High performance foreign-dopant-free ZnO/AlxGa1−xN ultraviolet phototransistors using atomic-layer-deposited ZnO emitter layer

Abstract

High-performance foreign-dopant-free ZnO/AlxGa1−xN heterojunction ultraviolet (UV) phototransistors were fabricated and characterized. The ZnO layer with high electron concentration was grown as emitter by atomic layer deposition, while the AlxGa1−xN/GaN heterostructure was epitaxied as base and collector by metal organic chemical vapor deposition. A linearly upgraded/downgraded AlxGa1−xN layer was used as polarization-induced n/p type layer without dopant. The prominent feature of the resulting n+-p-n ZnO/AlxGa1−xN phototransistors is a three-stage rising spectral response matching the biological action spectrum of solar UV radiation. Moreover, the phototransistors demonstrate a low dark current of less than 1 pA at 2 V, a maximum responsivity of ∼8.7 A/W at 5 V and 300 nm, a normalized detectivity of ∼1 × 1013 Jones, and a high response speed with a rise/fall time of 3.5 μs/450 μs. This work shows a feasible and simple-process approach for developing high-performance multiband spectral response photodetectors based on different wide band gap material systems.