10:00 〜 10:15
▼ [7a-A404-4] Characterizations of a Hexagonal BN-encapsulated Multilayer MoS2 Photodetector
キーワード：transition metal dichalcogenide, photodetector
Atomically thin-layered semiconductor transition metal dichalcogenides have attracted considerable attention for applications such as field-effect transistors (FETs) and photodectors. High photoresponsivity has been demonstrated in molybdenum disulfide (MoS2) FETs, but the photoresponsivity was suffered by the scatterings of the carriers by, for example, the oxide fixed charges and the trapping states induced by adsorbates on the MoS2 channel. In this presentation, we report on characterizations of a photodetector with hexagonal boron nitride (h-BN) /MoS2/h-BN heterostructure as a channel to reduce the extrinsic scatterings. Multilayer MoS2 thin film is used as a channel because higher photo-responsivity is expected for multilayer MoS2 with indirect band gap than for monolayer MoS2 with direct band gap due to the longer photo-generated carrier lifetime.
A polydimethly siloxane/polypropylene carbonate dry transfer method was employed to prepare the h-BN/MoS2/h-BN heterostructures. The thickness of the MoS2 channel layer was characterized by an AFM to be 4.3 nm. The thicknesses of the upper and the lower layer h-BN were 13.0 and 18.3 nm, respectively. Cr/Au contacts were prepared for the source and drain contacts and for the back gate. Laser light at the wavelength of 532 nm was incident on the sample with the spot size of 12 μm at the incident power less than 2 μW. All the measurements were performed at room temperature.
The fabricated h-BN/MoS2/h-BN heterostructure back-gated device was normally-on and operated as a depletion-mode n-channel FET, in stark contrast to the previously reported photodetectors with MoS2 channel prepared directly on SiO2, operated as an enhancement-mode. The device had a subthreshold swing of 208 mV/dec and a current on-off ratio of more than 105 at the drain voltage VDS = 0.1 V. The field-effect mobility was 25 cm2/Vs. The hysteresis in the drain current (IDS)-back-gate voltage (VG) curve was small probably because of the h-BN capsulate that reduces the effect of adsorbed water molecules. The IDS-VDS characteristics in dark were linear in the low VDS region. The nonlinear and the saturation regions were observed in the high VDS region in dark. Under illumination, the linear region shifts to the higher VDS. We observed large photocurrent at VDS which was in the nonlinear or the saturation regions in dark. This indicates that the photocurrent in the high VDS region is associated with the nonlinear screening in the electron gas near the drain contact. Photo-responsivity exceeding 900 A/W was observed at 0.82 mW/cm2 at VG = 20 V.
A polydimethly siloxane/polypropylene carbonate dry transfer method was employed to prepare the h-BN/MoS2/h-BN heterostructures. The thickness of the MoS2 channel layer was characterized by an AFM to be 4.3 nm. The thicknesses of the upper and the lower layer h-BN were 13.0 and 18.3 nm, respectively. Cr/Au contacts were prepared for the source and drain contacts and for the back gate. Laser light at the wavelength of 532 nm was incident on the sample with the spot size of 12 μm at the incident power less than 2 μW. All the measurements were performed at room temperature.
The fabricated h-BN/MoS2/h-BN heterostructure back-gated device was normally-on and operated as a depletion-mode n-channel FET, in stark contrast to the previously reported photodetectors with MoS2 channel prepared directly on SiO2, operated as an enhancement-mode. The device had a subthreshold swing of 208 mV/dec and a current on-off ratio of more than 105 at the drain voltage VDS = 0.1 V. The field-effect mobility was 25 cm2/Vs. The hysteresis in the drain current (IDS)-back-gate voltage (VG) curve was small probably because of the h-BN capsulate that reduces the effect of adsorbed water molecules. The IDS-VDS characteristics in dark were linear in the low VDS region. The nonlinear and the saturation regions were observed in the high VDS region in dark. Under illumination, the linear region shifts to the higher VDS. We observed large photocurrent at VDS which was in the nonlinear or the saturation regions in dark. This indicates that the photocurrent in the high VDS region is associated with the nonlinear screening in the electron gas near the drain contact. Photo-responsivity exceeding 900 A/W was observed at 0.82 mW/cm2 at VG = 20 V.