Prof. Arie Ruzin (D. Sc.)
Department of Physical Electronics
Faculty of Engineering
69978 Tel
WELCOME TO MY WEB PAGE !!
This page includes information about my research
activities, list of publications, open positions, collaborations, related sites
and some cool stuff.
Numerous scientific, medical,
technological, and environmental applications and systems require particle
detection. Such particles could be photons, neutrons, protons, etc. Among the
most known application one finds all forms of medical imaging (Computerized
Tomography, Mammography, Nuclear Medicine, etc.), mechanical non destructive
testing (imaging), security baggage
imaging (at the airport for instance), particle and nuclear physics
experiments, and so on.
In order to be detected the particles
have to interact with the detectors, which means that
the detectors should be tailored to the desired interaction mechanism/s of the
specific particle. In the case of
medical imaging mainly high energy photons have to be detected (~10 keV to ~0.5
MeV), for which the most probable interactions are the photoelectric effect and
Beside generating the free carriers which
enable the detection operation, the particles could introduce lattice damage by
dislocating one or more absorbing atoms. The effect is caused by Non-Ionizing
Energy Loss (NIEL) mainly in the case of non-zero resting-mass particles, but
also for particularly high energy photons, etc. The defects caused by the
incident particles can be electrically active, introducing carrier traps and
generation-recombination centers. In this case the detector's performance could
deteriorate with time (as the accumulated damage increases). Understanding of
the defects is the first and vital step on the way to designing of radiation
tolerant detectors. One of the possible ways to minimize the effect of the
radiation induced damage is by introducing defect engineering. Namely, by
creating certain defects in the semiconductor material of the detector one
could neutralize the electrical activity of the radiation-induced defects.
Research Activities:
Compound II-VI
semiconductor detectors for X- and Gamma-rays
The wide band-gap Cd1-xZnxTe
semiconductors have very beneficial properties for Gamma-ray detector
application. The forbidden band gap of the ternary compound semiconductor
depends on the Zn content, x: Eg(x)@Eg,CdTe×(1-x)+ x×Eg,ZnTe - x×b× (1-x), where b
is the bowing factor (b@0.11). The average ionization energy of CdZnTe with
low Zn content is ~4.4 eV (the average energy required to generate one
electron-hole pair). The electron and hole mobilities are about 1000 and 100
[cm2/V×sec], respectively. We
study macroscopic as well as microscopic properties of these semiconductors and
related devices. We use device characterization such as I-V(T), Noise PSD, TCT
(Transient Current Technique), X-ray spectroscopy, etc., to evaluate the
overall properties and performance of the resulting device. We use TSC
(Thermally Stimulated Current) and Laplace-DLTS setup combined with optical
injection (PITS) to characterize the deep levels in the band-gap, and AFM based
measurements to study local electrical activity.
Silicon detectors for MIPs (Minimum Ionizing Particles), X- and Gamma-rays
Silicon is the most
studied and probably best understood material on the planet, but unfortunately
it is not suitable for many of the imaging applications, because of the low
atomic number (14). In other words, many of the high energy photons simply do
not interact with the detector's volume and therefore are not detected.
However, silicon detectors are useable in some photon applications, when low
efficiency detection is acceptable or when "soft x-rays" (photons
with energy range up to ~30 keV) have to be measured. In the case of
relativistic, Minimum Ionizing Particles (MIPs), such
as fast electrons, protons, pions, etc., the ionization signal is not strongly
dependent on the atomic number of the detector's media (compared to photons).
In such application silicon detectors have an advantage of low cost,
availability of large area detectors, advanced technology
(developed mostly for VLSI), etc.
However, the silicon used
for these application has to be of high resistivity (usually grown by Floating
Zone method), while the VLSI technology uses low resistivity silicon, grown by
Czochralski method. The high resistivity silicon and its processing were not
studied as extensively as those of the low resistivity material. We study some
aspects of the dependence of device technology and geometry on performance and
yield.
Radiation
hardness of semiconductor detectors and VLSI electronics
Electronic systems operated in harsh
radiation environments sustain significant radiation-induced damage. Some of
the 'mechanical' defects in the lattice are electrically active and therefore
may alter system's operation. Such harsh radiation environment exists in space,
in nuclear reactors, in high-energy physics experiments, etc. Often the same
particles that the sensors were built to detect introduce lattice damage into
the sensors, making them un-usable. Another aspect of radiation damage has to
do with 'single event upsets'. Even if the incoming particle does not introduce
permanent lattice damage, it still may generate electron-hole pairs, which may
yield a false electronic signal.
