Lattice-mismatched epitaxy of III-V semiconductors for LEDs and solar cells

Departments: Electrical Engineering
Time: Monday, November 17, 2014 - 1:00pm - 2:00pm
Type: Seminar Series
Presenter: Kunal Mukherjee, Department of Materials Science and Engineering, MIT
Room/Office: Becton 508
Location:
15 Prospect Street
New Haven, CT 06511
United States
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Department of Electrical Engineering Seminar

Lattice-mismatched epitaxy of III-V semiconductors for LEDs and solar cells

Kunal Mukherjee
Department of Materials Science and Engineering
MIT

Abstract: The growth of high-quality III-V ternary alloy semiconductors is vital to the success of devices such as LEDs, laser diodes and high-efficiency multi-junction photovoltaics. Matching the lattice-constant of a ternary alloy to a substrate is a severe constraint that can limit access to all but a few alloy compositions. Additionally, the epitaxy of ternary alloys can be complicated due to the dissimilar behavior of constituent atoms on the growth surface. A technologically important alloy in which both lattice matching and surface kinetics is crucial is the wide band-gap AlxIn1-xP system, about which little is known. In this work, we show that AlxIn1-xP has the highest direct band-gap (2.33 eV) amongst all non-nitride III-V semiconductors, which can potentially enable more efficient red and yellow LEDs and top sub-cells in multi-junction photovoltaics. We use InyGa1-yAs compositionally graded buffers to bridge the lattice-constant mismatch to a GaAs substrate, leading to thin films with low threading dislocation densities and oxygen content. We conduct experiments studying the occurrence of non-randomness such as phase separation and atomic ordering in AlxIn1-xP. The optoelectronic properties of these non-random alloys are utilized to demonstrate the first double-heterostructure yellow-green and amber AlxIn1-xP LEDs.

Biography: Kunal Mukherjee received his B.Eng degree in Electrical Engineering from Nanyang Technological University in Singapore in 2007 and a PhD in Materials Science and Engineering in 2014 from MIT. His doctoral research explored the epitaxy of AlGaInP III-V materials using MOCVD in collaboration with NREL, supported by an IBM fellowship. He is currently a postdoctoral research associate at MIT working on the growth and spectroscopy of mixed ionic-electronic conductors for fuel cells. His research interests include understanding surface processes during epitaxy and characterizing extended defects using electron microscopy and luminescence spectroscopy.

Monday Nov 17, 2014 
1 PM 
Becton 508 
Host: Minjoo Larry Lee