Question

Design an ideal abrupt silicon PN-junction at 300 K such that the donor impurity concentration Nd (in cm^?3 ) in n-side is Nd = 5×10^15 /cm3 and the acceptor impurity concentration Na in the p-side is Na = 817 ×10^15 /cm3

Given: the diode area A = 2×10^?3 cm2 , ni = 10^10/cm3 , ?n = 10^?8 s and ?p = 10^?7 s,

Refer to text books, lecture notes, etc for other parameters such Dn, etc., and state clearly in your work.

1. What are the values (in µm) of the depletion width at the p-side of the junction xp0 and the depletion width at the n-side xn0.

Determine the following when a forward bias of 0.6 V is applied to the diode:

2. Minority carrier hole diffusion current ,Ip(xno) at the space charge edge.

3. Minority carrier electron diffusion current,In(-xpo) at the space charge edge.

4. The total diode current I.

5. Roughly, sketch the carrier distribution across the junction.

6. The reverse saturation current Io.

7. The junction capacitance Cj.

Answer 1

1) The depletion width is given as -

where is the contact potential, and is given as -

Hence -

Depletion width at the p-side is given as -

Similarly for n-side we have -

2) The hole diffusion current is given as -

3) Similarly for electron diffusion current -

4) Total current is given by -

5)

6) The reverse saturation current is given as -

7) The junction capacitance is given by -