Gate 2002 and 2003 Questions on Electronic Devices

Gate 2002 (1 mark)
Question: 1

In the figure, silicon diode is carrying a constant current of 1 mA. When the temperature of the diode is 20 ℃, VD is found to be 700 mV. If the temperature rises to 40℃,VD become approximately equal to(diagram)

a)740mv

b)660mV

c)680mV

d)700mV

Answer: b

Explanation

For either Si or Ge dVdt ≅ -2.5 V/℃

In order to maintain a constant value of I.

T2-T1 = 40 – 20= 20℃

-2.5 * 20mV = 50 mV

Therefore, VD = 700 – 50

=650 ≅ 660 mV

Question 2: 

If the transistor in the figure is saturation , then(diagram)

a)IC is always equal to βdcIB

b)Icis always equal to βdcIB

c)Icis greater than or equal to βdcIB

d)Icis less than or equal to βdcIB

Answer : d

Explanation:

Gate 2003 (1 mark)

Question:3 

n- type silicon is obtained by doping silicon with

a)Germanium

b) Aluminium.

c)Boron

d)Phosphorus

Answer : a

Question 4:

The band gap of silicon at 300 k is

a)1.36eV

b)1.10eV

c)0.80eV

d)0.67eV

Answer : b

Quesiton 5

The intrinsic carrier concentration of silicon sample at 300 k is 1.5 *10-6/m-3.If after doping the no of majority carriers is 5 * 1020/m3 , the minority carrier density is

a)4.50 * 1011/m3

b)3.33 * 104/m3

c)5.00*1020/m3

d)3.00 * 10-5/m3

Answer : a

Explanation:

ni2 = np

ni = intrinsic concentration

P = ni2ni =1.5*1016*1.5*1016520

=45*1010 =4.5*1011

Question 6 

choose the correct substitutes for X and Y to make the following statement correct tunnel diode and Avalanche photodiode are operated in X bias and y bias respectively,

a)X :reverse , Y: reverse

b)X:reverse , Y: forward

c)X :forward , Y:reverse

d)X:forward ,Y:forward

Answer: c

Question 7

For an n-channel enhancement type MOSFET , if the source connected at a high potential then that of the bulk ( i.e. VSB> 0) the threshold voltage VT of the MOSFET will

a) remain unchanged

b)decreases

c)change polarity

d)increases

Answer : d

Explanation:

VT =VTo+γ-2ϕF+VSB - 2ϕF

VSB= substrate bias voltage

γ = substrate bias coefficient