Physics
Doped Semiconductor
Doped semiconductor refers to a semiconductor material that has been intentionally impurity-doped to alter its electrical properties. This process involves adding small amounts of specific elements, such as phosphorus or boron, to the semiconductor crystal lattice. Doping can increase the semiconductor's conductivity, making it useful for various electronic applications like transistors and diodes.
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10 Key excerpts on "Doped Semiconductor"
eBook - PDF- Giovanni Saggio(Author)
- 2014(Publication Date)
- CRC Press(Publisher)
253 Semiconductor Components Semiconductor components, or devices, are basic elements for all modern electronic products. Therefore, detailed study of them is fundamental, starting from the basic material that they are made of, that is, the semiconductors (Section 3.8 in Chapter 3), and analyzing the artificial treatment they undergo, that is, dop-ing, in order to define their practical use. 8.1 DOPING OF SEMICONDUCTORS A pure matter consists of only one component with definite physical and chemical properties. Curiosity Pure water, H 2 O, consists of two parts hydrogen, 11.1888% by weight, and one part oxygen, 88.812% by weight. It is free from contaminants like particulate, minerals, salts, bacteria, and so on. Be aware that pure water is likely to be found only in laboratories and only under ideal conditions. Distillation and deionization are the common methods of purifying water. Going against common sense, pure water is not a good conductor of electricity at all, but the conductivity rapidly increases as water dissolves ionic species. 8 Principles of Analog Electronics 254 Typical conductivity σ H O 2 values are for ultra pure water S m 5.5 *10 / 6 [ ] -, for drinking water [ ] S m 0.01 / , and for sea water [ ] S m 5 / . A way to measure the “purity” of water is by means of its conductivity. When an arbitrary matter is added with foreign elements that should not be part of the material itself, we talk about impurity . When the foreign elements have been artificially and intentionally added to the material, then we use the term doping . Basically, doping is necessary to change the electrical properties of the pure material. More exactly, to dope means to replace some lattice atoms by suitable doping atoms without changing anything else. For our purposes, the material used to dope must be a semiconductor, the choice of which, among all possibilities, is conditioned by its mechanical and electrical properties.
eBook - PDF- Michael R Fisch(Author)
- 2004(Publication Date)
- WSPC(Publisher)
One exception, the thermistor, is a temperature-sensitive device that is used in temperature control and mea- surement. It utilizes the fact that the number of electron-hole pairs, n, is a strong function of temperature. It increases about 5% per C at room tem- perature. The most important applications employ semiconductors that are made extremely pure and then have their electrical properties very precisely modified by adding controlled, very small amounts of impurities. The pro- cess of adding controlled amounts of impurities is called doping. Transistors and, by extension, all integrated circuits use Doped Semiconductors. Column VB, Group 15 5 valence electrons Z=7, Nitrogen, N 11.4 Doped Semiconductors Z=13, Aluminum, A1 Z=31, Gallium, Ga The normal dopants for silicon and germanium are pentavalent (5 valence electrons) and trivalent (3 valence electrons) elements which are in columns of the periodic table adjacent to silicon and germanium. The following table reproduces part of this area of the periodic table. Z=14, Silicon, Si Z=32, Germanium, Ge Z=15, Phosphorus, P Z=33, Arsenic, As To illustrate how doping works, assume one adds a controlled amount of a pentavalent element to otherwise pure silicon. Only four of the five valence electrons of this element are needed for chemical bonding. At room temper- ature, the extra electron becomes free and goes into the conduction band and becomes a conduction electron. The dopant has donated an electron; therefore, this dopant is called a donor. Since the Doped Semiconductor has negatively charged charge carriers, it is called an n-type semiconductor. Its structure is shown schematically in Fig. 11.3. Once more, the material is electrically neutral overall. Similarly, consider doping a semiconductor with a trivalent element. When the three valence electrons of this element are incorporated, there are too few electrons to form all the covalent bonds, resulting in an unfilled bond.