We study radiation-induced damage in
semiconductors and semiconductor devices. Our group participates in the RD-50
Collaboration at CERN (European center for nuclear and particle Physics). The
aim of the collaboration is to advance the understanding of the nature of the
defects introduced by various particles to detectors, and to find ways to
improve the radiations hardness (tolerance) of the detectors.
Silicon-germanium
detectors
Silicon-germanium has a great potential to
replace silicon detectors in many soft X-ray applications. The atomic number of
germanium is significantly higher than that of silicon (32 compared to 14),
therefore even a small fraction of germanium atoms should improve significantly
the absorption efficiency. The main problem is that for gamma photon detection
thick detectors must be used, therefore the epitaxial layer technology used in
fast VLSI devices could not be applied directly to the detector realization.
Bulk SiGe is rather difficult to grow due to Ge segregation. Silicon-germanium
grown by Float Zone technique is only available at this time in small ingots (~1
cm diameter). Czochralski grown Si1-xGex can be grown in
larger ingots, however the resistivity is rather low, thus the active region of
the detectors is very limited. To overcome the resistivity issue we try
diffusing and drifting compensating lithium atoms.
We study the electrical properties of
currently available SiGe bulk semiconductors (with and without lithium
diffusion) and devices by means of "dark" properties
characterization, as well as by Laplace DLTS and other techniques.
Indium-Antimonite
detectors
Indium-Antimonite semiconductor has high
carrier mobility and bandgap suitable for infra red absorption. The binary
semiconductor is often used for IR detectors. We investigate the bulk material
and passivation layer for this semiconductor .
Nano-contacts
When the size of devices/structures is
reduced below a certain threshold, classical (textbook) assumptions and
approximations no longer apply. Nano-contacts are interesting subjects for
research for two main reasons: (i) with the down-scaling
of VLSI technology nano size contacts become feasible and thus important to
understand. ; (ii) Less averaging effect often yields better
understanding. Semiconductors in general and "exotic" semiconductors
in particular can not be grown without defects, thus when making large contacts
one includes various material "abnormalities" in the overall behavior.
The smaller the contact size, the less
averaging there is.
However, with size reduction come increased
edge effects, high electric field, etc.
Atomic
Force Microscopy (AFM)
Atomic force microscopy is a part of a
larger family called Scanning Probe Microscopy (SPM). Contrary to the optical
microscopy (limited by the visible wavelength), in scanning probe microscopes
the surface of the sample is scanned by a tiny probe with the signal recorded
at each point to produce an image. In its origin AFM was used mainly for topography
characterization using Van der Waals forces between
the surface and the tip of AFM. Later on many applications were developed on
the AFM platform for studies of other material properties: electrical,
mechanical, magnetic, etc. For electrical characterization we use Contact
Potential Difference (CPD), Electrostatic Force Microscopy (EFM), Scanning
Capacitance Microscopy (SCM), Tunneling current (TUNA), Scanning Spreading
Resistance Microscopy (SSRM). For subtle contacts and surfaces Torsion mode is
used.
Open positions:
M. Sc.
and D. Sc. students are wanted
In the following fields of research: CdZnTe detectors for x- and gamma-rays, silicon detectors for soft x-rays, computer simulations of various detectors (with existing and self-written software), Atomic Force Microscopy (AFM) measurements of various detectors, radiation damage to detectors and VLSI electronics, VLSI design and testing of front-end electronic circuits (fabrication will be performed elsewhere).
B. Sc. Students for interesting projects are wanted
A variety of interesting projects is offered to fine students: Design and LabView programming of automatic electronic measurements; Design, simulation and testing of analog and digital VLSI circuits; Computer simulation of novel semiconductor devices by a commercial simulation software; Hardware and software design for student laboratory upgrades, etc.
Our
Laboratory
Conferences
Photo Gallery
1 November
2009
Hot Links
CERN
- European Research Center for Nuclear and Particle Physics
CERN - RD50 Homepage
Tel
Aviv University Home Page
Analog Electronic Circuits (Course home
page)
Advanced Laboratory for
electronic devices (Lab home page)
If you have comments
or suggestions, email me at 
aruzin@eng.tau.ac.il