Detector types photovoltaic

The rectification properties of semiconductor interfaces are the most important electrical characteristic of semiconductor contacts. Certain types of devices, such as transistors, require both ohmic and rectifying contacts on a given semiconductor surface, whereas other devices, such as Schottky barriers, are based on the inherent rectification properties of semiconductor/metal Junctions. Numerous photonic devices, such as photon detectors and photovoltaic cells, require rectification at a semiconductor Junction, and light-emitting diodes require both ohmic contacts and rectifying Junctions in a well-defined geometry. Thus, successful fabrication of a desired device structure depends entirely on the electrical properties of the specific semiconductor contacts that are formed in the process. The principles described above allow the rational fabrication of contacts with the desired properties, and also describe the operation of the resulting devices within a simple, chemically intuitive, kinetic framework. 

Although not specifically delineated, the volume is also divided into three general sections. The first addresses the full spectrum of infrared detectors and contains a limited coverage of all the material presented in subsequent chapters. It serves as an introduction to the volume and presents to the reader an overall view of the present state of the infrared technology art. It also serves as the mortar between the more in-depth discussions which follow. The midsection. Chapters 3,4, and 5, is a detailed analysis of those detector types which are most widely used today thermal, photoconductive/photovoltaic and photoemissive. 

In order to be consistent with the earlier chapters of this volume the detector advances are segregated into general detector types (thermal, photoconductor and photovoltaic, photoemissive, charge transfer devices, and heterodyne). The final section of this chapter presents future detector and related technology advances (from the author s point of view) that would greatly enhance our ability to use optical and infrared detectors to solve basic problems of our society. 

Chapter 4 discussed the general characteristics of photon detectors, provided some details for two classic detector types simple photoconductive (PC) and photovoltaic (PV) detectors, and described general detector operation. That information will suffice for many users of most IR detectors, but we need to at least acknowledge some of the many other photon detectors now available. 

With the advent of newer detector types, usage of the term photoconductor is a bit ambiguous. Sometimes people use it to mean the simple photoconductors described in Chapter 4, and sometimes they mean detectors that behave somewhat like the simple photoconductors. A similar problem is found with the word photovoltaic. ... 

The materials and design of the various photoelectric detectors available are such that the absorption of radiation results in the displacement of electrons and hence in the development of a potential difference between two electrodes. The main types of photoelectric detectors may be classified as either photovoltaic or photoconductive (Figure 2.24). 

Infrared spectrophotometers use photovoltaic-type detectors to measure the intensity of radiation... 

The covalent chemistry of fullerenes has developed very rapidly in the past decade in an effort to modify fuUerene properties for a number of applications such as photovoltaic cells, infrared detectors, optical limiting devices, chemical gas sensors, three-dimensional electroactive polymers, and molecular wires [8, 25, 26, 80-82]. Systematic studies of the redox properties of Cgo derivatives have played a crucial role in the characterization of their unique electronic properties, which lie at the center of these potential applications. Furthermore, electrochemical techniques have been used to synthesize and separate new fullerene derivatives and their isomers as well as to prepare fullerene containing thin films and polymers. In this section, to facilitate discussion of their redox properties, Cgo derivatives have been classified in three groups on the basis of the type of attachment of the addend to the fullerene. In group one, the addends are attached via single bonds to the Cgo surface as shown in Fig. 6(a) and are referred to as singly bonded functionalized derivatives. The group includes... 

The luminous intensity for various types of illuminating and tracer flares is measured by using a photometer which mainly consists of two parts-optical part (mainly photovoltaic detector) and electronic part (consisting of amplifier, digital meter, computer with interface card and printer). The experimental set-up is shown in Figure 5.5. 

The photomultipliers equipped in the Jasco J-500A and Jasco 500C are Hamatsu R-376 and R-316, respectively. The latter is of S-l type. An InSb photovoltaic cell (Judson) is used as a detector for the wavelength region from 1000 to 2400 nm 283). The InSb detector is cooled with liquid nitrogen. An extension of the CD measurements to 11 p can be conducted by using HgCdTe detectors cooled at liquid He temperature 287). 

The imager comprises a silicon substrate 1 in which a read-out circuit such as a CCD is integrated. The read-out circuit has input regions 2 and metal electrodes 3. An array of photovoltaic detector elements 10 are formed in a p-type mercury cadmium telluride body 11 which is mounted by an insulating adhesive 21 on the substrate. Each detector element... 

There are a number of different types of photon detectors, including the photomultiplier tube, the silicon photodiode, the photovoltaic cell, and a class of multichannel detectors called charge transfer devices. Charge transfer detectors include photodiode arrays, charge-coupled devices (CCDs), and charge-injection devices (ClDs). These detectors are used in the UV/VIS and IR regions for both atomic and molecular spectroscopy. 

The type of detector used in an FT-IR spectrometer is highly dependent upon the bandwidth (i.e. the spectral frequencies), the modulation rate of the interferometer, and the intensity of the radiant flux. Several types of detectors are used in the infrared regions photoconductive, photovoltaic, bolometers, pyroelectric and Golay cells. A detailed discussion of detectors may be found elsewhere.12 In general, the photovoltaic and photoconductive detectors can be used in the near- and mid-infrared regions as rapid response, high sensitivity detectors. Usually the bandwidths are limited and will not cover the total ran passed by the beamsplitter. Examples of such detectors are given in Table I. As can be seen from the... 

Schottky barrier if > E, a layer of the semiconductor next to the surface is inverted in type, and there is then a p-n junction within the material. Let us estimate RA with these limitations for a Schottky barrier photovoltaic detector operating at T=77 K we obtain RA <470ohm-cm from (4.29). This estimate represents the upper limit of RA achievable with a Schottky barrier. We should keep this result in mind for comparison later with the RA values calculated for p-n junction photovoltaic detectors. 

We can conclude from Figs. 4.5 and 4.7 that there is no clear theoretical advantage of one of these two alloy systems over the other with respect to R/4, and the same conclusion applies also to However, better understanding and improvement of the carrier lifetimes in both types of Pb,, jSn,jTe and in p-type Hgj j.Cd,jTe are needed to permit realization of the potential photovoltaic detector performance. If Auger recombination is in fact strong in Pb,. n Te [4.39], then Hg, j,Cd,(Te with a p-type layer as the active photodiode region would be preferable. There is also the question of whether a back contact like that of Case (c) can be made. 

Thus the zinc blende structure semiconductors can be useful for intrinsic photoconductive detectors. Compounds such as InSb have been used as intrinsic photoconductors [4.20], as well as for photovoltaic detectors, but greater versatility of wavelength response is possible with the Hg j tCd Te alloy system. The Hgi j.Cd,Te alloys have received considerable development effort in recent years and are the most prominent intrinsic photoconductor materials they will be analyzed in this subsection. The development of Hg, Cd Te has concentrated almost entirely on n-type material since it provides high photoconductive gain however, p-type Hg, Cd,(Te crystals may be useful for intrinsic photoconductive detectors also [4.21]. 

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