Victor Karpov
(Theoretical Physics, Condensed Matter, Semiconductors, Photovoltaics, Device Physics)
Professor of Physics
Dr. of Science, 1986, Institute for Nuclear Physics, Academy of Science, Russia;
Ph.D., 1979,
Polytechnic University, Russia
My current research interests are in condensed matter theory and device physics, including disordered systems, phase transitions, thin films, and photovoltaics.
One broad topic is thin-film devices, which remain poorly
understood in spite of many applications in microchips, photovoltaics, and
others. We have established a new area of the physics of thin photovoltaics (as
opposed to the classical crystalline solar cells) encompassing many unique
phenomena and helping to better engineer solar modules with improved efficiency
and stability. Our contributions include the following. (1) The concept of weak
micro-diodes that has now become the standard element of device operation
analysis. It takes into account that different microscopic areas in thin film
junctions have quite different diode characteristics. Because they are all
interconnected through the device electrodes, the system operates as an array
of random diodes strongly affecting each other and the system integral
parameters. The related fundamental concept is the nonuniformity screening
length that determines the maximum device size and its nonuniformity effects.
(2) The piezo-(pyro-) photovoltaic coupling is another fundamental contribution
of our group based on the realization that the standard component of thin film
PV, CdS is a strong piezo-electric and its piezo-electric field strongly
interacts with PV electricity leading to new physical effects. That new
understanding resulted in recipes of improving the device parameters. (3)
Perhaps the most known to the general photovoltaic community contribution by
our group is the red
wine effect, which is a practical remedy of
improving the device efficiency through mitigating its nonuniformity loss (in
the simplest settings achieved by applying some red wine before the final
metallization). That concept was patented as an efficient self-healing remedy,
and the patent exclusively licensed to a major photovoltaic company. Our
photovoltaic research was funded through DOE and NSF grants. We have published
a textbook Physics of thin-Film Photovoltaics (in co-authorship with Dr.
Shvydka) with Wiley Publishers.
A significant effort was devoted to creating a theory of metal
phase nucleation in symmetry breaking strong electric fields, which phenomenon
is central to the operations of the emerging solid state memory. Our work has shown, that in strong enough, yet practically
important electric fields, needle shaped conductive filaments appear in insulating
hosts of glassy semiconductors. This theory triggered extensive experimental
work of Intel Corporation (that funded our research) and has now become a
common base in the field of solid state memory technology. That theory of field
induced nucleation has been significantly extended later to explain the
nonphotochemical laser induced nucleation in some solutions, anisotropic metal
particle formation in insulators, and laser induced pancake shaped void
formation in metal films. The fundamental nature of these results is that they
reveal the possibility of symmetry breaking phase transformations (needles
instead of spheres) in isotropic systems.
A more recent activity was in the field of metal
whiskers that often grow across leads of electric
equipment and electronic package causing current leakage or short circuits and
raising significant reliability issues, especially in the case of tin that
serves as a base for various soldering alloys. The nature of metal whiskers
remains a mystery after several decades of research. Recently, Karpov proposed
a theory of metal whiskers that for the first time provided understanding of
their underlying physics and corresponding quantitative description. The theory
is based on the electrostatic of imperfect metal surfaces that are capable of
generating random local electric field. Simultaneously, that theory proposed
practical recipes of accelerated testing of whisker growing propensity of
metals and venues of whisker mitigation. This work sparked significant interest
in the community of engineers and researchers and was highlighted in the media. Also, it triggered experimental research in metal whiskers
revolving around the external field effects of their nucleation and growth. Our
preliminary results have shown strong field effects in the capacitive field
configuration and under e-beam of linear medical accelerator. This research
direction is being enthusiastically developed.
