Studies On Photodetectors Based On Two-dimensional Molybdenum Disulfide And Gallium Selenide

Traditional devices are usually inflexible and opaque.With the development of wearable devices,flexible and transparent devices have attracted more attention.Two-dimensional semiconductor materials have great potential in the field of new devices.In this thesis,gallium selenide(GaSe),molybdenum disulfide(MoS₂),and hexagonal boron nitride(h-BN)have been studied.Their nanosheets have been fabricated by mechanical exfoliation.A method is proposed to fabricate flexible photodetectors by transferring two-dimensional materials onto flexible electrodes.It is suitable to fabricate devices based on various two-dimensional materials and their heterostructures.The flexible photodetectors based on GaSe,h-BN/GaSe,MoS₂,h-BN/MoS₂,GaSe/MoS₂ respectively have been fabricated.Their performance was characterized and studied.Thin GaSe is easily oxidized in the air,which leads to destroy the performance of devices.Thick GaSe devices have improved stability in the air.The photodetector based on thick GaSe has different responsivities to 405 ? 635 nm light and the ratio of photocurrent to dark-current is near to 1000.The performance of the thick GaSe device has been improved by h-BN packaging.The device has a responsivity of 12.2A/W,and the response/recovery time is 100/40 ms.MoS₂ devices have a large response to 405?670 nm light.The responsivity of the thin MoS₂ device is 101A/W under the illumination of light.The response time is too long and up to tens of seconds.The ratio of current in light to in dark is lower to 1.4.At a bias of 0V,thicker MoS₂ devices also have response to visible light due to the different contact between MoS₂ and two Au electrodes.The responsivity is 0.4A/W.The GaSe/MoS₂ heterostructure is type II.Under the same conditions,the responsivities of the GaSe/MoS₂ heterostructure,the MoS₂ and the GaSe used for heterostructure were 22,5100,and 11 mA/W,respectively.Their on-off ratios were 2300,2.6,and 900,respectively.The heterostructure photodetector has the highest on-off ratio,and its responsivity is lower than MoS₂ and higher than GaSe.Its response time is 40 ms,which is half of the response time of the GaSe device,and three orders lower than the response time of the MoS₂ device.The results in this thesis demonstrate the potential of the heterostructure in the field of photodetector for fast detection.