Unipolar device

In an HBT the charge carriers from an emitter layer are transported across a thin base layer and coUected by a third layer called the coUector. A small base current is present which iacludes the carriers that did not successfully cross the base layer from the emitter to the coUector. The FET is a unipolar device making use of a single charge carrier in each device, either electrons or holes. The HBT is a bipolar device, using both electrons and holes in each device. The emitter and coUector layers are doped the same polarity n- or -type), with the base being the opposite polarity (p- or n-ty- e). An HBT with a n-ty e emitter is referred to as a n—p—n device ap—n—p device has a -type emitter. The n—p—n transistors are typicaUy faster and have been the focus of more research. For the sake of simplicity, the foUowing discussion wiU focus on n—p—n transistors. 

When determining where the power is used, it may come as a surprise that most power is used in a relatively narrow range between a couple of hundred volts to a couple of thousand volts and between an amp to several hundred amps, as can be seen in Figure 1.12. This range lies within the sweet spot for SiC unipolar devices. 

Figure 1.12 The application for power devices relative to their blocking voltage and current ratings. Most power is used in a comparatively narrow range of voltage (200-2,000V) and between 1 Ato several hundred amps. This lies within the sweet spot for SiC unipolar devices. (After [67].)...

Thus, if we begin substituting the old-fashioned Si devices with fresh new ultra-fast SiC unipolar devices, more than 75% of the power will go through an SiC device. 

The single-layer devices, the bilayer devices (with and without the PAN-CSA network electrode), and the inverted devices discussed are unipolar devices operating under a single-bias condition. We now discuss two novel device configurations that can be operated in both forward and reverse dc biases as well as in ac modes the SCALE devices and color-variable bipolar/ac light-emitting devices. 

Gross IN, Platt S, Ritacco R, Andrews C, Furman S, The clinical relevance of electro-myopotential oversensing in current unipolar devices, PACE 1992 15 2023-2027. 

Abstract We review the methods used to simulate the optoelectronic response of organic solar cells and focus on the application of one-dimensional drift-diffusion simulations. We discuss how the important physical processes are treated and review some of the experiments necessary to determine the input parameters for device simulations. To illustrate the usefulness of drift-diffusion simulations, we discuss several case studies, addressing the influence of charged defects on transport in bipolar and unipolar devices, the influence of defects on recombination, device performance and ideality factors. To illustrate frequency domain simulations, we show how to determine the validity range of Mott-Schottky plots for thin devices. Finally, we discuss an example where optical simulations are used to calculate the parasitic absorption in contact layers. 

An important consequence of the use of nonequUibrium methods is that they enable the operation of bipolar and unipolar devices in narrow-bandgap semiconductors at elevated temperamres and offer the possibility to use doping level adjustment to control their performance. This is called pseudo-extrinsic behavior. 

Field effect transistors (FETs) work on an entirely different principle than junction transistors. These devices are sometimes called unipolar devices since only one type of carrier is involved. Although they are much simpler and faster than junction transistors, their development did not begin as early because specialized methods and controls had to be invent for their manufacture. 

As can be seen from the figure of merit in Table 1, diamond fulfills the expectations for power devices from various points of view, unless the technologies are not mature at present. One of the problems with diamond at this stage is that only p-type doping is possible with boron. For varieties of devices and integrated circuits, n-type diamond is preferable, but this is not inevitable because in most cases unipolar devices are possible. 

We have found that the polymer prepared in this way is very well suited for use in semiconductor device structures in which a semiconductor of one carrier type only is required (unipolar devices). The polymer as prepared is extrinsically doped with p-type carriers, to a concentration in the range lO to 10 8 cm 3, and these dopants are not readily mobile under the applied electric fields within these structures. We have made and measured Schottky-barrier diodes, MIS (Metal Insulator Semiconductor) diodes and MISFETs (MIS Field Effect Transistors), and it is the results of these investigations, some of which are published elsewhere [11-17], which are presented in the present chapter. 

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