Direct experimental determination of the spontaneous polarization of GaN
  We present a universal approach for determining the spontaneous polarization Psp of a wurtzite semiconductor from the emission energies of excitons bound to the different types of stacking faults in these crystals. Employing micro-photoluminescence and cathodoluminescence spectroscopy, we observe emission lines from the intrinsic and extrinsic stacking faults in strain-free GaN micro-crystals. By treating the polarization sheet charges associated with these stacking faults as a plate capacitor, Psp can be obtained from the observed transition energies with no additional assumptions. Self-consistent Poisson-Schroedinger calculations, aided by the microscopic electrostatic potential computed using density-functional theory, lead to nearly identical values for Psp. Our recommended value for Psp of GaN is -0.022+/-0.007 C/m^{2}. 
Jonas L\"ahnemann, Oliver Brandt, Uwe Jahn, Carsten Pf\"uller, Claudia   Roder, Pinar Dogan, Frank Grosse, Abderrezak Belabb...
cond-mat.mtrl-sci cond-mat.mes-hall