Appl. Phys. Lett. 99, 251112 (2011)

AlN and GaN — wurtzite group-III nitrides — are promising semiconductors for use in ultraviolet LEDs at wavelengths of 210–365 nm. To obtain high crystalline quality, scientists often grow AlGaN on a template such as sapphire or SiC, which ensures that the ultraviolet emitting surface is always perpendicular to the c-axis. Unfortunately, the light polarization of AlN-based LEDs is parallel to the c-axis. Yoshitaka Taniyasu and Makoto Kasu of NTT Basic Research Laboratories in Japan have now proposed the use of short-period superlattices to modify the polarization of the emitting light. The researchers first fabricated c-plane 30-period AlN/GaN superlattices by metalorganic vapour phase epitaxy. The AlN and GaN layers were 7 and 0.9–2.5 monolayers thick, respectively, and the quantized hole energy level was determined by the heavy-hole band of GaN. The transition between the electron and hole quantized energy levels was therefore allowed for electric fields perpendicular to the c-axis. The radiation angle dependence of photoluminescence from the AlN/GaN short-period superlattices showed a maximum intensity when parallel to the c-axis.