An Essential Guide to Electronic Material Surfaces and Interfaces (eBook)

Leonard J. Brillson (Autor)

eBook Download: EPUB

2016
John Wiley & Sons (Verlag)
9781119027126 (ISBN)

Infos

An Essential Guide to Electronic Material Surfaces and Interfaces is a streamlined yet comprehensive introduction that covers the basic physical properties of electronic materials, the experimental techniques used to measure them, and the theoretical methods used to understand, predict, and design them.

Starting with the fundamental electronic properties of semiconductors and electrical measurements of semiconductor interfaces, this text introduces students to the importance of characterizing and controlling macroscopic electrical properties by atomic-scale techniques. The chapters that follow present the full range of surface and interface techniques now being used to characterize electronic, optical, chemical, and structural properties of electronic materials, including semiconductors, insulators, nanostructures, and organics. The essential physics and chemistry underlying each technique is described in sufficient depth for students to master the fundamental principles, with numerous examples to illustrate the strengths and limitations for specific applications. As well as references to the most authoritative sources for broader discussions, the text includes internet links to additional examples, mathematical derivations, tables, and literature references for the advanced student, as well as professionals in these fields. This textbook fills a gap in the existing literature for an entry-level course that provides the physical properties, experimental techniques, and theoretical methods essential for students and professionals to understand and participate in solid-state electronics, physics, and materials science research.

An Essential Guide to Electronic Material Surfaces and Interfaces is an introductory-to-intermediate level textbook suitable for students of physics, electrical engineering, materials science, and other disciplines. It is essential reading for any student or professional engaged in surface and interface research, semiconductor processing, or electronic device design. 

Autor

Leonard Brillson is a professor of Electrical & Computer Engineering, of Physics, and a Center for Materials Research Scholar at The Ohio State University in Columbus, OH, USA. Prior to that, he directed Xerox Corporation's Materials Research Laboratory and had responsibility for Xerox's long-range physical science and technology programs at the company's research headquarters in Rochester, N.Y. He is a Fellow of IEEE, AAAS, AVS, APS, and MRS and a former Governing Board member of the American Institute of Physics. Professor Brillson has authored over 350 scientific publications in solid-state physics, microelectronics, surface science and materials science and received numerous scientific awards, including the AVS Gaede-Langmuir Award and the National Science Foundation American Competitiveness and Innovation Fellowship for leadership in the field of electrical and computer engineering.

Textauszug

Chapter 1
Why Surfaces and Interfaces of Electronic Materials

1.1 The Impact of Electronic Materials

This is the age of materials – we now have the ability to design and create new materials with properties not found in nature. Electronic materials are one of the most exciting classes of these new materials. Historically, electronic materials have meant semiconductors, the substances that can emit and react to light, generate and control current, as well as respond to temperature, pressure, and a host of other physical stimuli. These materials and their coupling with insulators and metals have formed the basis of modern electronics and are the key ingredient in computers, lasers, cell phones, displays, communication networks, and many other devices. The ability of these electronic materials to perform these functions depends not only on their inherent properties in bulk form but also, and increasingly so, on the properties of their surfaces and interfaces. Indeed, the evolution of these materials over the past 70 years has been for ever decreasing size and increasing complexity, features that have driven ever increasing speeds and the ability to manage ever larger bodies of information. In turn, these are enabling our modern day quality of life.

1.2 Surface and Interface Importance as Electronics Shrink

Surfaces and interfaces are central to microelectronics. One of the most common microelectronic devices is the transistor, whose function can illustrate the interfaces involved and their increasing importance as the scale of electronics shrinks. Figure 1.1 shows the basic structure of a transistor and the functions of its interfaces. Current passes from a source metal to a drain metal through a semiconductor, in this case, Si. Voltage applied to a gate metal positioned between the source and drain serves to attract or repel charge from the semiconductor region, the “channel”, through which current travels. The result is to control or “gate” the current flow by this third electrode. This device is at the core of the microelectronics industry.

Figure 1.1 Source–gate–drain structure of a silicon transistor.

(Brillson 2010. Reproduced with permission of Wiley.)

The interfaces between the semiconductor, metal, and insulator of this device play a central role in its operation. Barriers to charge transport across the metal–semiconductor interface are a major concern for all electronic devices. Low resistance contacts at Si source and drain contacts typically involve metals that produce interface reactions, for example, Ti contacts that react with Si with high temperature annealing to form between Ti and Si, as shown in Figure 1.2a. These reacted layers reduce such barriers to charge transport and the contact resistivity . Such interfacial silicide layers form low resistance, planar junctions that can be integrated into the manufacturing process for integrated circuits and whose penetration into the semiconductor can be controlled on a nanometer scale.

Figure 1.2 Interfaces involved in forming the transistor structure including: (a) the source or drain metal–semiconductor contact with a reacted interface, (b) the gate metal–semiconductor contact separated by an insulator in and near which charges are trapped, and (c) dopant impurity atoms implanted below the surface of a semiconductor to control its carrier concentration.

(Brillson 2010. Reproduced with permission of Wiley.)

The gate–semiconductor interface is another important interface. This junction may involve either: (i) a metal in direct contact with the semiconductor where the interfacial barrier inhibits charge flow or (ii) as widely used in Si microelectronics, a metal–insulator–semiconductor stack to apply voltage without current leakage to the semiconductor's channel region (Figure 1.2b). Lattice sites within the insulator and at the insulator–semiconductor interface can trap charges and introduce electric dipoles that oppose the voltage applied to the gate metal and its control of the channel current. A major goal of the microelectronics industry since the 1950s has been to minimize the formation of these localized charge states.

