PHYSICS 1070 2020
Tutorial 6
1. Consider a silicon sample at 300 K is doped with a concentration of donor atoms Nd = 2 x
1015 cm-3.
a) Is this sample intrinsic or extrinsic?
b) Is this sample n-type or p-type?
c) Are electrons or holes the majority carriers?
d) Use the intrinsic carrier concentration in Si at 300 K from Table B.4 to show no ≈ Nd
and po is negligible.
e) Find the conductivity of the sample, in (Ω-cm)-1, if the electron mobility is μn = 1350
cm2/V-s and the hole mobility is μp = 480 cm2/V-s.
f) What is the resistivity of the sample at 300 K, in Ω-m?
2. (P. 5.2 from your textbook.) A p-type silicon material is to have a conductivity σ = 1.80
(Ω-cm)-1. Find the acceptor impurity concentration, if the mobility values are μn = 1250
cm2/V-s and the hole mobility is μp = 380 cm2/V-s.
3. (Variation of P. 5.8 from your textbook.) A rectangular silicon semiconductor sample, at
room temperature, which is to be used as a resistor has a cross-sectional area 8.5 x 10-4
cm2, a length of 0.075 cm. The sample is doped with boron at a concentration of 2 x 1016
cm-3.
a) Is the sample n-type or p-type? Extrinsic or intrinsic? Direct or indirect?
b) What is the resistance of the sample?
c) What is the current density J in the sample, in A/m2, if 2 V is applied across the length
of the sample?