## Thursday, 6 June 2013

### Video Solutions for GATE 2003 ECE : Two Mark Questions (Electron Devices)

1. An n-type silicon bar 0.1 cm long and µm2 in cross sectional

area  has a majority carrier concentration of 5 x 1020 /m3 and the

carrier mobility is 0.13 m2/V-s at 3000K. if the charge of an

electron is 1.6x10-19 coulomb, then the resistance of the bar is

2. The electron concentration in a sample of uniformly doped

n-type silicon at 300oK varies linearly from 1017 /cm3

at x = 0 µm to 6 x 1016 /cm3 at x = 2 µm. Assume a situation

that electrons are supplied to keep this concentration gradient

constant with time. If electronic charge is 1.6 x 10-19 coulomb

and the diffusion constant Dn = 35 cm2/s, the current density in

the silicon, if no electric field is present, is

3. Match items in Group 1 with items in Group 2, most suitably.

4. At 300oK, for a diode current of 1 mA, a certain germanium

diode requires a forward bias of 0.1435 volts, where as a certain

silicon diode requires a forward bias of 0.718 volts. Under the

conditions stated above, the closest approximation of the ratio of

reverse saturation current in germanium diode to that of silicon

diode is

(A)  1            (B)  5                (C)   4 x103               (D)  8 x103

5. A particular green LED emits light of wavelength 5490oA.

The energy band gap of the semiconductor material used there

is (Planck’s constant = 6.626x10-34 J-s)

(A)   2.26 eV                              (B)      1.98 eV

(C)     1.17 eV                            (D)     0.74 eV

6. When the gate to source voltage (VGS) of a MOSFET with

threshold voltage of 400 mV, working in saturation is 900 mV,

the drain current in observed to be 1 mA. Neglecting the

channel length modulation effect, and assuming that the

MOSFET is operating at saturation, the drain current for

an applied VGS of 1400 mV is

(A)     0.5 mA                 (B)       2.0 mA

(C)     3.5 mA                 (D)      4.0 mA

7. If P is Passivation, Q is n-well implant, R is metallization and

S is source/drain diffusion, then the order in which they are

carried out in a standard n-well CMOS fabrication process, is

8. The action of a JFET in its equivalent circuit can best be

represented as a

(A)   Current controlled current source

(B)   Current controlled voltage source

(C)   Voltage controlled voltage source

(D)   Voltage controlled voltage source