A third important interface involves the implantation of impurity atoms into the semiconductor to add donor or acceptor “dopants” that control the transistor's n- or p-type carrier type and density within specific regions of the device. This process involves acceleration and penetration of ionized atoms at well-defined depths, nanometers to microns, into the semiconductor, as Figure 1.2c illustrates. This ion implantation also produces lattice damage that high temperature annealing can heal. However, such annealing can introduce diffusion and unintentional doping in other regions of the semiconductor that can change their electronic activity. Outdiffusion of semiconductor constituents due to annealing is also possible, leaving behind electronically active lattice sites. Precise design of materials, surface and interface preparation, thermal treatments, and device architectures are required in order to balance these competing effects.

At the circuit level, there are multiple interfaces between semiconductors, oxides, and metals. For Si transistors, the manufacturing process involves (i) growing a Si boule in a molten bath that can be sectioned into wafers, (ii) oxidizing, diffusing, and implanting with dopants, (iii) overcoating with various metal and organic layers, (iv) photolithographically patterning and etching the wafers into monolithic arrays of devices, and (v) dicing the wafer into individual circuits that can be mounted, wire bonded, and packaged into chips. Within individual circuit elements, there can be many layers of interconnected conductors, insulators, and their interfaces. Figure 1.3 illustrates the different materials and interfaces associated with a transistor at the bottom of a multilayer Al–W–Si-oxide dielectric assembly [1]. Reaction, adhesion, interdiffusion, and the formation of localized electronic states must be carefully controlled at all of these interfaces during the many patterning, etching, and annealing steps involved in assembling the full structure. The materials used in this multilayer device architecture have continued to change over decades to compensate for the otherwise increasing electrical resistance as interconnects between layers shrink into the nanometer regime. These microelectronic materials and architectures continue to evolve in order to achieve higher speeds, reliability, and packing density. This continuing evolution highlights the importance of interfaces since they are an increasing proportion of the entire structure as circuit sizes decrease and become ever more complex.

Figure 1.3 Multilayer, multi-material interconnect architectures at the nanoscale. Feature size of interconnects at right is 45 nm [1].

Besides transistors, many other electronic devices rely on interfaces for their operation. For example, solar cells operate by converting incident light into free electrons and holes that separate and generate current or voltage in an external circuit. The charge separation requires built-in electric fields that occur at metal–semiconductor or semiconductor–semiconductor interfaces. These will be discussed in later chapters. Transistors without metal gates are another such device. Channel current is controlled instead by molecules that adsorb on this otherwise free surface, exchanging charge and inducing electric fields analogous to that of a gate. Interfaces are also important in devices that generate photons, microwaves, and acoustic waves. These devices require low resistance contacts to inject current or apply voltage to the layer that generates the radiation. Otherwise, power is lost at these contacts, reducing or totally blocking power conversion inside the semiconductor. Semiconductor cathodes that emit electrons when excited by incident photons are also sensitive to surface conditions. Surface chemical treatments of specific semiconductors are required in order to promote the emission of multiple electrons when struck by single photons, useful for electron pulse generation or photomultipliers.

For devices on the quantum scale, surfaces and interfaces have an even larger impact. A prime example is the quantum well, one of the workhorses of optoelectronics. Here a semiconductor is sandwiched between two larger gap semiconductors that localize both electrons and holes in the smaller gap semiconductor. This spatial overlap between electrons and holes increases electron–hole recombination and light emission. Since the quantum well formed by this sandwich is only a few monolayers thick, the allowed energies of electrons and holes inside the well are quantized at discrete energies, which promotes efficient carrier population inversion and laser light emission. Imperfections at the interfaces of these quantum wells introduce alternative pathways for recombination that reduce the desired emission involving the quantized states. Such recombination is even more serious for three-dimensional quantum wells, termed quantum dots. Another such example is the two-dimensional electron gas (2DEG) formed when charges accumulate in narrow interfacial layers, only a few tens of nanometers thick, between two semiconductors. The high carrier concentration, high mobility 2DEG is the basis of high electron mobility transistors (HEMTs). As with quantum wells,...

Produkt-Details

• Erscheint lt. Verlag: 12.5.2016
• Sprache: englisch
• Themenwelt: Naturwissenschaften ► Chemie
• Themenwelt: Naturwissenschaften ► Physik / Astronomie ► Festkörperphysik
• Themenwelt: Technik ► Elektrotechnik / Energietechnik
• Themenwelt: Technik ► Maschinenbau
• Schlagworte: Atomic-scale characterization • Chemie • Chemistry • Dünne Schichten, Oberflächen u. Grenzflächen • Dünne Schichten, Oberflächen u. Grenzflächen • Electrical & Electronics Engineering • electronic material • Electronic materials • Elektronische Materialien • Elektrotechnik u. Elektronik • Heterojunction • interfaces • Materials Science • Materialwissenschaften • Nanometer characterization • Oberfläche • Oberfläche • Schottky barrier • semiconductor • spectroscopy • Spektroskopie • Surfaces • Thin Films, Surfaces & Interfaces • Ultrahigh vacuum
• ISBN-13: 9781119027126 / 9781119027126