Photoluminescent properties of vacuum deposited cadmium sulfide films
Bleha, William Paul, Jr.
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https://hdl.handle.net/2142/25814
Description
Title
Photoluminescent properties of vacuum deposited cadmium sulfide films
Author(s)
Bleha, William Paul, Jr.
Issue Date
1970
Doctoral Committee Chair(s)
Peacock, R.N.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
photoluminescent properties
vacuum deposited cadmium sulfide films
phonon-assisted edge emission
Language
en
Abstract
"Green and blue photoluminescence has been observed below 1000K in
vacuum deposited, low resistivity CdS films given no post deposition treatment.
The films were deposited in a heated chamber inside the bell jar on
o fused quartz substrates held at temperatures from 140-180 C. The background
pressure in the vacuum system was 10-6 Torr. The evaporant sed was
chlorine-doped CdS powder. The chlorine doping activated the luminescence
and gave films that had resistivities at 3000K in the range of 1-102 ohm-cm
parallel to the substrate.
o
The green luminescence in the films at 77 K wa.s similar to the emission
reported for donor-doped CdS. Donor-doped CdS emission differ8~:
from the phonon-assisted ""edge emission"" starting at 5140 ~ observed in
pure CdS in that the emission peak at 5230 ~, corresponding to emission
of one k=O LO phonon, is more intense than the zero phonon peak, The
relative peak intensities of the zero phonon and phonon replicas in pure
CdS can be described by a Poisson distribution in N where N is the mean
number of phonons emitted in the transition.
ponent peaks also have equal half-w'idths H.
These Gaussian shaped compotent peaks pure OdS at 77 oK values
found are N :: 0.9-1.0 and H :: 0.03 eV. For the CdS films good agreement
could be obtained with N :: 1.1-1.4 and H ;: 0.04-0.06 eV. How'ever, , it is
also possible that the film luminescence i.s the superposition of two emission
series.
The green emission spectra. observed at lOoK became better resolved
than at 77 oK, and the peak position shift with temperature was small. The
-6 0 decay time of/the green emission was less than 10 sec at 77 K, and thermal
quenching of the luminescence began around 100oK, with an activation energy
of -0.15 eV. The quenching is due to the thermal ionization of the acceptor
center involved in the transition. Baking in saturated cadmium vapor at
500 C quenched the green emission, and for films baked in H2
S at 600 C,
emission similar to that observed in pure CdS was obtained.
The blue emission peak observed in the films was at 4892 R at 77°K,
which is in the fundamental absorption edge. It shifted to 4875 A and
became more intense and narrower at lOoK. This emission persists to 3000K
with the peak position decreasing in energy similar to the decrease in
energy of the band gap. The peak is quenched by baking in H2S but not
by baking in saturated Cd vapor. The blue emission is probably associated
with a shallow donor or isoelectronic trap near the conduction band edge and
could be due to the decay of a bound exciton.
Some of the literature relating to the theory and practice of CdS
vacuum deposition is reviewed. Also a summary of the properties of the
green luminescence of pure and donor-doped CdS is given."
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