Physics
Photodiode
A photodiode is a semiconductor device that converts light into an electrical current. When photons strike the photodiode, they create electron-hole pairs, generating a flow of current. This process is used in various applications, including light detection, solar cells, and optical communication systems.
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11 Key excerpts on "Photodiode"
eBook - PDF- James C. Daly(Author)
- 2018(Publication Date)
- CRC Press(Publisher)
Among various 111-V materials, InGaAs and InGaAsP have emerged as best candidates for the Photodiode materials. A considerable portion of the discussion is devoted for a review of this development and to point out present achievements and research interests. Several previous review articles on photo diode^,',^ and on photodetectors in generaP9 can be useful for supplementary readings. 11. PRINCIPLES OF PhotodiodeS The basic principle of operation of a Photodiode is the conversion of the incident optical signals into electrical currents by the absorption process in the material employed. The performance characteristics of such devices include: 1 ) photoresponsivity, (2) speed of response, (3) internal current gain, if any, and (4) noise properties. In this section. we shall discuss the fundamental consideration of these characteristics. A. PIN Photodiodes I . Photorespon.sivity ~ l n d Q~luntum Efliciet7c.y In a reverse-biased semiconductor PIN Photodiode, as illustrated in Figure , incoming photons are absorbed, and electron-hole carrier pairs are generated primarily in the depleted I-region (I stands for intrinsic). The photogenerated carrier pairs are separated by the high electric field in the depletion region and are collected across the reverse-biased junction. As the carriers traverse the depletion region, a displacement current is induced at the load as the signal current. For a semiconductor with absorption coefficient a,, at wavelength X, the primary photo-current produced by the absorption of incident light of optical power P, is given by where q is the electronic charge, hv is the photon energy (hv = 1.24IX eV, where A is wavelength in microns), r is the Fresnel reflection coefficient at the semiconductor-air interface, and W is the width of the absorption region. The quantum efficiency q is defined as, (number of carriers generated) ' (number of incident photons)
eBook - PDF- George H. Rieke(Author)
- 2021(Publication Date)
- Cambridge University Press(Publisher)
2 Photodetector Basics This chapter introduces semiconductor physics, which is the basis of many detector types including those discussed in the following four chapters. As an illustration of the basic operation of semiconductor detectors, it discusses in some detail the simplest form of such devices, in which an incident photon stream is absorbed and modifies the conductivity of a chip of semiconductor material. We complete that discussion with a description of the shortcomings of this approach, to motivate the following chapters describing improved detector types. 2.1 Solid State Physics Semiconductors are the basis for most electronic devices, including those used for amplification of photoexcited currents as well as those used to detect photons and create such currents. The electrical properties of a semiconductor are altered dramatically by the absorption of an ultraviolet, visible, or infrared photon. A broad variety of detectors is based on this behavior. Metals, on the other hand, have high electrical conductivity that is only insignificantly modified by the absorption of photons, and insulators require more energy to excite electrical changes than is available from individual visible or infrared photons. Pure semiconductors are described as having intrinsic photoconductivity; small amounts of impurities added to them yield extrinsic photoconductivity, which allows detection of photons with lower energy than that required to excite intrinsic photoconductivity. Most detec- tors operating from the X-ray through the mid-infrared depend on these materials. Because of the broad applications of semiconductors, there is a large infrastructure for their manufacture that is critical for production of sophisticated detector types. To facilitate our discussion, we will first review some of the properties of semi- conductors. The concepts introduced below are used throughout the remaining chapters.
