GaN Based Optoelectronic Devices: From Ultraviolet Detectors and Visible Emitters towards THz Intersubband Devices

III-Nitride material system (AlGaInN) possesses unique optical, electrical and structural properties such as a wide tunable direct bandgap, large longitudinal optical phonon energy, inherit fast carrier dynamics; good carrier transport properties, high breakdown fields; and high robustness and chemical stability. Thanks to these inherit advantages, they are investigated for everyday to military and scientific applications such as illumination sources; bio-agent detection, concealed weapons/drugs detection; and space exploration.

In the first part of the talk, we will be focusing on ultraviolet (UV) spectrum. Ultraviolet region is very important as many biological agents (such as anthrax) are luminescent in UV. Scattering of short-wavelengths in atmosphere enables non-line-of-sight secure communications in rugged terrains whereas strong reflection/absorption of UV at ionosphere promises secure space-to-space communications. Where photomultiplier tubes are found to be bulky and fragile, and Si(C)-based photodiodes require external filter elements, compact high performance UV (Al)GaN avalanche photodiodes (APDs) can be employed. Via Geiger-mode operation of these APDs, single UV photons can be counted that could enable quantum computing and data encryption in near future.

In the second part of the talk, we will be focusing on visible spectrum. The total annual energy consumption in the United States for lighting is approximately 800 Terawatt-hours and costs $80 billion to the public. The energy consumed for lighting throughout the world entails to greenhouse gas emission equivalent to 70% of the emissions from all the cars in the world. InGaN-based novel light emitting diodes are the key components of an affordable, durable and environmentally benign lighting solution that can achieve unique spectral quality and promise superior energy conversion efficiency than current lighting sources.

In the third part of the talk, we will be focusing towards Terahertz (THz) spectrum. Terahertz spectral range offers promising applications for science (such as cancer detection), industry (such as product defect detection), and military (such as drug, concealed weapon or explosives detection), and III-Nitrides are the integral part of unique quantum cascade laser designs that are theoretically capable of THz lasing at room temperature (RT).  Recently, AlN/GaN and AlGaN/GaN superlattices are employed to show intersubband absorption in near- and mid-infrared spectra, respectively. Moreover, AlN/GaN resonant tunneling diodes have been shown to possess negative differential resistance at RT. These recent demonstrations motivate THz emitters at RT.

In conclusion, with continuous developments in material growth/characterization and device processing/measurement technologies, gap engineered III-Nitride materials extend their unique solutions from ultraviolet and visible regime towards THz spectra.