Abstract
Here, an engineered tunneling layer enhanced photocurrent multiplication through the impact ionization effect was proposed and experimentally demonstrated on the graphene/silicon heterojunction photodetectors. With considering the suitable band structure of the insulation material and their special defect states, an atomic layer deposition (ALD) prepared wide-bandgap insulating (WBI) layer of AlN was introduced into the interface of graphene/silicon heterojunction. The promoted tunneling process from this designed structure demonstrated that can effectively help the impact ionization with photogain not only for the regular minority carriers from silicon, but also for the novel hot carries from graphene. As a result, significantly enhanced photocurrent as well as simultaneously decreased dark current about one order were accomplished in this graphene/insulation/silicon (GIS) heterojunction devices with the optimized AlN thickness of ~15 nm compared to the conventional graphene/silicon (GS) devices. Specifically, at the reverse bias of −10 V, a 3.96-A W−1 responsivity with the photogain of ~5.8 for the peak response under 850-nm light illumination, and a 1.03-A W−1 responsivity with ∼3.5 photogain under the 365 nm ultraviolet (UV) illumination were realized, which are even remarkably higher than those in GIS devices with either Al2O3 or the commonly employed SiO2 insulation layers. This work demonstrates a universal strategy to fabricate broadband, low-cost and high-performance photo-detecting devices towards the graphene-silicon optoelectronic integration.
Highlights
Benefited from the series of excellent electrical and optical properties, such as broadband absorption, high carrier mobility, high carrier concentration, and good transparency[1], graphene demonstrates attractive applications in high-performance photodetectors with excellent broadband operation and ultra-fast response[1,2,3]
The photo-generated carriers can be separated by the built-in electric field: the holes move to top electrode through graphene while the electrons move to the bottom electrode through silicon
The dark current is expected to be suppressed due to the increased Schottky barrier height (SBH), and the photo-generated excess holes would accumulate at the insulation-semiconductor interface
Summary
Benefited from the series of excellent electrical and optical properties, such as broadband absorption, high carrier mobility, high carrier concentration, and good transparency[1], graphene demonstrates attractive applications in high-performance photodetectors with excellent broadband operation and ultra-fast response[1,2,3]. While for the tunneling structure, which is usually constructed by inserting an insulating layer into metal-semiconductor (MS) interface, it has been considered to be the most attractive method to obviously increase the detectivity with the much constructed device structures[27,28] This functionalized layer can serve as an interface passivation material to inhibit the static charges’ transfer[29,30], which is similar to that used in other strategies including the integration of plasmonics and quantum dots, and can potentially enable the impact ionization resulting in a significant increase in the photocurrent multiplication[29,31]. The time-related photo-response shown in Fig. 3b clearly demonstrated the tunneling-effect induced prominent characteristics in the GIS device: much stronger photocurrent and lower dark current were obtained showing a significantly increased detectivity
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