High quality photovoltaic semiconductor material and laser ablation

Abstract

A high quality, narrow band gap, hydrogenated amorphous germanium or amorphous silicon alloy material characterized by a host matrix in which all hydrogen is incorporated therein in germanium monohydride or silicon monohydride form, respectively; their mobility-lifetime product for non-equilibrium charge carriers is about 10.sup.-8 and about 10.sup.-7, respectively; their density of defect states in the band gap thereof is less than about 1.times.10.sup.17 and about 2.times.10.sup.16 /cm.sup.3, respectively; and their band gap is about 1.5 and about 0.9 eV, respectively. There is also disclosed a structure formed from a plurality of very thin layer pairs of hydrogenated amorphous germanium and amorphous silicon alloy material, each layer pair of which cooperates to provide narrow band gap material. From about 3 to about 7 atomic percent fluorine is added to the germanium and/or silicon alloy material so as to provide a strong bond (as compared to hydrogen) so as to provide reduced sensitivity to Stabler/Wronski degradation. The preferred method of fabricating such improved narrow band gap materials is through a laser ablation process in which hydrogen or fluorine gas is introduced for incorporation into the germanium or silicon host matrix, thereby eliminating the reliance on the zoo of precursor species present in r.f. or microwave plasma process.