EXCITON RESONANCE OF 2ND-HARMONIC GENERATION IN ZNSE

We have shown that the normally forbidden second harmonic generation s ignal is enhanced drastically when twice tile incident photon energy i s resonant with the excitation energy of a 2P exciton in ZnSe/GaAs thi n films. Using this resonant effect end a novel spectroscopic techniqu e which utilizes a phase-locked laser pulse pair, we have investigated the dynamical behavior of 2P excitons. The interferogram of exciton p olarization has a tail of a few picoseconds. Beating structure was obs erved in tile decay profile. This structure can be explained by polari zation interference between tile heavy hole and light hole excitons sp lit by strain. Further, we have studied the fine structure of the 2P e xciton ill ZnSe films grown on GaAs substrates using this resonance ph enomenon. Tile 2P exciton line is found to show distinct fine structur e caused by envelope-hole coupling, in addition to splitting of the ex citon state due to strain effects.