eBook - PDFInformation Photonics
Fundamentals, Technologies, and Applications
- Asit Kumar Datta, Soumika Munshi(Authors)
- 2016(Publication Date)
- CRC Press(Publisher)
Photodetectors based on the external photoelectric effect are photoemissive devices, such as vacuum Photodiodes and the photomultiplier tubes, in which photoelectrons are ejected from the surface of a photocath-ode. Thermal detectors, on the other hand, convert optical energy into heat and thus respond to the optical energy, rather than the number of photons absorbed by the detector [20]. The choice of a photodetector for a particular application depends on the wavelength range of operation, speed of response or response time, and quan-tum efficiency. The wavelength range over which a photodetector operates is determined by the material structure. Various photodetectors used in informa-tion communication are the photoconductors, p-n junction Photodiodes, p-i-n photodetectors, avalanche Photodiodes, and charge-coupled devices (CCDs). Other photodetectors such as, photon detectors are extremely sensitive and can have a high speed of response. In contrast, thermal detectors are rela-tively slow in response because of the slow process of heat diffusion. For these reasons, photon detectors are suitable for detecting low level optical signals in photonic systems, whereas thermal detectors are most often used for optical power measurement or infrared imaging. Photonic Sources and Detectors for Information Processing 159 The characteristic properties of a photodetector are its responsivity or dynamic wavelength range of detection, quantum efficiency, damage threshold or maximum tolerable power, response time, and dark current [21]. Some of these properties are explained below: 1. Quantum efficiency: Quantum efficiency η is defined as the ratio of the number of photo-electrons produced for every photon incident on the photosensitive surface. In other words, quantum efficiency is the prob-ability of generating a charge carrier for each incident photon.
eBook - PDF- L. W. Turner(Author)
- 2013(Publication Date)
- Butterworth-Heinemann(Publisher)
9 PHOTO-ELECTRONIC DEVICES Semiconductor materials can be used to construct many practical devices which use or produce visible or infra-red radiation. The former are described in this Section under the heading of'Photo-electronic Devices' and the latter in Section 10 under the heading of 'Electro-optic Devices'. They are based either on electronic effects resulting from the absorption of such radiation in the material (the photoconductive, photovoltaic, and photoemissive effects), or on the emission of radiation resulting from electronic action inside the material (electroluminescence, see Section 10). Radiation falling on a semiconductor material can produce electron-hole pairs in the material which can be used as charge carriers. Thus the conductivity of the illuminated material is increased considerably. This is the photoconductive effect, and it can be used in various solid-state devices to detect visible and infra-red radiation. If the electron-hole pairs are generated in or near a pn junction, the electrons and holes will be separated by the built-in electric field of the junction. An open-circuit voltage or a short-circuit current will be generated. This photovoltaic effect can be used in Photodiodes to produce both voltage and current in an external circuit. A special form of Photodiode used considerably in practice is the solar cell (9-42). Another device using the photovoltaic effect is the phototransistor. In the phototransistor, the photovoltaic current generated at the collector-base diode is amplified by the transistor action of the emitter. In certain materials, the energy absorbed from the radiation is sufficient not only for the creation of electron-hole pairs but gives the freed electrons enough energy to be emitted from the material. This is the photoemissive effect which is used in such devices as photoemissive tubes, photomultipliers, and image intensifiers.
