Solar-blind AlxGa1-xN-based avalanche photodiodes

Cataloged from PDF version of article.We report the Metalorganic Chemical Vapor Deposition (MOCVD) growth, fabrication, and characterization of solar blind AlxGa1-xN/GaN-based avalanche photodiodes. The photocurrent voltage characteristics indicate a reproducible avalanche gain higher than 25 at a 72 V applied reverse bias. Under a 25 V reverse bias voltage, the 100 mu m diameter devices had a maximum quantum efficiency of 55% and a peak responsivity of 0.11 A/W at 254 nm, and a NEP of 1.89x10(-16) W/Hz(1/2). (c) 2005 American Institute of Physics

Leakage current by Frenkel-Poole emission in Ni/Au Schottky contacts on Al0.83In0.17N/AlN/GaN heterostructures

Cataloged from PDF version of article.In order to determine the reverse-bias leakage current mechanisms in Schottky diodes on Al0.83In0.17N/AlN/GaN heterostructures, the temperature-dependent current-voltage measurements were performed in the temperature range of 250-375 K. In this temperature range, the leakage current was found to be in agreement with the predicted characteristics, which is based on the Frenkel-Poole emission model. The analysis of the reverse current-voltage characteristics dictates that the main process in leakage current flow is the emission of electrons from a trapped state near the metal-semiconductor interface into a continuum of states which associated with each conductive dislocation

Nanoantenna coupled UV subwavelength photodtectors based on GaN

Cataloged from PDF version of article.The integration of nano structures with opto-electronic devices has many potential applications. It allows the coupling of more light into or out of the device while decreasing the size of the device itself. Such devices are reported in the VIS and NIR regions. However, making plasmonic structures for the UV region is still a challenge. Here, we report on a UV nano-antenna integrated metal semiconductor metal (MSM) photodetector based on GaN. We designed and fabricated Al grating structures. Well defined plasmonic resonances were measured in the reflectance spectra. Optimized grating structure integrated photodetectors exhibited more than sevenfold photocurrent enhancement. Finite difference time domain simulations revealed that both geometrical and plasmonic effects played role in photocurrent enhancement. (C) 2012 Optical Society of Americ

LSPR enhanced MSM UV photodetectors

Cataloged from PDF version of article.We fabricated localized surface plasmon resonance enhanced UV photodetectors on MOCVD grown semi-insulating GaN. Plasmonic resonance in the UV region was attained using 36nm diameter Al nanoparticles. Extinction spectra of the nanoparticles were measured through spectral transmission measurements. A resonant extinction peak around 300nm was obtained with Al nanoparticles. These particles gave rise to enhanced absorption in GaN at 340nm. Spectral responsivity measurements revealed an enhancement factor of 1.5. These results provided experimental verification for obtaining field enhancement by using Al nanoparticles on GaN. © 2012 IOP Publishing Ltd

Electron beam lithography designed silver nano-disks used as label free nano-biosensors based on localized surface plasmon resonance

Cataloged from PDF version of article.We present a label-free, optical nano-biosensor based on the Localized Surface Plasmon Resonance (LSPR) that is observed at the metaldielectric interface of silver nano-disk arrays located periodically on a sapphire substrate by Electron-Beam Lithography (EBL). The nano-disk array was designed by finite-difference and time-domain (FDTD) algorithm-based simulations. Refractive index sensitivity was calculated experimentally as 221-354 nm/RIU for different sized arrays. The sensing mechanism was first tested with a biotin-avidin pair, and then a preliminary trial for sensing heat-killed Escherichia coli (E. coli) O157:H7 bacteria was done. Although the study is at an early stage, the results indicate that such a plasmonic structure can be applied to bio-sensing applications and then extended to the detection of specific bacteria species as a fast and low cost alternative. © 2012 Optical Society of America

Metal–semiconductor–metal photodetector on as-deposited TiO2 thin films on sapphire substrate

Cataloged from PDF version of article.TiO2 thin films are prepared on c-plane sapphire substrates by the RF magnetron sputtering method. The performance of the Pt contact metal–semiconductor–metal (MSM) photodetector fabricated on as-deposited films is studied. The dark current density and the responsivity obtained were 1.57 × 10−9 A/cm2 at 5 V bias and 1.73 A/W at 50 V bias, respectively. Breakdown is not observed up to 50 V bias. Rise and fall times for the photocurrent were 7 and 3 s, respectively. Our results show that high quality MSM photodetectors can be fabricated without high temperature and complicated fabrication steps

The persistent photoconductivity effect in AIGaN/GaN heterostructures grown on sapphire and SiC substrates

