Semiconductors and Basic Electronics: Electricity & Magnetism - Module III, Slides of Physics of semiconductor devices

Download Semiconductors and Basic Electronics: Electricity & Magnetism - Module III and more Slides Physics of semiconductor devices in PDF only on Docsity!

SEMICONDUCTORS AND

BASIC ELECTRONICS

MODULE III: ELECTRICITY & MAGNETISM

Contd……

Instructor-

Ambar Bajpai, Ph.D.

2 Moore’s Law and Computing Power Moore’s law, showing the progress in computing power over a 30-year span, illustrated here with Intel chip names. The Pentium 4 contains over 50 million transistors. Courtesy of Intel Corporation. Graph from https://www.extremetech.com/extreme/210872-extremetech-explains-what-is-moores-law

Energy Bands at room temperature 25° eV (electron volt) – the energy absorbed by an electron when it is subjected to a 1V difference of potential 1.2 Semiconductors, Conductors and Insulators

Semiconductor Semiconductors

• Old Days – Germanium (Ge)
• Now – Silicon (Si)
• Now – Gallium Arsenide (GaAs) used for high speed and optical devices.
• New – Silicon Carbide (SiC) – High voltage Schottky diodes. If the material is pure semiconductor material like silicon, the crystal lattice structure forms an excellent insulator since all the atoms are bound to one another and are not free for current flow.

Doping To make the semiconductor conduct electricity, other atoms called impurities must be added. “Impurities” are different elements. This process is called doping.

Semiconductors can be Conductors ■ An impurity, or element like arsenic (As), has 5 valence electrons. ■ Adding arsenic (doping) will allow four of the arsenic valence electrons to bond with the neighbouring silicon atoms. ■ The one electron left over for each arsenic atom becomes available to conduct current flow. ■ DONOR (D) impurity

Another Way to Dope ■ You can also dope a semiconductor material with an atom such as boron that has only 3 valence electrons. ■ The 3 electrons in the outer orbit do form covalent bonds with its neighbouring semiconductor atoms as before. But one electron is missing from the bond. ■ This place where a fourth electron should be is referred to as a hole. ■ The hole assumes a positive charge so it can attract electrons from some other source. ■ Holes become a type of current carrier like the electron to support current flow. ■ B is an ACCEPTOR (A) impurity

Types of Semiconductor Materials ■ The silicon doped with extra electrons is called an “N type” semiconductor. ■ “N” is for negative, which is the charge of an electron. ■ “n-type material”  ND > NA ■ Silicon doped with material missing electrons that produce locations called holes is called “P type” semiconductor. ■ “P” is for positive, which is the charge of a hole. ■ “p-type material”  NA > ND

SEMICONDUCTOR DEVICES

16 Operation of a pn-junction Diode The operation of a pn - junction diode. (a) This is the no-bias case. The small thermal electron current ( It ) is offset by the electron recombination current ( Ir ). The net positive current ( I net) is zero. (b) With a DC voltage applied as shown, the diode is in reverse bias. Now Ir is slightly less than It. Thus there is a small net flow of electrons from p to n and positive current from n to p. (c) Here the diode is in forward bias. Because current can readily flow from p to n , Ir can be much greater than It. [ Note: In each case, It and Ir are electron (negative) currents, but I net indicates positive current.]

10V

1.0kΩ 5V 1.0kΩ Determine the forward voltage and forward current [ forward bias ] for each of the diode model also find the voltage across the limiting

resistor in each cases. Assumed R= 10  at the determined value of

forward current. Diode Models