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Contract No. DE-AC36-08GO28308

Low-Defect Heteroepitaxy 

on Porous Si Substrates

Cooperative Research and 

Development Final Report

CRADA Number: CRD-13-534

NREL Technical Contact: Benjamin Lee

CRADA Report

NREL/TP-5J00-63409

December 2014
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Cover Photos: (left to right) photo by Pat Corkery, NREL 16416, photo from SunEdison, NREL 17423, photo by Pat Corkery, NREL 

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This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Cooperative Research and Development Final Report

In accordance with Requirements set forth in Article XI.A(3) of the CRADA document, this 

document is the final CRADA report, including a list of Subject Inventions, to be forwarded to 

the Office of Science and Technical Information as part of the commitment to the public to 

demonstrate results of federally funded research.

Parties to the Agreement: Crystal Solar

CRADA Number: CRD-13-534

CRADA Title: Low-defect Heteroepitaxy on Porous Si Substrates

Joint Work Statement Funding Table Showing DOE Commitment:

Estimated Costs NREL Shared Resources

Year 1 $ 30,000.00

Year 2 $ 00.00

Year 3 $ 00.00

TOTALS $ 30,000.00

Abstract of CRADA Work:

In this collaboration, NREL will grow Ge, SiGe, and III-V layers on porous Si (pSi) substrates 

prepared either by Crystal Solar or at NREL. The intent is to grow low-defect epitaxial III-V 

alloys using the porous Si layer to prevent defect formation. Finally, we aim to fabricate solar 

cells from the III-V layers to prove the electronic quality.

Summary of Research Results:

NREL grew Ge, SiGe and GaAs layers on top of porous Si prepared by Crystal Solar and 

shipped to NREL. The growth of Ge and SiGe was done by hot wire CVD (HWCVD), while 

GaAs growth was done by MOCVD. The grown layers were examined by optical microscopy 

and also transmission electron microscopy (TEM). Unfortunately the grown films were highly 

defective, even after some attempts at optimization. Thus, our hope that the porous Si substrate 

would allow low-defect epitaxial growth of III-V materials was not realized. We did not proceed 

to make devices or solar cells since the III-V growth experiments had negative results. In the 

course of the collaboration we also evaluated the quality of some Si wafers grown epitaxially by 

Crystal Solar, making minority carrier lifetime measurements. The quality of Crystal Solar 

epitaxial Si wafers is good, with minority carrier lifetimes of several hundred microseconds.

Subject Inventions Listing: None.

Report Date: 11/10/14 Responsible Technical Contact at Alliance/NREL: Benjamin Lee

This document contains NO confidential, protectable, or proprietary information.