Observation of the size effect in ultrathin PbTe semiconductor films by biharmonic pumping

An experimental investigation was made of the dependence of the efficiency η of self-diffraction of picosecond (~20 ps) light pulses on their frequency offset Ω in ultrathin (6–30 nm) narrow-gap PbTe semiconductor films. The dependences η(Ω) exhibit complex two-photon electron resonances with positions that change radically with the film thickness. The results are interpreted as a manifestation of the quantum size effect in the course of transitions from the light-hole to the heavy-hole band.