Artificial
Intelligence (AI) was the most recent field of my research. We developed a
theory of percolation with plasticity media (PWPs) rendering properties of
interest for neuromorphic computing. Unlike the standard percolation, they have
multiple interfaces and exponentially large number of conductive pathways
between them. These pathways consist of non-ohmic random resistors that can
undergo bias induced nonvolatile modifications (plasticity). The neuromorphic
properties of PWPs include multi-valued memory, high dimensionality and
nonlinearity capable of transforming input data into spatiotemporal
patterns,
tunably fading memory ensuring outputs that depend more on recent inputs, and
no need for massive interconnects. A few conceptual examples of functionality
here are random number generation, matrix-vector multiplication, and
associative memory. Understanding PWP topology, statistics, and operations
opens a field of its own calling upon further theoretical and
experimental insights.
My former graduate students work on different aspects of Device Physics, Photovoltaics, and Theoretical Physics:
Lilani Cooray, PhD program, theoretical physics, photovoltaics;
Mukut Mitra, PhD program, experimental physics, phase change memory;
Marco Nardone, PhD program, theoretical and device physics;
Trevor Wilson, MS program, theoretical biophysics;
Tim Muszynski, MS program, theoretical device physics;
Mark Simon, PhD program, theoretical physics, phase change memory.
Dipesh Niraula, PhD program, theoretical physics, device physics.
Osama Oudat, PhD program, experimental research in metal whiskers
Maria Patmiou. PhD program, disordered systems and AI
Victor Karpov and Diana Shvydka, Physics of
Thin-Film Photovoltaics
Book, Wiley publishers 2021 https://www.amazon.com/Physics-Thin-Film-Photovoltaics-Victor-Karpov/dp/111965100X
Vamsi Borra, Srikanth Itapu, Victor G. Karpov, Daniel G. Georgiev,
Modification of Tin (Sn) metal’s surface by Surface Plasmon
Polariton Excitation,
Scripta Materialia, 208, 114357 (2022)
VG Karpov, D Shvydka, SS Bista, Threshold
switching in solar cells and a no-scribe photovoltaic technology, Appl.
Phys. Lett. , 119, 193904 (2021)
VG Karpov, Adiabatic
theory of SET and RESET transitions
Journal of Applied Physics 129 (11),
114501 (2021)
V. G. Karpov, S. Gursel, and Maria Patmiou
Percolation
with plasticity for neuromorphic systems
J. Physics: Complexity 1, 035009 (2020),
M. Patmiou, V. G. Karpov, S.
Gursel, B.R. Weborg,
Numerical modeling of
percolation conduction and Poole-Frenkel laws,
J. Appl. Phys. 128,
035701 (2020).
V. G. Karpov and M. Patmiou, Physics in the information age:
Qualitative methods in quantum theory, Eur.
J. Phys. 41 (2020) 035407
V.G. Karpov, M. Patmiou, S.
Gursel, D. Shvydka
Pulse percolation conduction
and multivalued memory,
AIP
Advances 10, 045324 (2020)
O. Oudat, V. Arora, E. Parsai, V. G. Karpov, and D. Shvydka,
Gamma-
and x-ray accelerated whisker development
J.
Phys. D: Appl. Phys. 53 (2020)
V. G. Karpov and D. Niraula, OFF
state conductivity in RRAM structures,
Electron Device Letters, 40, 551 (2019)
Maria Patmiou, D, Niraula, and V. G. Karpov
The Poole-Frenkel
laws and a pathway to multi-valued memory,
Appl. Phys. Lett. 115, 083507 (2019);
D. Niraula and V. G. Karpov,
Comprehensive modeling of
filamentary RRAM devices,
J. Appl. Phys. 124,
174502 (2018);
Osama A Oudat, Vamsi Borra, Daniel G Georgiev and Victor G Karpov,
The
statistics of tin whisker diameters versus the underlying film grains,
J.
Phys. D: Appl. Phys. 52 (2019) 165305
V. G. Karpov and D. Niraula, Resistive switching in
nano-structures, Scientific Reports, Nature, 8, 12212 (2018).
