Bulk emission and interface probing of thin film CdS by two-photon spectroscopy Original Research Article

Two-photon excitation is used to probe the bulk region of differently prepared thin CdS films on transparent substrates. The excitation is performed at room temperature by 200 fs laser pulses at 1.54 eV. By applying the Roosbroeck–Shockley relation, besides self-absorption, it is demonstrated that the emission of films fabricated by spray pyrolysis on Pyrex® and close-spaced vapor transport on CaF2 takes place according to direct absorption inversion. The sample formed by pulsed-laser deposition on glass shows perfect agreement with the theoretical fit whereas the theory does not describe the emission of the evaporated film on glass. By comparison of top and rear face emission, the interface absorption is probed. Absorption increase at the interface of evaporated and laser deposited samples shifts the rear emission 40 meV towards lower energies with respect to the top emission. No interfacial absorption increase takes place in the other samples.