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Physics Review Practice Problems
1. Consider a NMOS transistor with following p[arameters:
Substrate doping = 1015/cc, Active region doping = 1018/cc
(a) Sketch the transistor and label substrate, active region, gate and channel
(b) Compute the majority and minority carriers in the substrate and active
region
(c) Compute the Fermi level for substrate and active region
(d) Sketch the energy band diagram of the channel region if the gate is made
with Gold. The work function for Gild is 5.1 ev.
Assuming m*e = 0.16, m*h = 0.56,  due to phonon scattering = 1.36x10-13
sec and a potential difference of 5V at a distance of 2 m.
(e) Compute drift velocity Vd, mobility  and conductivity  for both holes
and electron in intrinsic silicon. Stipulate your assumptions for the
calculation of the Electric Field
(f) If the mobility of electrons in doped silicon is reduced to 700 cm2/volt sec
due to impurity scattering determine the relaxation time t due to impurity
scattering. Use Mathieson’s Rule 1/ = i 1/i . Also, note the unit of
mobility.
2. Given three voltage buses carrying –4V, -5V and –7V. Connect a PMOS and
a NMOS transistor to these busses so that both devices will conduct. Assume
|Vt| = 1.2 V for these transistors. For each transistor stipulate Vds and Vgs.