V. Borra, D. Georgiev, V. G. Karpov, and D. Shvydka,
Microscopic structure of metal whiskers, Phys. Rev.
Applied, 9, 054029 (2018)
V. G. Karpov, Dipesh Niraula, and I. V. Karpov, Thermodynamic
analysis of
conductive filaments, Appl. Phys Lett. 109,
093501 (2016).
Diana Shvydka and V. G. Karpov Surface parameters determining a
metal propensity for whiskers, J. Appl. Phys. 119, 085301 (2016).
D. Niraula, J. McCulloch, G.
R. Warrell, R. Irving, V. G. Karpov, and Diana Shvydka, Electric Field Stimulated
growth of Zn whiskers, AIP Advances, 6,
075201 (2016).
V. G. Karpov, Electrostatic Mechanism of Nucleation and Growth of Metal Whiskers, SMT Magazine, February 2015, p. 28. http://iconnect007.uberflip.com/i/455818/44
V.G.Karpov, Electrostatic Theory of Metal Whiskers, Phys. Rev. Applied, 1, 044001 (2014).
V. G.
Karpov, A. Vasko, and A. Vijh, Hot spot runaway in thin film photovoltaics and
related structures, Appl. Phys. Lett. 103, 074105 (2013)
M. Nardone, M. Simon, I. V. Karpov, and V. G. Karpov, Electrical
Conduction in Chalcogenide Glasses of Phase Change Memory (focused review), J.
Appl. Phys. 112, 071101 (2012)
V. G. Karpov, M. Nardone, and N. I. Grigorchuk, Plasmonic Mediated Nucleation of Nanoparticles, Phys. Rev. B 86, 075463 (2012)
V. G. Karpov, Coupled Electron-Heat Transport in Thin Nonuniform Films, Phys. Rev. B 86, 165317 (2012)
M. Nardone, M. Simon and V. G. Karpov, Shunting
Path Formation in Thin Film Structures, Appl. Phys. Lett. 96, 163501
(2010)
M. Nardone, V. G. Karpov, D.
Shvydka, and M. L. C. Attygalle, Theory
of electronic transport in noncrystalline junctions, J.
Appl. Phys., 106, 074503 (2009)
J. Kang, E. I. Parsai, D. Albin, V.
G. Karpov, and Diana Shvydka, From
photovoltaics to medical imaging: Applications of thin-film CdTe in x-ray Detection,
Appl. Phys. Lett., 93, 223507 (2008)
Diana Shvydka and V. G. Karpov, Nanodipole
photovoltaics, Appl. Phys. Lett. 92, 053507 (2008)
M. Mitra, J. Drayton, M. L. C. Cooray, V. G.
Karpov, and Diana Shvydka, Piezo-photovoltaic coupling in CdS-based thin-film
photovoltaics J. Appl. Phys. 102, 034505 (2007)
M. L. C. Cooray and V. G. Karpov, Long range
fluctuations in thin-film structures, Phys. Rev. B. 75, 155303 (2007).
V.
G. Karpov, Critical disorder and phase transition in random diode arrays, Phys.
Rev. Lett., 91, 226806 (2003)
V.
G. Karpov, A. D. Compaan, and Diana Shvydka, Random diode arrays and mesoscale
physics of large-area semiconductor devices, Phys. Rev B 69, 045325
(2004).
V.
G. Karpov, David W. Oxtoby, Nucleation in Disordered Systems, Phys. Rev. B 54,
9734 (1996)
M.
Grimsditch, V. G. Karpov, Fluctuations During Melting, J. Phys, C, Condensed
Matter, 8 L439 (1996)
V.
G. Karpov, Instability in the Classic Theory of Coarsening, Phys. Rev. Lett. 74,
3185 (1995)
V.
G. Karpov, Negative Diffusion and Clustering of Growing Particles, Phys. Rev.
Lett. 75, 2702 (1995)