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Final Report to Division of Materials Science

Office of Basic Energy Sciences United States Department of Energy

For

Irradiation-Induced Phase Transformations Grant # DE-FG03-89ER45395

Duration: 711195-6130197

Attention: Dr. Helen Kerch

United States Department of Energy

19901 Germantown Rd. Germantown MD 20874 ER-131, G-236 GTN

Principal Investigator Hany A. Atwater

Thomas J. Watson Laboratory of Applied Physics California Institute of Technology

Pasadena, CA 9 1 125

tel: (626) 395-2197

email: haa@daedalus.caltech.edu FAX: (626) 795-7258

8/1/98

DISCLAIMER

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or use- fulness of any information, apparatus, product. or process disdosed, or represents that its use would not infringe privately owned rights. Reference herein to any spe- cific commercial product, process, or service by trade name, trademark, manufac- turer, or otherwise does not necessarily constitute or imply its endorsement, Tccom- mcndktion, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

DISCLAIMER

Portions of this document may be illegible ejectronic image products. Images are produced from the best available original document.

I. Summary of Research Executive Summary:

During the course of this two year program, our attention focused largely on the synthesis, structure and properties of group IV semiconductor nanocrystals. We also drew to a close our investigations of defects in amorphous silicon. Work on control of nucleation in amorphous silicon and germanium is ongoing, and has taken important new directions at the interface between basic and applied research under DOE Office of Energy Efficiency support via a subcontract from the National Renewable Energy Laboratory and the BES Center for Synthesis and Processing of Advanced Materials' project on High Efficiency Thin Film Photovoltaics. During the course of this project, which brings to an end Department of Energy Grant DE-FG03-89ER45395, scientific and scholarly output included

10 invited talks related to work on Si and Ge nanocrystals. 5 Applied Physics Letters published on Si and Ge nanocrystals. 3 Caltech PhD. Theses on Si and Ge nanocrystal work. New directions on control of crystallization in thin semiconductor f h s .

Scientific Accomplishments:

Prior to our work on correlation of structure and luminescence mechanisms in Si and Ge nanocrystals, approximately 1-2 dozen groups around the world had observed luminescence fiom ion beam synthesized nanocrystals. Various contradictory claims for the origin of nanocrystal luminescence in these materials. Largely as a result of our work clarifying the passivation state for ion-implanted group IV nanocrystals, consensus about defect vs. quantum confined carrier luminescence mechanisms has largely been reached, and samples from different laboratories can be quantitatively compared.

precipitation from a supersaturated solid solution of Ge in SiO, made by Ge ion implantation. The fdms exhibited strong room-temperature visible photoluminescence. The measured photoluminescence peak energy and lifetimes showed poor correlation with nanocrystal size compared to calculations involving radiative recombination of quantum-confmed excitons in Ge 'quantum dots'. In addition, the photoluminescence - spectra and lifetime measurements show only a weak temperature dependence. These observations strongly suggested that the observed visible luminescence in our samples is not due to the radiative recombination of quantum-confined excitons in Ge nanocrystals . Instead, observations of similar luminescence in Xe+-implanted samples and reversible PL quenching by hydrogen or deuterium suggest that radiative defect centers in the SiO, matrix are responsible for the observed luminescence. While essentially a negative result (in that quantum confined carrier excitation is not responsible for luminescence) his was a important advance for the community in understanding and controlling the role of

In our Ge work, synthesis of Ge nanocrystals in SiO, films is carried out by

defects, and led researchers in this field only to subsequently compare well-passivated samples when assessing luminescence mechanisms.

identified from ion beam synthesized SiO, films containing Si nanocrystals. From a comparison of luminescence spectra and lifetime measurements between Xe’-implanted SiO, films and SiO, films containing Si nanocrystals, a luminescence feature attributable to defects in the SiO, matrix was unambiguously identified. Hydrogen passivation of the films selectively quenches the matrix defect luminescence, after which the presence of a luminescence feature attributable to Si nanocrystals is evident, with lifetimes on the order of milliseconds. The peak energy of the remaining luminescence feature attributable to Si nanocrystals “red shifts” as a function of different processing parameters and the luminescence intensity is directly correlated to the formation of Si nanocrystals, as indicated by transmission electron microscopy and X-ray photoemission studies. Upon further annealing hydrogen-passivated samples at low temperatures (<SOo”C), the intensity of nanocrystal luminescence increases by more than a factor of ten. Our work thus has enabled intellectual contact between ion-implantation synthesized nanocrystals and porous Si or other forms of nanostructured Si, in which materials with similar passivation can be compared.

