Solid-state photodetector

Solid-state photodetectors are semiconductors. Because of their small size and the fact that they do not need high voltage, they are suited for portable instruments. Several subtypes are in use ... 

There are other light detectors of interest in luminescence measurements such as photodiodes and other solid-state devices. Their sensitivity is very low compared with PM tubes, and there is a requirement for considerable amplification of the photocurrents. The solid-state photodetectors have the advantage of broad wavelength response in the IR region, beyond the range of PM tubes. 

Figure 3.5. Engineering drawing of a solid-state photodetector with integrated amplifier, current-to-voltage converter, and temperature controller, (courtesy PerkinElmer Optoelectronics)...

Charge coupled device (CCD) A solid-state two-dimensional detector array used for spectroscopy and imaging. Charge-injection device (CID) A solid-state photodetector array used in spectroscopy. 

The laser has a frequency of 780 nm. At the glass fluid interface a component of the laser beam is reflected back down the opposite leg of the waveguide to a solid state photodetector. This is referred to as the reference beam. This will consist of a large amplitude component FT. As this is a direct reflection of the laser output this component will be relatively large and constant. 

Solid-state multi-element detector arrays in the focal planes of simple grating monochromators can simultaneously monitor several absorption features. These devices were first used for uv—vis spectroscopy. Infrared coverage is limited (see Table 3), but research continues to extend the response to longer wavelengths. Less expensive nir array detectors have been applied to on-line process instmmentation (125) (see Photodetectors). 

The basic components of spectrophotometers are a light source, wavelength selector, absorption cell (cuvette), and photodetector. Colorimeters or absorptiometers commonly use nondispersive wavelength selection (a filter with bandwidth 4 -40 nm) and solid state or simple phototube detectors, while spectrophotometers employ a prism or grating monochromator (with bandwidth down to 0.2 nm) and a photomultiplier. Colorimeters are inexpensive and most appropriate for repetitive measurements of absorption at a fixed wavelength. The more expensive spectrophotometer can also fulfill this function, but its main purpose, by virtue of its accurate and variable wavelength control, is the measurement of absorption spectra. 

Photodetectors are devices that convert light into an electric signal that is proportional to the number of photons striking its photosensitive surface. The photomultipfier tube is a commonly used photodetector for measuring light intensity in the UV and visible regions of the spectrum. Photodiodes are solid-state devices that are also used in modern instruments. In older instruments, barrier layer cells (also known as photovoltaic cells) were used as photodetectors, because they were rugged and less expensive. ... 

Figure 1 Typical flow-through cells used for spectrophotometric detection in flowing stream methods. (A) U-shaped cell for implementation in standard spectrophotometers (B) Z-shaped cell as commonly employed in liquid chromatography (C) oval-shaped cell used for both liquid-phase measurements and solid-phase optosensing detection (D) solid-state detector with radially transmitted light beam. LS, light source LED, light-emitting diode PD, photodetector.

Weckler, G.P., Operation of p-n Junction Photodetectors in a Phton Flux Integrating Mode. IEEE Journal of Solid State Circuits, 1967. SC-2(3) p. 65-73. 

I.M. Baker, F.A. Capocci, D.E. Charlton, J.T.M. Wotherspoon, Recombination in cadmium mercury telluride photodetectors. Solid State Electron. 21(11-12), 1475-1480 (1978)... 

Z. Djuric, J. Piotrowsld, Dember IR photodetectors. Solid State Election. 34(3), 265-269 (1991)... 

Infrared detectors fall into the two broad categories— thermal detectors and photodetectors. The former are relatively nonselective and are therefore the most common in infrared spectrophotometers. The latter encompass mostly solid state devices, which tend to be quite limited in useful wavelength range and have found application in infrared analytical equipment only under unique circumstances. 

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