phone (416) 978-4395
fax: (416) 978- 5848
e-mail: serge@physics.utoronto.ca
EDUCATION
Thesis : " Study of Photoelectronic Properties of Semiconductors by the Advanced Method of Transient Microwave Photoconductivity (AMTMP)."
Thesis: " Application of Photoacoustic Spectroscopy to the Study of Dispersed Non-transparent AgHal Materials"
Analytical Spectroscopy, Surface Analysis, Chemical Instrumentation, Kinetics-Dynamics , Physics and Chemistry of Electrified Interfaces, Comprehensive exam. in Physical Chemistry.
NSERC Postdoctoral Fellowship
(1999-2000)
Ontario Graduate Scholarship
(1997)
Summer Research Fellowship
of the Electrochemical Society and the U.S. Department of Energy
(1996)
University of Guelph Graduate
Scholarship (1995),
(GWC)2 M.Sc. Graduate
Seminar Prize (1994),
Bruker Spectrospin Graduate
Scholarship (1994),
University of Guelph Graduate
Scholarship (1993)
TEACHING EXPERIENCE
1993-1996 Graduate Teaching Assistantship- Dept. of Chemistry, University of Guelph (taught a first year undergraduate lab "General Chemistry" for five semesters and a second year undergraduate lab "Physical Chemistry" for two semesters)
WORK EXPERIENCE
Project: "Characterization and optimization of thin film semiconductor materials and devices". Work was supported by a grant to S. Grabtchak under Going Global - STEP (Science and Technology with European partners) Program
Was involved in the study of electron-ion processes in light-sensitive silver halides. Investigated the fundamental electronic and transport properties of compound semiconductors and dielectrics at photo- and electron- excitation by the contactless nondestructive microwave photoconductivity method. Was the developer of the advanced method of transient microwave photoconductivity (AMTMP) which permits simultaneous measurement of changes in a real and an imaginary parts of the dielectric constant of semiconductors or dielectrics under excitation at short time scale (nsec) .
SCIENTIFIC INTERESTS AND SKILLS
Current interests include such topics as
transport and photoelectronic
properties of monocrystalline and polycrystalline materials, including
thin films (SI GaAs, CdSe films, Si, diamond films etc.): trapping,
recombination, thermallization
transient measurements
of induced changes in the complex dielectric constant
modeling of transport
phenomena in polycrystalline semiconductors
modeling of effects of
collective/elementary excitations in semiconductors on the complex
dielectric constant
developments in the second
cavity perturbation theory
extension of the basic
AMTMP to a) the pump/probe AMTMP and b) AMTMP with transient luminescence
detection
characterization of basic
materials for solar energy devices
Experienced in the application of microwave techniques, pulsed electrical methods, lasers, vacuum and low temperature ( 77 K) technique (and computers !).
MOST SIGNIFICANT CONTRIBUTIONS TO RESEARCH AND DEVELOPMENT
From the all contributions the following 3 publications represent the most significant contributions to the research of photoelectronic properties of semiconductors:
1. Grabtchak, S. and Cocivera, M. (1998) Microwave response due to light induced changes in the complex dielectric constant of semiconductors. Phys. Rev. B , 58, 4701-4707
2. Grabtchak, S. and Cocivera, M. (1996) Contactless microwave study of dispersive transport in thin film CdSe. Journal of Applied Physics. 79: 786-793 (Ph.D. work )
3. Grabtchak, S. and Cocivera, M (1994) Contactless microwave study of shallow traps in thin film CdSe. Phys.Rev.B. 50: 18219-18225 (Ph.D. work)
To consider the importance of these contributions I will review them in chronological order.
In the article (3) the original concept of AMTMP measurements, i.e. a separation of the cavity quality factor changes and the shift of the resonance frequency contributions to the observed photoresponse was introduced for the first time. It was clearly shown that a difference between the dark resonance curve and the resonance curves at particular instants after optical excitation can be reconstructed using photoresponses collected at various frequencies within a bandwidth of the cavity. The first approach to extract kinetics of the cavity quality factor changes and of the shift of the resonance frequency from the difference signal was introduced. Although the experimental technique, data analysis and physical understanding of the observed phenomena were significantly improved in the subsequent years this article still has historical value as a first birth of what I called AMTMP later. I was a major developer of the method and the major writer of the article. Therefore, I have all the reasons to call my self the "father" of the new method, AMTMP. (I must add that the initial concept of the method was presented earlier in the following publication in Russian: Novikov,G., Grabtchak,S., and Alfimov, M. (1990) The contribution of free electron to laser induced microwave absorption in melted silver bromide, 300 K. Zhournal Nauchnoi i Prikladnoi Fotografii I Kinematografii (Soviet Journal of Scientific and Applied Photography and Cinematography) (in Russian) 35, 18-26 ).
The article (2) and all subsequent publications correspond to the second birth and flourishing of AMTMP here, at the University of Guelph. This article described a new method for the unambiguous determination of the changes in the real and imaginary parts of the dielectric constant. The relation of these changes to the contributions of free and trapped electrons was analyzed using experimental results for the thin film CdSe. A phenomenon never observed previously in this type of sample, a dispersive transport, was revealed. It was shown that the model consistent with the observed effects was very similar to one used to treat photoconductivity in amorphous materials. According to this model, localized subband gap states have a continuos exponential distribution in energy, and multiple trapping occurs with the electron distribution weighted toward deeper traps as time progresses. This would cause a very peculiar behavior of free and trapped electron decays, which was indeed observed in our experiments. In addition, the range of energies responsible for the dispersive transport was estimated. This research provided a deeper insight into the nature of carrier transport in the CdSe thin films which is important, for example, in regards to making thin film transistors or photovoltaic devices based on CdSe.
The article (3) presents the latest most important developments in all aspects of AMTMP. First, a rigorous treatment of the light induced changes in the complex dielectric constant in the microwave cavity led us to extending the basic cavity perturbation theory developed by Slater in mid 40's and developing a "second " perturbation theory. We developed general expressions from which the simple analytical forms presented by earlier workers could be obtained for the geometric shapes of samples. Furthermore the first perturbation could be obtained as a special case of our more general expressions. Second, it was shown that in a context of our AMTMP results the harmonic oscillator model provided an adequate description of free and trapped electrons including plasma effects in terms of contributions to the real and imaginary parts of the dielectric constant. We also were able to extend this model to incorporate other types of bound electrons, i.e. electron-hole droplets and excitons. A review of the phenomena that can be detected by AMTMP was given. Third, using our data for semi-insulating (SI) GaAs and thin film CdSe, we showed how free electron effects can dominate over those of trapped electrons when the electron mobility is high (SI GaAs), and the reverse occurred in thin film CdSe which has a substantially smaller mobility. Finally, we showed how the mobility changes can be separated from the carrier concentration changes in photoconductivity measurements. The last issue is of particular importance for any photoconductivity experiments in which the signal is often assumed to be proportional to the excess carrier concentration only. I believe that because of the deep development of the complex dielectric constant treatment the value of this article can not be overestimated.
PROFESSIONAL TRAINING
AVS short course "Fundamentals of Semiconductor Characterization: Electrical and Optical Techniques", August 1997
ACHIEVEMENTS
PROFESSIONAL MEMBERSHIPS
The Electrochemical Society
since 1995
The Chemical Institute
of Canada, the Canadian Society for Chemistry since 1995
The American Chemical
Society since 1995
The American Institute
of Physics, the American Physical Society since 1995
The Materials Research
Society since 1995
REFERENCES
(available on request)