The structure is then etched in {HEAD ~ a suitable etching solution} to form porous silicon in {TAIL ~ the boron doped region} of the silicon substrate 80 
The structure is then etched in { HEAD ~ a suitable etching solution } to form porous silicon in { TAIL ~ the boron doped region } of the silicon substrate 80
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH