Far-infrared emission by resonant-polaron effects in narrow-band-gap Hg(1-x)Cd(x)Te

We report on the first experimental observation of far-infrared emission within the reststrahlen band of a semiconductor. We have performed Fourier-transform emission experiments on narrow-band-gap Hg1-xCdxTe (x is approximately equal to 0.17). Under Arhighplus-laser excitation, we find an emission spectrum at the longitudinal-optical-phonon energies of the material (137.5 and 157.5 cmhigh-1). The appearance of the optical emission signal is caused by interband polaron effects arising from the resonant matching between longitudinal-optical phonons and electron-hole excitations, as suggested in recent theoretical calculations.