Intersubband Absorption at lambda ~ 1.55microns in well- and Modulation-doped GaN/AlGaN Multiple Quantum Wells with Superlattice Barriers

Intersubband optical absorption around 1.55microns has been measured in GaN/AlGaN multiple quantum wells (MQWs) grown by molecular beam epitaxy. First, peak absorption wavelengths as short as 1.41microns are reported for ultra-narrow, >= 11angstroms wide, well-doped MQWs with high, 85%, AlN mole-fraction barriers. Secondly, in order to enable modulation doping as well as the use of lower AlN mole-fraction barriers, we designed and fabricated QWs embedded in barriers consisting of a short period superlattice of narrow GaN QWs and only 65% AlN mole- fraction barriers. The resulting electron Bragg-confinement allows peak absorption wavelengths as short as 1.52 1.52microns. Furthermore, the structures can now be modulation-doped through doping of the narrow superlattice wells and subsequent charge transfer into the active well. We observe a reduction of the absorption linewidth, from ~ 200 meV to ~ 130 meV, for these structures.