This gain [G.sub.S], derived from the photo-FET devices that the naked surface and the bottom interface with the substrate created in GaAsepilayers, is inversely proportional to the illumination power [P.sub.L] impinging on the photresistor thus, it is orders of magnitude greater than the "photoconductive" gain [G.sub.B] due to the conductivity modulation of the GaAs bulk by photogenerated electron-hole pairs at low illumination levels.
We apologise for making this mistake, which shows that we ourselves found it very hard to abandon our prejudices regarding conductivity modulation, which most people assume.
This bottom photo-FET reinforces our proposal regarding photoresistors presented in : under a weak light source, the PC system will behave as a photo-FET, where photons will reduce the depleted thickness W of their SBB and not as photoresistors with noticeable conductivity modulation.
While the same must be true for bipolar junction transistors, the effect is mitigated by the bipolar phenomenon of conductivity modulation
, whereby operation in the saturation region causes the injection of minority carriers into the collector region, resulting in a commensurate injection of majority carriers to preserve charge neutrality.