Challenge of applying ohmic contacts to gallium arsenide. Indepth look metal to semiconductor ms contacts are present in every semiconductor device. Metal semiconductor contact rectifying schottky junction nonrectifying ohmic contacts slideshare uses cookies to improve functionality and performance, and to provide you with relevant advertising. Lecture metal semiconductor contacts for mesfet contd. Field effect transistors an overview sciencedirect topics. Importance of metalsemiconductor contacts is due to. Schottky barrier height dependence on the metal work. Ohmic contact ms junction with large js v small linearize iv. At the same time, such contacts cannot be assumed to have a resistance as low as that of two connected metals. Metalsemiconductor contacts monographs in electrical and electronic engineering rhoderick, e. We need to understand several key energies in the metal and the semiconductor the topmost energy is the vacuum level, e 0. Dec 08, 2007 high speed devices and circuits lecture14 metal semiconductor contacts for mesfet contd.
According to the principle of metal semiconductor contact, for ntype semiconductor, the contact material with mall metal work function should be. Lecture 17 metalsemiconductor junction march 14, 2007 contents. Lecture 1 introduction to semiconductors and semiconductor. I also authorize the university or other individuals to make copies of this. To this end, we will reproduce the main calculations and theoretical analyses reported in the recent publication general atomistic approach for modeling metalsemiconductor interfaces using density functional theory and nonequilibrium greens function, which considers the agsi interface. Metal semiconductor contacts for schottky diode fabrication mark d. Loya bell telephone laboratories, incorporated, murray hill, new jersey 07974, u.
In such case, the carriers are free to flow in or out of the semiconductor so that there is a minimal resistance across the contact. Analytical model of the metalsemiconductor contact for. A description of modern semiconductor technology and the contacts between semiconducting devices and the metal conductors that connect them with the rest. A niau liftoff metallization was used to contact gan and in 2o 3 nws and cnts using electronbeam ebeam or optical lithography.
In order to render the metal semiconductor contacts ohmic, ebeamprocessed devices are found to require a postfabrication, hightemperature anneal, whereas the use of an oxygen plasma. There is no interdiffusion or intermixing of the metal and the semiconductor. Metalsemiconductor contacts schottky contacts metal on lightly doped silicon rectifying ohmic contacts metal on heavily doped silicon low resistance 2 november. The metalsemiconductor ms schottky barrier junction, formed by putting a metal in contact. Schenk et al analytical model of the metalsemiconductor contact for device simulation the wkb approximation is bypassed by interpolating analytically between the asymptotic forms of the eigenfunctions parabolic cylinder functions by means of airy functions. It is well known that the quality of metal semiconductor contacts plays an important role in the performance of various semiconductor devices and integrated circuits. Metal semiconductor interfaces rectifying schottky junction nonrectifying ohmic contacts 4.
Metalsemiconductor contacts for schottky diode fabrication. In particular, a large mismatch between the fermi energy of the metal and semiconductor can result is a highresistance rectifying contact. The rectification property of metalsemiconductor contacts was discovered by ferdinand braun in 1874 using mercury metal contacted with copper sulfide and iron sulfide semiconductors. Introduction formation of barrier current transport processes measurement of barrier height device structures ohmic contact metal. Equation 3 shows that a rectifying junction is formed when a lightly doped semiconductor is contacted with a metal. I understand that this thesis will be made available from the ohiolink etd center and the maag library circulation desk for public access. How ever, irregularities of the metal film such as varia w.
Metalsemiconductor junctions barrier basics shorted metal and semiconductor in physical contact as the distance between the metal and semiconductor decreases to zero, the depletion region grows qf m e f qc s e e c qf b qf m qc s v the final depletion region width is that needed to support a potential change equal to the builtin potential, f b. Contacts between metals and doped semiconductors are ubiquitous in modern technology and find applications in several important areas, e. The difference between the fermi energy and the vacuum level is the workfunction. The metal oxide semiconductor field effect transistor mosfet is one of the cornerstones of modern semiconductor technology. Challenge of applying ohmic contacts to gallium arsenide devices. The term metal silicon contact includes silicidesi contacts. Examples of typical con tacts are given in the table, together with their minimum contact resistances. A fundamental study of advanced metalsemiconductor contacts. The general structure is a lightly doped ptype substrate, into which two regions, the source and the drain, both of heavily doped ntype semiconductor have been embedded. Lecture 1 introduction to semiconductors and semiconductor devices. For gan and other highly ionic semiconductors the schottky barrier heights of metal to iiinitride contacts strongly depend on the difference between the work function of the metal and the electron af. There are no adsorbed impurities or surface charges at the ms interface. Doitpoms tlp library introduction to semiconductors metal.
