Description

[Note: In the following problems, assume T = 300 K and the following parameters unless otherwise stated. For silicon pn junctions: Dn = 25 cm2/s,Dp = 10 cm2/s,τn0 = 5 × 10−7 s, τp0 = 10−7 s. For GaAs pn junctions: Dn = 205 cm2/s,Dp = 9.8 cm2/s,τn0 =
5 × 10−8 s, τp0 = 10−8 s.]
Exercise 6.1
(a) Consider an ideal pn junction diode at T = 300 K operating in the forward-bias region. Calculate the change in diode voltage that will cause a factor of 10 increase in current.
(b) Repeat part (a) for a factor of 100 increase in current.
Exercise 6.2
Consider a GaAs pn junction diode at T = 300 K. The parameters of the device are Nd = 2 × 1016 cm−3,Na = 8 × 1015 cm−3,Dn = 210 cm2/s,Dp = 8 cm2/s,τno = 10−7 s, and τpo = 5 × 10−8 s. Determine the ideal reverse-saturation current density.
Exercise 6.3
Consider an ideal silicon pn junction diode.
Exercise 6.4
Consider a silicon pn junction diode with an applied reverse-biased voltage of VR = 5 V. The doping concentrations are Na = Nd = 4×1016 cm−3 and the cross-sectional area is A = 10−4 cm2. Assume minority carrier lifetimes of τ0 = τn0 = τp0 = 10−7 s. Calculate the
(a) ideal reverse-saturation current
(b) reverse-biased generation current
(c) the ratio of the generation current to ideal saturation current.
Exercise 6.5
Consider, as shown in Figure, a uniformly doped silicon pn junction at T = 300 K with impurity doping concentrations of Na = Nd = 5×1015 cm−3 and minority carrier lifetimes of τn0 = τp0 = τ0 = 10−7 s. A reverse-biased voltage of VR = 10 V is applied. A light source is incident only on the space charge region, producing an excess carrier generation rate of g′ = 4 × 1019 cm−3 s−1. Calculate the generation current density.

Figure 1: Figure for Problem 6.5
Exercise 6.6
A silicon pn junction at T = 300 K is reverse biased at VR = 8 V. The doping concentrations are Na = 5 ×1016 cm−3 and Nd = 5 × 1015 cm−3. Draw the band diagram of the pn junction, and determine xn,xp,W, and |Emax|. Please provide the process of derivation.
Exercise 6.7
(a) Sketch the energy bands in a zero-biased, reverse-biased, and forward-biased pn junction.
(b) Sketch the steady-state minority carrier concentrations in a forward-biased pn junction.
(c) Sketch the forward-bias I–V characteristics of a pn junction diode showing the effectsof recombination and high-level injection.
Reference
1. Neamen, Donald A. Semiconductor physics and devices: basic principles. McGrawhill, 2003.