Manijeh Razeghi

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High quality Al 0.2 Ga 0.8 N / GaN superlattices ͑SLs͒ with various ͑GaN͒ well widths ͑1.6 to 6.4 nm͒ have been grown on polar c-plane and nonpolar m-plane freestanding GaN substrates by metal-organic chemical vapor deposition. Atomic force microscopy, high resolution x-ray diffraction, and photoluminescence ͑PL͒ studies of SLs have been carried out to(More)
Avalanche p-in photodiodes were fabricated on AlN templates for back illumination. Structures with different intrinsic layer thicknesses were tested. A critical electric field of 2.73 MV/ cm was estimated from the variation of the breakdown voltage with thickness. From the device response under back and front illumination and the consequent selective(More)
Research into avalanche photodiodes (APDs) is motivated by the need for high sensitivity ultraviolet (UV) detectors in numerous civilian and military applications. By designing photodetectors to utilize low-noise impact ionization based gain, GaN APDs operating in Geiger mode can deliver gains exceeding 1×10 7. Thus with careful design, it becomes possible(More)
M-plane GaN avalanche p-in photodiodes on low dislocation density freestanding m-plane GaN substrates were realized using metal-organic chemical vapor deposition. High quality homoepitaxial m-plane GaN layers were developed; the root-mean-square surface roughness was less than 1 Å and the full-width-at-half-maximum value of the x-ray rocking curve for ͑101(More)
The authors report the Geiger-mode operation of back-illuminated GaN avalanche photodiodes. The devices were fabricated on transparent AlN templates specifically for back illumination in order to enhance hole-initiated multiplication. The spectral response in Geiger-mode operation was analyzed under low photon fluxes. Single photon detection capabilities(More)
Growths of blue and green multi-quantum wells (MQWs) and light-emitting diodes (LEDs) are realized on lateral epitaxial overgrowth (LEO) GaN, and compared with identical structures grown on conventional GaN. Atomic force microscopy is used to confirm the significant reduction of dislocations in the wing region of our LEO samples before active-region growth.(More)
Hybrid green light-emitting diodes ͑LEDs͒ comprised of n-ZnO/ ͑InGaN/ GaN͒ multi-quantum-wells/p-GaN were grown on semi-insulating AlN/sapphire using pulsed laser deposition for the n-ZnO and metal organic chemical vapor deposition for the other layers. X-ray diffraction revealed that high crystallographic quality was preserved after the n-ZnO growth. LEDs(More)
(Invited Talk) SUMMARY 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(More)
Delta ͑␦−͒ doping is studied in order to achieve high quality p-type GaN. Atomic force microscopy, x-ray diffraction, photoluminescence, and Hall measurements are performed on the samples to optimize the ␦-doping characteristics. The effect of annealing on the electrical, optical, and structural quality is also investigated for different ␦-doping(More)
AlGaN/GaN resonant tunneling diodes ͑RTDs͒, consisting of 20% ͑10%͒ aluminum-content in double-barrier ͑DB͒ active layer, were grown by metal-organic chemical vapor deposition on freestanding polar ͑c-plane͒ and nonpolar ͑m-plane͒ GaN substrates. RTDs were fabricated into 35-␮m-diameter devices for electrical characterization. Lower aluminum content in the(More)