In-situ electrical characterisation of a photodiode during nano-structuring with a focussed ion beam
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We study the fabrication and power conversion efficiency of GaAs photodiodes, which have been nano-structured and covered with colloidal quantum dots. A focussed ion beam is used to etch vertical channels into the photodiodes and the detrimental effects of this treatment are characterised in-situ during the fabrication process. A novel experimental configuration allows the electrical characterization of the photodiodes under laser illumination during the nano-fabrication process and reveals the gradual decrease of the photodiodes’ shunt resistance with increasing laterally revealed surface along the etched channels. This is interpreted as evidence for leakage currents through redeposited material and surface states on the lateral channel surface. After the fabrication step the channels are filled with colloidal quantum dots, which upon absorption of light transfer electronic excitations to the photodiode via resonance energy transfer. It is found that after the addition of quantum dots the nano-structured photodiodes show larger enhancements of the energy conversion efficiency under simulated solar irradiance than the pristine photodiodes. Nevertheless, the device degradation induced by the ion beam treatment itself cannot be compensated for.
KeywordsGaAs Power Conversion Efficiency Short Circuit Current Shunt Resistance Depletion Zone
We acknowledge funding from the EPSRC through Contract No. EP/G063494/1 as well as the European Network of Excellence Nanophotonics for Energy Efficiency (N4E) and the European project ITN-ICARUS. We also thank Dmitri V. Talapin for the provision of the colloidal QDs. J.J.R. is indebted to the Reiner–Lemoine–Stiftung, Germany, for financial support.