UV Photodiodes Research Articles

Silicon photodiodes as the VUV photosensor in gas proportional scintillation counters

The application of recently developed VUV silicon photodiodes as a replacement for the standard photomultiplier tube (PMT) in a gas proportional scintillation counter (GPSC) is investigated. A photodiode positioned within the gas envelope would result in a GPSC that is more compact, robust, and simpler to operate. At the 170 nm wavelength of the scintillation light from xenon, UV photodiodes achieve an effective quantum efficiency of 72%, better than the typically 20% figure for PMTs. On the other hand, the lack of amplification in the photodiode readout limits the signal-to-noise ratio that can be achieved. A GPSC based on a silicon photodiode with an active area of 100 mm/sup 2/ and no additional amplification stage achieved energy resolutions of 20.5, 14.5 and 13.4% for 5.9, 22.1, and 59.6 keV X-rays, respectively. Signal noise in the low energy limit extends up to approximately 3 keV.

UV and blue-enhanced avalanche photodiodes for nuclear spectroscopy applications

Avalanche photodiodes of the bevel-edge type have been developed with improved blue and UV response. The detectors have been characterized for use in low-light level applications such as nuclear spectroscopy. An etching technique not used before in avalanche photodiodes has been used to obtain improved blue and UV response. Quantum efficiency up to 40% has been obtained above 200 nm. The gain and dark current are dependent on external voltage, and gains up to 400 are obtained at 1980 V without excess noise, and breakdown occurs at ∼2000 V. The detector exhibits low noise and fast response, necessary for use in nuclear spectroscopy systems. The energy resolution from a 57Co gamma-ray source was measured to be 942 eV (6.4 keV X-rays), which corresponds to 111 r.m.s. noise electrons at the input. We measured the energy resolution of the detector coupled with a 3×3×3 mm 3 BGO scintillator from a 22Na gamma-ray source. The energy resolution at the 511 keV line was 12.5%, which is comparable to photomultiplier tubes coupled to a scintillator of the same size. The resolution with a 3×3×25 mm 3 LSO scintillator was also measured, the energy resolution at 511 keV was 12.1%.

SiC flame sensors for gas turbine control systems

The research and development activities carried out to develop a SiC flame sensor for gas turbines utilized for power generation are discussed. These activities included the fabrication and characterization of SiC UV photodiodes and small SiC signal diodes as well as the designing and testing of production flame detector assemblies. The characteristics that make this solid state flame detector particularly useful for dry low NO x (DLN) premixed oil and natural gas fuels will be described. Since this device provides both analog dc and ac output signals, turbine combustor mode tracking, combustion flame dynamics and flame intensity tracking have been demonstrated. Sensors designed for production have been built, qualified and field tested. These sensors are now being installed in gas turbine power plants and are a component part of the turbine control system. This development has resulted in the first commercialized turbine control application to use SiC electronic devices.

6H-Silicon Carbide Light Emitting Diodes and UV Photodiodes

Silicon carbide has been used to fabricate a variety of short wavelength optoelectronic devices including blue LEDs, green LEDs and UV photodiodes. As a light emitter, 6H-SiC junctions can be tailored to emit light across the visible spectrum. The most widely commercialized device is the blue LED. Over the past years, the quantum efficiency of the Cree Research blue LED has increased significantly. The devices emit light with a peak wavelength of 470 nm with a spectral halfwidth of ≈︂70 nm. The optical power output is typically between 25 and 35 μW at a forward current of 20 mA and 3.2 V. This represents an external quantum efficiency of ≈︂0.05 to 0.07%. Green LEDs have been demonstrated which emit with a peak wavelength of 530 nm. As opposed to the epitaxial junction used in the blue LED, the green devices use ion implanted junctions. The typical output power is similar to that of the blue LED. However, with respect to photometric units, the die luminous intensity is a factor of two higher than the blue LED, 1.2 mcd (millicandela) for a radiant flux output of 33 μW. In addition to short wavelength light emission, the energy bandgap of ≈︂3.0 eV allows for inherently low dark currents and high quantum efficiencies for ultraviolet photodiode detectors made in 6H-SiC, even at high temperatures. These devices typically exhibit a quantum efficiency of 80 to 100% and peak response of ≈︂250 to 280 nm. These characteristics are maintained to at least 350 °C. The dark current density at —1.0 V and 473 K is ≈︂10—11 A/cm2. This corresponds to an extrapolated room temperature current density of ≈︂2 × 10—17 A/cm2 at —1.0 V.

Blue LEDs, UV photodiodes and high-temperature rectifiers in 6H-SiC

Single junction devices in silicon carbide have been developed for use as blue LEDs, UV photodiodes and high- temperature rectifiers. As a light emitter, 6H-SiC junctions can be tailored to emit light across the visible spectrum. The most widely commercialized device is the blue LED. Over the past two years, the quantum efficiency of the Cree blue LED has increased significantly. The devices emit light with a peak wavelength of 470 nm with a spectral halfwidth of ∼70 nm. The optical power output is typically between 12 and 18 μW for a forward current of 20 mA at 3 V. This represents a power efficiency of ∼0.02–0.03%. In addition to blue emission, the energy bandgap of ∼3.0 eV allows for inherently low dark currents and high quantum efficiencies for ultraviolet photodiode detectors made in 6H-SiC, even at high temperatures. These devices typically exhibit a quantum efficiency of 80–100% and peak response of ∼250–280 nm. These characteristics are maintained to at least 623 K. The dark current density at -1.0 V and 473 K is ∼10 -11 A/cm 2. This corresponds to an extrapolated room temperature current density of ∼2 × 10 -17 A/cm 2 at -1.0 V. Rectifiers with blocking voltages as high as ∼1400 V and a forward current rating of 400 mA at ∼3.0 V have been fabricated. For a 710 V rectifier, the reverse bias leakage current density at 200 V is shown to increase from ∼10 -9 to ∼10 -7 A/cm 2 from 300 to 673 K, respectively. The reverse bias breakdown appears to occur via avalanche multiplication processes exhibiting a sharp knee at breakdown. For a ∼1400 V rectifier, the reverse bias leakage current at 1375 V is less than 1 μA at room temperature.

UV photodetectors in 6HSiC

Abstract We have fabricated two types of UV photodetector in 6HSiC: UV photodiodes using SiC Schottky-barrier structures; SiC photodiodes using shallow p-n junctions. The monochromatic sensitivity of the Schottky-barrier photodetectors (at a wavelength of 215 nm) is 0.15 A/W, and of the p-n junction photodetectors (at a wavelength of 225 nm) 0.13 A/W.

Fabrication of SiC epitaxial structures for devices by the method of sublimation in an open system

The growth conditions of 6H-SiC epitaxial layers by an open sublimation method have been studied. Diodes, field effect transistors, UV photodiodes and Schottky barrier diodes are demonstrated.