EQE larger than 100% has been reported from photodetectors made on many semiconductor materials such as beta-Ga2O3, ZnO, GaN, and black Si, etc. I have never seen this from any types of Ge photodetectors. Is it possible to get over 100% of EQE from Ge photodetectors? Possible mechanism could be deep level defects which makes photoconductive gain. But, I am not sure.
As a suggestion, it could be a multi-electron process in which absorption of a photon (I would think at least twice the bandgap) will excite first one, then a second by secondary interactions to produce two electrons into the conduction band instead of just highly exciting a single electron deep into the conduction band. The resultant charge carrier/absorbed photons ratio would therefore be larger than one-to-one.
EQE = number of charge carriers collected by the solar cell to the number of photons of a given energy
Yes, it can over 100% if you can generate two pairs of carriers in one photon.
But it is hard for Ge to do this. There are many possible solutions. For examples, find a material/structure that can generate two carriers on top of your Ge detectors. Try to generate it within Ge.
It is unclear whether to me whether you are talking about multi-carrier generation by the photon or the delivery to the external circuit of multiple carriers for each phto-generated pair. Either way there a multiple ways for such an effect to occur.
Starting with multiple pair generation per photon: in principle the simplest process is for the photon energy to exceed 2x the bandgap. However, optical and near-UV photons would be absorbed very near the surface, so this is rarely practical other than in a Schottky diode. (At yet shorter wavelengths the absorbtion rate reduces again, so PN diodes can become viable - but photo-generated damage can be a problem here). Reverse-biased devices can have the effective bandgap reduced by incorporation of impurities, but such devices would normally be very leaky in room-temperature germanium. There are more complex schemes, but I'm not certain I would classify any that I know as "germanium detectors".
More commonly, we see multiple carriers released to the external circuit for each generated hole-electron pair. Device types to implement this effect include photoconductors, avalanche photodiodes and phototransistors.
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