Exam text content

Tampere University of Technology

FYS-6106 Basic Semiconductor Technology

Exam, Tuesday K1705 12.12.2017, 13:00-16:00

Examiner: Antti Tukiainen, Optoelectronics Research Centre/Laboratory of Photonics, SL202

Obs.: Non-programmable calculator is allowed! Attached you can also find a separate sheet of
formulas, tables and physical constants that can be used in the exam.

!Please remember to give feedback through the Kaiku-system to get the credit points from the
course!

Answer to FIVE (5) guestions!

Ouestion 1. Explain the following terms:
a) Ouasi-Fermi level
b) Charge carrier effective mass
c) Zinc blende lattice
d) Electron-hole pair
e) Einstein relation
f) Recombination center

Ouestion 2. Explain shortly the following terms:
a) Photoelectric effect
b) Direct and indirect band semiconductors
c) Formation of population inversion in pn-junction

Ouestion 3.

You need to design the active region (light generation region) of a light emitting diode (LED). The
active region is to be formed using a guantum well (OW) made of Gao 5Ino sP. The Gao 5Ino sP OW
is sandwiched between 200 nm thick barrier layers made of (Alo 5Gao 5)0.52110.48P. Determine the
thickness of the OW so that its emission wavelength is 630 nm (the base level transition). Use the
infinite potential well approximation. mn (Gao sIno sP)=0.11*me, mp (Gao Ino sP)=0.45me,

mn (Alo.5Ga0.5)0.521n0.48P)=0.1*me, mp (Alo.5Ga0.5)0.521n0.48P)=0.55me, The energy band gaps are:
Eg(Gao sIno.sP)=1.88 eV and Es(Alo.5Gao 5)0.521n0.48P)=2.3 eV. Draw the energy band profile in the
given structure.

n?m?(h bar)?

Tip! For an infinite potential well: E, = 22

Ouestion 4. Explain the formation of pn-junction. Draw also energy band diagrams/profiles for
each voltage configuration. Indicate also the formation of the contact potential and how the applied
voltage is linked with the energy band diagram through the Ouasi-Fermi levels.

Ouestion 5. Compare different (photo)lithography technigues. Give the pros and cons for each
method. Indicate also the obtainable feature size range for each of the discussed method and
physical background for the resolution.

Ouestion 6. A Si p-n junction has a donor doping of 5x10'6 cm3 on the n-side and a cross-sectional
area of 10% cm?. If 7;=14s and Dp=10 cm?/s, calculate the current with a forward bias of 0.5 Vat
300 K.

Continues on the next page! >

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Ouestion 7. A Schottky barrier is formed between a metal having a work function of 4.3 eV and p-
type Si (electron affinity=4 eV) The acceptor doping in the Si is 10'7cm".

a) Draw the eguilibrium band diagram, showing a numerical value g Vo.
b) Draw the band diagram with 0.3 V forward bias. Repeat for 2 V reverse bias.

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