Technology of GaAs metal—Oxide—Semiconductor solar cells

Abstract

The growth of an oxide interfacial layer was recently found to increase the open-circuit voltage (V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oc</inf> ) and efficiency by up to 60 percent in GaAs metal-semiconductor solar cells. Several oxidation techniques have been developed which will provide the necessary oxide thickness and chemical structure. Details of these techniques using ozone, water-vapor-saturated oxygen, or oxygen gas discharges are described, as well as apparent crystallographic orientation effects. Preliminary results of the oxide chemistry obtained from X-ray, photoelectron spectroscopy are given. Ratios of arsenic oxide to gallium oxide of unity or less seem to be preferable. Samples with the highest V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oc</inf> predominantly have As <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+3</sup> in the arsenic oxide rather than As <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+5</sup> . A major difficulty at this time is a reduction in open-circuit Voltage by 100-200 mv when the antireflection coating is vacuum deposited. Without this effect, values of about 750 mV for V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oc</inf> and 15-percent efficiency with air mass of 1 sun can be obtained with single-crystal GaAs. All techniques are compatible with polycrystalline GaAs thin films.