DESCRIPTION OF THE ACTIVITIES
Presently,
we are studying the structural, electrical, dielectric and optical properties of
amorphous semiconductors as they draw great attention due to their extensive use
in the solid state devices. One of the main application of the chalcogenide
glasses is Xerography where selenium is used as one of the chalcogen elements.
The shortcoming of the pure glassy selenium for use in the photographic drums
are such as its short life time and low sensitivity which can
overcome by the use of certain additives such as Ge, Te, Bi,In, and Sb.
The binary alloy is of great interest owing to their greater hardness, higher
sensitivity, higher crystallinity and small ageing effect in comparison to pure
amorphous selenium.
THIN
FILM PREPARATION
Quenching
technique has been adopted to prepare glassy alloys . Thin films of the glassy
alloys were prepared by vacuum evaporation technique in a vacuum of ~10-6
torr. Specially designed cryostat is used to measure dc conductivity of the thin
films. For optical properties, films are deposited on quartz substrate by vacuum
evaporation technique. A Hitachi spectrophotometer (U-3400) is used to measure
the optical absorption, reflection and transmission of the films.
CHARACTERISATION
OF THE AMORPHOUS SEMICONDUCTING ALLOYS
In
structural part, we have studied the shift in X-ray K- absorption edge in
a-Se-In, Se-Te-In , Se-Ge-In , Ga-Se-Ag , Se-Te-Ga etc. w.r.t. Se which leads us
to the conclusion that Se-K edge shifts towards the low energy side [1-9]. The
negative shift of Se indicates that
bonding of Se atoms may arise owing to the considerable difference in
electronegativity,
showing iono-covalant nature of bonds
in these glasses. A simple method of characterisation of compounds and alloys by
using data of chemical shift for X-ray absorption edges has also been suggested.
It has been found that the calculated composition of compounds (major
constituents) are in a good agreement with the standard composition
values.
In
electrical properties, We have studied the temperature dependence of dark
conductivity , photoconductivity and thermoelectric power of thin films of
a-Se-Te-In , Se-Ge-In , Ga-Se-Ag , Se-Te-Ga ,Ga-Se-Bi and Ga-Se-Sb etc. On the
basis of these results, we have explained the conduction mechanism in these
glasses. On electrical transport, we have also published a number of research
papers in various international journals [10-22].
In
recent years ,Optical memory effects in amorphous semiconductor films have been
investigated and utilized for various device applications. These have distinct
advantage viz. large packing density , mass replication , fast data rate , high
signal to noise ratio and high immunity to defects . Glassy chalcogenide
semicondoctors has great varities of band gaps and are transparent in IR region
. In optical studies, we have measured the optical band gap and optical
constants of thin films of a Ga-Se-Te
, Ga-Se-Sb , Ga-Se-Bi , Ga-Se etc. [15-19]. The results show that the optical
band gap decreases with increase in concentration in all the samples . The
spectral dependence of the the refractive index and extinction coefficient shows
that the refractive index (n) decreases and the coefficient of extinction (k)
increases with photon energy. The electronegativity for all samples of the
present system has also been calculated. It is also observed that the
electronegativity decreases with the decrease in the optical band gap for all
the samples of the present system .
In
dielectric properties , the temperature and frequency dependence of dielectric
constant and dielectric losses are
studied in the bulk glassy samples of Ga –Se , Ga-Te , etc. in the temperature
and frequency range of (300-360 k) and (0.12khz-100khz) respectively [20-21] . A
strong dielectric dispersion has been observed when Ga is added to a-Se in the
entire temperature range . The dc conductivity has also been measured to see the
effect of Ga on dc conduction losses which are found to be prominent . The
resuls are interpreted in terms of dc conduction losses and Maxwell Wagner type
losses .
Educational Qualification :
M.Sc. (Physics) with Electronics
Ph.D. (Physics) Experimental Solid Physics
Vocational Experience
: Completed a short course in
Computer
Programming from H.B.T.I. Kanpur.
Teaching Experience
:
10 Years
(i).
Jan 22, 1990 to Jan.22, 1995 worked as a Lecturer in Physics Department,
Jamia Millia Islamia, New Delhi.
(ii).
Since Jan.22, 1995 working as a Sr.
Lecturer in Physics Department, Jamia
Millia Islamia, New Delhi.
Research Experience
:
14 Years
(i)
Worked as JRF and SRF in HBTI Kanpur
for 3 year under CSIR Scheme “Electrical and Dielectric Properties of Hot
Pressed AlN Ceramic”.
(ii)
Worked as a Project Scientist (DST
Project) in Physics Department, IIT Kanpur under guidance of Prof.D.C.Khan. This
project belongs to the “Experimental Studies on High Tc
Superconductor” from Dec.1988 to Jan 1990.
Particulars of Guiding Research
:
See appendix-A
(i).
No. of candidates who have
(ii).
No. of candidates presently working for Ph.D.
: 2
Publications
(i).
Research Papers
: 27
(ii). Conference/Workshop/Symposium
: 13
(iii)
Communicated
: 2
Area of Research
:
Experimental Solid State Physics
(i)
Amorphous Semiconductor
(ii)
Ceramic
17.
Ph.D. Thesis Title
:
“Electrical
& Dielectric Properties
of Hot-Pressed
Aluminium
Nitride Ceramic”
18.
Research Project Undertaken
:
Project
entitled "Estimation of Density of
Localized States in chalcogenide glasses from electrical properties"
funded by the University Grant Commission, New Delhi.
19.
Foreign Visits
:(i).
PAKISTAN
Participated in Nathiagali Summer College on Physics and Contemporary
Needs (1991).
(ii).
ITALY
Participated in Workshop on
Materials Science and Physics of Non-Conventional Energy Sources at
I.C.T.P., Trieste (July. 1993).
(iii). ITALY
Visited ICTP, Trieste as affiliate to carry out our own research work on
Condensed Matter Physics at I.C.T.P.,Trieste (Nov-Dec. 1996).
20.
Membership of
Academic Societies
:
(i). Indian Chapter of ICTP, IIT
New Delhi.
(ii).
Meteorological Society
of India.
21.
Scholarship & Awards
:
(i). Merit Scholarship
at High School Level.
(ii).
Principal Award Scholarship at Intermediate
at Level.
(iii).
JRF/SRF at Ph.D.Level.
21.
Administrative
Responsibilities
:
(i).
Co-ordinator
B.Sc.(Instrumentation)
course Feb.-May 1997
(ii).
Advisor,
Jamia Physics
Association (1995 to date).
22.
Name and Addresses of Referees
:
(i).
Dr. A.Kumar
Department of Physics
Harcourt Butler Tecnological
Institute,Kanpur-208002(UP)
(ii).
Dr. S. K. Agarwal
Scientist F,
Solid State
Physics Laboratory, Lucknow Road, Delhi.
(iii). Prof. M. Y .Khan
Department of Physics,
Jamia
Millia Islamia,
New Delhi-110025
Appendix-A
THESIS AWARDED
(i).
Topic
:
Electrical, Optical and Dielectric Studies of
Glassy Semiconducting Alloys.
Name of the Student :
Mr. Mohd. Ilyas, Year
1998
WORK UNDER
PROGRESS
(i).
Topic
: Estimation of Density of Localized
States in
chalcogenide glasses from electrical properties.
Name
of the Student : Mr. Mohd. Abdul Majeed Khan
(ii).
Topic
: Crystallization Kinetics and Phase
change study in
Amorphous Semiconductor .
Name
of the Student : Mr. Samshad Ahmad Khan