In our Si work, two sources of room temperature visible luminescence were

I. Invited Presentations by Principal Investigator under Grant

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“ Group IV Semiconductor Nanocrystals ” AMOLF Summer School on Nanostructured Optoelectronic Materials, July 10-12, 1995. “Synthesis, Size Control and Optoelectronic Properties Group IV Nanocrystals ”, International Vacuum Conference IVC-13, Yokohama Japan, September 26th 1995. “Synthesis, Size Selection and Optoelectronic Properties of Silicon and Germanium Nanocrystals ”, University of California, San Diego, Electrical and Computer Engineering Seminar, October 1995. “Synthesis, Size Selection and Optoelectronic Properh’es of Silicon and Germanium Nanocrystals ”, Oak Ridge National Laboratory, Solid State Division Seminar, Feb. 6&, 1996. “Synthesis, Size Selection and Optoelectronic Properties of Silicon and Germanium Nanoctystals ”, U. Of Illinois, Materials Science Seminar, March 15’, 1996. “Visible Luminescence and Passivation of Germanium Nanocrystals ’, M R S - J, Chiba, Japan, June 10,1996. “Synthesis, Size Selection and Passivation of Silicon and Germanium Nanocrystals ”, International Materials Research Congress, Cancun, Mexico, September loth, 1996. Materials Research Lecture, California Institute of Technology, May 7&, 1997

9. “Synthesis, Size Selection and Passivation of Silicon and Germanium Nanocrystals ”, University of Southern California Materials Science Seminar, February 7h, 1997.

10. “Manipulation of Size, Location and Passivation of Silicon and Germanium Nanocrystals ”, Gordon Research Conference on Materials Processing Far From Equilibrium, August 22nd, 1997.

II. Publications under Grant

Journal Publications: 1. “Group VI- V and Group IV Quantum Dot Synthesis, HA. Atwater, K J

Vahala, R.C. Flagan, R. Camata, R.B. Lee, K. VShcheglov, C.S. Tsai and C.M. Yang”, Proceedings of NATO Advanced Workshop on Low- Dimensional Structures (1 995). Generalized Defect Annihilation Kinetics for Structural Relaxation in Amorphous Silicon, J.H. Shin and H.A. Atwater, Phil. Mag. 72 1 (1 995). “Correlation of Size and Photoluminescence of Ge Nanocrystals in Si02 Matrices”, C.M. Yang, K.V. Shcheglov, M.L. Brongersma, A. Polman and H.A. Atwater, Nucl. Instnun. And Meth. Phys. Res. B 106,433 (1995). “Electroluminescence and Photoluminescence of Ge-Implanted Si/SiOz/Si Structures” K.V. Shcheglov, C.M. Yang, K.J. Vahala and H.A. Atwater, Appl. Phys. Lett. 66 745 (1995). “The Role of Quantum-ConJipzed Excitons vs. Defects in Visible Luminescence of Si02 Films Containing Ge Nanocrystals ”, K.S. Min, K.V. Shcheglov, C.M. Yang, H.A. Atwater, M.L. Brongersma and A. Polman, Appl. Phys. Lett. 68 251 1 (1996). “Defect-Related vs. Excitonic Visible-Light Emission fiom Ion-Beam Synthesized Si Nanocrystals in SiOz”, K.S. Min, K.V. Shcheglov, C.M. Yang, H.A. Atwater, M.L. Brongersma and A. Polman, Appl. Phys. Lett. 69 2033 (1996). “Size ClassiJication of Silicon Nanocrystals ” R.P. Camata, HA. Atwater, K.J. Vahala and R.C. Flagan, Appl. Phys. Lett. 68 3 162 (1 996). “Selective Solid Phase Crystallization of Control of Grain Size and Location in Ge Thin Films on Silicon Dioxide”, C.M. Yang and H.A. Atwater, Appl. Phys. Lett. 68 3392 (1996). “Size-Dependent Evolution of Si Ciystals in Amorphous Si under Ion Irradation”, C.M. Yang and H.A. Atwater, to be submitted to J. Appl. Phys. “Tuning the Emission Wavelength of Si Nanocrystals in Si02 by Oxidation”, M.L. Brongersma, A. Polman, K.S. Min, E. Boer, T. Tambo and H.A. Atwater, Appl. Phys. Lett. 72 2577 (1998).

