Paper NS-TuP13
Quenching of Photoluminescence in Silicon Oxide Layers with Silicon Nanocrystals under Ion-Beam Irradiation: Analysis of Experimental Data

Tuesday, October 16, 2007, 6:00 pm, Room 4C

A quantitative analysis of experimental data on photoluminescence (PL) quenching in silicon oxide layers with embedded Si nanocrystals (nc's) under ion-beam irradiation is presented. The analysis was performed using the data of¹, obtained for an nc-system with mean nc size R=2.9 nm irradiated with 2 MeV He, Ge, and Au ions, and our data obtained for an nc-system with R=3.8 nm, irradiated with 130-200 keV He, F, and P ions. A method to allow for the PL lifetime degradation is proposed, which can be applied if the available dataset for a particular nc-system contains data obtained using irradiation of this system with light ions. A simple model is considered to predict the number N_lum of luminescing nc's versus the fraction η of atoms displaced in the system at low irradiation doses with allowance for the density of collision cascades and the size distribution of nc's. In this model, the well-known expression for N_lum vs η in the case of random rare displacements is used (see, e.g.,¹), with the density of atomic displacements corrected for the damage factor of individual nc's. The experimental PL quenching curves were used to determine the average number of stable nonradiative centers introduced into one nc (N_exp). The quantity N_exp was then compared with the mean number N of displacements per nc obtained in a computer analysis of TRIM simulation data on 3D coordinates of displacements. The yields N_exp/N of stable nonradiative centers with respect to primary displacements in the nc-systems irradiated with the various ions were determined. The obtained values suggest that in dense collision cascades close vacancies choose to combine in divacancies, whereas in rare cascades they prefer to form nonradiative centers individually, possible coming to the nc/matrix interface with the formation of dangling bonds there. A physical interpretation is given to the curves of PL lifetime versus the damaged fraction of nc's. The exciton tunneling times between adjacent nc grains in the nc-systems under consideration were evaluated (120 and 15 μs for the systems with R=2.9 and 3.8 nm). Based on these values, estimates of the decay length of the excitonic wavefunction into the dielectric matrix, and the excitonic recombination cross section at deep traps introduced by ion-beam irradiation in the host dielectric, were obtained.

¹ D. Pacifici et al. Phys. Rev. B 65, 144109 (2002).