Stress dependence of the nitrogen-bound excitons in GaP: N

We investigate the effect of uniaxial compressions on the zero-phonon luminescence and absorption spectra of the nitrogen-bound excitons in GaP. All data have been collected at pumped-liquid-helium temperature for the stress directions [111], [110], and [001], respectively. The low-stress behavior of the exciton states is consistent with the simple $j-j$ coupling scheme for the excitons, and the stress-induced splitting of the bound hole is found isotropic. The high-stress behavior is quantitatively consistent with an exciton wave function primarily associated with the $〈100〉$ conduction-band minima. The corresponding valley-orbit splitting is $E_{12}=24\mathrm{}$ meV. Under stress, the valley-orbit coupling matrix element appears to be stress dependent. We find $\Delta =(8+4\mathrm{}\times {10}^{-4\mathrm{}}X)$ meV. This result clearly shows that the nitrogen potential is also stress dependent. On the other hand, since the stress dependence of the exciton binding energy $E_b$ cannot be accounted for by a combined $X-L$ nature of the bound-electron wave function, it results from the stress dependence of the potential extension via the stress dependence of the valley-orbit coupling matrix element.