eBook - PDFNavigating the Materials World
A Guide to Understanding Materials Behavior
- Caroline Baillie, Linda Vanasupa(Authors)
- 2003(Publication Date)
- Academic Press(Publisher)
For example, in Figure 9.1 there is a connector between temperature and carrier concentration. To check that you understand how these two are related, find the sections in this chapter that discuss these concepts. Also, study the challenge calculations. If you can navigate the concept map in this chapter, then you have a good beginning understanding of semicon-ductor materials. 198 Navigating the Materials World Semiconductors pure elements electrical properties optical properties compounds crystal structure Impurity doping are useful for their can be or have have are determined by atomic structure determines bonding may allow Photon emission Photon absorption Photoconductivity Temperature carrier mobility carrier concentration increases extrinsic Impurity doping Temperature Increases intrinsic energy band structure n-type or p-type electrical conductivity determines defines values of or results in Decreases mobility Si C Ge covalent bonds: ionic bonds: GaAs SiC GaN, InP Figure 9.1 Concept map showing some of the basic features of semiconductor materials. What Is a Semiconductor? Simply put, a semiconductor is a material that sometimes conducts elec-trical current. Fortunately, engineers can control when and if the semi-conductor will act as a conductor and when it will act as an insulator, by controlling the properties of the material through processing. Some semiconductor devices, such as diodes and transistors, function as am-plifiers, switches, and memory devices by using the various electrical properties of semiconductors. Other devices, such as solar cells and photodiodes, work by either emitting or absorbing light, and use the optical properties of the material. This chapter does not discuss semicon-ductor devices, but rather provides some guidelines on how to think about semiconductor materials and their properties. Semiconductor materials are either covalently or ionically bonded, sometimes with a mixture of the two types of bonding.
- Wei Gao, Zhengwei Li;Nigel Sammes;;(Authors)
- 2011(Publication Date)
- WSPC(Publisher)
Fig. 5.5 Conductivity σ versus 1/T for Si and Ge (source: L.A.A. Warnes, “Electronic Materials”, Macmillan Education Ltd. 1990). 10 -4 10 -2 10 -0 10 2 10 4 0.8 1.6 2.4 3.2 4.0 σ (S/m) Si Ge 300K 1000 T -1 (K -1 ) 96 Introduction to Electronic Materials for Engineers Fig. 5.6 Schematics showing electron excitation in Si (a) and Ge (b). 5.4 Extrinsic Semiconductor One of the main reasons that semiconductors are useful in electronics is that their properties can be altered in a controllable way by adding small amounts of impurities. These impurities are called dopants. Heavily dop-ing a semiconductor can increase its conductivity by a factor greater than a billion. In modern integrated circuits, for instance, heavily-doped poly-crystalline silicon is often used as a replacement for metals. An extrinsic semiconductor is a semiconductor that has been doped with impurities to modify the number and type of free charge carriers present. 5.4.1 n-type extrinsic semiconductors The purpose of n -type doping is to produce an abundance of mobile or “carrier” electrons in the material. If an atom with five valence electrons, such as phosphorus (P), arsenic (As), or antimony (Sb), is incorporated into the crystal lattice in place of a Si atom, then that atom will have four covalent bonds and one unbonded electron. This • • • • • • ° ° • • ° ° • • • • • • • • • • • • ° • • • • • • • • • • • • 300 K E c E v • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • E f 1.12eV E c E v 0 K (a) • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • E f 0.6 7 eV E c E v 0 K • ° • • • • • ° ° • • ° ° • • ° • • • • • ° • • • ° • • • • • • • • • • • 300 K E c E v • • • (b) Semiconductor, Properties and Materials 97 extra electron is only weakly bound to the atom; and this new state of bonding energy is rather low, ~0.01 eV. It can then be easily excited into the conduction band. At room temperatures, virtually all such electrons are excited into the conduction band.
eBook - PDF- Enrico Prati, Takahiro Shinada, Enrico Prati, Takahiro Shinada(Authors)
- 2016(Publication Date)
- Jenny Stanford Publishing(Publisher)
In this successful history, silicon—the dominant material in electronics today—had to be doped with n-type or p-type impurities [2] for achieving various functionalities and allowing continuous improvements in device performance [3] (Fig. 13.1). In this chapter, we will review our approach in investigat-ing single-dopant transistors and dopant-based functionalities in silicon-on-insulator (SOI) devices containing more than just one impurity atom in their channel. These dopant-rich environments are attractive in terms of applications for mainly two reasons. First, it is still possible to identify single-electron tunneling transport via individual dopant atoms, even though many dopants are present in the channel. Second, several other dopant atoms surrounding Figure 13.1 Integration of dopant-based electronics, focused on electron transport, capture, and detection, with single-photon detection techniques, toward the development of dopant-based optoelectronics. Single-Dopant Transistors in Dopant-Rich Environments 307 the transport dopant can effectively work as charge traps. Charge trapping in these satellite dopant atoms can be studied by using a single-electron tunneling current flowing through the transport dopant. In the first part, results will be introduced for single-dopant transistors, together with several functions, such as single-electron memory and single-electron turnstile. In addition, direct observa-tion of dopant potentials and electron charging in individual dopants by using a low-temperature Kelvin probe force microscopy (KFM) technique will be shown. These observations provide the basis for achieving and monitoring charge trapping at the level of single dopants. In the second part, focus will fall on our results on photon detection, demonstrating trapping of photo-excited electrons in single dopants. These findings open the door to dopant-based optoelectronics and related physics and applications.