Cataloged from PDF version of article.In the present study, we reported the results of the investigation of electrical and optical measurements in Al(x)Ga(1-x)N/GaN heterostructures (x=0.20) that were grown by way of metal-organic chemical vapor deposition on sapphire and SiC substrates with the same buffer structures and similar conditions. We investigated the substrate material effects on the electrical and optical properties of Al(0.20)Ga(0.80)N/GaN heterostructures. The related electrical and optical properties of Al(x)Ga(1-x)N/GaN heterostructures were investigated by variable-temperature Hall effect measurements, photoluminescence (PL), photocurrent, and persistent photoconductivity (PPC) that in turn illuminated the samples with a blue (lambda=470 nm) light-emitting diode (LED) and thereby induced a persistent increase in the carrier density and two-dimensional electron gas (2DEG) electron mobility. In sample A (Al(0.20)Ga(0.80)N/GaN/sapphire), the carrier density increased from 7.59x10(12) to 9.9x10(12) cm(-2) via illumination at 30 K. On the other hand, in sample B (Al(0.20)Ga(0.80)N/GaN/SiC), the increments in the carrier density were larger than those in sample A, in which it increased from 7.62x10(12) to 1.23x10(13) cm(-2) at the same temperature. The 2DEG mobility increased from 1.22x10(4) to 1.37x10(4) cm(-2)/V s for samples A and B, in which 2DEG mobility increments occurred from 3.83x10(3) to 5.47x10(3) cm(-2)/V s at 30 K. The PL results show that the samples possessed a strong near-band-edge exciton luminescence line at around 3.44 and 3.43 eV for samples A and B, respectively. The samples showed a broad yellow band spreading from 1.80 to 2.60 eV with a peak maximum at 2.25 eV with a ratio of a near-band-edge excitation peak intensity up to a deep-level emission peak intensity ratio that were equal to 3 and 1.8 for samples A and B, respectively. Both of the samples that were illuminated with three different energy photon PPC decay behaviors can be well described by a stretched-exponential function and relaxation time constant tau as well as a decay exponent beta that changes with the substrate type. The energy barrier for the capture of electrons in the 2DEG channel via the deep-level impurities (DX-like centers) in AlGaN for the Al(0.20)Ga(0.80)N/GaN/sapphire and Al(0.20)Ga(0.80)N/GaN/SiC heterojunction samples are 343 and 228 meV, respectively. The activation energy for the thermal capture of an electron by the defects Delta E changed with the substrate materials. Our results show that the substrate material strongly affects the electrical and optical properties of Al(0.20)Ga(0.80)N/GaN heterostructures. These results can be explained with the differing degrees of the lattice mismatch between the grown layers and substrates. (C) 2008 American Institute of Physics

Integrated AlGaN quadruple-band ultraviolet photodetectors

Cataloged from PDF version of article.Monolithically integrated quadruple back-illuminated ultraviolet metalsemiconductormetal photodetectors with four different spectral responsivity bands were demonstrated on each of two different Al xGa 1-xN heterostructures. The average of the full-width at half-maximum (FWHM) of the quantum efficiency peaks was 18.15nm for sample A, which incorporated five 1000nm thick epitaxial layers. In comparison, the average FWHM for sample B was 9.98 nm, which incorporated nine 500nm thick epitaxial layers. © 2012 IOP Publishing Ltd

Low dark current and high speed ZnO metal–semiconductor–metal photodetector on SiO2/Si substrate

Cataloged from PDF version of article.ZnO thin films are deposited by radio-frequency magnetron sputtering on thermally grown SiO2 on Si substrates. Pt/Au contacts are fabricated by standard photolithography and lift-off in order to form a metal-semiconductor-metal (MSM) photodetector. The dark current of the photodetector is measured as 1 pA at 100V bias, corresponding to 100 pA/cm(2) current density. Spectral photoresponse measurement showed the usual spectral behavior and 0.35 A/W responsivity at a 100V bias. The rise and fall times for the photocurrent are measured as 22 ps and 8 ns, respectively, which are the lowest values to date. Scanning electron microscope image shows high aspect ratio and dense grains indicating high surface area. Low dark current density and high speed response are attributed to high number of recombination centers due to film morphology, deducing from photoluminescence measurements. These results show that as deposited ZnO thin film MSM photodetectors can be used for the applications needed for low light level detection and fast operation. (C) 2014 AIP Publishing LLC

Dual-color ultraviolet metal-semiconductor-metal AlGaN photodetectors

Backilluminated ultraviolet metal-semiconductor-metal photodetectors with different spectral responsivity bands were demonstrated on a single Alx Ga1-x N heterostructure. This was accomplished by the incorporation of an epitaxial filter layer and the recess etching of the surface. The 11 nm full width at half maximum (FWHM) responsivity peak of the detector that was fabricated on the as-grown surface was 0.12 AW at 310 nm with 10 V bias, whereas the 22 nm FWHM responsivity peak of the detector fabricated on the recess-etched surface was 0.1 AW at 254 nm with 25 V bias. Both detectors exhibited excellent dark current characteristics with less than 10 fA leakage current. © 2006 American Institute of Physics