On the dark currents in germanium Schottky-barrier photodetectors

It is shown that for experimentally observed values of Schottky-barrier height of metal-n-type germanium photodetector structures, the dominant component of dark current can be due to the injection of minority carriers, rather than to the usual majority-carrier component. For barrier heights approaching 0.6 eV, for doping concentrations
N_{d} \lsim 10^{15}
cm
^-3
, for short minority-carrier lifetime
\tau_{p} \lsim 1
µs, for narrow base width
W_{b} \lsim 10
µm, or combinations of these conditions, the minority-carrier injection ratio approaches unity and these devices behave in the same way as p
⁺
-n junctions, with identical dark currents. The low-temperature fabrication requirements and processing simplicity of germanium Schottky barriers makes these devices more attractive under these conditions than germanium p-n junction photodetectors.