ENERGY DEVICES (Mod 4) - SEMICONDUCTORS

Question 1

define semiconductors

Answer 1

• A semiconductor is a substance, usually a solid chemical element or compound that can conduct electricity under some conditions but not others, making it a good medium for the control of electrical current.
• It has almost filled valence band, empty conduction band and very narrow energy gap i.e., of the order of 1 eV. Energy gap of Silicon (Si) and Germanium (Ge) are 1.0 and 0.7 eV respectively. Consequently Si and Ge are semiconductors.

Question 2

Effect of temperature on conductivity of semiconductors:

0 KELVIN

Answer 2

At 0 K electrons freeze at valence band and hence all semiconductors are insulators.

Question 3

Effect of temperature on conductivity of semiconductors:

increasing temperature

Answer 3

• Electrical conductivity of a semiconductor material increases with increasing temperature as resistivity decreases.
• At higher temperature transition from the valence band to the conduction band gets facilitated ⇒ higher conductivity or lower resistivity.

Question 4

TYPES OF SEMICONDUCTORS

Answer 4

1. INTRINSIC: pure form of Ge, Si
2. EXTRINSIC
   i. p type: trivalent impurity (G, B, In, Al) = holes» electrons
   ii. n type: pentavalent impurity (P, As, Sb) = electrons» holes

Question 5

intrinsic semiconductor

Answer 5

• Intrinsic semiconductor material is chemically very pure and possesses poor conductivity.
• It has equal numbers of negative carriers (electrons) and positive carriers (holes)

Question 6

extrinsic semiconductor

Answer 6

-Extrinsic semiconductor is an improved intrinsic semiconductor with a small amount of impurities added by a process, known as doping, which alters the electrical properties of the semiconductor and improves its conductivity

Question 7

dopin

Answer 7

• Introducing impurities into the semiconductor materials (doping process) can control their conductivity.
• Doping process produces two groups of semiconductors:
  i. The negative charge conductor (n-type)
  ii. the positive charge conductor (p-type)

Question 8

Semiconductors are available as either ___ or ___

Answer 8

Semiconductors are available as either elements or compounds.

Question 9

the most common elemental semiconductors.

Answer 9

Silicon and Germanium are the most common elemental semiconductors.

Question 10

examples of Compound Semiconductors

Answer 10

nclude InSb, InAs, GaP, GaSb, GaAs, SiC, and GaN.