eBook - ePubMicrowaves Photonic Links
Components and Circuits
- Christian Rumelhard, Catherine Algani, Anne-Laure Billabert(Authors)
- 2013(Publication Date)
- Wiley-ISTE(Publisher)
Chapter 4Photodetectors
4.1. Photodetector definition
Regarding photodetectors, it is possible to speak of current response in units of incident optical power.In the first English texts concerning optoelectronics, current response as a function of optical power (A/W) of a photodetector was called sensitivity . This significant term was gradually replaced by responsivity , which more specifically describes the sensitivity of a photodetector. This nomenclature will be adopted in this text.For photodetectors, it is also possible to speak of quantum efficiency, expressed as:[4.1]with:–np =number of electron-hole pairs generated per second;-φ = number of incident photons per second.The relation between quantum efficiency and responsivityRpdin A/W is:[4.2 ]with:– q= electron charge = 1.602×10-19 C;– h = Planck’s constant = 6.626×10-34 J/s;ν= light wave frequency in hertz.Responsivity takes into account the frequency of the light wave. Consequently, by referring to Table 5.1 , it should be noted that for a quantum efficiency of 100%, the responsivity of an optical photodetector at 1.55 µm is 1.25 A/W, whereas to obtain identical quantum efficiency the responsivity of a photodetector at 0.8 µm is only 0.64 A/W.In the sections below, quantum efficiency notion is used for Photodiodes, while responsivity is used for phototransistors. It is nonetheless possible to go from one to the other through equation [4.2] .4.2. Photodiodes
4.2.1. Presentation
After having been transported by an optical fiber, the amplitude-modulated light flux (or Intensity Modulation) must be demodulated. Amplitude-modulated photodetection (or Direct Detection) is sufficient to detect a modulated microwave frequency or an ultra-wide band signal. This photodetection can be performed by Photodiodes or phototransistors. Phototransistors shall be considered in a subsequent section, whereas Photodiodes are considered below.Optical absorption, i.e. the transformation of photons in electron-hole pairs in different semiconductors assumed to constitute Photodiodes, is first considered. The varying configurations of different Photodiodes will be reviewed and an equivalent electrical model to these components will be detailed. Nonlinearities and their origins will then be considered and how UTC diodes push the limits of these nonlinearities will be discussed. An outline of the different configurations allowing maximum frequency operation of these components is provided. Finally, different configurations allowing an increase in quantum efficiency are presented.
eBook - PDF- Ronald C. Lasky, Ulf L. Osterberg, Daniel P. Stigliani(Authors)
- 1995(Publication Date)
- Academic Press(Publisher)
Sources and detectors are the link between the electronic world of the control systems and the optical world of the fiber. Electronic devices (transistors) and optoelectronic devices (sources and detectors) both operate by virtue of the unique properties of semiconductors. Silicon rules the electronics world primarily because it is amenable to high-volume production. The enormous volume of silicon device production makes silicon by far the least expensive semiconductor. However, silicon has an unfortunate property that makes it less than ideal for use in optoelectronic devices, as will be explained later in this chapter. This property makes it extremely difficult to use silicon for light sources; so light-emitting diodes (LEDs) and laser diodes are made from other semiconducting materials. It turns out that silicon will work as a light detector, just not as efficiently as other semiconductors. So, depending on the application, a silicon detector or another type of detector may be chosen. In this chapter, we start with some basic optics and discuss the optical properties of semiconductors in general and a few common semiconductor materials in particular. Next, we discuss the p-n junction diode—the basic structure is common to all sources and detectors. Then, we look at each type of optoelectronic device in turn, Photodiode detector, avalanche Photodiode detectors, LED, and several different lasers. 3.2 Basic Optics In this section we review some fiindamental optics required for a basic understanding of lasers, LEDs, and detectors. We begin by looking at Fresnel and Bragg reflections—the two most common methods of obtaining reflec-tion within semiconductor devices. Next, we look at waveguiding in a multilayer structure, and finally, we look at the effective index technique that approximates a two-dimensional waveguide to one that is one-dimensional. The objective here is to introduce these concepts without delving too deep into the theory.
