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Si 1-x-y-zGexCySnz Cubic Alloys and Heterostructures

Advisor: Paul R. Berger
Students: Al-Sameen Khan (graduated with Ph.D. in October 1996)
  Xiaoping Shao (graduated with Ph.D. in September 1997)
  Hao Feng (graduated with Master's thesis in March 1998)
  Sean L. Rommel (graduated with Bachelor's in May 1996)
Collaborators: James Kolodzey (University of Delaware, Elec. Engin.)
  S. S. Iyer (Sibond/IBM)
  F. Guarin (IBM)
  S. Ismat Shah (Dupont)
  K. M. Unruh (University of Delaware, Physics)


Importance of the Problem:

The predominance of Si-based circuits in the marketplace is due to the easy maufacturability of silicon. Consumers expect the semiconductor industry to continue marching along Moore's Law which is outlined in the Semiconductor Roadmap as reaching 0.18 $\mu$m gate lengths by 2001 and 0.07 $\mu$m gate lengths by 2010. However, as device dimensions shrink, the cost of further miniaturization to improve performance is becoming prohibitive. Current estimates are that a new fabrication line for a microprocessor based chip is 1 billion dollars. It will be difficult to achieve these expected results using Si only without a major breakthrough.

SiGeCSn would open the door to a wide variety of Si-based heterostructure devices commonly reserved for III-V compounds. The SiGe material system has already pushed Si devices in this direction and clearly demonstrates improved performance. However, SiGe is not lattice-matched. By additions of Ge and C in an 8:1 ratio an alloy would maintain Si lattice matching.

However, the SiGeCSn material system is in its infancy. Unlike Si and Ge which mix well, the GeC binary system does not occur under equilibrium conditions, and SiC alloys want to precipitate out as a carbide. Carbon, which has a much smaller lattice constant and atomic radius is difficult to get incorporated into the crystal lattice substitutionally. Much of the carbon goes interstitially. We are in the process of investigating the SiGeCSn material system using molecular beam epitaxy which is a far-from-equilibrium growth technique. We are investigating the fundamental material properties using transmission electron microscopy (TEM) and photoluminescence (PL).

The first application of these materials will be for electronic devices but further refinement could lead to photonic devices as well. III-V compounds are the leading semiconductor materials for light emission and detection due to their inherent direct bandgap. Their direct bandgap dramatically improves the quantum efficiency of optical transistions. However, Si-based opto-electronics, which have an indirect bandgap, have very poor optical emission efficiency. Si-based materials are also poor optical detectors due to their indirect bandgap. But, since Si is cheap and plentiful, it is utilized for simple commercial photodetectors. On the other hand, Si-based electronics have matured rapidly and impacts us in virtually every aspect of our lives. The relative maturity of Si-based electronics compared to III-V electronics make it very attractive to be able to incorporate Si-based optical devices (emitters and detectors) with Si-based electronics on the same chip. The union of both electronic and optical devices would make a very powerful combination for optoelectronic integrated circuits (OEIC). We are investigating Group IV-based photodetectors as well as ways to improve Si-based opto-electronics efficiency by making materials which are quasi-direct bandgap.

It has been proposed that Brillioun Zone folding by growing short period superlattices could convert the SiGeC indirect bandgap to a quasi-direct bandgap. This new binary superlattice is viewed as a new crystal with a different Bravais lattice. Within the material, a new energy state is created at the zone center by which efficient optical transistions could occur. Also, by tailoring the ternary alloy or buffer composition, strain can be independently controlled about the lattice matching condition for Si substrates. Strain can act to modify the band structure as well.

Brief Description of Work and Results:

We have been investigating the Si 1-x-y-zGexCySnzmaterial system focusing on the constituent ternary alloy Si1-x-yGexCy and binary alloys Ge1-xCx, Si1-xSnx and Si1-xCx. The layers studied to date have been grown by molecular beam epitaxy (MBE). Initial work focused on the materials charaterization of the epilayers. The specimens are studied structurally for defect structure and physical manifestation by transmission electron microscopy (TEM). Also, the optical quality of the epilayers is characterized by photoluminescence (PL), and the electrical quality by Hall measurements.

Current work is branching off to investigate the etching and contact resistance of these new materials. Work is commencing to develop these materials into infrared photodetectors and electronic devices, such as heterojunction bipolar transitors (HBT), field effect transitors (FET), and resonant tunneling diodes (RTD).

The goal of these projects is to develop Si 1-x-y-zGexCySnz cubic alloys and heterostructures for infrared light detection and emission as well as enhanced electronic devices. An ultimate realization would be monolithically integrated optoelectronic devices such as detectors and emitters in the Si 1-x-y-zGexCySnz material system which would be compatible with existing Si-based or SiGeCSn-based electronic technology.

