Polarization and Band Gap Engineered III-Nitride Optoelectronic Device Structures

Immense progress has been made in III-Nitride optical devices since the demonstration of blue lasers in mid 90's. The attention of the solid state lighting has shifted to longer wavelength (green), and to short wavelength (ultraviolet: UV). At the same time, major challenges remain in improving the efficiency of III-Nitride optical emitters.

In this work, we explore the many consequences of the electronic polarization fields at heterojunctions of long-$lambda$ (green) and very short-$lambda$ (UV) light emitters. By using molecular beam epitaxy (MBE), we grow III-Nitride heterostructures with high composition In-composition InGaN on GaN substrates for investigating very long-$lambda$ visible emitters and detectors. We also investigate the growth of high Al-composition AlGaN on AlN substrates for UV emitters.

A careful analysis of the role of polarization in heterostructures enables us to design and demonstrate novel N-face quantum well (QW) light emitting diode (LED) heterostructure that incorporates polarization-induced doped p-type layers. These QWs emit at room temperature (RT) at and near GaN QW band gap. For shorter-$lambda$ emission, we design and demonstrate a novel quantum dot (QD) UV LED that uses tunnel-injection of carriers. This QD UV LED emits at RT at 261 nm, 301 nm and 341 nm. Besides, we incorporate polarization-induced doping with GaN/AlN QD active region to improve the emission intensity at 259 nm and subdue the relatively longer wavelength emission at 290 nm. Both demonstrations help us identify unique opportunities for improvements in III-Nitride LEDs and lasers of the future.