CAN BAYRAM

RESEARCH AREAS

His research focuses on III-Nitride photonic devices which are made of direct bandgap AlGaInN compounds covering a wide spectra from deep ultraviolet (UV) to near infrared. Robustness of this material system makes them promising candidates for applications in harsh environments such as everyday life, battlegrounds, outdoors and space.

Ultraviolet region is very important as many biological agents (such as anthrax and plague) 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, his world’s highest performing UV avalanche photodiodes (APDs) (gains of 51000, and external quantum efficiency of 57%) can be employed. Via Geiger-mode operation, he has realized (world’s first) UV single photon detectors (SPDs) with single photon detection efficiencies as high as 20%, that could detect (identify) even a single photon (chemical). The use of III-Nitride APDs presents key advantages such as lower operation voltages, much reduced sizes, and no need for cooling, which enable the fabrication of more compact, lower power, and all-solid-state APD/CMOS integrated arrays, suitable for integration into space shuttles/stations, airplanes, and military vehicles for secure communication and aerial countermeasures.

Solid state lighting (SSL) holds the promise of a more energy-efficient, longer-lasting, more compact, and lower maintenance substitute for today's incandescent and fluorescent light sources. 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. A novel solution to lighting with higher efficiency will drastically reduce the energy consumption and help greenhouse gas emissions to be lowered. Novel green light emitting diodes are the key components of an affordable, durable and environmentally benign lighting solution that can perform at superior energy conversion efficiency.

Terahertz (THz) emitters enable identification of pharmaceutical ingredients (for example, in a drug). Penetration through nonconductors (fabrics, wood, plastic) enables a more efficient way of performing security checks (for example at airports) with THz emission, as illegal drugs and explosives could be detected. Being a non-ionizing radiation, THz radiation is environment-friendly enabling a safer analysis environment than conventional X-ray based techniques. Thanks to the large longitudinal optical phonon energy, III-Nitrides is a promising candidate for room temperature operation of terahertz emitters. His on-going research on III-Nitride intersubband devices will lead to a continuous monitoring of an environment ensuring a better security than conventional security check-points in airports without effecting privacy.

RESEARCH INTERESTS

Mr. Bayram's Ph.D. research area is wide bandgap semiconductor devices including III-N materials (AlGaInN) and II-VI materials (ZnO). His research interests include semiconductor device design/simulation, material growth/characterization, device processing/packaging/measurement.

He has performed more than 2000 MOCVD growths up-to-date. He has improved AlxGayIn(1-x-y)N layers (where [0,0]< [x, y] < [1,1]), and integrated them into self-designed nitride optoelectronic devices. By using state of the art material characterization tools such as atomic force microscopy, scanning electron microscopy, photoluminsecence measurements, X-ray diffraction equipments, and Hall measurements, he has correlated the material growth, characterization and (structural (surface, crystallographic), optical, electrical) material quality that leaded to world's first and world's highest performance nitride optoelectronic devices.

By using conventional and state-of-the-art semiconductor fabrication techniques and equipments (such as rapid thermal annealing, electron cyclotron resonance reactive ion etching, electron beam metal evaporator, plasma-enhanced chemical vapor deposition, photo- and e-beam-lithography systems), he has fabricated more than 300 wide bandgap semiconductor devices ranging from UV APDs to blue and green LEDs. Combining the device performance with the material growth, a unique blend of semiconductor knowledge is gathered in-house, and being implemented.

His current research interests include avalanche and single photon detection in UV spectral region, and high power blue-green-white light emitting diodes. He is currently developing high quality Al(Ga)N/GaN superlattices for intersubband devices operating in near-, mid-, far-infrared, and THz regime.

HIS PRIMARY CONTRIBUTIONS TO THE ULTRAVIOLET DETECTORS

(7) Demonstration of world's first nanopillar GaN photodiodes (2008),

(6) Demonstration of world's highest quantum efficiency inheritly-ultraviolet APDs (2008),

(5) Demonstration of world's highest linear gain in UV GaN APDs (2008),

(4) Demonstration of world's first back-illuminated Separate Absorption & Multiplication GaN APDs (2008),

(3) Demonstration of world's first UV Single Photon Detection with GaN APDs (2007),

(2) Demonstration of world's highest linear gain in UV GaN APDs (2007),

(1) Demonstration of world's first back-illuminated linear mode GaN APDs (2007).

HIS PRIMARY CONTRIBUTIONS TO THE SOLID STATE LIGHTING

(3) Demonstration of world's first white light emitting diodes based on Stranski-Krastanov mode-grown InGaN quantum dots (2009),

(2) Demonstration of world's first green light emitting diodes grown on LEO GaN (2008),

(1) Demonstration of world's first hybrid green LED based on n-ZnO / (In)GaN MQW / p-GaN (2008).

HIS PRIMARY CONTRIBUTIONS TO THE III-NITRIDE INTERSUBBAND RESEARCH

(3) Demonstration of world's first MOCVD-grown AlN/GaN SLs with intersubband absorbance in complete optical communications wavelengths (2009).

(2) Demonstration of world's first MOCVD-grown AlGaN/GaN SLs with intersubband absorbance as high as 5.3 µm (2009).

(1) Demonstration of world's first MOCVD-grown AlN/GaN SLs absorbing at optical communication wavelengths (as low as at 1.5 µm) (2009).

HIS PRIMARY CONTRIBUTIONS TO THE MATERIAL GROWTH OF III-NITRIDES

(7) Development of high quality AlGaN/GaN SLs with intersubband absorptions as high as 5.3 µm (2009),

(6) Establishment of a unique pulsed growth scheme for high quality AlN/GaN SLs for intersubband absorption at near-infrared regime (2009),

(5) Development of self-assembled InGaN quantum dots emitting in green spectra at room temperature (2009),

(4) Establishment of a unique five-step growth scheme for high quality and reproducable lateral epitaxial overgrowth (LEO) GaN leading to world's first green LEDs on LEO GaN (2008),

(3) Realization of high quality AlGaN leading to world's highest quantum efficiency inheritly-ultraviolet APDs (2008),

(2) Realization of highly doped high quality p-GaN via delta-doping on AlN/Sapphire leading to world's first hybrid green LED based on n-ZnO / (In)GaN MQW / p-GaN , and world's highest linear gain in UV GaN APDs by delta-doped p-GaN (2008),

(1) Realization of high quality GaN regrowth and inherit AlN templates leading to world's highest linear gain in UV GaN APDs and world's first UV Single Photon Detector (2007).