Professor of Physics
Dr. of Sciences in Theoretical Physics, 1986, Institute for Nuclear Physics, Academy of Science, Russia;
Ph.D. in Solid State Physics, 1979, Polytechnic University, Russia
My research interests are in condensed matter, semiconductors, and theoretical physics, including disordered systems, phase transitions, thin films, device physics, and photovoltaics.
The ongoing activities include:
1) Physics of Thin Film Photovoltaics where our research concentrates on the following directions shaping up the subject and making it quite different from the classical physics of crystalline solar cells:
a. Nonuniformities. This explores the consequences of thin film devices being non-crystalline and thus nonuniform. Lateral nonuniformities make them operating as circuits of random elements connected in parallel through a resistive electrode. This understanding has brought about a new class of disordered systems, random diode arrays with practical applications including our patented method of nonuniformity healing (the ‘red-wine effect’ highlighted in the media). We develop a theory, modeling, and diagnostics for such systems.
b. Piezo-PV coupling work explores the physics of thin-film junctions having pyroelectric or piezoelectric components with applications to the major types of thin-film PV (CdTe and CIGS), in which one of the layers (CdS) is a strong piezo-electric. These devices are operating in a mode significantly different from that of p-n junctions.
c. Nanodipole PV is a novel concept of PV without p-n or Schottky junctions where the built in electric field is generated by electric dipole nanoparticles embedded in a photoconductive host. A wide variety of materials can be used for the host media and dipole particles; hence, no material feedstock problem and toxic materials can be avoided.
2) Our work on the Physics of Phase Change Memory (PCM) and Threshold Switches (TS) started several years ago in collaboration with (and funded by) Intel Corporation. We worked on the physics of phase change processes in response to electric pulses concentrating on the following problems:
a. Mechanism of nano-crystal nucleation in a host of semi-insulating chalcogenide glass. Our developed theory of electric field induced nucleation was experimentally verified and has become widely accepted in the PCM community.
b. Drift of parameters in semiconducting glasses and their based devices (such as threshold voltage and resistivity) was related by our work to the fundamental properties of glasses where some fraction of atoms retains mobility moving in double well potentials. The mobile atomic units gradually change their state which explains not only the phenomenon of glass aging but low temperature properties of glasses and their time dependent resistivity and switching voltage as well. This understanding was thoroughly verified and became leading in drift phenomena.
c. The parameters of electric filaments in PCM and TS devices are described in the framework of physical kinetics including phase transformation, heat transport and the triggering electric bias. This topic remains rather general and appealing as the phenomenon of filament formation is known far beyond PCM and TS applications.
3) Electric (including laser) field induced phase transformations have been shaping up into a new exciting field during the last decade. Our approach extends the classical nucleation theory to include the following field effects:
a. Static field induced nucleation of needle shaped conducting particles.
b. Laser induced nucleation dominated by plasmonic excitations in embryos that provide resonance with the applied ac field
c. Non-photochemical laser induced nucleation of insulating particles evolving through metal progenitor particles.
The above research was funded through DOE, DARPA, NSF, First Solar, and Intel Corporation grants. We are currently working on a textbook “Physics of thin-Film Photovoltaics” (in co-authorship with Dr. Shvydka) for Wiley Publishers.
My recent graduate students worked on different aspects of Device Physics and Theoretical Physics:
MS 2010, theoretical device physics
V. G. Karpov, Coupled Electron-Heat Transport in Nonuniform Films, submitted in PRB (2012). arXiv:1207.6709v1
V. G. Karpov, M. Nardone, and N. I. Grigorchuk, Plasmonic Mediated Nucleation of Nanoparticles, accepted in PRB (2012). arXiv:1205.3988v2
M. Nardone and V. G. Karpov, Phenomenological theory of non-photochemical laser induced nucleation, Phys. Chem. Chem. Phys., DOI:10.1039/C2CP41880K (2012)
A.B. Pevtsov, A. V. Medvedev, D. A. Kurdyukov, N. D. Il’inskaya, V. G. Golubev and V. G. Karpov, Evidence of field induced nucleation in V02 and VO2 opal composites, Phys. Rev. B 85, 024110 (2012).
V. G. Karpov, M. Nardone and A. V. Subashiev, Plasmonic Mediated Nucleation of Resonant Nanocavities, Appl. Phys. Lett. 101, 031911 (2012).
M. Nardone and V. G. Karpov, Nucleation of Metals by Strong Electric Fields, Appl. Phys. Lett. 100, 151912 (2012).
V. G. Karpov, M. Nardone and M. Simon, Thermodynamics of second phase conductive filaments, J. Appl. Phys., 109, 114507-13 (2011).
M. Nardone, M. Simon and V. G. Karpov, Shunting Path Formation in Thin Film Structures, Appl. Phys. Lett. 96, 163501 (2010).
V. G. Karpov, Electric field driven optical recording, Appl. Phys. Lett., 97, 033505 (2010).
M. Nardone, V. G. Karpov, and I. V. Karpov, Relaxation oscillations in phase change memory, J. Appl. Phys. 107, 054519 (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).
V. G. Karpov, Y. A. Kryukov, S. D. Savransky, and I. V. Karpov, Nucleation Switching in Phase Change Memory, Appl. Phys. Lett. 90, 123504 (2007).
V. G. Karpov, Y. Roussillon, D. Shvydka, A. D. Compaan, and D. M. Giolando, Photovoltaic healing of Nonuniformities in semiconductor device, US patent 7,098,058 B1, 29 Aug (2006).
V. G. Karpov, M. L.C. Cooray, and D. Shvydka, Physics of Ultrathin Photovoltaics, Appl. Phys. Lett., 89, 163518, 2006.
D. Shvydka, J. Drayton, A. D. Compaan, and V. G. Karpov, Piezo-effect and physics of CdS based thin-film photovoltaics, Appl. Phys. Lett., 87, 123505 (2005).
Diana Shvydka and V. G. Karpov, Power generation in random diode arrays, Phys. Rev., B 71, 115314 (2005).
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).
Y. Roussillon, D. Giolando, Diana Shvydka, A. D. Compaan, and V. G. Karpov, Blocking thin film nonuniformities: photovoltaic self-healing, Appl. Phys. Lett. 84, 616 (2004).
V. G. Karpov, D. Shvydka, U. Jayamaha and A. D. Compaan, Admittance spectroscopy revisited: Single defect admittance and displacement current, J. Appl. Phys. 94, (2003).
V. G. Karpov, G. Rich, A. V. Subashiev, and G. Dorer, Shunt screening and size dependent effects in thin-film photovoltaics, J. Appl. Phys. 89, 4975 (2001).
V. G. Karpov, D. W. Oxtoby, Self-organization of Growing Particles, Phys. Rev. E 55, 7253 (1997).
V. G. Karpov, David W. Oxtoby, Nucleation in Disordered Systems, Phys. Rev. B 54, 9734 (1996).
M. Grimsditch, V. G. Karpov, Fluctuations During Melting, 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).
Classes -- Fall 2012