Unlike conventional ohmic contact thin-film transistors (TFTs), contact-controlled TFTs [1], [2] rely on source energy barriers to produce a range of benefits including: low saturation voltages; extremely high intrinsic gain; power-efficiency; electrical stability; and uniformity of operation, notably with imprecise processes [3]. Generally, these benefits come at the expense of transconductance, however in materials such as polysilicon, similar levels of on-current can be obtained in a more compact footprint without any trace of kink-effect [4], [5].

In this article, the operation of avalanche photo-diodes in the medium gain, continuous operation mode is investigated. In other words, we are not considering diode operation in transient “Gieger” or “single photon” detection mode, but rather in a region safely below secondary breakdown, where a well-designed avalanche photo diode can exhibit a moderate photo-generated current multiplication factor of an order of magnitude or higher.