## Friday, 7 June 2013

### Video Solutions for GATE 2004 EC : Two Mark Questions (Electron Devices)

1. In abrupt PN junction, the doping concentrations on the p-side

and n-side are NA = 9 x 1016 /cm3 and ND = 1 x 1016 /cm3

respectively. The PN junction is reverse biased and the total

depletion width is 3 µm. The depletion width on the p-side is

(A)     2.7 µm                          (B)   0.3 µm

(C)     2.25 µm                        (D)   0.75 µm

2. The resistivity of a uniformly doped n-type silicon sample is

0.5 -cm. If the electron mobility (µn) is 1250 cm2/V-sec and

the charge of an electron is 1.6 x 10-19 coulomb, the donor

impurity concentration (ND) in the sample is

3. Consider an abrupt PN junction. Let Vbi be the built in potential

of this junction and VR be the applied reverse bias. If the

junction capacitance (Cj) is 1 pF for Vbi + VR = 1 volt, then for

Vbi + VR = 4 volts, Cj will be

(A)  4 pF         (B)  2 pF          (C)  0.25 pF         (D)  0.25 pF

4. Consider the following statements S1 and S2.

S1 : The threshold voltage (VT) of a MOS capacitor

decreases with increase in gate oxide thickness

S2 : The threshold voltage (VT) of a MOS capacitor
decreases with increase in substrate doping
concentration.

Which one of the following is correct ?

5. The drain of an n-channel MOSFET is shorted to the gate so that

VGS = VDS. The threshold voltage (VT) of MOSFET is 1 volt.

If the drain current (ID) is 1 mA for VGS = 2 volts, then

for VGS = 3 volts, ID is

(A)   2 mA                           (B)   3 mA

(C)   9 mA                           (D)   4 mA

6. The longest wavelength that can be absorbed by silicon, which

has the bandgap of 1.12 eV, is 1.1 µm. If the longest wavelength

that can be absorbed by another material is 0.87 µm, then the

bandgap of this material is

(A)  1.416 eV              (B)  0.886 eV

(C)  0.854 eV              (D)  0.706 eV

7. The neutral base width of a bipolar transistor, biased in the

active region, is 0.5 µm. The maximum electron concentration

and the diffusion constant in the base are 1014 /cm3 and

Dn = 25 cm2/sec respectively. Assuming negligible

recombination in the base, the collector current density is

8. Assuming that the β of the transistor is extremely large and

VBE = 0.7 volts, IC and VCE in the circuit shown are,

9. In the voltage regulator shown , the load current can vary from

100 mA to 500 mA. Assuming that the zener diode is ideal

(i.e. the zener knee current is negligibly small and zener

resistance is zero in the breakdown region), the value of R is

#### 1 comment:

1. why old some subjects no signals and systems questions and solutions aare seen