifts at low temperatures which are attributed to bound-magnetic-polaron formation. The exchange contribution to the bound-hole energy in the x=0.05 material is derived from a line-shape analysis of the photoionization cross section. The values thus obtained are in good agreement with results from other experiments and from theoretical models.