Semiconductor diode detector

In EDXRF the secondary X-ray emitted by the excited atom is considered to be a particle (an X-ray photon) whose energy is characteristic of the atom whence it came. The major development which has facilitated this technique is the solid state semiconductor diode detector. An EDXRF system consists of a solid state device which provides an electronic output that is... 

The detector is the most important part of a MMW spectrometer. The photon energy at MMW frequencies is similar to kT (Equation 1.15) and so the noise naturally occurring in the semiconductor diode detectors is significant at these frequencies. The sources are spectrally bright and their close-in sideband noise... 

A cylindrical piece of pure, single-crystal silicon is used. The size of this piece is 4-19 nun in diameter and 3-5 mm thick. The density of free electrons in the silicon is very low, constituting a p-type semiconductor. If the density of free electrons is high in a saniconductor, then we have an n-type semiconductor. Semiconductor diode detectors always operate with a combination of these two types. 

Some spectrophotometric techniques work to enhance sensitivity or utility in other ways. The advent of semiconductor diode array detectors permits entire spectra to be acquired simultaneously instead of one wavelength band at a time. Also, automated spectrophotometric analyzers originally developed for clinical use have been adapted for use at sea when many samples... 

The most common detector for AES is the photomultiplier tube (see p. 174). An alternative approach for the detection of multielement (multiwavelength) information is the charged-coupled device (CCD). A CCD is essentially an array of closely spaced metal-insulator-semiconductor diodes formed on a wafer of semiconductor material. Incident light striking the CCD is converted into an electrical signal. 

The semiconductor detector is similar to an ordinary semiconductor diode composed of p-type and n-type semiconductor material. This detector has become dominant for nuclear spectroscopy (i.e. determination of the energy of nuclear radiation) but it is not so often used for simple measuremrat of count rates. 

Figure 2(a) depicts a typical photodiode detector circuit, in this case ac coupled to an amplifier. The equivalent circuit, in Figure 2(b), shows a current source proportional to incident optical power, a parallel dark current, //), a noise current source which represents the shot or photon noise associated with these currents, and a resistance and capacitance attributable to both the detector and the electrical amplifier. For the vacuum or semiconductor diode, the responsivity, DI, determined for a given wavelength, X, and quantum efficiency, rj, is... 

Semiconductor diodes are used in current mode to measure charged particles and are known as surface barrier detectors. They have very linear responses and are available with thin entrance windows. Surface barrier detectors are good beam monitors when used with low-noise current amplifiers. To understand the action of the particle detector, we will have to understand the basics of the semiconductor detectors. 

This radio receiver is a "crystal set," with a "diode detector." The functions of each part will be described later in this chapter. The crystal in this case is the silicon inside the diode. However, as many readers already know, historically it used to be a single crystal of the mineral galena (lead sulfide), which is a natural semiconductor. It had to be contacted with a sharp metal wire. Surprisingly, the sharp point forces a small region of the N-type galena to become P-type, making a special kind of "point contact" PN junction. At any rate, old style or new, the detector is a rectifier. (It could be a three-wire transistor, with a battery, etc.)... 

T. Ashley, C. Elliott, N. Gordon, R. Hall, A. Johnson, G. Pryce, Room temperature narrow gap semiconductor diodes as sources and detectors in the 5-10 pm wavelength region. J. Cryst Growth 159(1), 1100-1103 (1996)... 

The operation of solid-state microelectronic devices largely depends on specific electrical responses occurring at the interface between materials of different nature. A representative example for this statement is the rectifying property of the metal-semiconductor contact, which has been identified as early as the end of the nineteenth century (the semiconductor properties of galena were identified by Karl Ferdinand Braun in 1874 32 years later, Greenleaf Whittier Pickard patented a crystal radio receiver [1], which used a crystal detector that was actually a metal-semiconductor diode made of galena). As a consequence, the performance of these devices critically depends on the quality and reliability of their interfaces. Organic electronic devices do not escape this universal rule. 

Up to now the heterodyne technique is the most accurate method to determine such line splittings. Its accuracy is comparable with the optical-rf double-resonance method but its application range is more general. Two independent lasers are stabilized onto the line centers of two different molecular transitions (Fig.10.48). The output of the two lasers is superimposed on a nonlinear detector, such as a photomultiplier in the visible range or a semiconductor diode in the infrared. 

The relevance of photonics technology is best measured by its omnipresence. Semiconductor lasers, for example, are found in compact disk players, CD-ROM drives, and bar code scaimers, as well as in data communication systems such as telephone systems. Compound semiconductor-based LEDs utilized in multicolor displays, automobile indicators, and most recendy in traffic lights represent an even bigger market, with approximately 1 biUion in aimual sales. The trend to faster and smaller systems with lower power requirements and lower loss has led toward the development of optical communication and computing systems and thus rapid technological advancement in photonics systems is expected for the future. In this section, compound semiconductor photonics technology is reviewed with a focus on three primary photonic devices LEDs, laser diodes, and detectors. Overviews of other important compound semiconductor-based photonic devices can be found in References 75—78. 

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