High power transistors

Semiconductor High-power transistors High-power microwave Photovoltaic elements Field-effect transistors UV sensors... 

Such efficient minority-carrier injectors have been proposed as emitters for high-power transistors (Kroemer, 1957) and demonstrated using an n-type oxygen-rich polycrystalline Si emitter on a p-type c-Si base (Oh-uchi et al., 1979). The main problem expected to occur at heterojunctions between dissimilar materials is that associated with interfacial states that may either pin the Fermi level or act as generation-recombination centers. However, in the case of a-Si H the abundance of atomic hydrogen should help eliminate the interfacial states. 

In recent times there has been a rapid development in the design of high-power transistors, to such an extent that they are feasible alternatives to thyristors for many applications. The main advantage of transistors is that they can be switched on and off at any point in the conducting half-cycle that can appear across their emitter and collector terminals. They must be protected against the reversal of voltage when the second half-cycle appears across the terminals. It is therefore possible to synthesise the waveforms in such a manner as to reduce the harmonic distortion at the supply terminals to a low level. 

Tra.nsitorAmplifiers. Most gaUium-based field-effect transitor amplifiers (FETs) are manufactured using ion implantation (qv) (52), except for high microwave frequencies and low noise requirements where epitaxy is used. The majority of discrete high electron mobiHty transistor (HEMT) low noise amplifiers are currently produced on MBE substrates. Discrete high barrier transistor (HBT) power amplifiers use MOCVD and MBE technologies. 

The remaining class depicted in Figure 2 is that of soHd-state devices, ie, transistors, various types of semiconductor diode amplifiers, etc. At frequencies below 1 GHz, generation of hundreds or even at the lower frequencies, kilowatts, is feasible by soHd state. Above 1 GHz power capabiHty of soHd-state sources drops. Development of efficient (- 50%) sources at about the 50 W level at S-band (2 GHz) has been demonstrated. It is reasonable to expect soHd-state sources to replace tubes for low frequency and low (<100 W) power appHcations (52). For high power or high frequency, however, tube sources should continue to prevail. 

Another eonsideration is the type of pass unit to be used. From a headroom loss standpoint, it makes absolutely no differenee whether a bipolar power transistor or a power MOSFET is used. The differenee eomes in the drive eireuitry. If the headroom voltage is high, the eontroller (usually a ground-oriented eireuit) must pull eurrent from the input or output voltage to ground. For a single bipolar pass transistor this eurrent is... 

The operation of switehing power supplies ean be relatively easy to understand. Unlike linear regulators whieh operate the power transistor in the linear mode, the PWM switehing power supply operates the power transistors in both the saturated and eutoff states. In these states, the volt-ampere produet aeross the power transistor is always kept low (saturated, low-U/high-/ and eutoff, Hi-T/No-T). This El produet within the power deviee is the loss within all the power semieonduetors. 

With such properties, it could be the ideal material for many semiconductor applications, such as high-power and high-frequency transistors and cold cathodes, or in the harsh environment found in internal-combustion and jet engines. With the advent of CVD diamond, it is now possible to take advantage of these properties. 

High-resistivity, single-crystal silicon Power transistors Floating zone... 

However, the key components to provide the power generating functionality are based on semiconductors. Novel materials and transistor structures based on InP, SiGe and GaN represent an area of extensive R D activities with emphasis on high power, low noise and high operation frequencies. The performance of a real device such as the phase noise of a microwave oscillator depends both on the noise properties of the transistor and on the loss tangent of the oxide material which forms the stabilising resonator. Therefore, material and device related R D activities both on semiconductors and on oxides are essential to open new horizons for microwave communication and sensor applications. 

High electronic properties High-power, high-frequency transistors, high-voltage diodes, ion sensors, active heat sinks, gas sensors, and thermistors... 

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