Solar-blind detectors

GaN/AlGaN heterostructures for solar-blind detectors have been grown by both RMBE and PMBE. By tuning the AIGaN bandgap the cut-off wavelength has been varied from 360 to 310 nm in p-i-n photovoltaic devices [72,73], Very competitive data were achieved, regarding the responsivity of 0.15 A/W and external quantum efficiencies of over 50%. 

If the flame background emission intensity is reduced considerably by use of an inert gas-sheathed (separated) flame, then an interference filter may be used rather than a monochromator, to give a non-dispersive atomic fluorescence spectrometer as illustrated in Figure 14.36-38 Noise levels are often further reduced by employing a solar blind photomultiplier as a detector of fluorescence emission at UV wavelengths. Such detectors do not respond to visible light. The excitation source is generally placed at 90° to the monochromator or detector. Surface-silvered or quartz mirrors and lenses are often used to increase the amount of fluorescence emission seen by the detector. 

We have also realized interdigital metal-semiconductor-metal (MSM) contacts. We found a strong increase of the current through the stmcture by illuminating it with UV-light. If the stability under reverse bias of regular Schottky diodes (see Fig. 7) is achieved for interdigital stmctures we are confident that MSM stmctures are well suited for the realization of solar-blind UV-detectors. 

Photoplates, films and photo multipliers are used as detectors. Normally, gratings are used at low orders (m < 4) and they have a small grating constant (1/3600 mm < a < 1/300 mm). The different orders can be separated by using special photomultipliers. For instance, with a solar-blind photomultiplier only radiation with a wavelength below 330 nm can be detected. This allows separation of the 1st order radiation at 400 nm from the 2nd order radiation at 200 nm. This can, for example, be applied in polychromators to double the practical resolution. 

Photomultiplier tubes have also been developed with response limited to the ultraviolet region (160 to 320 nm), the so-called solar-blind photomultipliers. They are helpful in reducing stray light effects from visible radiation and are useful as UV detectors in nondispersive systems. 

The photomultiplier tube (PMT) has been widely used as the detector for AFS because of its sensitivity and long linear dynamic range. The operation of the PMT is described elsewhere in this encyclopedia. Commercial AFS instrumentation employs a solar-blind PMT, which is highly sensitive for wavelengths in the UV and vacuum UV wavelengths. 

To realize these important advantages, it is necessary that the output of the source be free of contaminating lines from other elements in addition, the atomizer should emit no significant background radiation. In some instances with electrothermal atomizers, background radiation is minimal, but certainly, it is not with typical flames. To overcome this problem, filters, located between the source and detector, have often been used to remove most of the background radiation. Alternatively, solar-blind photomultipliers, which respond only to radiation of wavelengths shorter than 320 nm. have been applied. For these devices to be used effectively, analyte emission must be below 320 nm. , ... 

Goudjil, K. (2002) Solar blind-UVC photochromic detector and method for calibration. US Patent 6,437,346. 

It responds well to a wide range of hydrocarbon fires and is blind to welding arcs except when very close to the detector. It can see through smoke and other contaminates that could blind a UV detector. It generally ignores lightning, electrical arcs and other forms of radiation. It is blind to solar radiation and resistant to most forms of artificial lighting. 

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