Absorption edge and ion bombardment of silicon nitride

Abstract

The optical absorption edge for chemical-vapor-deposited silicon nitride films on sapphire substrates has been measured for different deposition conditions, and as a function of ion bombardment and subsequent annealing. An exponential form for the absorption edge, consistent with a disorder-limited edge, is observed for all films. While the slope of the absorption edge is independent of the measurement temperature, the energy for the edge decreases with increasing temperature by (2–4) ×10−4 eV/°C. The energy and slope of the absorption edge are lower for films deposited at 760 °C than for films deposited at 1000 °C, and displacement damage introduced by ion bombardment causes a decrease in both the slope and energy for the edge. Ion-bombardment-induced changes saturate when the energy deposition into damage processes is ∼10 eV/atom. The effects of a lower deposition temperature and of ion bombardment upon the absorption edge are attributed to a degradation of short-range order. Annealing of the bombardment-induced effects occurs over a broad temperature range, and the prebombardment absorption edge is essentially recovered by annealing at the deposition temperature.