EE-130/230A, Spring 2020
HW 4
Due in the beginning of class on 03/31/2020
Problem 1[10 pts] Consider a Metal Semiconductor Schottky diode is fabricated with PtSi
contact and a p-doped Si (NA=1018cm-3).
(a) Draw the energy band diagram
(b) Draw the profile of charge density in this diode. Can you comment on the nature of the
charge density that you are drawing for the PtSi side of the junction?
(c) Draw the potential profile and calculate the built in potential.
(d) Draw the energy band profile under forward bias
(e) Qualitatively explain how current flows in this device in forward and reverse bias.
Problem 2[10 pts] A MS contact is formed between a metal and a semiconductor such that
fm=c. Under what conditions will the contact be ohmic and under what conditions will the
contact be rectifying?
Problem 3[10 pts] Consider a tungsten barrier on silicon with a measured barrier height of
efBn=0.67 eV. The effective Richardson constant is K=114 A/˚K2-cm2 . T=300K. Find out the
reverse saturation current density. Now consider a pn junction diode at T=300K with the
following parameters:
Na= 1018 /cm3
Nd=1016 /cm3
tp=tn=10-7 sec.
Find out the reverse saturation current for this pn junction diode. Comment on the reverse
saturation current of these two diodes.
Problem 4[10 pts] For a Schottky barrier diode where Si is doped to Nd=7x1018 /cm3, and
barrier height is 0.67 eV, find out the depletion region width.
Problem 5 [10 pts] Construct a plot of the equilibrium depletion width versus the Nd doping
concentration in silicon MS diodes maintained at T=300K. Vary Nd over the range
1014/cm3<Nd<1017/cm3 and include curves corresponding to barrier heights of 0.5, 0.6 and 0.7
eV.