Point contact rectifier

Winkler, Clemens Alexander (1838-1904) German chemist who discovered germanium, one of the elements predicted by Dmitry Mendeleyev on the basis of the periodic table. Germanium became well known when the physicists William Shockley, Walter Brattain, and John Bardeen used it to make a point contact rectifier and then the first transistor. 

In addition to its use as a rectifier, the p—n junction (26) is the fundamental building block for bipolar, junction EFT (fFET), and MOSFET transistors. A thorough understanding of p—n junctions explains much of transistor behavior. The theory (5) of the p—n junction and its role in bipolar transistors was presented within a year of the discovery of the point-contact transistor. 

Considerable interest in the sohd-state physics of sihcon carbide, that is, the relation between its semiconductor characteristics and crystal growth, has resulted from the expectation that SiC would be useflil as a high temperature-resistant semiconductor in devices such as point-contact diodes (148), rectifiers (149), and transistors (150,151) for use at temperatures above those where sihcon or germanium metals fail (see Semiconductors). 

The formation of barrier layers at point contacts of organic crystals. Example arrays of silver/phthalocyanine mixed crystal/Al point contacts with a forward/backward current ratio of 3000 1 can rectify alternating currents up to 104 Hz 124> see Fig. 10. 

The detector used to convert incident microwave power into an output voltage is often a crystal detector consisting of a fine metal whisker in point contact with a semiconductor. The contact resistance is greater in one direction than in the other, and the small contact capacitance means that the crystal acts as a fast rectifier which is sensitive to microwave radiation. Incident microwave power on the crystal causes a voltage drop so that a current flows. At very low incident microwave power levels the rectified current is proportional to the power and, since this is proportional to the square of the voltage drop across the crystal, the detector is known as a square-law detector. At higher incident powers the rectified current is proportional to the first power of the voltage and the detector is then a linear detector. 

With the extension of radio-communication to ultra-high frequencies the use of point-contact crystal rectifiers in telecommunication circuits has become an established practice. Both silicon and germanium (p. 174) crystal rectifiers are now in use. 

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.)... 

Current-controlling rectifiers are constructed in general on the same circuit principles as potential-controlling rectifiers only with them, the protection current is converted to a voltage via a constant shunt in the control circuit and fed in as the actual value. With devices with two-point control, the ammeter has limiting value contacts that control the motor-driven controlled transformer. 

The cell and the circuit diagram are shown in Fig. 1. The cell consists of a test electrode, El, reference electrode, R, and counter electrode, E2. The ac potential between the test electrode Ej and the reference electrode R is measured by connecting them to a sensitive ac millivoltmeter through the contact key (by connecting point a to point b). The rectified voltage between Ej and R is measured across a dc microvoltmeter (sensitivity, 1 tV/smallest... 

Walter Haus Schottky (1886-1976) received his doctorate in physics under Max Planck from the Humboldt University in Berlin in 1912. Although his thesis was on the special theory of relativity, Schottky spent his life s work in the area of semiconductor physics. He alternated between industrial and academic positions in Germany for several years. He was with Siemens AG until 1919 and the University of Wurzburg from 1920 to 1923. From 1923 to 1927, Schottky was professor of theoretical physics at the University of Rostock. He rejoined Siemens in 1927, where he finished out his career. Schottky s inventions include the ribbon microphone, the superheterodyne radio receiver, and the tetrode vacuum tube. In 1929, he published Thermodynamik, a book on the thermodynamics of solids. Schottky and Wagner studied the statistical thermodynamics of point defect formation. The cation/anion vacancy pair in ionic solids is named the Schottky defect. In 1938, he produced a barrier layer theory to explain the rectifying behavior of metal-semiconductor contacts. Metal-semiconductor diodes are now called Schottky barrier diodes. 

A dilatometer constructed by Sauer is shown in Fig. 45. The sensing element is a linear variable differential transformer, whose rectified output is recorded directly. A pivot arm connects the transformer (A) to the bearing arm (B) and a micrometer screw allows for calibration and adjustment of the transformer. By adjustment of the compensating screw, the pivot arm can be moved so that the contact point (B) is exactly one sample length from the fulcrum. Temperatures above and below ambient can be obtained by circulating gas round the specimen. 

In summary, this study shows the great possibility of generating Cu/n-Si junctions with a nearly perfect rectifying behavior from CuCN solutions. Diode characteristics are comparable to those reported for contacts prepared by physical methods and are not appreciably subject to modification with time. The second promising point is the high adherence of Cu films, which was exploited to electrodeposit adherent Ni films from a modified Watts bath. This two step procedure seems to solve the major difficulty encountered upon growing thick metal layers onto H-Si surfaces from acidic solutions and enables to prepare stable electrical junctions with defined electrical properties. 

Overhead Recycle (OHR) Process- the OHR has often been used instead of GSP for Propane recovery from Natural gas. Although typically used in a two column configuration, this process essentially withdraws a vapor stream from an intermediate point in the column that is then condensed and used as a reflux for the upper portion of the first column. This again produced cold liquids to contact and rectify the vapor leaving the expander, the absorbing the propane plus components for recovery in the bottom product of the second column. 

These MIM diodes can be used as mixing elements at optical frequencies. When illuminating the contact point with a focused CO2 laser, a response time of 10 s or better has been demonstrated by the measurement of the 88-THz emission from the third harmonic of the CO2 laser. If the beams of two lasers with the frequencies f and /2 are focused onto the junction between the nickel oxide layer and the sharp tip of a tungsten wire, the MIM diode acts as a rectifier and the wire as an antenna, and a signal with the difference frequency f — f2 is generated. Difference frequencies up into the terahertz range can be monitored [4.111] (see Sect. 5.8.7). The basic processes in these MIM diodes represent very interesting phenomena of solid-state physics. They could be clarified only recently [4.111]. 

---