Silicon concentration dependence of optical polarization in AlGaN epitaxial layers

The optical polarization of Si-doped Al(x)Ga(1-x)N epitaxial layers (x=0.37-0.95) has been studied by means of photoluminescence (PL) spectroscopy. The predominant polarization component of the band-edge PL switched from E perpendicular to c to E parallel to c at an Al composition between 0.68 and 0.81. This critical Al composition was much higher than in previous reports for AlGaN epitaxial layers. In addition, the predominant polarization in Al(0.55)Ga(0.45)N epitaxial layers switched from E perpendicular to c to E parallel to c with increasing Si concentration. Therefore, the topmost valence band changed from the heavy-hole band to the crystal-field split-off-hole band with decreasing in-plane compressive strain induced by Si doping. (C) 2011 American Institute of Physics. [doi:10.1063/1.3543631]