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 $\mathcal{E}$, 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 $X_1$ symmetry, with masses $m_l=(1.35\mathrm{}\pm 0.1)m_0$ and $m_t=(0.175\mathrm{}\pm 0.01)m_0$.