# Chapter 15 : Semiconductors¶

## Example 15.1 Page No : 520¶

In [3]:

import math

# Variables
U_n = 1350.			#mobility of electron in cm2/volt-sec
U_h = 480.			#hole mobility in cm2/volt-sec

# Calculation
Sigma = 1.072*10**10			#density of electron hole pair per cc at 300°K for a pure silicon crystal
e = 1.6*10**(-19);			#charge on the electron in C
Sigma_i = Sigma*e*(U_n+U_h);			#Conductivity of pure silicon crystal
p_i = 1/(Sigma_i);			#Resistivity of silicon crystal in Ohm-cm
P_i = p_i*10**(-2);			#Resistivity of silicon crystal in Ohm-m

# Results
print 'Conductivity of pure silicon crystal = %.2e mho/cm'%Sigma_i
print 'Resistivity of silicon crystal = %.2e Ohm-m'%P_i

Conductivity of pure silicon crystal = 3.14e-06 mho/cm
Resistivity of silicon crystal = 3.19e+03 Ohm-m


## Example 15.2 Page No : 521¶

In [2]:

import math

# Variables
U = 1200;			#electron mobility in cm2/Volt-sec
e = 1.6*10**(-19);			#charge on the electron in C

# Calculation
n = 10**13;			#concentration of phosphorus
sigma = U*e*n;			#conductivity of crystal in mho/cm
p_i = 1/sigma;			#resistivity of silicon wafer if all donor atom are active

# Results
print 'resistivity of silicon wafer if all donor atom are active is %.1e ohm-cm'%p_i

resistivity of silicon wafer if all donor atom are active is 5.2e+02 ohm-cm


## Example 15.3 Page No : 521¶

In [1]:

import math

# Variables
U_n = 3900			#mobility of electron in cm2/volt-sec
U_h = 1900			#hole mobility in cm2/volt-sec
n_i = 2.5*10**13;			#concentration of electron
u_n = U_n*10**(-4);			#mobility of electron in m2/volt-sec
u_h = U_h*10**(-4);			#hole mobility in m2/volt-sec
e = 1.6*10**(-19);			#charge on the electron in C

# Calculation
Sigma_i = n_i*e*(u_n+u_h)*10**6;			#Conductivity
p_i = 1/(Sigma_i);			#resistivity of intrinsic germanium rod
l = 1*10**(-2);			#length of germanium rod in m
w = 1*10**(-3);			#width of germanium rod in m
t = 1*10**(-3);			#thick of germanium rod in m
A = w*t;			#Area of cross section in m2
R = p_i*l/A;			#Resistance of an intrinsic germanium rod in Ohm

# Results
print 'Resistance of an intrinsic germanium rod is %.2f K-Ohm'%(R/10**3)

Resistance of an intrinsic germanium rod is 4.31 K-Ohm


## Example 15.4 Page No : 521¶

In [1]:

import math

# Variables
N_a = 1.1*10**20;			#acceptor density in atoms/m3
n_i = 2.5*10**19;			#concentration of majority carrier per m3

# Calculation
n_p = (n_i**2)/N_a;			#intrinsic density
R = n_p/n_i;			#Ratio of n_p and n_i

# Results
print 'n_p/n_i = %.2f'%R

# rounding off error

n_p/n_i = 0.23