Direct experimental determination of the spontaneous polarization of GaN

We present a universal approach for determining the spontaneous polarization P _sp of a wurtzite semiconductor from the emission energies of excitons bound to the different types of stacking faults in these crystals. Employing microphotoluminescence and cathodoluminescence spectroscopy, we observe emission lines from the intrinsic and extrinsic stacking faults in strain-free GaN microcrystals. By treating the polarization sheet charges associated with these stacking faults as a plate capacitor, P _sp can be obtained from the observed transition energies with no additional assumptions. Self-consistent Poisson-Schrödinger calculations, aided by the microscopic electrostatic potential computed using density-functional theory, lead to nearly identical values for P _sp. Our recommended value for P _sp of GaN is -0.022±0.007 C/m2.