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Department of Electrical & Computer Engineering
kmontgomery.net
@KyleMontgomery0
Future Generation Solid-State Energy Conversion
Kyle Montgomery
May 12, 2014
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About Me
To 2000 In the beginning…
2004 Bachelor’s
2004-2007 Professional
2008 Master’s
2012 PhD
Present Research & Lecturer
Intern
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InfluencesJerry WoodallDistinguished Professor, UC DavisNAE Member, National Medal of TechnologyCompound Semiconductor Materials & Devices
David WiltTech Lead, Air Force Research Lab, Space VehiclesFormer Lead PV Engineer at NASASpace Photovoltaics, III-V MOVPE
Mark LundstromDistinguished Professor, PurdueNAE MemberElectron Transport and Device Modeling
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Overview
Motivation• The Energy Dilemma• Opportunities
Research• Photovoltaics• Future Directions
Teaching• Experience: Purdue & UC Davis• Future Directions
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Overview
Motivation• The Energy Dilemma• Opportunities
Research• Photovoltaics• Future Directions
Teaching• Experience: Purdue & UC Davis• Future Directions
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The Energy Dilemma (1/2)
1. We use too much energy
EIA, International Energy Outlook 2013
Total Global Energy Total Energy by Country
OECD: Organization for Economic Cooperation and Development
+60%
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The Energy Dilemma (2/2)
2. We waste too much energy
Conversion Loss (62%)Coal (41%)
Natural Gas (25%)
Nuclear (21%)
Renewables (12%)Residential (12%)
Commercial (12%)
Industrial (9%)
Mostly Waste Heat
US EIA, Monthly Energy Review (January 2014)
Opportunity: Solar Resource
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Covering US~20M TWh / yr
2011 US Electricity Consumption 4100 TWh
Equiv. Land Area ~2000 km2 ½ the size of Rhode Island
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Wide Bandgap Cells for Multijunctions
K. Montgomery, PhD Thesis, 2012
Eg > 2 eV
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Opportunity: Lighting Efficiency
17% Percentage of total residential & commercial electricity used for lighting in US (EIA, 2011)
Efficacy [lm / W]
US DoE, Solid-State Lighting Technology Fact Sheet, PNNL-SA-94206, March 2013.
Incandescent
Halogen
Compact Fluorescent
Linear Fluorescent
High Intensity Discharge (HID)
Light Emitting Diode (LED)
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Better Ways for Solid State Lighting
Current Technology:Low Cost, Decent Quality
Ideal Technology:High Cost, Superior Quality
NEED:True Green LED
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Overview
Motivation• The Energy Dilemma• Opportunities
Research• Photovoltaics• Future Directions
Teaching• Experience: Purdue & UC Davis• Future Directions
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Research Contributions
• Reviving Liquid Phase Epitaxy• GaP Solar Cells
– 2x improvement in spectral response
• AlGaAs Solar Cells– Enhanced Luminescence Near Crossover– Towards Dual Junction Integration on Si
• III-V / II-VI Digital Alloys• Integration to Novel Energy Conversion
Systems
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Semiconductor Menu
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Liquid Phase Epitaxy – Rotating Chamber
K. Montgomery, PhD Thesis, 2012
Benefits:
• Perfected Crystal Structure
• Better Stoichiometry
• High Growth Rates
• Economical
Challenges:
• Stable Growth Conditions
• Low Supersaturation
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GaP Solar Cells
C. R. Allen, et al., Sol. Energ. Mat. Sol. C., 94, 865 (2010).
Voltage (V)
Wavelength (nm)
Cur
rent
Den
sity
(m
A/c
m2)
Inte
rnal
QE
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Gettering in GaP
K. Montgomery, et. al., JEM, 40, 1457-1460 (2011).
Al-Ga @ 975°C
O-
Liquid
Solid
Ga
Al
GaP Substrate
AlGaP
Mol
e Fr
actio
n A
l
Mole Fraction P P
Mole Fraction G
a
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Gettering Yields Higher Response
