The construction

characteristics and theory of a new type of thermionic photodetector are described.It is a maiority-carrier device

which differs from conventional p-i-n photodiodes

avalanche photodiodes and photo transistors in basic structure.The main differences between this detetor and other majority-carrier devices are:①There is a large central p+ n- juncture area

whose function is similar to a hole storehouse.②In perphery of pn diode

there is a special ring frame n++ p+ n- sandwich structure.The absolute responsivrty of the new device is 1.36A/W

while that of the ordinary diode is 0.35A/W.