Extrinsic Electroabsorption: N Symmetry in GaP

The field-dependent absorption of N in GaP is determined by a new method employing depletion-region modulation. To explain the line shape and the peak increase with E, we propose a Franz-Keldysh-type mechanism. It is based on the field's permitting nondirect transitions, with an orientation dependence determined by the impurity symmetry. We deduce that N has the GaP X₁ symmetry, with masses mₗ=(1.35±0.1)m₀ and mₜ=(0.175±0.01)m₀.