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 N_D = 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.