K. Montgomery, et. al., JEM, 40, 1457-1460 (2011).
Zn-O
Zn-S
Exciton
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AlGaAs Solar Cells by LPE
X. Zhao et.al, PVSC 40 (2014), K. Montgomery, et. al., EMC (2012)
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Non-Isovalent Alloys
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ZnSe-GaAs Digital Alloy
• Superlattice Miniband formation• Potential problem: intermediary
compounds at interfaces
S. Agarwal, K. H. Montgomery, et. al., Electrochemical and Solid-State Letters, 13, H5 (2010).
Effective Band Gap
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Wide Bandgap Cells for Hybrid PV-PT
• Goal: Maximize solar energy conversion using PV + Heat
• Benefit: Direct heat absorption allows for storage
K. Montgomery, et. al., PVSC 39 (2013) & Manuscript in Preparation
System Efficiency (@100x)
Tem
pera
ture
(°C
)
PV Bandgap (eV)
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Future Directions
Wide Bandgap Solar Cells Engineered Superstrates
Non-Isovalent Semiconductors
• Gettered Devices• Integrated Nanostructures• Tandem Integration
• Hybrid Epitaxy• III-V on Si• Polycrystalline III-V
• ZnSe-GaAs Epitaxy• Growth & Doping• Heterojunction Devices
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Overview
Motivation• The Energy Dilemma• Opportunities
Research• Photovoltaics• Future Directions
Teaching• Experience: Purdue & UC Davis• Future Directions
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Teaching Experience: Purdue
• Teaching Assistant– 2 semesters: Grad Level Microfabrication
• Lessons Learned– Textbook Knowledge ≠ Fab Skills– Laboratory Safety
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Teaching Experience: UC Davis• Lecturer
– Undergrad Circuits Analysis– ~200 students
• Lessons Learned (& still learning!)– Minimize loss in translation– Emphasize fundamentals, Expose details
kmontgomery.net/eng17
“…not only does he go on to teach us what we need to know to get by in circuits, he is a compelling lecturer, caring person, and above all he is able to deal with classroom issues with grace.”
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Mentorship: UC Davis
PhD Students Undergraduates
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Teaching Plans: Graduate
• Materials Science for Microsystems Engineering
• Microelectronics I• Proposed Course
Solid-State Energy Conversion Materials & Devices
REVIEW: Solid-State Physics, Material Properties, Thermodynamics
PhotovoltaicsLight Emitting Diodes
Thermoelectrics Piezoelectrics
“Direct Energy Conversion” by Angrist (w/supplements)
Emphasis on Recent Research
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Teaching Plans: Undergraduate
• Circuits I-II• (Adv.) Semiconductor Devices• MATLAB Programming• Clean and Renewable Energy Systems
and Sources
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Overview
Motivation• The Energy Dilemma• Opportunities
Research• Photovoltaics• Future Directions
Teaching• Experience: Purdue & UC Davis• Future Directions
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Acknowledgements
Purdue UniversityProf. Mark Lundstrom, ECEProf. David Janes, ECEProf. Peide Ye, ECEProf. Eric Kvam, MSEProf. Peter Bermel, ECEProf. Gerhard Klimeck, ECEProf. Anant Ramdas, PhysicsDionisis Berdebes, ECEDr. Jayprakash Bhosale, Physics
Yale UniversityProf. Minjoo Larry Lee, EE
UC DavisProf. Jerry Woodall, ECEProf. Saif Islam, ECEProf. Subhash Mahajan, CHMSXin Zhao, ECE
UCLADr. Paul Simmonds
Air Force Research LaboratoryDavid WiltDr. Alex HowardJohn Merrill
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Department of Electrical & Computer Engineering
kmontgomery.net
@KyleMontgomery0
Thank you!
Any questions?
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Department of Electrical & Computer Engineering
kmontgomery.net
@KyleMontgomery0
Supplemental
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ZnSe-GaAs Physical Alloy
• Miscibility previously demonstrated
• N-type conductivity generally found
• Lack of prior work due to difficulty in suitable deposition technique
W. M. Yim, JAP, 40, 2617–2623, 1969.
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SiC Solar Cells150 suns
R. P. Raffaelle et. al., 28th PVSC, 2000, pp. 1257–1260.
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AlGaAs Growth by LPE
K. Montgomery, et. al., EMC (2012)
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InGaN Solar Cells
Full Spectrum Coverage
Phase separationInGaN (37% In)
Jampana, et al., Electron Devic. Lett., 31, 32 (2010).R. Singh and D. Doppalapudi, Appl. Phys. Lett., 70, 1089 (1997).
DefectsInGaN (16.8% In,
2.67 eV)
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2.19 eV GaInP w/GaAsP Buffers on GaP
S. Tomasulo, et. al., PVSC 39, 2013.
In0.26Ga0.74P
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Wide Bandgap Cells for High-T
G. A. Landis, et. al., “High-Temperature Solar Cell Development,” NASA, 2004.
Temperatures up to 450°C
1.0 2.0 3.0
Bandgap
Eff
icie
ncy
20
10
27°C
900°C
AM0 (FF = 0.80, Pin = 1366.1 W/cm2)
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Engineered Superstrates
• Superstrate: Substrate templated with a heterogeneous material
• III-V on Si– Needs thick buffer layers– Problem: Dislocation densities
• LPE may help (w/MOCVD)
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0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.80
2
4
6
8
10
12
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Voltage [V]
Cu
rre
nt
De
ns
ity
[m
A/c
m2
]
Al0.23Ga0.77As(Eg ~ 1.75 eV)
Voc = 771 mVJsc = 13.8 mA/cm2FF = 63.4%Efficiency = 6.8%
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Primary Photovoltaic Technologies
Low Cost, Low Efficiency
η ~ 6-22% η ~ 28-39% (at xx suns)
High Cost, High Efficiency
First Solar SolFocus