Sharp Cutoff Wavelength Research Articles

The growth of ZnMgO alloy films for deep ultraviolet detection

ZnMgO films are prepared by RF magnetron sputtering using a composite target and the Mg composition of the samples can be controlled easily even at a high growth temperature. The metal–semiconductor–metal photodetector based on the wurtzite Zn0.6Mg0.4O film exhibits a very low dark current (5 pA at |Vbias| = 3 V) and a high UV/visible rejection ratio (more than three orders of magnitude). The peak responsivity of the photodetector is at around 270 nm and a very sharp cutoff wavelength is at a wavelength of about 295 nm corresponding to the absorption edge of the Zn0.6Mg0.4O film.

193 nm deep-ultraviolet solar-blind cubic boron nitride based photodetectors

Deep-ultraviolet (DUV) solar-blind photodetectors based on high-quality cubic boron nitride (cBN) films with a metal/semiconductor/metal configuration were fabricated. The design of interdigitated circular electrodes enables high homogeneity of electric field between pads. The DUV photodetectors present a peak responsivity at 180nm with a very sharp cutoff wavelength at 193nm and a visible rejection ratio (180 versus 250nm) of more than four orders of magnitude. The characteristics of the photodetectors present extremely low dark current, high breakdown voltage, and high responsivity, suggesting that cBN films are very promising for DUV sensing.

THE STUDY OF Pd SCHOTTKY CONTACT ON POROUS GaN FOR UV METAL–SEMICONDUCTOR–METAL (MSM) PHOTODETECTORS

High quality unintentionally doped n-type GaN layers were grown on Si (111) substrate using AlN (about 200 nm) as buffer layer by radio frequency (RF) nitrogen plasma-assisted molecular beam epitaxy (MBE). This paper presents the structural and optical studies of porous GaN sample compared to the corresponding as-grown GaN. Metal–semiconductor–metal (MSM) photodiode was fabricated on the samples. For as-grown GaN-based MSM, the detector shows a sharp cut-off wavelength at 362 nm, with a maximum responsivity of 0.254 A/W achieved at 360 nm. For porous GaN MSM detector, a sharp cut-off wavelength at 360 nm with a maximum responsivity of 0.655 A/W was achieved at 359 nm. Both the detectors show a little decrease in responsivity in the UV spectral region. The MSM photodiode based on porous GaN shows enhanced (2×) magnitude of responsivity relative to the as-grown GaN MSM photodiode. Enhancement of responsivity can be attributed to the relaxation of tensile stress and reduction of surface pit density in the porous sample.

Enhanced UV Photodetector Responsivity in Porous GaN/Si(111) by Metal-Assisted Electroless Etching

This paper presents the structural and optical studies of porous GaN sample compared to the corresponding as grown GaN. The samples were investigated by scanning electron microscopy (SEM), high resolution x-ray diffraction (HRXRD), and photoluminescence (PL). The porous area is very uniform, with pore diameter in the range of 80-110 nm. XRD measurements showed that the (0002) diffraction plane peak width of porous samples was slightly broader than the as-grown sample. PL measurements revealed that the near band edge peak of the porous samples were redshifted. Metal-semiconductor-metal (MSM) photodiode was fabricated on the samples. For as grown GaN sample, this detector shows a sharp cut-off wavelength at 362 nm. A maximum responsivity of 0.258 A/W was achieved at 360 nm. For the porous GaN sample, this detector shows a sharp cut-off wavelength at 364 nm. A maximum responsivity of 0.771 A/W was achieved at 363 nm.

Hybrid AlN–SiC deep ultraviolet Schottky barrier photodetectors

Deep ultraviolet (DUV) Schottky barrier photodetectors have been demonstrated by exploiting the epitaxial growth of high quality AlN epilayer on n-type SiC substrate. The fabricated AlN∕n-SiC hybrid Schottky barrier detectors exhibited a peak responsivity at 200nm with very sharp cutoff wavelength at 210nm, very high reverse breakdown voltages (>200V), very low dark currents (about 10fA at a reverse bias of 50V), and high responsivity and DUV to UV/visible rejection ratio. These outstanding features are direct attributes of the fundamental material properties and high quality of AlN epilayers. The fabricated photodetectors also have a thermal energy limited detectivity at zero bias of about 1.0×1015cmHz1∕2W−1. These results demonstrated that AlN epilayers are an excellent candidate as an active material for DUV optoelectronic device applications.

200 nm deep ultraviolet photodetectors based on AlN

High quality AlN epilayers were grown on sapphire substrates by metal organic vapor deposition and exploited as active deep ultraviolet (DUV) optoelectronic materials through the demonstration of AlN metal-semiconductor-metal (MSM) photodetectors. DUV photodetectors with peak responsivity at 200nm with a very sharp cutoff wavelength at 207nm have been attained. The AlN MSM photodetectors are shown to possess outstanding features that are direct attributes of the fundamental properties of AlN, including extremely low dark current, high breakdown voltage, and high DUV to visible rejection ratio and high responsivity. The results demonstrate the high promise of AlN as an active material for DUV device applications.

Growth of high quality GaN layers with AlN buffer on Si(1 1 1) substrates

High quality GaN layers were grown on Si(111) substrates using high-temperature-grown AlN as buffer layer by rapid thermal process low-pressure metalorganic chemical vapor deposition. The growth and characteristics of AlN buffer layer and the GaN layers were investigated by using scanning electron microscope, X-ray diffraction, photoluminescence (PL), Raman scattering, and Hall measurements at room temperature. It was found that pre-seeding Al to Si surface is a critical condition for AlN growth on Si. Two-dimensional growth of AlN was achieved under optimized conditions. Raman scattering shows a narrow GaN E2 peak and broad AlN E2, E1 peaks. At room temperature, the investigated films are unintentionally doped n-type. The carrier concentration is about 1.3×1017cm−3 and the Hall mobility is about 210cm2/Vs. Metal–semiconductor–metal photoconductive detectors were fabricated on the GaN/Si(111) films. These detectors show a sharp cut-off wavelength at 363nm. A maximum responsivity of 6.9A/W was achieved at 357nm under a 5.0V bias. These results indicate that high quality GaN films on Si(111) can be obtained using the AlN buffer layer, and the potential application of GaN films based on Si substrates.

Low noise AlGaN metal-semiconductor-metal photodiodes

Low noise AlGaN metal-semiconductor-metal photodiodes AlGaN metal-semiconductor-metal photodiodes with a sharp cutoff wavelength as short as 310 nm are reported for the first time. The devices show a low dark current, < 0.3 µA at 40 V. The responsivity is flat over the bandgap, with a high visible rejection. At 28 V bias, the noise equivalent power is lower than 17 pW/Hz1/2 and ~24 pW/Hz1/2 in GaN and Al0.25Ga0.75N photodiodes, respectively.

Radiation limitation of stagnation temperature in high temperature selective absorbers

A sharp-cutoff wavelength high temperature selective surface has been modelled, with a view to determining the stagnation temperature as well as the likely operating temperature. It has been found that, under conditions of low optical concentration, a solar collector receiver coated in a sharp-cutoff surface may be able to operate with acceptable efficiency at temperatures approaching 400°C. Yet, because of a very sudden increase in losses at elevated temperatures, radiation losses may be enough to prevent stagnation (no load) temperatures above 500°C. This result makes it possible to consider using inexpensive all-glass solar evacuated tube construction to drive steam turbines for the production of electricity on an industrial or utility scale.