Exam

Question 1

Explain zener breakdown

Answer 1

• with sucfficantley high reverse bias conduction band aligns with valance band
• if the width of the SCR is small enough electrons tunnel from P to N to generate a reverse current
  1. High Vr
  2. High doping > 5x10^17
  3. Sharp junction to achieve small W

Question 2

Explain bonding and its energy level

Answer 2

• High mangitube of omega ^2 between peaks results in high q between carriers hence Pe is more negative (lower energy)
• In the middle of joining 2 neculi omega^2 is high - higher probability of finding an electron

Question 3

Explain anti bonding and its energy level

Answer 3

Low magnitude of omega^2 between peaks results in low q between carriers hence Pe is more positive(higher energy)
In the middle of joining 2 neculi omega^2 is low henche very low probability of finding an electron

Question 4

What are the three a parts of a band diagram for MOS inversion

Answer 4

Metal oxide p-type semicondctor

Question 5

What are the steps to dervie the ideal diode equation

Answer 5

Step 1: Calculate the concentration of minority carriers at the edges of SCR after biasing
* Step 2: Find the spatial distribution profile of the minority carrier
concentration in each of the QNR
* Step 3; Calculate minority carrier diffusion currents at the SCR edges
* Step 4: Add minority carrier diffusion currents at the SCR edges

Question 6

What steps can be takes to minimise Rc

Answer 6

1. Increase barrier height
2. Increase doping

Question 7

Mathimatacally show that for Pn junction the SCR always penetrates more into the lightly doped side of the junction

Answer 7

qAxnNd = qAxpNa
ND>NA -> Xp>Xn
Nd<Na - > xp<xn