Wednesday June 29, 2005
Thursday June 30, 2005

"Intersubband Absorption in GaN Quantum Wells"
Ms. Kristina Driscoll
Boston University

Many well-established optoelectronic devices, including quantum well infrared photodetectors and quantum cascade lasers, are based on intersubband (ISB) optical transitions, but are limited to mid- and far- infrared operation by the relatively small conduction band offsets (ΔEC) of their composite materials. Recently, there has been growing interest to extend the accessible spectral range of these devices through the investigation of ISB transitions in novel material systems. Particularly promising is the use of GaN/AlGaN quantum wells whose ΔEc can be as a large as 1.8 eV. In this work, we investigate the dependence of intersubband absorption features of GaN/AlGaN multiple quantum wells (MQWs) on the main design parameters, such as well and barrier thickness and composition, buffer layer composition, and doping profile. The MQWs were grown by RF plasma assisted molecular beam epitaxy on sapphire substrates and the absorption spectra of these structures were obtained from polarization sensitive transmission measurements using a Fourier transform infrared spectrometer. The spectral location of the observed absorption features, from the MQW structure, is in good agreement with computer simulations utilizing a Schrödinger solver that accounts for intrinsic piezoelectric and spontaneous modifications to the potential profile as well as the energy dependence of the effective masses. In addition, a narrowing of the transition line width is observed with increasing well and barrier thicknesses and is attributed to a decreased sensitivity to thickness fluctuations.