Electronic Materials Science

Electronic Materials Science

Modern science and technology requires highly trained materials scientists who can func- 

tion in diverse areas such as metallurgy,biology,ceramics,electronics,and optics,to name 

several fields.It is clear that there are many commonalities in the fields.For example,for 

all solid state materials,structure with all its implications is important.For biology,mol- 

ecular structure is more important than is electronic energy band structure at this junc- 

ture in development. That is not to say that with the development of biomaterials and 

nanotechnology the future will bring bio-inspired electronic and optical devices. For 

many fields structural defects are important as are mechanical properties. For the fields 

of electronics and optics, electronic structure and properties are fundamental to under- 

stand the resulting devices.However,defects and mechanical interactions are also crucial. 

Thus topics in this text were chosen more as a matter ofpracticality,in that to adequately 

cover all areas ofimportance to electronic materials would result in an impractically large 

text. Careful choices had to be made in selecting the most germane material for elec- 

tronic materials science. 

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Electronic Materials Science

Electronic Materials Science

Modern science and technology requires highly trained materials scientists who can func- 

tion in diverse areas such as metallurgy,biology,ceramics,electronics,and optics,to name 

several fields.It is clear that there are many commonalities in the fields.For example,for 

all solid state materials,structure with all its implications is important.For biology,mol- 

ecular structure is more important than is electronic energy band structure at this junc- 

ture in development. That is not to say that with the development of biomaterials and 

nanotechnology the future will bring bio-inspired electronic and optical devices. For 

many fields structural defects are important as are mechanical properties. For the fields 

of electronics and optics, electronic structure and properties are fundamental to under- 

stand the resulting devices.However,defects and mechanical interactions are also crucial. 

Thus topics in this text were chosen more as a matter ofpracticality,in that to adequately 

cover all areas ofimportance to electronic materials would result in an impractically large 

text. Careful choices had to be made in selecting the most germane material for elec- 

tronic materials science. 

Ramon A. Carmona C

C,I 17646653

CRF

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Electronic Properties and Devices.

Electronic Properties and Devices.

In Chapter 10 on electronic properties we make heavy use of the results from Chapter 9, 

in particular, the electronic energy band structure, and adds to this development the use 

of the statistics for electrons, namely Fermi statistics. An estimate is made about the 

number of electronic states for materials, the so-called density of states (DOS) is calcu- 

lated. From the energy band structure, the density of states (DOS), and the probability 

for occupancy, the Fermi-Dirac distribution function, the electronic arrangement for 

solids is deduced. From this arrangement the electronic nature of the materials is 

revealed, and resulting properties are understood. The different kinds of electronic 

materials are also discussed: conductors, semiconductors, superconductors, and non- 

conductors. Electronic conduction is treated both classically and in terms of quantum 

mechanical ideas. For superconduction the popular BCS theory is introduced. Lastly in 

Chapter 10 the electronic nature of organic materials is introduced, and since many of 

the organic materials in use are amorphous, the electronic nature of amorphous mate- 

rials is discussed.In the final chapter,Chapter 11 on junctions,devices,and the nanoscale, 

we reach a point where we can distill the ideas developed in Chapters 9 and 10 that are 

fundamental to designing and understanding electronic and optical devices.Virtually all 

modern electronic and optical devices use the junctions of materials.Thus in Chapter 11 

we commence with junctions and the electronics implications of joining dissimilar mate- 

rials. From junctions, passive devices that do not change flowing currents or applied 

potentials can be constructed such as thermocouples and solid state refrigerators. Then, 

using various junctions, this chapter introduces electronic devices that are important in 

today's microelectronic technology such as diodes,solar cells,transistors,and the devices 

that comprise computer chips. The basis ideas about optical devices are introduced with 

examples. The last section deals with nanotechnology and the kinds of devices that will 

emerge from ongoing research in fabricating nanoscale structures from materials. 

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Electronic Structur

Electronic Structur

In Chapter 9 on electronic structure we consider another aspect ofthe structure ofmate- 

rials, namely the electronic structure. The basic ideas relating to electronic structure

include a consideration of the arrangement of atoms and molecules as was introduced 

in Chapters 2 and 3 plus the addition of a consideration of the interactions of the atoms 

or molecules in their various structural motifs. The interactions among atoms and 

molecules is handled using quantum mechanics. Quantum mechanics enables chemists 

to estimate, if not calculate, the structure of many important molecules using the 

Schrödinger equation. Similarly quantum mechanics enables the calculation of the 

allowed and disallowed energies for the electrons in an array of atoms or molecules in 

condensed phases,such as liquids or solids.The allowed energies are called energy bands, 

and the disallowed energies are called the forbidden energy gaps (FEG) or simply band 

gaps.An old (1931) but useful model for the calculation of electronic energy band struc- 

ture for solids is presented,the Kronig-Penney (KP) model.Despite its simplicity the KP 

model contains many of the important physical ideas that are used in more modern 

models, but without difficult mathematics. Consequently the KP model is useful as a 

vehicle to understand the origin ofallowed electronic energy bands and gaps,but the KP 

model does not enable quantitative estimations of energy bands. Nonetheless, many 

important conclusions can be made regarding the electronic structure of materials using 

the KP model. Associated with the energy band structure is an extensive nomenclature 

and representation language,and this language is introduced to describe electron energy 

band structure. In this chapter there is heavy reliance on the structural ideas and recip- 

rocal space that were introduced in Chapters 2 and 3. 

It is clear that fundamental to understanding electronic and optical properties of 

solids and the devices is the electronic energy band structure; thus Chapters 10 and 11 

make heavy use of the ideas developed in this chapter.Furthermore modern ideas about 

nanotechnology that include quantum well structures, quantum dots, and other small 

intricate structures are understood in terms of the energy band structure and the com- 

parisons that are made to larger devices.

