CAREER: Fundamental Physics and Device Issues of Novel GaAs Thermophotovoltaic Cells

Yale University, New Haven CT

Investigators

Abstract

TNumerous civilian and military ventures are showing keen interest in the thermo photovoltaic (TPV) generation of electricity as an attractive, clean, efficient, and inexpensive alternative energy. The low power (about 1400 C) of TPV heat sources makes gallium antimonide (GaSb), rather than silicon, the most common material for TPV cells. Research on GaSb TPV cells is currently focused on: (1) increasing the TPV efficiency, and (2) reducing the cost of production. This document proposes the first study of gallium arsenide (GaAs) as a viable material for TPV cells. There are two compelling reasons. First, the manufacture of TPV cells on a GaAs substrate could take advantage of existing GaAs facilities for low-cost, high-yield, large-volume production compatible with GaAs integrated circuits (ICs) on large six-inch substrates. Second, our innovative TPV cells can be designed for exceptionally high efficiency because of their simultaneous response, on the same GaAs substrate, to both the near infrared (less than 1.5micron) and the mid-infrared (2-5micron). This proposal develops three enabling technologies for making high efficiency TPV cells on GaAs: (1) innovative design of intersubband TPV devices for high power conversion efficiency of broadband heat sources; (2) novel Low-Temperature Grown (LTG) GaAs designed for strong absorption at the 1.5micron wavelength (an important TPV wavelength); (3) growth and annealing of very highly doped (10^{20}cm^{-3}) contacts, and highly doped tunnel junctions connecting series-TPV cells. This proposed work is ideally suited for an academic environment because of its interdisciplinary nature, emphasizing: both theory and experiment; fundamental studies of absorption, transport, and materials; and innovative TPV cells. One innovation is the proposed design of Intersubband Tandem TPV (ITTPV) cells, which have projected conversion efficiencies (35%) much higher than those (6%) of existing devices. The proposed study of LTG-GaAs goes beyond previous work in that it emphasizes the physics and engineering of a much stronger absorption at 1.5micron. The proposed work on very highly doped TPV tunnel junctions and contacts emphasizes: developing physical models of doping limitations; and a novel thermal anneal much more rapid (milliseconds instead of seconds) than the state-of-the-art capability. PI's educational program has three components: (1) new curriculum development, (2) mentoring activities, and (3) participation in research seminars.