The Birnie Group solar class and website were created with much-appreciated support from the NSF CRCD Program under grants 0203504 and 0509886. Continuing Support from the McLaren Endowment is also greatly appreciated!
MBE – Molecular Beam Epitaxial Growth of Semiconductors
Slides on these other topics might also be of interest (most collected during teaching years 2004 and 2005): http://www.rci.rutgers.edu/~dbirnie/solarclass/BandGapandDopingLecture.pdf Band Gap Engineering of Semiconductor Properties http://www.rci.rutgers.edu/~dbirnie/solarclass/MultijunctionLecture.pdf Multi‐Junction Solar Device Design http://www.rci.rutgers.edu/~dbirnie/solarclass/amorphousSi.pdf Amorphous Silicon Solar Cells http://www.rci.rutgers.edu/~dbirnie/solarclass/TransparentConductors.pdf Transparent Conductors for Solar http://www.rci.rutgers.edu/~dbirnie/solarclass/ARCoatings.pdf Anti‐Reflection Coatings for Solar http://www.rci.rutgers.edu/~dbirnie/solarclass/OrganicPV.pdf Organic PV http://www.rci.rutgers.edu/~dbirnie/solarclass/DSSC.pdf Dye Sensitized Solar Cells http://www.rci.rutgers.edu/~dbirnie/solarclass/MotorPrimerGaTech.pdf Working with Simple DC Motors for Student Solar Projects http://www.rci.rutgers.edu/~dbirnie/solarclass/2005ProjectResultsindex.htm Examples of Previous Years’ Student Solar Projects Note: in some cases it may be possible to design custom courses that expand on the above materials (send me email!)
Journal Publications of Some Recent Research:
(best viewed through department home index: http://mse.rutgers.edu/dunbar_p_birnie_iii)
Other Birnie Group Research: Sol-Gel Coating Quality and Defects Analysis (mostly Spin Coating): http://www.coatings.rutgers.edu Solar Research at Rutgers: Broader Overview http://www.solar.rutgers.edu Solar and Electric Vehicles System Projects (early stage emphasis) http://www.rave.rutgers.edu
Professor Dunbar P. Birnie, III (
[email protected]) Department of Materials Science and Engineering http://mse.rutgers.edu/faculty/dunbar_p_birnie
Solar Cell Design and Processing MBE – Molecular Beam Epitaxy and Applications in Solar Cell Fabrication Dunbar P. Birnie, III
[email protected]
Department of Materials Science and Engineering www.MSE.Rutgers.edu
Outline • • • • •
Basic overview of What is MBE? Atomistic level processes important in MBE Views in Commercial Systems Characterization during MBE growth. Application to Solar
Department of Materials Science and Engineering www.MSE.Rutgers.edu
What is Epitaxy? • Epitaxy “Epi” and “ taxis” » “surface”
and
“arrangement”
• Basically deals with the ordered placement of atoms, carefully, on the surface of a substrate or template. • Could be liquid sourced (Liquid Phase Epitaxy – LPE), Vapor source – VPE, or molecular source (MBE) Department of Materials Science and Engineering www.MSE.Rutgers.edu
What defines MBE in particular? • Thermal-driven molecular or atomic sources of precursor species. • Crystalline substrate at (usually) elevated temperature. • High vacuum lower contamination from unwanted species. • “A versatile technique for growing thin epitaxial structures made of semiconductors, metals or insulators”--defined by Dr. Morton B. Panish. Department of Materials Science and Engineering www.MSE.Rutgers.edu
Some attributes of MBE Chambers
Source: T. D. Brown, PhD Diss, GaTech 2003 – attributed to A. S. Brown in Encyclopedia of Advanced Materials 1990.
Department of Materials Science and Engineering www.MSE.Rutgers.edu
• Critical Processes: Impinging flux of adatoms Surface Diffusion Attachment at ledges or other aggregation and nucleation Thermal desorption Interdiffusion/mixing with the lattice Source: T. D. Brown, PhD Diss, GaTech 2003 – attributed to M. A. Herman, H. Sitter, Molecular Beam Epitaxy Fundamentals and Current Status, New York, New York: Springer-Verlag (1989).
Department of Materials Science and Engineering www.MSE.Rutgers.edu
Physical Limitations • Lattice Strain – Lattice Mismatch • Very thin layers are OK, but as thickness rises then strain energy is too high and defects are generated: could be misfit dislocations or island growth • Figures shows plan-view TEM of islands in AlInAs/AlGaAs epitaxy
Source: Fafard et al, Superlattices and Microstructures, 1999.
Department of Materials Science and Engineering www.MSE.Rutgers.edu
A commercial MBE system by VG Semicon
Department of Materials Science and Engineering www.MSE.Rutgers.edu
Schematic illustration of MBE system interior
Department of Materials Science and Engineering www.MSE.Rutgers.edu
Deposition Chamber with Sources for All Required Elements
Multiport source placement
Effusion cells, various, depending on nature of precursor, temps, composition.
Source: Veeco product literature
Department of Materials Science and Engineering www.MSE.Rutgers.edu
Source: J. R. Arthur, 2002 Surface Science
Department of Materials Science and Engineering www.MSE.Rutgers.edu
Important Issues • Stoichiometry especially when mixing two different III’s or V’s • Doping and activation of dopants • Vacuum level – purity • Lattice matching level – needs to be close
Department of Materials Science and Engineering www.MSE.Rutgers.edu
Diagnostics in MBE • Auger Electron Spectroscopy – surface sensitive chemical probing • Ellipsometry – very precise optical thin film measurement of thickness and opt constants • Laser interferometry • RHEED – reflection high-energy electron diffraction • SAW and quartz-crystal microbalances – running parallel to the actual substrate Department of Materials Science and Engineering www.MSE.Rutgers.edu
Placement of RHEED: glancing angle
Department of Materials Science and Engineering www.MSE.Rutgers.edu
Schematic Surface Coverage and RHEED
Source: J. R. Arthur, 2002 Surface Science
Department of Materials Science and Engineering www.MSE.Rutgers.edu
RHEED Pattern Maps
Photo from http://www.k-space.com/
Department of Materials Science and Engineering www.MSE.Rutgers.edu
RHEED versus Time
Photo from http://www.k-space.com/
Department of Materials Science and Engineering www.MSE.Rutgers.edu
MBE and Solar Cells • Perfect Epitaxy is the Ideal Situation • Defects are Recombination sites – lower efficiency • MBE may give high perfection in many cases – but the deposition rate is problem (slow) • Composition space that is typical is also that needed for multijunction solar cells. Can make a stack with different band gaps and reach higher solar energy capture efficiency Department of Materials Science and Engineering www.MSE.Rutgers.edu
Band Gaps and Lattice Size • Important for many semiconductor growth methods such as MBE and CVD, when high crystal quality is required.
Source: http://web.tiscali.it/decartes/phd_html/ III-Vms-latgap.png
Department of Materials Science and Engineering www.MSE.Rutgers.edu
