Development of Three-Terminal Photodiodes Based on a-Si:H with an Additional Buried TCO Electrode

This work presents the development of three-terminal photodiodes which have their origin in bipolar pinipip-diode-structures [1,2]. The idea is to develop an unipolar diode and to contact a buried p-layer by an interior TCO-anode (transparent conductive oxide) instead of nip-stacking. The simulation of the optical material properties shows promising results. At first, both parts of the diode-structure were produced separately. The manufactured bottom (Cr/nip/TCO) and top (TCO/pip/TCO) parts were measured optically and electrically. These measurements are required to simulate the SR of the total-diode. Finally, a Cr/nip-a-Si:H/TCO/pip-a-Si:H/TCO multi-layer stack was deposited. The measured SR of the integrated diode validates the simulated data. The SR maximum shift amounts to 100nm, from 540nm by contacting the interior anode, to 640nm at the top anode. Furthermore, the curves are clearly split and do not enclose each other. The presented approach, with additional bandgap engineering, promises good prospects to improve color separation compared to currently existing detectors and should lead to a tunable multi-spectral photodiodes for high quality color recognition. Such a diode can be used in photonic devices, e.g. for safety and security applications.