The metal and semiconductor are in intimate contact on the atomic scale with no layers of any type between the components. Gold has a work function closely matching that of high resistivity cdznte and is a popular choice of contact metal. Quantumatk provides an excellent toolbox to study such interfaces, because it correctly accounts for the semiconductor band gap and doping, and describes the interface using the physically. Metalsemiconductor ohmic and schottky contacts byu. The work function of a material is the energy required to remove an electron from the level of the chemical potential and give it enough energy to escape to infinity and arrive there with zero energy. Chapter 4 metalsemiconductor contacts and semiconductorsemiconductor heterojunctions 4. However, it was not until the twentieth century that the atomic theory of matter became firmly established as an unassailable, demonstrated fact. As with all of these lecture slides, i am indebted to dr. This rela tionship states that for an ntype semiconductor the barrier height is equal to the work function of the metal, m, minus the electron. A high doping narrows the depletion region and increases the probability for tunneling significantly. Therefore, the correct contact preparation is the key technology to fabricate schottky and photoconductive devices.
Metalsemiconductor contacts fermi level pinning is the lack of barrier height modulation with metal work function due to either large density of intrinsic states. Written for semiconductor technologists and physicists engaged in research on semiconductor interfaces, this text emphasizes practical implications wherever they are relevant to device technology. The principle of forming different types of the metalsemiconductor contact is the mismatch of the fermi energy between metal and semiconductor material, which is due to the difference in work functions. Metal semiconductor contacts and devices issn, cohen. The rectifying metal semiconductor junction forms a schottky barrier, making a device known as a schottky diode, while. Thus, optimizing the contacts between 2d semiconductors and metal electrodes is an important technological challenge. The properties of these contacts can vary considerably depending on the nature of the interface with the semiconductor. Platinum metals in ohmic contacts to 111v semiconductors. Importance of metal semiconductor contacts is due to l ohmic metal semiconductor junctions e. For a schottky contact the current governed by thermionic emission over the barrier is given. This behavior is commonly used for creating metal contacts to the outside. Metal semiconductor interfaces rectifying schottky junction nonrectifying ohmic contacts 3. Indeed, the ancient greeks put this hypothesis forward over two millennia ago.
Schottky contacts are formed when doping in the semiconductor is not very high i. Nevertheless, eam explains several aspects depletion widths, capacitance, general iv shape, etc of ohmic and. Conduction mechanisms for metalsemiconductor contacts. Metal semiconductor contacts are an obvious component of any semiconductor device. In solidstate physics, a metal semiconductor ms junction is a type of electrical junction in which a metal comes in close contact with a semiconductor material. Shorted metal and semiconductor, with surface states, in physical contact when the density of surface states is high, as it typically is, the potential barrier that develops is dominated by the location of the surface states in the semiconductor band.
Twodimensional materials inserted at the metalsemiconductor. Its a user clean room facility for semiconductor processing. Nov 02, 2015 metalsemiconductor contacts kasif nabi imi2015007 department of microelectronics indian institute of information technology allahabad 2nd november 2 november 2015 1 2. Sir jagadish chandra bose applied for a us patent for a metalsemiconductor diode in 1901. Most metalsemiconductor contacts are annealed or alloyed after the initial deposition of the metal in an effort to further improve the contact resistivity. By having proper doping profiles and having a smooth interfacial contact layer. This second edition brings a greatly expanded treatment of th.
Unlimited viewing of the articlechapter pdf and any associated supplements and figures. Improved control of the parasitic transistor in the trench mosfet is also achieved and cell size and pitch is reduced relative to conventional structures. The present approach models the charge transfer between the metal and the metalinduced gap states of the semiconductor by the electronegativity difference x x and, therefore, it predicts the chargeneutrality barrier height bn for metalsemiconductor pairs with a,a0. Metaloxidesemiconductor mos fundamentals engineering. Topics covered include the factors that determine the height of the schottky barrier, its currentvoltage characteristics, and its capacitance. Metalsemiconductor ohmic contacts stanford university. Written for semiconductor technologists and physicists engaged in research on. Lecture14 metal semiconductor contacts for mesfet contd. Characterization of the metalsemiconductor interface of. Basic semiconductor material science and solidstate physics all terrestrial materials are made up of atoms. This section describes each of these contacts as well as an analysis of the contact resistance between a metal and a thin semiconductor layer. Comparing the barrier heights of each material in the table, and combining with. Alan doolittle school of electrical and computer engineering.
Semiconductor contact for schottky barrier transistors. We mainly focus on metal semiconductor contacts on molybdenum disulfide. Figure 1 shows the energy band diagram after the contact is made. Plummer, quick reference manual for silicon integrated circuit. Most metal semiconductor contacts are annealed or alloyed after the initial deposition of the metal in an effort to further improve the contact resistivity. Twodimensional ferromagnetsemiconductor transition metal. Ye, school of electrical and computer engineering and birck nanotechnology center, purdue university, west lafayette. Ms junctions can either be rectifying or nonrectifying. In this chapter, the basic device physics, the electrical and transport properties, and the formation and characterization of various metalsemiconductor contacts are presented. The scaling of transistors to sub10 nm dimensions is strongly limited by their contact resistance rc. Switching speed is much higher than that of pn junction diodes.