eBook - PDF- Pradeep Fulay, Jung-Kun Lee(Authors)
- 2016(Publication Date)
- CRC Press(Publisher)
It is different from the mass of an electron in a vacuum ( m 0 ). Electron–hole pair (EHP): The process by which an electron in the valence band is promoted to the conduction band, creating a hole in the valence band. Elemental semiconductor: An element that shows semiconducting behavior (e.g., silicon). Extrinsic semiconductor: A donor-doped or acceptor-Doped Semiconductor. The conductivity of an extrinsic semiconductor is controlled by the addition of dopants. Freeze-out range: The low-temperature range in which the electrons and the holes remain bonded to the dopant atoms and are not available for conduction. Hole: A missing electron in a bond that is treated as an imaginary particle with a positive charge q. Impurities: Elements or compounds present in semiconductors either inadvertently or because of processing limitations. Their presence is usually considered undesirable. Impurity- or dopant-scattering limited mobility: The value of mobility at low temperatures (but above the carrier freeze-out) limited by the conduction electrons scattering off of the dop-ant or impurity atoms. Indirect band gap semiconductor: A semiconductor in which an electron that has been excited into the conduction band transfers into the conduction band with a change in its momentum. Intrinsic semiconductor: A material whose properties are controlled by thermally generated car-riers. It does not contain any dopants. Isoelectronic dopants: Dopants that have the same valence as the sites they occupy (e.g., germa-nium in silicon or nitrogen in GaP–GaAs materials). This does not create n-type or p-type behavior. Kröger–Vink notation: Notation used for expressing point defects in materials. Lattice-scattering limited mobility: The limited mobility of carriers at high temperatures caused by the scattering of vibrations of atoms known as phonons.
eBook - PDFTransistors: From Crystals To Integrated Circuits
From Crystals to Integrated Circuits
- Michael E Levinshtein, Grigory S Simin, Minna M Perelman(Authors)
- 1998(Publication Date)
- World Scientific(Publisher)
Sometimes it is important for electrons and holes to perish in the device as soon as possible. It is often quite essential for the fast switching of semiconductor devices. Then impurities creating effective recombination centres should be incorporated into the material. Sometimes, on the contrary, electrons and holes must live long. In this case, the semiconductor is to be thoroughly purified. 1.4 Summary Semiconductors are such materials whose conductivity at the temperature of absolute zero is equal to zero, all valence electrons being bound in the inter-atomic orbits and thus unable to conduct an electric current. The energy of the electron bonds is not very great, and even when the temperature is not high, the electron bonds break down on account of thermal motion. There appear free electrons (conduction electrons) and holes. Their concentration increases exponentially with the increase of temperature. And accordingly with the rise of temperature, the conductivity of semiconductors increases exponentially too. Some impurities (donors) are able to give away their electrons quite easily, while others (acceptors) can take electrons from the semiconductor atoms. Introducing such impurities, shallow impurities, even in very small quantities, may increase the number of free carriers to a very great extent and thus greatly increase the semiconductor conductivity. Chapter 1. The Main Properties of Semiconductors 37 Introducing into a semiconductor deep levels with a great ionization energy AE increases both the generation rate and the recombination rate of electrons and holes. With AE ss E g /2 the increase of the rates of generation and recombination is especially great. The influence of the deep levels is especially strong in non-equilibrium situations. When the concentration of electrons and holes is greater than under the equilibrium conditions, the presence of deep centres is displayed by an abrupt decrease of the lifetime of non-equilibrium carriers r.