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Mechanical Properties

Mechanical Properties

In the first of the two chapters on mechanical properties the emphasis is the develop- 

ment of the basic ideas and the resulting relationships among the elastic constants. In 

Chapter 7 on the elasticity property of solids, these constants are used to describe the 

behavior of materials that deform elastically,which means that as forces are applied,the 

material deforms, but the material returns to its original state as the forces are removed. 

Most materials exhibit this behavior when small forces are applied for short periods of 

time. There is more interest when larger forces are applied that leave a material perma- 

nently deformed or even causes fracture of the material, since deformation and failure 

relate the usefulness of a material for fabricating products such as cars, bridges, and 

homes. However, as was the case for structure, first the simpler ideal case of elasticity is 

considered and then consideration is given to a more complicated behavior called plas- 

ticity.In Chapter 8 on the plasticity property of solids the underlying ideas are presented 

for permanent deformation or plasticity. The implication of dislocations for the plastic 

deformation of crystalline materials is discussed and creep is briefly discussed. In this 

chapter the deformation of noncrystalline materials such as polymers is discussed, and 

several models that are used to interpret the mechanical response ofthese kinds ofmate- 

rials are developed. 

In microelectronics and photonics many of the devices are constructed by layering 

films of dissimilar materials.Therefore differences in thermal expansion as well as chem- 

ical incompatibilities at the interfaces can lead to performance and reliability issues for 

the devices. Furthermore many of the extreme structural features and extremely small 

sizes of features of the modern devices can exacerbate the mechanical issues that may 

exist for planar and larger devices. In addition the applications of forces on a crystal 

lattice can alter the atomic spacing and therefore affect the electronic nature, meaning 

the electronic energy band structure, of a material. A full analysis of these complicated 

structural and electronic issues is beyond the scope of this text, but a first-order treat- 

ment of the important relationships properties is essential so that advanced study and 

appreciation of the implications of mechanical properties can be accomplished. 

Many modern microelectronics products such as computer chips are fabricated from 

thin films of dissimilar materials.Also,once the layered structures are formed,the prod- 

ucts go through various temperature cycles as part ofthe further processing.These struc- 

tures are prone to the development of stresses that can lead to device failure and to 

shorter useful lifetimes. Consequently the mechanical issues of thermal expansion, 

stresses,and defect formation that are crucial to further study of electronic material reli- 

ability are covered in these two chapters.

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PHASE EQUILIBRIA

Phase Equilibria

Traditional introductory materials science texts usually cover the topic of phase equilib- 

ria adequately for understanding electronic materials. The main reason is based on the 

fact that most introductory materials science texts emphasize metallurgical materials, 

namely metals and alloys, even though these texts have often been modernized with the 

addition of polymers and electronic materials. Metallurgy deals extensively with mixed 

composition alloys such as steel. An understanding of steel and other important alloys 

requires a detailed knowledge of the phase diagram for the system, in order to know 

under what conditions to expect certain alloy phases and the composition of the phases. 

However, oftentimes advanced physics and chemistry courses spend little time on this 

topic, and while some forms of phase equilibrium are covered in undergraduate chem- 

istry courses, solid state phase diagrams are often barely mentioned. It is clear, however, 

that modern trends in materials science and electronic materials science include complex 

materials that can have several phases and wide homogeneity (stoichiometry) ranges. 

Included in the kinds of electronic and photonic materials in which phase equilibria are 

important are modern binary semiconductors that are used extensively for both elec- 

tronic and optical devices, ceramic superconductors, alloy superconductors, magnetic 

alloys, high dielectric constant insulators, and polymer blends. 

In Chapter 6 on phase equilibria we provide simple derivations of the Gibbs phase 

rule and the lever rule and outlines the procedure to estimate phase diagrams from known 

thermodynamic data. All materials scientists deal with the formation of phases from 

some primal state, and hence often the initial stage of phase formation, nucleation 

becomes important in determining final product morphologies. For this reason nucle- 

ation is added in the chapter.An understanding of nucleation phenomena is also impor- 

tant to the understanding of the processes that are used to prepare the thin films used 

for most modern electronic and optical devices. 

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Diffusion

Diffusion

In virtually all solid state reactions and transformation, matter moves; that is, atoms 

and/or molecules are transported to and from the reaction site. Often in the solid state 

that motion is by a random process, and such random processes are termed diffusive 

processes. Early in Chapter 5 on diffusion in solids the form for a variety of diffusion 

equations are compared,and it is observed that seemingly unrelated phenomena are gov- 

erned by equations with the same form,namely there is a flux in response to a force.That 

flux (with units of amount/area · time) can be matter, heat, charge, energy, and so on. 

Even the famous Schroedinger equation of quantum mechanics (see Chapter 9) has the 

form of a diffusion equation.Although only mass diffusion is covered in Chapter 5,heat 

transport, for example, involves the solution of similar equations. 

In the field ofmass diffusion many treatments deal purely with the underlying physics 

that enable random matter transport, while other approaches deal exclusively with the 

mathematics of solving the differential diffusion equations. In Chapter 5 both areas are 

addressed. In addition another fundamental tenet in materials science is introduced, 

namely the random walk problem. While applied strictly to diffusion in this chapter, the 

random walk problem yields insight into how random processes can yield simple under- 

standable results precisely because of the assumed randomness of the system. This is a 

powerful idea that helps hone the intuition of a materials scientist who must often deal 

with seemingly unsolvable problems involving randomness and complexity. In the field 

of electronic materials diffusion plays a central role that includes the transport of 

dopants,other point defects (vacancies and impurities,and electronic carrier diffusion in 

electronic and optical devices.

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C.I 17646653

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