Browsing by Subject "Electric breakdown"

Now showing 1 - 6 of 6

Open Access
Electric breakdown in polycrystalline semiconductors with highly nonlinear I-V characteristics: Simulations for simple barrier height models
(1997) Yildirim H.E.; Tanatar, Bilal; Canessa, E.
An extension of the Canessa and Nguyen binary model for the nonlinear current-voltage (I-V) characteristics of polycrystalline semiconductors, based on the electrical properties of individual grains, is presented. Simple analytical models for the nonuniform distribution of barrier heights at grain boundaries are assumed. The set of nonlinear Kirchhoff equations, that determine the macroscopic current across the specimen, and the nonlinearity coefficient α are solved numerically. The applied voltage dependence of the barrier height models gives α values reaching ≈ 50, indicating high nonlinearity as required by potential commercial applications. © Tübi̇tak.
Open Access
High-performance solar-blind AlGaN photodetectors
(IEEE, 2004) Özbay, Ekmel; Bıyıklı, Necmi; Kimukin, İbrahim; Tut, Turgut; Kartaloğlu, Tolga; Aytür, Orhan
High-performance aluminum gallium nitride (AlGaN)-based solar-blind (SB) photodetectors were demonstrated using different device structures. The Al x-Ga1-xN layers structure were grown by metalorganic chemical vapor deposition (MOCVD) on sapphire structures. n+ and p+ ohmic contacts on GaN were formed with non-annealed titanium (Ti)/aluminum (Al) and nickel (Ni)/ gold (Au) alloys. Spectral UV photoresponse measurements confirmed the solar-blind response of the devices.
Open Access
High-speed solar-blind photodetectors with indium-tin-oxide Schottky contacts
(American Institute of Physics, 2003) Bıyıklı, Necmi; Kimukin, I.; Kartaloglu, T.; Aytur, O.; Özbay, Ekmel
AlGaN/GaN-based high-speed solar-blind photodetectors were discussed. Current-voltage, spectral responsivity, and high-frequency response characterizations were performed. Breakdown voltages larger than 40 V were obtained. A maximum responsivity of 44 mA/W at 263 nm was measured. True solar-blind detection was also ensured.
Open Access
Investigation of AlGaN buffer layers on sapphire grown by MOVPE
(SPIE, 2004) Van Gemmern, P.; Dikme, Y.; Bıyıklı, Necmi; Kalisch, H.; Özbay, Ekmel; Jansen, R. H.; Heuken, M.
In this work, AlGaN layers were grown on sapphire by metal-organic vapor phase epitaxy (MOVPE) on (0001)-oriented sapphire substrates, with the intention to investigate the effect of varying Al/MO and V/III ratios on the Al incorporation into the AlGaN layers. The parameters Al/MO and V/III describe the proportions of source material inside the reactor. With the help of optical transmission measurements, characteristic cut-off wavelengths of the Al xGa(1-x)N layers were determined. These wavelengths were used to calculate the Al content x of the layers, leading to values between 26.6% and 52.1%. Using the two process parameters Al/MO and V/III as input and the Al content of the AlGaN layers as a response variable, the experimental results were further investigated with the help of the software STATGRAPHICS. An estimated response surface for the variable x was generated. It was found that the Al incorporation is only tunable within a wide range for high V/III ratios of about 900. For constant Al/MO ratios and varying V/III ratios, two different growth characteristics were observed at high and low Al/MO values. This behavior is ascribed to the superposition of two oppositional effects.
Open Access
Rate-distortion optimized layered stereoscopic video streaming with raptor codes
(IEEE, 2007) Tan, A. Serdar; Aksay, A.; Bilen, C.; Bozdağı-Akar, G.; Arıkan, Erdal
A near optimal streaming system for stereoscopic video is proposed. Initially, the stereoscopic video is separated into three layers and the approximate analytical model of the Rate-Distortion (RD) curve of each layer is calculated from sufficient number of rate and distortion samples. The analytical modeling includes the interdependency of the defined layers. Then, the analytical models are used to derive the optimal source encoding rates for a given channel bandwidth. The distortion in the quality of the stereoscopic video that is caused by losing a NAL unit from the defined layers is estimated to minimize the average distortion of a single NAL unit loss. The minimization is performed over protection rates allocated to each layer. Raptor codes are utilized as the error protection scheme due to their novelty and suitability in video transmission. The layers are protected unequally using Raptor codes according to the parity ratios allocated to the layers. Comparison of the defined scheme with two other protection allocation schemes is provided via simulations to observe the quality of stereoscopic video.
Open Access
Response of porcine articular cartilage to irradiation by an ultrafast, burst-mode laser
(Optical Society of America (OSA), 2019) Dzelzainis, T.; Hammouti, S.; Prickaerts, M.; Cassidy, K.; İlday, F. Ömer; Kalaycıoğlu, Hamit; Yavaş, S.; Karamuk, Ş.; Golaraei, A.; Barzda, V.; Akens, M.; Lilge, L.; Marjoribanks, R.
Plasma-mediated ablation by ultrafast pulses is generally considered to be a material-independent process. We show that, in certain circumstances, this assumption may be invalid. Physical processes involved and the impact on applications are discussed.