eBook - PDF- Simon M. Sze, Yiming Li, Kwok K. Ng(Authors)
- 2021(Publication Date)
- Wiley(Publisher)
22 13.3.4 Metal-Semiconductor Photodiode A metal–semiconductor diode can be used as a high-efficiency photodetector. 23 The energy-band diagram and current transport in a metal–semiconductor diode have been considered extensively in Chapter 3. A metal–semiconductor Photodiode (Fig. 11a) can be operated in two modes, depending on the photon energy: 1. For hν > E g , Fig. 11b, the radiation produces electron–hole pairs in the semicon- ductor, and the characteristics of the Photodiode are similar to those of a p–i–n Photodiode. The quantum efficiency is given by an expression identical to Eq. 25. 2. For smaller photon energy qφ B < hν < E g , Fig. 11c, the photoexcited electrons in the metal can surmount the barrier and be collected by the semiconductor. This process is called internal photoemission and has been used to determine the Schottky-barrier height and to study the hot-electron transport in metal films. 25 For the first process hν > E g and with high reverse bias at breakdown, the diode can be operated as an APD. This will be included in the discussion in the next section— APD. For internal photoemission, the photon is absorbed in the metal layer and a carrier is excited to a higher energy. These hot carriers have momentum in random directions, and those having excess energy larger than the barrier height and momentum toward the semiconductor contribute to the photocurrent. The internal photoemission process is energy dependent and quantum efficiency is given by , (32) where C F is the Fowler emission coefficient. This phenomenon is often applied to measure the barrier height. When a Schottky-barrier diode is scanned with light of variable wavelengths, Fig. 11d shows that the quantum efficiency has a threshold of qφ B , and it increases with the photon energy. When the photon energy reaches E g , η jumps to a much higher value. In practical applications, the internal photoemission only has η 1%.
eBook - PDFSemiconductor Microchips and Fabrication
A Practical Guide to Theory and Manufacturing
- Yaguang Lian(Author)
- 2022(Publication Date)
- Wiley-IEEE Press(Publisher)
77 8 Semiconductor Photonic Devices In the previous chapters, we discussed semiconductor microchips that deal with electrical signals. The characteristic of these microchips is that the input is an elec- trical signal, and the output is also an electrical signal. The protagonist of photonic devices is photons. Their main feature is that the input is electrical signals (energy) and the output is optical signals (radiation). Or on the contrary, the input is optical signals, and the output is electrical signals. Photonic devices can be divided into three categories: (i) convert electrical energy into optical radiation, (ii) detect opti- cal signals through electronic technology, and (iii) convert optical radiation into electrical energy [1]. To understand this kind of device, we need to understand the basic characteristics of light and the principles of luminescence. In this chapter, we introduce these basic characteristics and principles, the difference between spon- taneous emission and stimulated emission, and related devices. 8.1 Light-Emitting Devices and Light-Emitting Principles Photonic devices, sometimes they are called optoelectronic devices. In this type of devices, photons play a key role. It can be seen from Figure 7.20 that although light is also a part of electromagnetic waves, its frequency is much higher than those of RF and microwave used for radio communication and radar. Because photons have short wavelengths and high energy, they will produce some special phenomena in semiconductors. The use of light by humans can be traced back to ancient times. Torches, candles, and oil lamps have accompanied humans for thousands of years as lighting tools. But the true generation of optoelectronic technology is the inven- tion of electric light. Thomas Alva Edison (February 11, 1847–October 18, 1931) invented the incandescent lamp (electric light bulb) in 1879, which opened the era of converting electrical energy into light radiation.
eBook - PDF- Hari Singh Nalwa(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
This device involves the use of a Schottky barrier to produce both an optical absorption mechanism extend-ing beyond the bandgap and a built-in electric field for the collection of charge. A Schottky diode is a device in which an asymmetric potential is created, generally at a semiconductor/metal or semiconductor/metal silicide interface. The photore-sponse is determined by the barrier height at the semiconductor/metal silicide interface and depends on the type of barrier. The most common Schottky diode detector arrays today are based on PtSi and Pd2Si, with cut-off wavelengths of 5.6 and 3.5 , respectively. GaAs Schottky diodes are also used as very fast detectors for high-frequency applications. Schottky diodes are relatively simple to fabricate and are known for their high degree of uniformity. They can be cooled to limit thermal excitation for better performance at low light levels. However, despite various schemes to increase absorption in the silicide layer, the quantum efficiencies of these devices are gen-erally lower than for junction diodes at the same wavelength. This is because the metal silicide films within which the photons must be absorbed have high reflec-tivity and only a limited fraction of the photons can penetrate the metal layer. Moving farther into the far infrared, there is a wavelength limit to absorption by neutral impurities that corresponds to the long wavelength cut-off in intrin-sic detectors. A different absorption mechanism is required for wavelengths that extend beyond the ionization energy of the shallowest available dopants. In both Ge and Si hosts, this is generally achieved by using the temperature dependence Semiconductor Photoconductors 21 of the resistivity of the semiconductor, rather than a direct photon-to-charge con-version. These devices are known as bolometers and are power detectors that ab-sorb radiation and convert it into heat in a semiconductor thermistor [26].
