Infrared optoelectronic properties of metal-germanium Schottky barriers

An experimental study has been made of the electronic properties of rectifying metal-Ge (n-type) contacts for a range of metals (Au, Cu, Ag, Pb, and Ni) and their optoelectronic characteristics under monochromatic illumination for λ = 0.6328 µm and for 1 µm < λ ≲ 2 µm in the near infrared. For each metal, very ideal
I-V
characteristics were obtained with
n
values from the exponential forward bias region of 1.02 to 1.08 and excellent reverse saturation at 300 K. The dependence of photoresponse on thickness of various metal electrodes (from 50 to more than 1000 Å) was observed.
\phi_{B}'s
found from
IV C-V
, and photoresponse measurements are in close agreement within ±0.03 eV. The dependence of quantum efficiency (QE) upon metal thickness was measured for all metals and these results exhibit the expected decline in QE with
d \gsim 100
Å. For
d \lsim 100
Å, QE can be as high as 75 percent at λ = 6328 Å, and 48 percent in the wavelength range 1.1 µm < λ < 1.4 µm. QE versus
hv
(1 µm < λ < 2 µm) measurements have identified thresholds for the indirect and direct band-to-band excitation in the germanium and for the internal photoemission of electrons from the metal over the Schottky barrier induced by absorption of the infrared photons.