ENSC 324 HOMEWORK #2 Fall 2015
DUE: Monday October 19, 2015 at 2 PM (note new time!)
Please note that unless you show work in the derivations and solutions you will get no credit for the
answers. Obviously copied answers from study partners or other sources, etc., will also receive no credit.
Please do all parts of all eight problems. It is suggested that you make a copy of your homework before
turning it in in case it cannot be returned before Exam 2 (solution key will be provided).
In a particular sample of n-type silicon, the Fermi energy level varies linearly with distance over a short
range. At x=0, the difference between the Fermi level and the intrinsic Fermi level is 0.4 eV. At x=10-3
cm, the same difference is only 0.15eV. The electron diffusion coefficient is 25 cm2/s.
a) Write an expression for the Fermi level with respect to the intrinsic fermi level versus distance.
b) What is the electron concentration versus distance?
c) What is the electron diffusion current density at x=0, and at x=5 x 10−4 cm?
A rectangular bar shaped silicon semiconductor resistor with a cross-sectional area of 100 μm2,
and a length of 0.1 cm, is doped with a concentration of 5 x 1016 cm−3 arsenic atoms (and no
acceptors). Let T = 300 K. A bias of 5V is applied across the length of the silicon resistor.
a) Calculate the current in the resistor.
b) Repeat part a) if the length is reduced by 0.01 cm.
c) What is the drift current in parts a) and b)?
Assume we have silicon with typical mid-range doping levels of donors (no acceptors) at 300K. Assume
that the mobility for electrons is limited by lattice scattering and has a temperature dependence of
approximately T-3/2. Determine the electron mobility at: a) T=200K; b) 400K.
A silicon bar has a length of L = 0.1 cm and a cross-sectional area of A = 10−4 cm2. The
semiconductor is uniformly doped with phosphorous at a level 5 x 1016 cm−3 (no other doping).
A voltage of 5 V is applied across the length of the material which is at T=300K. The minority
carrier lifetime is 3 x 10−7 s. For t < 0, the semiconductor has been uniformly illuminated with
light, producing a uniform excess carrier generation rate of g‘ = 5 x 1021 cm−3 s−1. At t = 0, the
light source is turned off. Determine the current in the semiconductor as a function of time for -∞
≥t ≥ ∞.
An n-type GaAs semiconductor at 300 K is uniformly doped with donors (no acceptors) at a
level of 5 x 1015 cm−3 (mid level doping). The minority carrier lifetime is 5 x 10−8 s. A light
source is turned on at t = 0 generating excess carriers uniformly at a rate of g‘ = 4 x 1021 cm−3 s−1.
There is no external electric field.
a) Determine the excess carrier concentrations versus time over the range 0 ≤ t ≤ ∞.
b) Calculate the conductivity of the semiconductor versus time over the same time period as
Consider a bar of p-type silicon material at T=300K that is homogeneously doped to a value of 3
x 1015 cm−3 (ND=0), which may be considered mid level doping. The applied electric field is
zero. A light source is incident on the end of the semiconductor on one end (where x = 0, with x
increasing into the silicon bar). The excess carrier concentration generated at x = 0 is 1013 cm−3.
The lifetimes for electrons and holes are 0.5 μs and 0.1 μs, respectively.
a) Calculate the steady-state excess electron and hole concentrations as a function of
distance into the semiconductor.
b) Calculate the electron diffusion current density as a function of x.
Calculate the position of the quasi-Fermi level with respect to the intrinsic level for the following silicon
crystal that is steadily illuminated with an excess carrier generation rate of 1021 /cm3S:
NA = 1016 /cm3 , ND = 0
τn0 = τp0 = 1 μS
A silicon sample at 300K has the following impurity concentrations: ND = 1015 /cm3 and NA = 0 . The
equilibrium recombination rate is Rp0 = 1011 cm−3 s−1. A uniform generation rate produces an excess
carrier concentration of 1014 /cm3 .
a) What is the excess carrier lifetime?
b) By what factor does the total recombination rate increase?
Why Choose Us
We value our clients. For this reason, we ensure that each paper is written carefully as per the instructions provided by the client. Our editing team also checks all the papers to ensure that they have been completed as per the expectations.
Professional Academic Writers
Over the years, our Acme Homework has managed to secure the most qualified, reliable and experienced team of writers. The company has also ensured continued training and development of the team members to ensure that it keep up with the rising Academic Trends.
Our prices are fairly priced in such a way that ensures affordability. Additionally, you can get a free price quotation by clicking on the "Place Order" button.
We pay strict attention on deadlines. For this reason, we ensure that all papers are submitted earlier, even before the deadline indicated by the customer. For this reason, the client can go through the work and review everything.
At Essay USA, all papers are plagiarism-free as they are written from scratch. We have taken strict measures to ensure that there is no similarity on all papers and that citations are included as per the standards set.
Customer Support 24/7
Our support team is readily available to provide any guidance/help on our platform at any time of the day/night. Feel free to contact us via the Chat window or support email: email@example.com.
Try it now!
How it works?
Follow these simple steps to get your paper done
Place your order
Fill in the order form and provide all details of your assignment.
Proceed with the payment
Choose the payment system that suits you most.
Receive the final file
Once your paper is ready, we will email it to you.
Essay USA has stood as the world’s leading custom essay writing services providers. Once you enter all the details in the order form under the place order button, the rest is up to us.
At Essay USA, we prioritize on all aspects that bring about a good grade such as impeccable grammar, proper structure, zero-plagiarism and conformance to guidelines. Our experienced team of writers will help you completed your essays and other assignments.
Admission and Business Papers
Be assured that you’ll definitely get accepted to the Master’s level program at any university once you enter all the details in the order form. We won’t leave you here; we will also help you secure a good position in your aspired workplace by creating an outstanding resume or portfolio once you place an order.
Editing and Proofreading
Our skilled editing and writing team will help you restructure you paper, paraphrase, correct grammar and replace plagiarized sections on your paper just on time. The service is geared toward eliminating any mistakes and rather enhancing better quality.
We have writers in almost all fields including the most technical fields. You don’t have to worry about the complexity of your paper. Simply enter as much details as possible in the place order section.