The large conduction band offset between GaN and AlN offers great prospect for high performance intersubband transition (ISBT) devices operating at near infrared wavelength (1.3-1.5 microns). My work deals with electro-optics properties in nano-structures (quantum wells, quantum dots) in the III-nitrides material system.

The research focused on the following topics:

a.      Measuring the refractive index around intersubband transition resonance in GaN/AlN multi quantum wells. We present a new method for direct measurement of the variation in ISBT refractive index dispersion around the resonance, using free space Mach-Zehnder interferometer. Based on interference model, data fitting algorithms were employed for the analysis of the near IR (1.5 µm) interferograms. These results compare well with those derived using Kramers-Kronig relations for ISB absorption data obtained by FTIR close to the resonance.

b.      Inter sub-band transitions in non-polar crystal systems. Most of the published works on ISBT in the III-nitrides material system were done on the common polar structures. The huge internal polarization field in these structures complicates and prevents the design and implementation of advanced uni-polar devices such as quantum cascade lasers. In this work for the first time photocurrent (PC) was measured on a non-polar quantum well infrared photo-detector (QWIP), based on InGaN/GaN layers designed for peak PC responses at 9.3 µm and at 7.5 µm. The structure was homoepitaxially grown on free standing nominally on-axis m-plane GaN substrate. Based on the dark current measurement as function of the inverse temperature, the ISB-PC spectrum and the 8?8 bands k^.p calculations, we were able to extract the conduction band offset in the non-polar material system.