For further information contact:

Paul R. Berger

Professor
Electrical and Computer Engineering
Physics

Director
Nanofabrication and Materials Processing Center (NanoMPC)
Nanoscale Patterning Laboratory
Nanoelectronics and Optoelectronics Laboratory (NOEL)
Polymer Device Laboratory (PDL)

Campus Address:
201 Caldwell Laboratory

Mailing Address:
Department of Electrical and Computer Engineering
The Ohio State University
205 Dreese Laboratory
2015 Neil Avenue
Columbus, OH 43210 USA 

Direct phone: (614) 247-6235 
EE Dept. FAX: (614) 292-7596
Email: pberger@ieee.org


Supported By: Defense Advanced Research Projects Agency (DARPA)
  National Science Foundation (NSF)
  University of Delaware Research Foundation (UDRF)

Awards:

Ph.D. Theses:

1.
``Structural and Electrical Characteristics of SiGeC and GeC Alloys and their Application to Optical Detectors, '' Xiaoping Shao, graduated September 23, 1997.

2.
``Photoluminescence and Process Issues of SiGeCSn Alloys,'' Al-Sameen Tewfik Khan, graduated October 3, 1996.

Recent Publication Activity:

1.
``Strain Modification in Thin Si1-x-yGexCy Alloys on (100) Si for Formation of High Density and Uniformly Sized Quantum Dots,'' Xiaopinq Shao, Ralf Jonczyk, M. Dashiell, D. Hits, Al-Sameen Khan, K. Roe, J. Kolodzey, Paul R. Berger, M. Kaba, M. A. Barteau, and K. M. Unruh, Journal of Applied Physics, 85, pp. 578-582 (January 1, 1999). PDF (3024 kB)

2.
``Photoluminescence of SiSnC Alloys Grown on (100) Si Substrates,'' Nareen Wright, Al-Sameen T. Khan, Paul R. Berger, Fernando J. Guarin, and Subramanian S. Iyer, in Materials Research Society Symposium Proceedings, 533, pp. 327-332 (1998).

3.
``1.3 $\mu$m Photoresponsivity in Si-Based Ge1-xCxPhotodiodes,'' Xiaoping Shao, S. L. Rommel, B. A. Orner, H. Feng, M. W. Dashiell, R. T. Troeger, J. Kolodzey, Paul R. Berger, and Thomas Laursen, Applied Physics Letters, 72, pp. 1860-1862 (April 13, 1998). PDF (73 kB)

4.
``Ge1-xCx/Si Heterojunction Photodiodes,'' Xiaoping Shao, S. L. Rommel, B. A. Orner, H. Feng, M. Dashiell, J. Kolodzey, and Paul R. Berger, Proceedings of SPIE's Optoelectronics '97: Silicon-Based Monolithic and Hybrid Optoelectronic Devices, Vol. 3007, pp. 162-169 (1997).

5.
``A p-Ge1-xCx/n-Si Heterojunction Diode Grown by Molecular Beam Epitaxy,'' Xiaoping Shao, S. L. Rommel, B. A. Orner, J. Kolodzey, and Paul R. Berger, IEEE Electron Device Letters, 18, pp. 411-413 (1997). PDF (75 kB)

6.
``Near Band Edge Photoluminescence from Pseudomorphic Tensially Strained Si0.985C0.015 Alloy,'' Al-Sameen T. Khan, Paul R. Berger, Fernando J. Guarin, and Subramanian S. Iyer, Thin Solid Films, 294, pp. 122-124 (1997). PDF (238 kB)

7.
``Current Transport Characteristics of SiGeC/Si Heterojunction Diode,'' F. Chen, B. A. Orner, D. Guerin, A. Khan, P. R. Berger, S. Ismat Shah, and J. Kolodzey, IEEE Electron Device Letters, 17, pp. 589-591 (1996). PDF (257 kB)

8.
``Low Resistance Ohmic Contacts to p-Ge1-xCx on Si,'' Xiaoping Shao, S. L. Rommel, B. A. Orner, Paul R. Berger, J. Kolodzey, and K. M. Unruh, IEEE Electron Device Letters, 18, pp. 7-9 (1997). PDF (90 kB)

9.
``Band Edge Photoluminescence from Pseudomorphic Si0.96Sn0.04 Alloy,'' Al-Sameen T. Khan, Paul R. Berger, Fernando J. Guarin, and Subramanian S. Iyer, Applied Physics Letters, 68, pp. 3105-3107 (1996). PDF (66 kB)

10.
``Optical Properties of Ge1-yCy Alloys,'' B. A. Orner, A. Khan, D. Hits, F. Chen, K. Roe, J. Pickett, X. Shao, R. G. Wilson, P. R. Berger, and J. Kolodzey, Journal of Electronic Materials, 25, pp. 297-300 (1996).

11.
``Optical and Electronic Properties of SiGeC Alloys Grown on Si substrates,''J. Kolodzey, P. R. Berger, B. A. Orner, D. Hits, F. Chen, A. Khan, X. Shao, M. M. Waite, S. Ismat Shah, C. P. Swann, and K. M. Unruh, Journal of Crystal Growth, 157, pp. 386-391 (1995). PDF (380 kB)

Recent Conference Activity:

1.
``Photoluminescence of SiSnC Alloys Grown on (100) Si Substrates,'' Nareen Wright, Al-Sameen T. Khan, Paul R. Berger, Fernando J. Guarin, and Subramanian S. Iyer, 1998 Spring Meeting of the Materials Research Society in San Francisco, CA, April 13-17 (1998).

