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EE1080/EE 1427 (2015): Semiconductor Fundamentals Credit: 1Timing: Tuesday 10-11:30 am, Friday 8:30-10 amRoom # LH1

SyllabusValence band and Energy band models of intrinsic and extrinsic semiconductors, Thermal equilibrium carrier concentration, Fermi-Dirac distribution, Carrier transport by drift, resistivity, Excess carriers, lifetime, carrier transport by diffusion, Continuity equation. P-N Junction, structure, I-V characteristics, Forward and Reverse bias. Bipolar junction transistor: Structure,DC input and Output characteristics, Application as amplifier and switch. MOSFET: Structure, DC input and Output Characteristics, Applications.

Reading Materials:1. Semiconductor Devices By Sim Dimitrijev2. Solid state electronic devices By Streetman and Banerjee3. Semiconductor Device Fundamentals By Robert. F. Pierret

Grading patternQuiz test 30%End term 60%3. Attendance 10%

Basic Atomic Theory2

3STRUCTURE OF SOLIDSCan be classified under several criteria based on atomic arrangements, electrical properties, thermal properties, chemical bonds etc.Using electrical criterion: Conductors, Insulators, SemiconductorsUsing atomic arrangements: Amorphous, Polycrystalline, Crystalline.Amorphous SolidsNo regular long range order of arrangement in the atoms.Eg. Polymers, cotton candy, common window glass, ceramic.

Polycrystalline SolidsAtomic order present in sections (grains) of the solid.Different order of arrangement from grain to grain. Grain sizes = hundreds of m.An aggregate of a large number of small crystals or grains in which the structure is regular, but the crystals or grains are arranged in a random fashion.

Crystalline SolidsAtoms arranged in a 3-D long range order. Single crystals emphasizes one type of crystal order that exists as opposed to polycrystals.

What is a Semiconductor?Low resistivity => conductorHigh resistivity => insulatorIntermediate resistivity => semiconductorconductivity lies between that of conductors and insulatorsgenerally crystalline in structure for IC devicesIn recent years, however, non-crystalline semiconductors have become commercially very important

polycrystallineamorphous crystalline

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The maximum number of electrons that any shell may hold is described by the equation 2n2, where n is the principle quantum number. Thus, the first shell (n=1) can hold 2 electrons; the second shell (n=2) 8 electrons, and the third shell (n=3) 18 electrons.

Electrons in atoms exist in clouds of distributed probability, not as discrete chunks of matter orbiting the nucleus like tiny satellites, as common illustrations of atoms show.Individual electrons around an atomic nucleus seek unique states, described by fourquantum numbers: thePrincipal Quantum Number, known as theshell; theAngular Momentum Quantum Number, known as thesubshell; theMagnetic Quantum Number, describing theorbital(subshell orientation); and theSpin Quantum Number, or simplyspin. These states are quantized, meaning that no in-between conditions exist for an electron other than those states that fit into the quantum numbering scheme.ThePrincipal Quantum Number(n) describes the basic level or shell that an electron resides in. The larger this number, the greater radius the electron cloud has from the atom's nucleus, and the greater that electron's energy. Principal quantum numbers are whole numbers (positive integers).TheAngular Momentum Quantum Number(l) describes the shape of the electron cloud within a particular shell or level, and is often known as the subshell. There are as many subshells (electron cloud shapes) in any given shell as that shell's principal quantum number. Angular momentum quantum numbers are positive integers beginning at zero and ending at one less than the principal quantum number (n-1).TheMagnetic Quantum Number(ml) describes which orientation a subshell (electron cloud shape) has. Subshells may assume as many different orientations as 2-times the subshell number (l) plus 1, (2l+1) (E.g. for l=1, ml= -1, 0, 1) and each unique orientation is called anorbital. These numbers are integers ranging from the negative value of the subshell number (l) through 0 to the positive value of the subshell number.TheSpin Quantum Number(ms) describes another property of an electron, and may be a value of +1/2 or -1/2.Pauli's Exclusion Principlesays that no two electrons in an atom may share the exact same set of quantum numbers. Therefore, no more than two electrons may occupy each orbital (spin=1/2 and spin=-1/2),2l+1orbitals in every subshell, andnsubshells in every shell, and no more.Spectroscopic notationis a convention for denoting the electron configuration of an atom. Shells are shown as whole numbers, followed by subshell letters (s,p,d,f), with superscripted numbers totaling the number of electrons residing in each respective subshell.An atom's chemical behavior is solely determined by the electrons in the unfilled shells. Low-level shells that are completely filled have little or no effect on the chemical bonding characteristics of elements.Elements with completely filled electron shells are almost entirely unreactive, and are callednoble(formerly known asinert).

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Electrons in atoms exist in clouds of distributed probability, not as discrete chunks of matter orbiting the nucleus like tiny satellites, as common illustrations of atoms show.Individual electrons around an atomic nucleus seek unique states, described by fourquantum numbers: thePrincipal Quantum Number, known as theshell; theAngular Momentum Quantum Number, known as thesubshell; theMagnetic Quantum Number, describing the orbital(subshell orientation); and theSpin Quantum Number, or simplyspin.

These states are quantized, meaning that no in-between conditions exist for an electron other than those states that fit into the quantum numbering scheme.

ThePrincipal Quantum Number(n) describes the basic level or shell that an electron resides in. The larger this number, the greater radius the electron cloud has from the atom's nucleus, and the greater that electron's energy. Principal quantum numbers are whole numbers (positive integers).TheAngular Momentum Quantum Number(l) describes the shape of the electron cloud within a particular shell or level, and is often known as the subshell. There are as many subshells (electron cloud shapes) in any given shell as that shell's principal quantum number. Angular momentum quantum numbers are positive integers beginning at zero and ending at one less than the principal quantum number (n-1).12TheMagnetic Quantum Number(ml) describes which orientation a subshell (electron cloud shape) has. Subshells may assume as many different orientations as 2-times the subshell number (l) plus 1, (2l+1) (E.g. for l=1, ml= -1, 0, 1) and each unique orientation is called anorbital. These numbers are integers ranging from the negative value of the subshell number (l) through 0 to the positive value of the subshell number.

TheSpin Quantum Number(ms) describes another property of an electron, and may be a value of +1/2 or -1/2.

Pauli's Exclusion Principlesays that no two electrons in an atom may share the exact same set of quantum numbers. Therefore, no more than two electrons may occupy each orbital (spin=1/2 and spin=-1/2),2l+1orbitals in every subshell, andnsubshells in every shell, and no more.

Spectroscopic notationis a convention for denoting the electron configuration of an atom. Shells are shown as whole numbers, followed by subshell letters (s,p,d,f), with superscripted numbers totaling the number of electrons residing in each respective subshell.An atom's chemical behavior is solely determined by the electrons in the unfilled shells. Low-level shells that are completely filled have little or no effect on the chemical bonding characteristics of elements.Elements with completely filled electron shells are almost entirely unreactive, and are callednoble(formerly known asinert).

13Intrinsic Semiconductors

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20Electronic Properties of Si Silicon is a semiconductor material.Pure Si has a relatively high electrical resistivity at room temperature.

There are 2 types of mobile charge-carriers in Si:Conduction electrons are negatively charged;Holes are positively charged.

The concentration (#/cm3) of conduction electrons & holes in a semiconductor can be modulated in several ways:by adding special impurity atoms ( dopants )by applying an electric fieldby changing the temperatureby irradiationSemiconductor doping

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Czochralski process32

Summary of Charge Carriers

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