SEMICONDUCTOR DEVICE PHYSICS AND DESIGN

4.11. DESIGN PROBLEMS 211

structure in such cases. The width of then-region is smaller than the depletion region

width at breakdown.

Consider two Sip+-n-n+diodes with thenregion having a doping of 1014 cm−^3. In one

case then-region is 150μm long while in the other case it is 80μm. What are the

reverse-bias voltages that the diodes can tolerate before punch through occurs?

• Section 4.8
  Problem 4.35Consider a Si p-n junction where the p and n regions are much shorter than
  the diffusion length. Assume that the doping on both sides is 1017 cm−^3 .Use
  mp=mn= 1000cm

2

Vs,NA=ND=10

(^17) cm− (^3) and that the neutral region width on each
side isWn=Wp=0. 1 μmUseEg=1. 1 eV, NC=NV=10^19 cm−^3 andtGEN=1μs.

1. What is the reverse current in the this diode when no light shines on it? Assume a
   large reverse bias,qV >> kT, and room temperature.


2. Now, light incident on the devide leads to an optical EHP generation rate
   GOP=10^22 cm−^3 s−^1. What is the reverse current in the diode? Assume room
   temperature, as before.


3. Now, the temperature of the diode is reduced with the light left on. At what
   temperature will the reverse current be equal to that calculated in the first part of the
   problem?

4.11 DESIGN PROBLEMS ...............................

Problem 4.1Consider a Si long diode that must be able to operate up to a reverse bias of

10 V. The maximum electric field that the diode can tolerate anywhere within the structure

is 5 × 105 V/cm. Design the diode so that the reverse current isassmallaspossiblewithin

thegivenspecifications. Assume thatNa=Nd. What is the doping density you will use?

Problem 4.2Consider a Si shortp-ndiode with the following parameters:

n-side length =2. 0 × 10 −^4 cm

p-side length =2. 0 × 10 −^4 cm

n-side doping =10^17 cm−^3

p-side doping =10^17 cm−^3

minority carrier lifetimeτn = τp=10−^7 s

electron diffusion constant = 25 cm^2 /s

hole diffusion constant = 10 cm^2 /s

diode area = 10−^3 cm^2

Calculate the diode current (assuming that the diode is non-ideal) at a forward bias of 0.1

V and at 0.7 V at 300 K. What are the diode ideality factorsnear the two biasing values?