Efficient photovoltaic effect in graphene/h-BN/silicon heterostructure self-powered photodetector

Graphene(Gr)/Si-based optoelectronic devices have attracted a lot of academic attention due to the simpler fabrication processes,low costs,and higher performance of their two-dimensional(2D)/three-dimensional(3D)hybrid interfaces in Schottky junction that promotes electron-hole separation.However,due to the built-in potential of Gr/Si as a photodetector,the Iph/Idark ratio is often hindered near zero-bias at relatively low illumination intensity.This is a major drawback in self-powered photodetectors.In this study,we have demonstrated a self-powered van der Waals heterostructure photodetector in the visible range using a Gr/hexagonal boron nitride(h-BN)/Si structure and clarified that the thin h-BN insertion can engineer asymmetric carrier transport and avoid interlayer coupling at the interface.The dark current was able to be suppressed by inserting an h-BN insulator layer,while maintaining the photocurrent with minimal decrease at near zero-bias.As a result,the normalized photocurrent-to-dark ratio(NPDR)is improved more than 104 times.Also,both Iph/Idark ratio and detectivity,increase by more than 104 times at−0.03 V drain voltage.The proposed Gr/h-BN/Si heterostructure is able to contribute to the introduction of next-generation photodetectors and photovoltaic devices based on graphene or silicon.

Tuning the inhomogeneous charge transport in ZnO interfaces for ultrahigh on/off ratio top-gated field-effect-transistor arrays

The interface between oxide/oxide layers shows an inhomogeneous charge transport behavior,which reveals a high conductivity owing to interface-doped.One typical example is the hetero-interface between ZnO film and other wide band gap oxides(e.g.,Al_(2)O_(3),TiO_(2),and HfO_(2)).It is thus quite evident that the ZnO/other oxides hetero-interface contains high density electron carriers effectively screening the gate-induced electric field.Thus,an extremely weak gate modulation in ZnO film was showed,resulting in very low on/off ratio of 1.69 in top-gate field-effect-transistor(TG-FET)configuration.So,to extend the usage of ZnO TG-FET is not quite possible toward further practical application.Herein,we clarified the correlation of inhomogeneous region in oxide/oxide hetero-junction by systematically study.Our work suggests that a self-assembly of molecules(SAM)buffer layer is suitable for tuning the inhomogeneous charge transport in ZnO film,which not only reduces the interface trap density,but also effectively enhances the gate electric field modulation at the hetero-interface.We further report the robust fabrication of TG-FET arrays based on ZnO thin film,using an ultra-thin alkylphosphonic acid molecule monolayer as buffer layer.Our device demonstrates a pronounced ultrahigh on/off ratio of≥10^(8),which is 8-order of magnitude higher than that of a device without buffer layer.For the highly reliable arrays,our device exhibits a high yield of over 93%with an average on/off ratio of^10^(7) across the entire wafer scale,mobility(18.5 cm^(2)/(V·s)),an extended bias-stressing(~2,000 s)and long-stability(~150 days)under ambient conditions.

Ultra-high current gain tunneling hot-electron transfer amplifier based on vertical van der Waals heterojunctions

Due to the backscattered parasitic current from the barriers,the current gain of the widely used amplifier is far from ideal.In this work,we demonstrate a vertical Au/Al2O3/BP/MoS2 tunneling hot-electron transfer amplifier with a hot-electron emitter-base junction and a p-n junction as the base-collector barrier.Fairly monoenergetic electrons traverse through the ultrathin Al2O3 dielectric via tunneling,which are accelerated and shifted to the collector region.The devices exhibit a high current on-off ratio of>105 and a high current density(JC)of∼1,000 A/cm2 at the same time.Notably,this work demonstrates a common-emitter current gain(β)value of 1,384 with a nanowatt power consumption at room temperature,which is a record high value among the all 2D based hot-electron transistors.Furthermore,the temperature dependent performance is investigated,and theβvalue of 1,613 is obtained at 150 K.Therefore,this work presents the potential of 2D based transistors for high-performance applications.