Temperature Dependence of the Photoluminescence Intensity in Si3+xN4:H Films with Amorphous Si Nanoclusters: Evidence for Two Processes Involved in the Nonradiative Relaxation of Photoexcitations

Abstract

The temperature dependence of the photoluminescence intensity in Si3+xN4:H films grown on Si substrates in a PECVD process held at temperatures 100 and 380oC was analyzed versus the film stoichiomery. The film stoichiometry parameter x was varied in the range x = 0.08 to 3.7 via varying the NH3/SiH4 flow ratio (0.5 to 5). According to Raman scattering data, the films contained amorphous Si nanoclusters, whose sizes increased with x and substrate temperature. For the first time, the involvement of two different processes in the nonradiative relaxation of excitations optically generated in the system under study has been demonstrated. These processes were tentatively identified as the thermal dissociation of nanocluster-bound excitons and their nondissociative migration to nonradiative sites in neighboring Si nanoclusters. The activation energies and the frequency factors of the two processes were shown to be consistent with the quantum confinement model for the amorphous Si nanocluster related photoluminescence.