Characterization of ZnS:Cr films for Intermediate Band Solar Cells
In this thesis samples of ZnS:Cr thin films have been made through physical
vapor deposition (PVD) with resistive heating and characterized by several
methods. The thin films are of various thicknesses and contain different
concentration of Cr. ZnS:Cr is a candidate to a bulk material for intermediate
band solar cell, IBSC, and was therefore selected for this thesis. IBSC is a
concept for solar cells with a much higher effiency than todays common solar
The goal for the project was to put together the deposition system, make the
samples, measure the thicknesses and concentrations and characterize them.
Methods like X-Ray Diffraction (XRD), Auger electron spectroscopy (AES),
profilometer, four point measurement, Hall-measurement and optical transmission
measurements have been used to determine structure, concentrations,
thicknesses, resistivity, number of carriers and transmission respectively.
The samples and the characterization performed with XRD, AES, profilometer,
Hall-measurement and four point measurement were done at NTNU. The
spectrum measurements were done at NTNU and the University in Vienna.
Samples with thicknesses in the range of 200 Å to 3340 Å have been investigated.
Some were deposited in room temperature, some were annealed
afterwards for 2 hours at 4500C and some were deposited on substrates with
a temperature of 3000C. The thicknesses were measured with a contact profilometer.
The theoretical concentration of the samples were in the range of
4% to 31%. There was impossible to measure samples with a lower concentration
than 7%, even though these were made.
Transmission spectra were made in five overlapping specrophotometerss. Two
were used in the visible region (UV-VIS), two in the near infra-red (NIR)
region, and one Fourier Transform Infra-Red spectroscopy (FTIR) for the
long wavelength region. The range was from 250 nm up to 25000 nm. No
Cr2+ absorption lines were found. This can indicate a cluster form of the Cr
and not a substitution of Cr2+ with Zn2+ ions. The band gap found from
the transmission spectra were in the range of >4.5 eV to 2.95 eV. The high
band gap imply insulating samples and inactive Cr states in cluster form.
No peaks from lattice configuration were found in the XRD spectrum. This indicates an amorphous structure for both the samples deposited in room
temperature, the annealed samples and the sample deposited on hot substrate.
The lattice configuration of the sapphire substrate was found for 3
samples. This was the  reflection for sapphire at 68.2 degrees.
Four samples were investigated in AES. A 3340 Å 7% sample, a 800 Å <5%
sample, a 370 Å 31% sample and a 830 Å >4% deposited on hot substrate.
Less Cr than expected was found for the sample of 800 Å and 830 Å. However,
all samples contained O and C. The sample deposited on hot substrate should
contain 80 Å Cr theoretically, but no traces were found. The same applies
for the 800 Å sample with less than 5%. Both charged badly which imply
non-conductive samples. The 31% and the 7% sample did not show the same
charging which implies conductivity. The samples showed a great amount of
Cr, but did also contain O and C. However, from the Hall-measurement and
four probe measurement none of the samples showed conductive properties.
This emphasize the suspicion of incorporation of Cr clusters in inactive states
making the samples insulating.
Place, publisher, year, edition, pages
Institutt for fysikk , 2011. , 114 p.
ntnudaim:5778, MLREAL Lektorutdanning med master i realfag, Fysikk og matematikk
IdentifiersURN: urn:nbn:no:ntnu:diva-12828Local ID: ntnudaim:5778OAI: oai:DiVA.org:ntnu-12828DiVA: diva2:426661
Gibson, Ursula, Professor