Solid state device theory

Question

Assignment:

Question 1. A semiconductor sample has the band diagram below.

(a) Is this semiconductor in equilibrium? Explain.
(b) Sketch the electric field versus x.
(c) Roughly sketch n and p versus x.
(d) Make a rough sketch of the electron drift current density and the electron diffusion current density versus x. Be sure to graph the proper polarity of the current densities at all points.

Question 2. A semi-infinite p-type bar is illuminated with light generating GL electron-hole pairs/cm³-s uniformly throughout the volume of the semiconductor. Simultaneously, carriers are extracted at x=0 making Δn_p = 0 at x= 0. Assuming steady state condition has been established and Δn_p<0 , derive an expression for Δn_p(x).

Question 3. A p-Si photoconductor is to detect optical pulses having the waveform shown below.

Each pulse generates electron-hole pairs (ehp). When the pulse terminates, the ehp recombine

Δn_p(t) = Δn_p(0) exp( -t/Τ_SRH)

according to the relation where t = 0 refers to the time when the light pulse is turned off. ?n_p(t) must have decreased to 0.01?n_p(0) before the next pulse is applied for proper photoconductor operation.
For σn = 10^-16 cm²
and v_th = 10⁷ cm/s, determine N_T for this to happen.