When the connection is turned on, the photodiode is pinned to {HEAD ~ the substrate}, and kept at {TAIL ~ a specified potential} 
When the connection is turned on , the photodiode is pinned to { HEAD ~ the substrate } , and kept at { TAIL ~ a specified potential }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL