Optical Properties of Solids Under High Pressure

Optical properties of solids are studied using the techniques of laser  Raman scattering, photoluminescence,  photoreflectance, and photoconductivity. The focus is mainly on  semiconductors (such as silicon, gallium arsenide and cadmium  telluride) and semiconductor heterostructures (e.g., zinc  selenide/gallium arsenide). These heterostructures are used in  solar cells, fast integrated circuit chips, high-mobility  transistors and miniature solid state lasers, to name a few. The  technique of molecular beam epitaxy, which is used to grow these  multilayered systems, has developed to a high degree of  sophistication, so that synthetic layered materials with unusual  energy profiles can be grown. The emphasis is to study the  structures and properties of these materials via their electronic  and vibrational energy states.

Present studies include properties of heterostructures under high  pressure. For this purpose, a diamond anvil cell is used that can  be cooled to liquid helium temperatures and can produce pressures up  to 200 kbar (3 million psi). Such pressures are common in the  interiors of planets and stars. By subjecting semiconductors to  such pressures, their electronic properties can be studied as  functions of atomic volume. For instance, gallium arsenide, which  is normally gray, turns red, yellow, orange and finally green around  100 kbar, corresponding to a decrease in the atomic volume of about  10%. At even higher pressures, it undergoes a phase transition to a  different crystal structure. These studies allow tests of the  microscopic quantum mechanical theories of electronic and  vibrational energy levels and crystal structures. They often yield  results about their atmospheric pressure behavior that cannot be  obtained otherwise. These results also are useful in the  fabrication of new devices with unusual electronic properties.

Selected Publications

Neutron transmutation doping as an experimental probe for AsSe in ZnSe, E.D. Wheeler, Jack L. Boone, J.W. Farmer and H.R. Chandrasekhar, Phys. Rev. B53, 15617 (1996-I)

On the planarity of para-Hexaphenyl, S.Guha, W. Graupner, R. Resel, M. Chandrasekhar, H.R. Chandrasekhar, R. Glaser, and G. Leising, Phys. Rev. Lett. ., 82, 3625 (1999).

Optical and structural properties of ZnO films deposited on GaAs by pulsed laser deposition, Y.R. Ryu, S. Zhu, H.R. Chandrasekhar, P.F. Miceli and H.W. White, J. Appl. Phys.88, 201-204 (2000).

Geometry Dependent Electronic Properties of Highly Fluorescent Conjugated Molecules, S. Yang, W.Graupner, S. Guha, P. Puschnig, C. Martin, H. R. Chandrasekhar, M. Chandrasekhar, G. Leising, C.Ambrosch-Draxl and U. Scherf, Physical Review Letters, 85, 2388 (2000).

Ultrafast Formation of Nonemissive Species versus Intermolecular Interaction in Single Crystals of Conjugated Molecules M. A. Loi, A. Mura, G. Bongiovanni, Q. Cai, C. Martin, H. R. Chandrasekhar, M. Chandrasekhar W. Graupner, and F. Garnier, Phys. Rev. Letters, 86, 732 (2001).

Primary optical excitations and excited state interaction energies in sexithiophene, M.A. Loi, C. Martin, H.R. Chandrasekhar, M. Chandrasekhar, W. Graupner, F. Garnier, A. Mura and G. Bongiovanni, Phys. Rev. B66, 113102 (2002).

Temperature dependent photoluminescence of organic semiconductors with varying backbone conformation", S. Guha, J. D. Rice, Y. T. Yau, C. M. Martin, M. Chandrasekhar, H.R. Chandrasekhar, R. Guentner, P.Scandiucci de Freitas, U. Scherf, Phys. Rev. B67, 125204 (2003).

PUBLICATIONS RELATED TO BIOLOGICAL AND CANCER RESEARCH

Banerjee B, Miedema B, Chandrasekhar HR.  Emissioin spectra of colonic tissue and endogenous tissue fluorophores. Am J Med Sci 1998;316:220-226.

Banerjee B, Miedema B, Chandrasekhar HR.  Role of type IV Collagen and Elastin in colonic emission spectra.  J Invest Med 1999;47:326-332.

Banerjee B, Chandrasekhar HR.  Excitation spectra for the detection of dysplasia and carcinoma in Barrett's esophagus.  Gastrointest Endoscopy 1999;49:101.

Banerjee B, Agarwal S, Jonnalagada S, Chandrasekhar HR.  Use of a shorter wavelength autofluorescence band in Barrett’s esophagus: effect of dysplasia and inflammation.  Gastrointestinal Endoscopy 2000;51:119.15

B. Banerjee, S. Agarwal, HR Chandrasekhar.  The effect of epithelial geometry on  autofluorescence spectra. Gastrointestinal Endoscopy; 2001;53:AB122.

B. Banerjee, S. Agarwal, HR Chandrasekhar.  Autofluorescence spectrscopy to differentiate high grade dysplasia and cancer from low grade dysplasia in Barrett’s Esophagus. Gastrointestinal Endoscopy; 2001;53:AB153.

BOOKS, MANUALS  and REVIEW ARTICLES
 
 1. REESE LIGHT LABORATORY MANUAL.  This manual is for the course "Light and Modern Optics" and contains some experiments developed by the author, first published in 1983; revised edition 2001.

 2. GALLIUM ARSENIDE, edited by J.S. Blakemore, ISBN 0-88318-525-3, LC 87-932, 1987, book chapter with A.K. Ramdas. 

3. BANDGAP TUNING IN SEMICONDUCTOR HETEROSTRUCTURES, a book chapter in the Encyclopedia of Electrical and Electronic Engineering, ed; John G. Webster, Wiley & sons, vol 2, pp 206-218 (1999).

4. DICTIONARY OF PURE AND APPLIED PHYSICS, H.R. Chandrasekhar, This is a volume in the multi-volume series: “Comprehensive Dictionary of Physics”, Dipak Basu, Editor-in-Chief; CRC Press Inc. 2001, ISBN 0-8493-2890-X.

5. OPTICAL PROPERTIES OF ORGANIC WIDE BANDGAP SEMICONDUCTORS UNDER HIGH PRESSURE, S. Guha,  W. Graupner, S. Yang, M. Chandrasekhar, H. R. Chandrasekhar, "Anisotropic Organic Materials" - ACS Symposium Series 798, pp 127-142 (2002), edited by R. Glaser and P. Kaszynski, ISBN 0-8412-3689-5.