High quality photovoltaic semiconductor material and laser ablation method of fabrication same

A method of forming hydrogenated amorphous silicon alloy material, said material characterized by (a) the substantial absence of silicon hydrides, other than the monohydride, (b) a mobility-lifetime product for nonequilibrium charge carriers therein of about 10.sup.-7 cm.sup.2 /V, and (c) a density of defect states in the band gap of the host matrix thereof of less than about 2.times.10.sup.16 /cm.sup.3 ;

• said method comprising the steps of:
• providing a deposition chamber;
• providing a substrate in said deposition chamber;
• positioning at least one target of silicon containing material adjacent said substrate;
• providing a laser;
• evacuating said deposition chamber to a sub-atmospheric pressure;
• introducing into said evacuated deposition chamber a background gas including at least hydrogen;
• and
• depositing, by laser ablation, silicon from said target and hydrogen from said background pressure onto said substrate;
• thereby forming on said substrate a layer of hydrogenated silicon alloy material having an amorphous microstructure, said material characterized by the substantial absence of incorporated silicon hydrides, other than the monohydride, a mobility-lifetime product for nonequilibrium charge carriers therein of about 10.sup.-7 cm.sup.2 /V, and a density of defect states in the band gap of the host matrix thereof of less than about 2.times.10.sup.16 /cm.sup.3.

A method of forming a multi-layered structure of hydrogenated amorphous germanium and amorphous silicon alloy material;

• the structure defined by a plurality of layer pairs, each germanium and silicon layer of said layer pair characterized by (a) the substantial absence of germanium hydrides and silicon hydrides, other than the monohydrides, respectively, (b) a mobility-lifetime product for nonequilibrium charge carriers therein of about 10.sup.-8 and about 10.sup.-7 cm.sup.2 /V, respectively, and (c) a density of defects states in the host matrix thereof of about 1.times.10.sup.17 /cm.sup.3 and about 2.times.10.sup.16 /cm.sup.3, respectively;
• said method comprising the steps of:
• providing a deposition chamber;
• providing a substrate in said deposition chamber;
• positioning at least one target adjacent said substrate, said target including silicon and/or germanium material;
• providing a laser;
• evacuating said deposition chamber to a sub-atmospheric pressure;
• introducing into said evacuated deposition chamber a background gas including a partial pressure of at least hydrogen;
• and
• successively laser ablation depositing silicon and germanium from said at least one target and hydrogen from the background pressure onto said substrate;
• thereby forming on said substrate a plurality of layer pairs of hydrogenated amorphous germanium and amorphous silicon alloy material, each layer of said layer pair being about 5-30 .ANG. thick, each germanium and silicon layer of said layer of said pair characterized by the substantial absence of germanium hydrides and silicon hydrides, other than the monohydrides, respectively, a mobility-lifetime product for nonequilibrium charge carriers therein of about 10.sup.-8 and 10.sup.-7 cm.sup.2 /V, respectively, and a density of defect states in the host matrix thereof of about 1.times.10.sup.17 /cm.sup.3 and 2.times.10.sup.16 /cm.sup.3, respectively.