Homework 3 Problem 1: Sze Chapter 2, #20, pg. 133 Problem 2 ...

SDM II
Fall 2010
Problem 1:
Sze Chapter 2, #20, pg. 133
Homework 3
The alignment of heterojunction between GaAs and Al 0.4Ga0.6As is Type-I. The conduction-band
discontinuity is Ec=0.28 eV. The doping concentration is 1020 cm-3 in Al0.4Ga0.6As and 1016 cm-3 in GaAs, both doped with carbon.
(a) Find the total depletion width under thermal equilibrium condition, assuming the dielectric
constant is the same for both semiconductors
(b) Draw the band diagram for V=0
Problem 2:
Sze Chapter 2, #18, pg. 132
Prof. Shayla Sawyer
Homework 3
Consider an ideal abrupt heterojunction with a built-in potential of 1.6V. The impurity concentrations in semiconductor 1
and 2 are 1x10 16 donors/cm 3 and 3x10 19 acceptors/cm 3, and dielectric constants are 12 and 13, respectively. Find the
electrostatic potential and depletion width in each material for applied voltages of 0.5V and -5V.
Problem 3:
Sze Chapter 8, #5, pg. 464
Molecular beam epitaxy interfaces are typically abrupt to within on eor two monolayers (one monolayer ~ 2.8 Å in GaInAs),
due to terrace formation in the growth plane. Estimate the energy level broadening for the ground and first excited
electron states of a 15-nm GaInAs quantum well bound by thinck AlInAs barriers. (Hint: Assume the case of two
monolayer thickness fluctiaotn and an infinite deep QW. The electron effective mass in GaInAs is 0.0427m o .
Problem 4:
Sze Chapter 7, #10, pg. 413
(a) Find the threshold voltages of a conventional and a delta-doped heterostructure AlGaAs-GaAs FETs
(b) Evaluate the variations of these threshold voltages for two-monolayer fluctuations in AlGaAs layer thickness.
Assuming that one monolayer = 3 Å in AlGaAs, the Schottky barrier height is 0.9V, the conduction-band discontinuity is
0.3eV, the uniform doping in the conventional HFET is 10 18 cm-3 with a thickness of 40 nm, the delta doping is located 40
nm from the metal-semiconductor interface, with a sheet charge density of 1.5 x 10 12 cm-2, and the dielectric permittivity
for AlGaAs is assumed to be 10-12 F/cm.
Bonus, Problem 5:
NanoHub (H-S. Philip Wong)
Use software on nanoHUB.org to plot the I-V characteristics of a resonant tunneling diode. In this problem, we will use software on nanoHUB.org to plot
the I-V characteristic of a resonant tunneling diode. Visit the following page:
http://nanohub.org/tools/rtd
Please use the following parameters:
a) 2-barrier device
b) Barrier thickness (Al0.3Ga0.7As): 5nm
c) Well thickness (GaAs): 5 nm
d) Temperature: 300 K
e) Doping at contacts: 1018 /cm3 Plot the I-V characteristic for V=0 ~ 0.4 volt. What are the values of Ip & Iv? MORE BELOW!

SDM II
Fall 2010
p.s. DON'T turn the self-consistent potential on
2.Design a RTD that gives the largest PVCR (peak-to-valley current ratio). You can adjust any parameter in the simulator, and again, DON'T turn on
the self-consistent analysis.
Explain why and how you choose your parameters to maximize the PVCR.
Prof. Shayla Sawyer
Homework 3