Broad spectral responsivity in highly photoconductive InZnO/MoS2 heterojunction phototransistor with ultrathin transparent metal electrode

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An amorphous InZnO/MoS2 heterojunction-based phototransistor with excellent photoconductive gain and responsivity over the entire visible range has been demonstrated. The photogenerated current of the InZnO phototransistor at long light wavelength (>600 nm) was significantly improved by utilizing narrow bandgap MoS2 as the capping layer (1.3 eV). At lower wavelength, photocarriers are generated due to the optical absorption of both InZnO and MoS2 layers, whereas the latter ensures significant photocarrier generation even at the higher wavelength region of the visible spectrum. The photogenerated carriers subsequently transfer to the underlying InZnO layer of superior carrier mobility that has a high channel conduction of additional electrons from the optically-induced doubly positively charged oxygen vacancies (Vo++) where the gate field is screening, thereby leading to the higher photoconductive gain of the InZnO/MoS2 phototransistors. The dynamic photosensitivity behaviour of the aforesaid phototransistor reveals the presence of persistent photoconductivity (PPC) due to the oxygen vacancy associated with InZnO which can be removed by applying a reset gate pulse from −15 to +5 V. The optical properties of these phototransistors were further enhanced by replacing the opaque Ti/Au electrode by an ultrathin transparent Ti/Au electrode. Utilization of the transparent electrode results in enhanced electron injection from source to channel due to a reduced barrier height under illumination giving rise to a ten-fold improvement in the photocurrent and responsivity of the phototransistors. A position-dependent study of the photocurrent w.r.t beam position also reveals that the enhancement in photocurrent is strongly dependent on the position and is at its maximum when the beam is placed near the source region.
Publisher
IOP PUBLISHING LTD
Issue Date
2020-01
Language
English
Article Type
Article
Citation

NANOTECHNOLOGY, v.31, no.3

ISSN
0957-4484
DOI
10.1088/1361-6528/ab4526
URI
http://hdl.handle.net/10203/270698
Appears in Collection
EE-Journal Papers(저널논문)
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