ON THE FORMATION PROCESS OF LUMINESCING CENTERS IN SPARK-PROCESSED SILICON

Radiative and compositional properties of spark-processed silicon are studied by photoluminescence and x-ray photoelectron spectroscopy meas urements. Spark processing of silicon is performed in different atmosp heres composed of nitrogen and oxygen. As a result of the process, roo m-temperature radiative transitions occur at 2.35 eV and vary in inten sity over five orders of magnitude depending on the N-2/O-2 ratio. Aft er processing in pure nitrogen or pure oxygen, however, the green phot oluminescence (PL) is wiped out and weak blue (2.7 eV) or orange (1.9 eV) PL bands, respectively, are discernable. The temperature-dependent features of the 2.35 eV emission are characterized by an intensity in crease in conjunction with a red shift of the peak position at lowered temperatures. A cross-sectional study reveals that the green PL is ma inly generated in a near-surface layer having a chemical composition c lose to SiO2 and a nitrogen concentration below 1 at. %. Nearly no PL was observed from a deeper SiO2 layer enriched by silicon clusters and with an increased density of nitrogen (up to 7 at. %). The findings d o not support a quantum-dot-related PL mechanism in spark-processed si licon. It is proposed that nitrogen additions reduce the density of no nradiative centers introduced by silicon dangling bonds. (C) 1996 Amer ican Institute of Physics.