2.
``Raman Study of GexCy Islands Grown on Si Substrates,'' H. Shen, J. Pamulapati, X. Shao, R. Jonczyk, B. A. Orner, A-S. Khan, K. Roe, J. Kolodzey, P. R. Berger, M. Barteau, and K. M. Unruh, 1997 Fall Meeting of the Materials Research Society in Boston, MA, (December 1-5, 1997).

3.
``Electrical and Optical Properties of Phosphorus Doped GeC0.001,'' M. W. Dashiell, R. T. Troeger, L. V. Kulik, A-S. Khan, F. Chen, K. Roe, B. Orner, P. R. Berger, J. Kolodzey, and R. G. Wilson, Seventh International Symposium on Silicon Molecular Beam Epitaxy in Banff, Canada, (July 13-17, 1997).

4.
``Boron Diffusion in Si1-x-yGexCy Alloys Grown on a Silicon Substrate,'' Hao Feng, Mike Dashiell, B. A. Orner, J. Kolodzey, Paul R. Berger, Matthew H. Ervin, and Richard T. Lareau, 39th Electronic Materials Conference in Fort Colllins, CO, June 25-27 (1997).

5.
``Ordering of Si1-x-yGexCy Islands Grown on (100) and (311) Si Substrates,'' X. Shao, R. Jonczyk, M. Dashiell, D. Hits, B. A. Orner, A-S. Khan, L. Kulik, K. Roe, D. van der Weide, J. Kolodzey, P. R. Berger, M. Kaba, M. Barteau, and K. M. Unruh, 1997 Spring Meeting of the Materials Research Society in San Francisco, CA, March 31 - April 4 (1997).

6.
``Ge1-xCx/Si Heterojunction Photodiode,'' Xiaoping Shao, S. L. Rommel, B. A. Orner, Paul R. Berger, and J. Kolodzey, submitted to SPIE's Optoelectronics '97: Silicon-Based Monolithic and Hybrid Optoelectronic Devices in San Jose, CA, February 8-14 (1997).
7.
``Near Band Edge Photoluminescence from Pseudomorphic Tensially Strained Si0.985C0.015 Alloy,'' Al-Sameen T. Khan, Paul R. Berger, Fernando J. Guarin, and Subramanian S. Iyer, 1996 Spring Meeting of the European Materials Research Society in Strasbourg, France, June 4-7 (1996).

8.
``Photoluminescence of Ge1-xCx Alloys Grown on (100) Si Substrates,'' Al-Sameen T. Khan, Brad A. Orner, Paul R. Berger, and James Kolodzey, 1996 Spring Meeting of the Materials Research Society in San Francisco, CA, April 8-12 (1996).

9.
``Structural and Electrical Characterization of Ge1-xCx Cubic Heterostructures on Si,'' Xiaoping Shao, S. Rommel, B. Orner, F. Chen, Paul R. Berger, and J. Kolodzey, 1996 Spring Meeting of the Materials Research Society in San Francisco, CA, April 8-12 (1996).

10.
``Structural and Optical Properties of SiGeCSn Alloys,'' Paul R. Berger, Workshop on Compound Semiconductor Materials and Devices in Santa Fe, NM, February 19-21 (1996).

11.
``Properties of Group IV - Carbon Alloys Grown on Si Substrates,'' D. Hits, B. A. Orner, F. Chen, A. Khan, X. Shao, M. McClory, M. A. Barteau, G. H. Watson, P. R. Berger, and J. Kolodzey, 15th North American Conference on Molecular Beam Epitaxy in College Park, MD, September 17-20 (1995).

12.
``Optical Properties of Ge1-yCy Alloys,'' B. Orner, A. Khan, D. Hits, F. Chen, K. Roe, J. Pickett, X. Shao, R. G. Wilson, P. Berger, and J. Kolodzey, 37th Electronic Materials Conference in Charlottesville, VA, June 19-21 (1995).

13.
``Optical and Electronic Properties of SiGeC Alloys Grown on Si Substrates,'' J. Kolodzey, P. Berger, B. Orner, D. Hits, F. Chen, A. Khan, X. Shao, M. M. Waite, S. Ismat Shah, and K. M. Unruh, 6th International Symposium on Silicon Molecular Beam Epitaxy, part of E-MRS in Strasbourg, France (May 1995).

14.
``Photoluminescence and TEM of SiGeC Alloys,'' Paul R. Berger, Workshop on Compound Semiconductor Materials and Devices in New Orleans, LA, February 20-22 (1995).

15.
``Growth and Properties of Silicon Germanium Carbon Alloys,'' J. Kolodzey, P. A. O'Neil, S. Zhang, B. Orner, K. Roe, J. Pickett, D. Hits, F. Chen, P. Berger, A. Khan, X. Shao, S. I. Shah, M. Waite, C. P. Swann, and K. M. Unruh, 14th North American Conference on Molecular Beam Epitaxy in Urbana, IL, (October 1994).



 
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Paul R. Berger
1999-07-27