of 3000 angstroms silicon layer 20 is made amorphous by bombardment with high energy silicon ions then recrystallized by thermal annealing this step is done to achieve the desired electrical properties of the silicon epitaxial layers layer 20 is then ion implanted with a p type dopant such as boron to a doping level in the range of 10 18 cm 3 referring to fig8 lightly doped p type silicon layer 21 is epitaxially grown on top of silicon layer 20 the doping level of p type silicon layer 21 may be in the range of 10 15 to 10 16 cm 3 a typical dopant is boron and the thickness of silicon layer 20 may be in the range of 1 to 10 micrometers referring to fig9 top junction layers 22a 22d are formed by ion implantation of an n type dopant such as phosphorous to a doping level in the range of 10 16 to 10 18 cm 3 into p type silicon layer 21 top junctions layers 22a to 22d are implanted in selected regions of p type silicon layer 21 by the well know method of selective ion implantion briefly this consists of using optically patterned photoresist to form an implantion mask the photoresist is removed after ion implantation next referring to fig1 highly doped p type regions 23a 23c for making electrical contact to lightly doped p type layer 21 are formed by selective ion implantion the doping level of regions 23a 23d may be in the range of 10 18 cm 3.