## Thursday, 13 June 2013

### Video Solutions for GATE 1991 ECE : Five Mark Questions ( Electron Devices )

1.The current I in a forward biased P+N junction shown in
figure (a) is entirely due to diffusion of holes from x=0 to x=L.
The injected hole concentration distribution in the n- region
is linear as shown in figure (b), with P(0) = 1022 /cm3 and
L = 10-3 cm. Determine :

(a) The current density in the diode assuming that the diffusion
coefficient of holes is 12 cm2/sec.

(b) The velocity of holes in the n-region at x=0.

2.  It is required to use a JFET of figure as linear resistor.

The parameters of the JFET are as follows:

W = 100 µm, L =  µm, a = 2.5 µm.

The doping in the n-layer is ND = 1016 /cm3 and

the electron mobility is 1500 cm2/V-sec. The depletion layer

width of each junction due to the built in potential is 0.25 µm.

The two P+ gate regions are connected together externally.

The resistances of the regions outside the gate are negligible.

Determine the minimum value of the linear resistor which can be

realized using this JFET without forward biasing the gate

junctions.