Bayram Butun

High-performance visible-blind GaN-based p-i-n photodetectors

We report high performance visible-blind GaN-based p-i-n photodetectors grown by metal-organic chemical vapor deposition on c-plane sapphire substrates. The dark current of the 200μm diameter devices was measured to be lower than 20pA for bias voltages up to 5V. The breakdown voltages were higher than 120V. The responsivity of the photodetectors was ∼0.23A∕W at 356nm under 5V bias. The ultraviolet-visible rejection ratio was 6.7×103 for wavelengths longer than 400nm.

InGaAs-based high-performance p-i-n photodiodes

We have designed, fabricated, and characterized high-speed and high-efficiency InGaAs-based p-i-n photodetectors with a resonant cavity enhanced structure. The devices were fabricated by a microwave-compatible process. By using a postprocess recess etch, we tuned the resonance wavelength from 1605 to 1558 nm while keeping the peak efficiencies above 60%. The maximum quantum efficiency was 66% at 1572 nm which was in good agreement with our theoretical calculations. The photodiode had a linear response up to 6-mW optical power, where we obtained 5-mA photocurrent at 3-V reverse bias. The photodetector had a temporal response of 16 ps at 7-V bias. After system response deconvolution, the 3-dB bandwidth of the device was 31 GHz, which corresponds to a bandwidth-efficiency product of 20 GHz.

Silicon nanowire network metal-semiconductor-metal photodetectors

We report on the fabrication and characterization of solution-processed, highly flexible, silicon nanowire network based metal-semiconductor-metal photodetectors. Both the active part of the device and the electrodes are made of nanowire networks that provide both flexibility and transparency. Fabricated photodetectors showed a fast dynamic response, 0.43 ms for the rise and 0.58 ms for the fall-time, with a decent on/off ratio of 20. The effect of nanowire-density on transmittance and light on/off behavior were both investigated. Flexible photodetectors, on the other hand, were fabricated on polyethyleneterephthalate substrates and showed similar photodetector characteristics upon bending down to a radius of 1 cm.

Experimental evaluation of impact ionization coefficients in AlxGa1−xN based avalanche photodiodes

The authors report on the metal-organic chemical vapor deposition growth, fabrication, and characterization of high performance solar-blind avalanche photodetectors and the experimental evaluation of the impact ionization coefficients that are obtained from the photomultiplication data. A Schottky barrier, suitable for back and front illuminations, is used to determine the impact ionization coefficients of electrons and holes in an AlGaN based avalanche photodiode.

Solar-blind AlxGa1−xN-based avalanche photodiodes

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 μm diameter devices had a maximum quantum efficiency of 55% and a peak responsivity of 0.11A∕W at 254 nm, and a NEP of 1.89x10−16 W∕Hz1∕2.

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

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 100 V bias, corresponding to 100 pA/cm2 current density. Spectral photoresponse measurement showed the usual spectral behavior and 0.35 A/W responsivity at a 100 V 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 de...

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

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.

Deep-ultraviolet Al0.75Ga0.25N photodiodes with low cutoff wavelength

Deep ultraviolet Al0.75Ga0.25N metal-semiconductor-metal photodetectors with high Al concentration have been demonstrated. A metal-organic chemical vapor deposition grown high quality Al0.75Ga0.25N layer was used as a template. Spectral responsivity, current-voltage, optical transmission, and noise measurements were carried out. The photodetectors exhibited a 229nm cutoff wavelength and a peak responsivity of 0.53A∕W at 222nm. Some 100×100μm2 devices have shown a dark current density of 5.79×10−10A∕cm2 under 50V bias. An ultraviolet-visible rejection ratio of seven orders of magnitude was obtained from the fabricated devices.

ITO-Schottky photodiodes for high-performance detection in the UV-IR spectrum

High-performance vertically illuminated Schottky photodiodes with indium-tin-oxide (ITO) Schottky layers were designed, fabricated, and tested. Ternary and quarternary III-V material systems (AlGaN-GaN, AlGaAs-GaAs, InAlGaAs-InP, and InGaAsP-InP) were utilized for detection in the ultraviolet (UV) (/spl lambda/<400 nm), near-IR (/spl lambda//spl sim/850 nm), and IR (/spl lambda//spl sim/1550 nm) spectrum. The material properties of thin ITO films were characterized. Using resonant-cavity-enhanced (RCE) detector structures, improved efficiency performance was achieved. Current-voltage, spectral responsivity, and high-speed measurements were carried out on the fabricated ITO-Schottky devices. The device performances obtained with different material systems are compared.

Dual-color ultraviolet metal-semiconductor-metal AlGaN photodetectors

Backilluminated ultraviolet metal-semiconductor-metal photodetectors with different spectral responsivity bands were demonstrated on a single AlxGa1−xN heterostructure. This was accomplished by the incorporation of an epitaxial filter layer and the recess etching of the surface. The 11nm full width at half maximum (FWHM) responsivity peak of the detector that was fabricated on the as-grown surface was 0.12A∕W at 310nm with 10V bias, whereas the 22nm FWHM responsivity peak of the detector fabricated on the recess-etched surface was 0.1A∕W at 254nm with 25V bias. Both detectors exhibited excellent dark current characteristics with less than 10fA leakage current.