This chapter introduces several devices that are formed by joining two different. Fmde 6 where fs and fm are fermidirac distribution functions in metal and semiconductor. Metalsemiconductor contacts monographs in electrical and. For an ideal mosc structure, some properties should.
Schottky contacts using conducting probe atomic force microscopy cafm. This second edition brings a greatly expanded treatment of the physics of schottkybarrier formation to its comprehensive discussion of modern semiconductor technology. Figure 1 below shows a schematic of an ideal mosc device. Electrical properties of metal semiconductor contacts digital. Ee311 saraswat ohmic contacts 5 for a tunneling contact the net semiconductor to metal current is given by jsm at k. How important is the metal semiconductor contact for. In modern semiconductor technology, contacts between semiconducting devices and the metal conductors that connect them with the rest of the system are of fundamental importance.
Metal semiconductor contacts play a key role in modern electronic and photonic devices, since the created schottky barriers dominate the transport behavior. Including barrier height calculator and depletion width calculator whenever a metal and a semiconductor are in intimate contact, there exists a potential barrier between the two that prevents most charge carriers electrons or holes from passing from one to. Ideal metal semiconductor contacts assumptions ideal ms contacts metal m and semiconductor s are in intimate contact, on atomic scale no oxides or charges at the interface very bad assumption in some cases some interfaces are dominated by inte rfacial oxides or interface charge. Schottky barrier models 1 the schottkymott model according to schottky and mott 1938 the height of the barrier between a metal and an ntype semiconductor is given by q. Metalsemiconductor interfaces investigated by positron. Rhoderick, 1988, clarendon press, oxford university press edition, in english 2nd ed. Us6437399b1 semiconductor structures with trench contacts.
Metal semiconductor contacts and devices issn kindle edition by cohen, simon s. The importance of metal semiconductor interfaces comes from the fact that most electronic devices are interconnected using metallic wiring that forms metal semiconductor contacts. Topics covered include the currentvoltage relationship, the capacitance of rectifying contacts, and practical methods of fabricating contacts. It is well known that the quality of metalsemiconductor contacts plays an important role in the performance of various semiconductor devices and integrated circuits. Characterization of metal semiconductor contacts using circular transmission line measurement results. Metalsemiconductor contacts kasif nabi imi2015007 department of microelectronics indian institute of information technology allahabad 2nd november 2 november 2015 1 2. Here we present a systematic study of scaling mos2 devices and contacts with varying. Low resistance, stable contacts are critical for the performance and reliability of integrated circuits. Several strategies, such as phase engineering to create lat eral metal semiconductor metal heterojunctions 14, formation of. Semiconductor physics, quantum electronics and optoelectronics.
The role of interface effects and minority carriers in the metal. Gold contacts are often formed by electroless deposition however this forms a complex interface. Methods for fabricating ohmic contacts to nanowires and. My goal is to make some very simple samples, for use in student teaching labs. Metal semiconductor contacts energetic barriers are most often described by the electron affinity model eam. Metal semiconductor contact anchit biswas techno india,saltlake 2. Characterization of metalsemiconductor contacts using. Work purpose the determination of the potential difference that appears at the contact surface between a metal and a semiconductor, potential difference that is known under the name of contact, or diffusion, bias. Semiconductor contacts physics of semiconductor devices wiley online library. Metallic contact between mos2 and ni via au nanoglue cover page pdf available in small 1422 may 2018 with 150 reads how we measure reads. Gilbert ece 340 lecture 35 111611 ideal metalsemiconductor contacts what do the band diagrams look like. Twodimensional materials inserted at the metalsemiconductor interface. Printed in great britain current transport in metalsemiconductormetal msm structures s.
This book deals with the basic science of such contacts, and discusses the electrical properties that are relevant to semiconductor technology. Metalsemiconductor contacts 1988 edition open library. Analysis of currents through the schottky contacts with allowance for the. A short discussion is also given of practical contacts and their application in semiconductor. Metalsemiconductors contacts engineering libretexts. The term metalsilicon contact includes silicidesi contacts. Attractive candidates for semiconductor device contacts minhyun lee, yeonchoo cho, kyungeun byun, keun wook shin, seonggeol nam. To improve the contacts, the interface formed between metal and semiconductor during contact deposition must be better understood.
Ohmic contact ms junction with large js v small linearize iv characteristics. Ideal metalsemiconductor junction outside equilib rium reading assignment. In this chapter, we are concerned with the basic physical principles, electrical properties, and applications of the metal semiconductor contacts and devices. Semiconductor structures such as the trench and planar mosfets umos, trench and planar igbts and trench mcts using trenches to establish a conductor. Dec 08, 2007 high speed devices and circuits lecture metal semiconductor contacts for mesfet contd. Formation of ohmic contacts metal semiconductor contacts can be divided into two types, based on their currentvoltage. The doping profile is an important contributing factor to the currentvoltage relationship of a device.
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