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Conference Proceedings:

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1 1. “Correlation of Size and Photoluminescence of Ge Nanocrystals in Si02 Matrices”, C.M. Yang, K.V. Shcheglov, K.J. Vahala and H.A. Atwater, Mat. Res. SOC. Symp. Roc. 358 181 (1995). “Controlled Grain Size and Location in Ge Thin Films on Silicon Dioxide by Low Temperature Selective Solid Phase Crystallization ”, C.M. Yang and H.A. Atwater, Mat. Res. SOC. Symp. Proc. 403 113 (1996) LLOn the Origin of Visible Luminescence from Si02 Films Containing Ge Nanocrystals”, K.S. Mh, K.V. Shcheglov, C.M. Yang, R.P. Camata, H.A. Atwater, M.L. Brongersma and A. Polman, Mat. Res. SOC. Symp. Proc. 405 247 (1996) “Tailoring the Optical Properties of Si Nanocrystals in Si02: Materials Issues and Nanocrystal Laser Perspectives”, M.L. Brongersma, K.S. Min, E. Boer, T. Tambo, A. Polman and H.A. Atwater, , Mat. Res. SOC. Symp. Proc. 486 213 (1998).

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Ph.D. Theses Completed Under Grant

1 . “Synthesis, Optical and Electronic Properh’es of Semiconductor Nanocrystals ”, Kirill V. Shcheglov, Ph.D in Applied Physics, California Institute of Technology, submitted May 2nd, 1997. ‘Manipulation of Si and Ge Crystallization ”, Ph.D. in Materials Science, California Institute of Technology, submitted December 20”, 1996. Yerosol Synthesis and Characterization of Silicon Nanoparticles ”, Renato P. Camata, Ph.D in Applied Physics, California Institute of Technology, submitted July 29’, 1997.

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Personnel Associated with the Grant

1. Harry A. Atwater, Principal Investigator 2. Kirill V. Shcheglov, Graduate Student (Research Assistant) 3. Jimmy C.M. Yang, Graduate Student (Research Assistant) 4. Kyu S. Mh, Graduate Student (Intel Fellow) 5. Renato Camata, Graduate Student (Brazialian Government Fellow)

V. Collaborators

6 . Albert Polman, Group Leader, FOM Institute for Atomic and Molecular Physics, Amsterdam, the Netherlands

7. Mark Brongersma, graduate student, FOM Institute for Atomic and Molecular Physics, Amsterdam, the Netherlands

8. Kerry J. Vahala, Professor of Applied Physics, Caltech 9. Richard C. Flagan, Professor of Chemical Engineering, Caltech

VI. Principal Investigator

Harry Atwater is an Associate Professor of Applied Physics at the California Institute of Technology. He and his research group are engaged in research on synthesis, phase transformation and properties of electronic and optoelectronic materials. His research interests include growth and opticdelectronic properties of new epitaxial group IV compound semiconductors, and nanocrystalline group IV structures. Professor Atwater received his S.B., S.M. and Ph.D. degrees from the Massachusetts Institute of Technology in 1982,1983 and 1987, respectively. In 1988, he joined Caltech as an Assistant Professor of Applied Physics, and became an Associate Professor in 1994. In 1989 he received the NSF Presidential Young Investigator Award, and the IBM Faculty Development Award. Atwater has held visiting scientist appointments at IBM (1 992), Intel (1 993) and FOM Institute for Atomic and Molecular Physics in the Netherlands (1 999, and has consulted extensively for industry. He is currently a Councillor of the Materials Research Society, and Co-Chaired the 1997 M R S Fall Meeting in Boston. He is currently an Editorial Board member for Surfce Review and Letters. He is also Vice- Chair of the 1999 Gordon Conference on Materials Processing Far from Equilibrium.