Optical behavior near the fundamental absorption edge of sputter‐deposited microcrystalline aluminum nitride

摘要

The optical behavior near the fundamental absorption edge (4.1–6.6 eV) of sputter‐deposited microcrystalline aluminum nitride grown on unheated fused silica substrates is studied here. The absorption coefficient agr; shows three types of behavior with incident photon energyE: (1) a high‐energy region (>6.06 eV) in which agr; slowly varies withE, (2) a middle‐energy region (∼5.6–6.06 eV) in which agr; varies directly with exp E, and (3) a low‐energy shoulder. High‐ and medium‐energy absorption is modeled in terms of a disordered semiconductor, using a coherent potential approximation with Gaussian site disorder in the valence and conduction bands. agr; is expressed in terms of three interrelated energy parameters: the energy‐band gap of the virtual crystal (6.18 eV), the energy gap of the disordered crystal (5.50–5.64 eV), and the inverse slope of the exponential dependence of agr; onE(0.24–0.29 eV). Enhancement of agr; at low energy is explained in terms of a discrete absorption band whose strength is ∼6×1020/cm3.