eBook - PDFStatistical and Thermal Physics
Fundamentals and Applications
- M.D. Sturge(Author)
- 2018(Publication Date)
- A K Peters/CRC Press(Publisher)
A semiconductor is an insulator in which the bandgap is relatively small (for example, in silicon it is 1.1 eV, compared with 10 eV in a “good” insulator such as silicon dioxide). As is explained later in this chapter, a semiconductor, which is an insulator when pure, can be made to conduct at room temperature by the addition of rather small amounts of impurity. In a pure insulator or semiconductor, electrons can be excited from the valence band to the conduction band in two ways: by thermal excitation, or by the absorption of a photon with energy greater than E g . Such excitation leaves a hole (that is, an un h lled electron state) in the valence band. A hole behaves as a particle whose only qualitative di erence from an electron is its positive charge; just as a bubble in beer rises under the in 4 uence of gravity, so in an electric h eld a hole moves in the opposite direction to an electron. When an electron meets a hole, they mutually annihilate or recombine, releasing an energy of about E g . This process may be radiative, in which case a photon with h E g is emitted, or nonradiative, the energy released being dissipated as heat. 13.2 Density of States Near a Band Edge Just as in metals we are primarily interested in states near the Fermi en-ergy, so in semiconductors we are primarily interested in states close to the bandgap. We con h ne our attention to the simple case where the band edges–that is, the maximum in the valence band (VBM) and the minimum in the conduction band (CBM)–are both at k = 0; this is the so-called “direct” bandgap case, 3 illustrated in Figure 13.4. Unlike the case of met-3 The bandgap in semiconductors used for lasers, such as gallium arsenide, is always direct. Silicon and germanium on the other hand, have indirect bandgaps, with VBM 254 13. Electrons and Holes in Semiconductors Figure 13.4. Dispersion relation E ( k ) for electrons near the bandgap in a direct gap semiconductor.
eBook - PDF- John Linsley Hood(Author)
- 2013(Publication Date)
- Butterworth-Heinemann(Publisher)
To summarize the practical aspects of semiconduc-tor action, certain elements within the chemical group 4B will, when in crystal form, show electrical charac-teristics which are intermediate between insulators and conductors, and the normally low conductivity of these materials may be increased by doping them with certain types of impurities. Depending on the type of impurity present, this will cause them to have an excess of electrons, (N type), or conversely a defi-ciency of electrons (P type) giving rise to holes where these electrons should normally have occurred. When a junction is formed between an N type and a P type semiconductor, electronic current can normally flow only in one direction, from the N type region to the P type one, but only when a sufficient voltage is applied in the forward direction, and the size of this voltage will depend on the junction temperature and on the materials from which the junction is formed. The conductivity of semiconductor materials is in-creased by increasing the concentration of the doping impurity, but this also reduces the reverse breakdown voltage of the junction. Although it is convenient to visualize the carriers in P type materials as mobile holes, having the same characteristics as electrons but with a +ve rather than a -ve charge, in reality, the movement of a hole is due to the movement of a sequence of electrons, each leaving a hole behind when it move to fill another adjacent hole. For this reason, while the movement of holes, in response to an applied electric field, appears to be that of small positively charged bodies, the actual speed of movement of holes is much lower than that of electrons. Majority and minority carriers A P type material is defined as a material having a population of acceptor atoms, and an N type one as one with a population of donor ones.
eBook - PDF- R.S. Popovic(Author)
- 2003(Publication Date)
- CRC Press(Publisher)
Therefore, the electron concentration in n-type silicon will be constant to within about þ 1% in the temperature range from ÿ 40 8 C to 125 8 C if the donor concentration is in the range from 10 14 cm ÿ 3 to 10 16 cm ÿ 3 . Distribution and concentration of carriers 31 2.2.6 Heavy doping effects In the previous sections we have considered only pure and lightly Doped Semiconductors. In such semiconductors the energy bands and the density of states in the bands are determined solely by the host atoms of the crystal lattice. However, if more than roughly 10 per 10 6 host atoms are substituted by dopant atoms, the dopant atoms start to affect the band structure of the crystal. Then we say that a semiconductor is heavily doped. We shall now briefly discuss the heavy doping effects [8–10]. A qualitative picture that summarizes the changes that occur in the band structure of an n-type semiconductor due to the doping is given in figure 2.7. As the doping level increases, the band gap narrows, the conduction and valence band edges cease to be sharp and start developing tails, and the donor level broadens and approaches the conduction band. The physical cause of the band-gap narrowing is the interaction between the carriers. If many electrons are present in a crystal, they start to affect the periodic potential field in which each of the electrons moves. The result is a reduction of the electron potential energy and thus a downward shift of the conduction band edge. At the same time the dense electrons screen the electrostatic field of holes. This causes a reduction of the hole potential energy and thus a shift of the valence band edge towards the conduction band. The two effects add up and produce a band-gap narrowing. It is called rigid gap narrowing, since the effects described so far do not affect the sharpness of the band edges. Figure 2.7. Influence of the doping level on the energy band diagram of an n-type semi-conductor (adapted from [9]).
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