Injection efficiency in AlGaN‐based UV laser diodes

We evaluated AlGaN-based 355 nm UV laser diodes prepared under two different Mg activation conditions. The annealing processes for Mg activation in p-layers were carried out under N2 or O2 ambient to investigate the effect of the ambient gas on the laser characteristics. The threshold current densities and operating voltages of the UV laser diodes were improved by annealing under O2 compared with those under N2. We then estimated the injection efficiencies of the laser diode structures by considering the internal quantum efficiencies of optical excitation and electrical excitation. The internal quantum efficiency of the electrically excited spontaneous emission from the laser structure annealed under O2 reached 50% at a carrier density of 7.0×1018 cm-3, while the structure annealed under N2 required a 1.8-fold higher carrier density of 1.2×1019 cm-3 to reach the same internal quantum efficiency. In addition, the internal quantum efficiency estimated from optical excitation reached 50% even at a carrier density of 3.0×1018 cm-3. This implies that the injection efficiencies in the UV laser diode structures annealed under N2 and O2 were 25% and 45%, respectively. Mg activation by O2 annealing is effective for increasing the injection efficiency. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)