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Flashcards in Semiconductors Deck (19)
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1

What is a monolithic circuit

a circuit fabricated from a single silicon crystal

2

what is the most significant property of semiconductors

that their conductivity can be varied through the application of controlled amounts of impurity in a process called doping

3

what is a covalent bond

a pair of shared electrons

4

what is a free electron

one that can wander away from its parent atom and is able to conduct

5

what happens to semiconductor as temp increases

more covalent bonds are broken which increases the number of free electrons. temperature controlled conductivity

6

what is recombination

when electrons fills the holes

7

what is the band gap energy

the amount of energy needed to break a covalent bond

8

what is a bound charge

it does not move in the crystal it is left over after the carrier leaves the atom.

9

what is semiconductor mobility

the ease at which charge can move through the crystal. u_n = ~2.5 u_p. electrons can move more easily than holes

10

when does diffusion occur?

when carrier concentration is not uniform. diffusion of charge current leads to diffusion current. note: J=qD(dn(x)/dx)

11

what is drift current

due to free carriers being swept by electric field. Ix=Aqxv_drift=Aqpu_xE note Jx=Ix/A J=rE r=(q(pu_p + nu_n)

12

what are units of rho

ohm*cm

13

what is the concentration gradient

J=D

14

what is the Einstein relationship

Dx/u_x=v_t

15

how does the carrier depletion region form

diffusion uncovers bound charge which leads to a electric field which causes a junction potential. the junction potential reduces diffusion which balances drift current cause by thermal generation in a pn in equilibrium. Id=Is

16

how to calculate the built in potential of a pn junction

Vo=Vt*Ln(Na*Nd/ni^2)

17

describe a forward biased pn junction

Vb=(Vo-Vf) barrier lowers which allows more diffusion across the barrier to happen. due to the applied field an excess concentration of minor carriers builds up at the barrier. minority carriers will recombine with the majority carriers and concentration will decay exponentially with distance called the diffusion length although the current at the edge gives the resulting diffusion current.

18

what is the diode equation for a pn junction

I=Is(Exp(Vf/Vt)-1) Is=Aqni^2(Dp/LpNd+Dn/LnNa) Is=saturation current=scale current

19

describe a reverse biased pn junction

Vb=(Vo+Vr) barrier raises reducing diffusion current so all that is left is drift current, Is, which is very small