New experimental evidence for minority-carrier reflection at negative-barrier MIS contacts

Abstract

Recently, measurements of the open-circuit voltage of solar cells with negative-barrier metal-insulator-semiconductor (MIS) back contacts have been used to demonstrate that such contacts can function as the electrical analogues of metallurgical high-low junctions. In this brief, further experimental evidence for the minority-carrier reflecting properties of the negative-barrier MIS junction is presented. First, it is shown that a negative-barrier Mg-SiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> -nSi back contact can be used to enhance the long-wavelength photoresponse of p <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> -n solar cells in the same manner as a diffused n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> back-surface field. Secondly, measurements of the effective surface-recombination velocity for an Mg-SiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> -nSi contact and for a diffused n-n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> high-low junction formed on an identical substrate are reported. Both junctions gave very low values of recombination velocity, on the order of 50 cm/s.