EEE170 Semiconductor Diodes

Dr. Gordon E. Moore

presented a paper predicting that the transistor count in a single IC chip would double every two years.

Jack St. Clair Kilby

inventor of the integrated circuit and co-inventor of the electronic handheld calculator.

Semiconductors

a special class of elements having a conductivity between that of a good conductor and that of an insulator

Single-crystal semiconductors

such as germanium (Ge) and silicon (Si) have a repetitive crystal structure

compound semiconductors

such as gallium arsenide (GaAs), cadmium sulfide (CdS), gallium nitride (GaN), and gallium arsenide phosphide (GaAsP) are constructed of two or more semiconductor materials of different atomic structures.

Ge, Si, and GaAs.

The three semiconductors used most frequently in the construction of electronic devices

phaseshift oscillator

first integrated circuit invented by Jack S. Kilby in 1958.

valence electrons

For germanium and silicon there are four electrons in the outermost shell

tetravalent

Atoms that have four valence electrons are called

trivalent

those with three valence electrons are called

pentavalent

those with five valence electrons are called

valence

used to indicate that the potential (ionization potential) required to remove any one of these electrons from the atomic structure is significantly lower than that required for any other electron in the structure.

covalent bonding

This bonding of atoms, strengthened by the sharing of electrons

The term free

is applied to any electron that has separated from the fixed lattice structure and is very sensitive to any applied electric fields such as established by voltage sources or any difference in potential.

The term intrinsic

is applied to any semiconductor material that has been carefully ENERGY LEVELS 5 refined to reduce the number of impurities to a very low level—essentially as pure as can be made available through modern technology.

intrinsic carriers

The free electrons in a material due only to external causes are referred to as

relative mobility

the ability of the free carriers to move throughout the material.

doping

The ability to change the characteristics of a material through this process is called

a positive temperature coefficient

This is because the numbers of carriers in a conductor do not increase significantly with temperature, but their vibration pattern about a relatively fixed location makes it increasingly difficult for a sustained flow of carriers through the material. Materials that react in this manner are said to have a

n -type material

is created by introducing impurity elements that have five valence electrons ( pentavalent ), such as antimony , arsenic , and phosphorus.

donor atoms.

Diffused impurities with five valence electrons are called

p -type material

is formed by doping a pure germanium or silicon crystal with impurity atoms having three valence electrons.

acceptor atoms.

The diffused impurities with three valence electrons are called

conventional flow

transfer of holes to the left and electrons to the right, as shown in Fig. 1.10 . The direction to be used in this text is that of

electron, hole

In an n-type material ( Fig. 1.11a ) the ------ is called the majority carrier and the ------- the minority carrier.

hole, electron

In a p-type material the ------ is the majority carrier and the ------- is the minority carrier

semiconductor diode

with applications too numerous to mention, is created by simply joining an n -type and a p -type material together, nothing more, just the joining of one material with a majority carrier of electrons to one with a majority carrier of holes.

depletion region

This region of uncovered positive and negative ions is called ---------- due to the "depletion" of free carriers in the region.

The term bias

refers to the application of an external voltage across the two terminals of the device to extract a response.

zero

In the absence of an applied bias across a semiconductor diode, the net flow of charge in one direction is

Reverse-Bias or "off"Condition

such that the positive terminal is connected to the n -type material and the negative terminal is connected to the p -type materia

A forward-bias or "on" condition

is established by applying the positive potential to the p -type material and the negative potential to the n -type material

breakdown potential

The reverse-bias potential that results in this dramatic change in characteristics is called the

Germanium

is in limited production due to its temperature sensitivity and high reverse saturation current. It is still commercially available but is limited to some high-speed applications (due to a relatively high mobility factor) and applications that use its sensitivity to light and heat such as photodetectors and security systems.

Silicon

Without question the semiconductor used most frequently for the full range of electronic devices. It has the advantage of being readily available at low cost and has relatively low reverse saturation currents, good temperature characteristics, and excellent breakdown voltage levels.

Gallium Arsenide (GaAs)

Since the early 1990s the interest in GaAs has grown in leaps and bounds, and it will eventually take a good share of the development from silicon devices, especially in very large scale integrated circuits.

Resistance Levels

As the operating point of a diode moves from one region to another the resistance of the diode will also change due to the nonlinear shape of the characteristic curve.

dc voltage

The application of a ---------- to a circuit containing a semiconductor diode will result in an operating point on the characteristic curve that will not change with time

ac voltage

The varying input will move the instantaneous operating point up and down a region of the characteristics and thus defines a specific change in current and voltage

DC or static

Defined as a point on the characteristics

AC or dynamic

Defined by a tangent line at the Q -point

Average ac

Defined by a straight line between limits of operation

Curve Tracer

can display the characteristics of a host of devices, including the semiconductor diode