This document contains 20 analytical questions related to semiconductor devices. The questions cover topics such as determining resistivity of germanium under different doping conditions, calculating current density in silicon samples with both donor and acceptor impurities, finding carrier concentrations and resistances of PN junctions, calculating voltages and currents in diode circuits, and analyzing operational characteristics of transistors, MOSFETs, and SCRs. Solutions require using given parameters and equations related to semiconductor physics.

1. ECA01 SEMICONDUCTOR
DEVICES
ANALYTICAL QUESTIONS
08-07-2023

2. QUESTION 1
• Determine the resistivity of germanium (a) in instrinsic condition at 300 K, (b) with
donor impurity of 1 in 10e7, (c) with acceptor impurity of 1 in 10e8, and (d) with both
the above impurities simultaneously. Given that for germanium at room temperature ni =
2.5 × 10e13/cm3, mn = 3800 cm2/V-Vs, µp = 1800 cm2/V-Vs and a number of
Germanium atoms/cm3 = 4.4 × 10e22.

3. QUESTION 2
• A sample of silicon at a given temperatureT in intrinsic condition has a resistivity of 25 ×
10e4W-cm.The sample is now doped to the extent of 4 × 10e10 donor atoms/cm3 and
10e10 acceptor atoms/cm3. Find the total conduction current density if an electric field
of 4V/cm is applied across the sample. Given that µn = 1250 cm2/V-s, µp = 475 cm2/V-s
at the given temperature

4. QUESTION 3
• Find the concentration (densities) of holes and electrons in N-type silicon at 300 K, if the
conductivity is 500 S/cm.Also find these values for P-type silicon. Given that for Silicon at
300 K, ni = 1.5 × 10e10/cm3, µn = 1500 cm2/V-s and µp = 700 cm2/V-s

5. QUESTION 4
• (a) Find the concentration of holes and electrons in a p-type germanium at 300°K if the
conductivity is 100 (Ω cm)−1.Assume that the conductivity due to electrons is negligible
as compared to that due to holes.
• (b) Determine the position of the Fermi level with respect to the edge of the conduction
band of the germanium of part (a).Assume NV = 6.0 x10e19 cm−3 and EG = 0.72 eV at
300°K.

6. QUESTION 5
• In an n-type silicon the donor concentration is 1 atom per 2 x10e8 silicon atoms.Assume
that the effective mass of the electron equals the true mass and the density of atoms in
the silicon in 5 x10e22 atoms cm3.At what temperature will the Fermi level coincide
with the edge of the conduction band?

7. QUESTION 6
• Find the resistance of an intrinsic Ge rod 1 mm long, 1 mm wide and 1 mm thick at 300 K. the
intrinsic carrier density 2.5 ×10e19 m–3 is at 300 K and the mobility of electron and hole are
0.39 and 0.19 m2 v–1 s–1.

8. QUESTION 7
• In an N-type semiconductor,the Fermi level lies 0.2 eV below the conduction band. Find the new position of Fermi level if the
concentration of donor atoms is increased by a factor to (a) 4, and (b) 8.Assume kT = 0.025 eV

9. QUESTION 8

10. QUESTION 9
Find the value of dc resistance and ac resistance of a Germanium junction diode at 25 °C with Io
=25 µA and at an applied voltage of 0.2V across the diode

11. QUESTION 10
Calculate the dynamic forward and reverse resistances of a PN junction diode when the applied
voltage is 0.25V atT = 300 K given Io = 2 µA.

12. QUESTION 11
If two similar Germanium diodes are connected back to back and the voltageV is impressed upon,
calculate the voltage across each diode and current through each diode.Assume similar value of Io =
1 µA for both the diodes and n = 1.

13. QUESTION 12
Find the current through the diode in the circuit shown in figure.Assume the diode to be ideal

14. QUESTION 13
A HWR has a load of 3.5 kV. If the diode resistance and secondary coil resistance together have a
resistance of 800V and the input voltage has a signal voltage of peak value 240V. Calculate (a) Peak,
average and rms value of current flowing. (b) dc power output (c) ac power input (d) efficiency of
the rectifier

15. QUESTION 14
A voltage of 200 coswt is applied to HWR with load resistance of 5 kV. Find the maximum dc
current component, rms current, ripple factor,TUF and rectifier efficiency

16. QUESTION 15
The transformer of a half-wave rectifier has a secondary voltage of 30Vrms with a winding
resistance of 10 Ω.The semiconductor diode in the circuit has a forward resistance of 100 Ω.
Calculate (a) No load dc voltage (b) dc output voltage at IL = 25 mA(c) % regulation at IL = 25mA
(d) ripple voltage across the load (e) ripple frequency (f) ripple factor (g) dc power output and (h)
PIV of the semiconductor diode.

17. QUESTION 16
Given an NPN transistor for which α = 0.98, ICO = 2 µA and IEO = 1.6 µA.A common emitter
connection is used andVCC = 12V and RL = 4 kΩ.What is the minimum base current required in
order that transistor enter in to saturation region

18. QUESTION 17
For the circuit shown in Fig , determine IE,VC andVCE.AssumeVBE = 0.7V

19. QUESTION 18
The reverse leakage current of the transistor when connected in CB configuration is 0.2 µA and it is
18 µA when the same transistor is connected in CE configuration. Calculate αdc and βdc of the
transistor

20. QUESTION 19
a) For a P-channel silicon FET, with an effective channel width, a =2x10e4 cm and channel resistivity
ρ = 20 Ω -cm , find the pinchoff voltage
b) The data sheet for an enhanced MOSFET gives ID = 4.5 mA atVGS =12V and VGS(th) = 6V.
Determine the value of ID forVGS = 10V

21. QUESTION 20
In an SCR half wave rectifier, the forward breakdown voltage of SCR is 110V for a gate current of 1
mA. If a 50 Hz sinusoidal voltage of 220V peak is applied, find firing angle, conduction angle, average
voltage, average current, power output and the time during which SCR remains OFF.Assume load
resistance is 100V and the holding current to be zero.