eBook - PDF- Stewart Miller(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
The curves illustrate the tradeoff between speed of response and quantum efficiency at various wavelengths of interest (Mel-chior, 1973b). 18 Photodetectors 5 97 four materials c an be used for Photodiodes operating at λ = 0 .9 μτη, only Ge a nd I n G a A sP ( a nd o t h er I I I -V alloys s u ch as GaAsSb) are s u i t a b le for operation near 1.3 μιη. The advantage of I n G a A sP a nd other alloy mate-rials is t h at their bandgaps c an be v a r i ed by changing the relative concen-t r a t i o ns of their constituents . Germanium Photodiodes h a ve larger d a rk currents because of the narrower bandgap (compared to Si). In the spectra l r e g i on from the visible to 1 μχη, silicon is the preferred materia l s i n ce silicon technology is highly developed . Being an i n d i r e ct bandgap material, its absorption coefficient changes gradually with w a v e-l e n g t h; this allows silicon Photodiodes to be o p t i m i z ed for particular c o m-b i n a t i o ns of wavelength-of-operatio n a nd speed-of-respons e by varying the thickness of the depletion l a y e r. The tradeoffs between response speed ( c a r r i er transit time) a nd absorption e f f i c i e n cy for silicon p -i -n (PIN) Photodiodes a re s h o wn in Fig. 1 8 .2 for the wavelengths of interest for fiber systems (Melchior, 1973b). 1 8 . 2 .3 Noise Considerations The ultimate performance of a communication system is usually s et by n o i se fluctuations presen t at the input to the receiver. Noise degrades the signal a nd impairs the system performance . In an optical receiver, the e s-sentia l sources of n o i se a re associated with the detection a nd a m p l i f i c a t i on processes . Understanding the origin, characteristics , a nd interplay of the v a r i o us n o i se sources is essentia l to the design a nd evaluation of a ny o p-tical communication system .
eBook - PDF- Jia-Ming Liu(Author)
- 2016(Publication Date)
- Cambridge University Press(Publisher)
11.2 Photodetection Noise 381 11.3 PHOTODETECTION MEASURES .............................................................................................................. Several parameters are commonly used to define the performance characteristics of a photo- detector. These parameters can be considered as the figures of merit of a photodetector. They are used for comparing one photodetector to another and for determining the suitability of a photodetector for a particular application. In this section, the basic concepts of these parameters are defined and discussed. 11.3.1 Spectral Response Because the response of a photon detector is wavelength dependent, a given photodetector is responsive only within a finite, specific range of the optical spectrum. The spectral range of response for a photodetector is determined by the material, the structure, and the packaging of the photodetector. The spectral response of a photodetector is usually specified in terms of the spectral responsivity or the spectral detectivity of the photodetector. In choosing a photode- tector for an application, the match between the spectral content of the optical signal and the spectral response of the photodetector is the first thing to be verified. 11.3.2 Quantum Efficiency Quantum efficiency is the probability of generating a charge carrier in a photodetector for each photon that is incident on the photodetector. The external quantum efficiency, η e , is the probability for each photon incident from outside the photodetector to generate a charge carrier that is externally measured, whereas the internal quantum efficiency, η i , is the probability for each photon that actually reaches the active region of the photodetector to be absorbed and converted to an internal charge carrier.
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