Research On Two-dimensional Black Phosphorus Field Effect Transistor And Its Electronic Transport Property

Beneficial from the unique two dimensional structure and electronic properties,two-dimensional materials have been widely considered as the next generation semiconducting material beyond silicon.Black phosphorus?BP?is a latest?in 2014?found elemental two dimensional semiconducting material,showing to be an excellent candidate for 2D electronics and optoelectronics.Firstly,it shows high performance ambipolar behavior with high hole mobility up to 1000 cm²/Vs at room temperature.Secondly,black phosphorus has a narrow and direct bandgap around 0.3 eV in bulk as well as in few-layer flakes.Such a narrow bandgap fills up the missing gap between zero bandgap graphene and wide bandgap MoS₂,covering the spectrum range from visible to near infrared.Furthermore,black phosphorus shows strong anisotropic feature.Those unique properties make BP promising for future electronic device and broadband optoelectronic applications.In this work,we will focus our attention on the transport properties and potential applications of BP and its heterostructures based electronic devices.The detailed research contains the following parts:Firstly,we develop the classic“silicon-oxide-semiconductor”structure to fabricate back-gate black phosphorus field effect transistors.And we then carry out a systematical study on transport properties of the device under different temperatures.Next,we demonstrate various logic devices by using p-type black phosphorus field effect transistor in-series with n-type MoS₂ field effect transistor,including high gain CMOS binary inverter and tunable ternary inverter.The binary inverter contains one black phosphorus transistor and one MoS₂ transistor.The threshold voltage can be well tuned by channel length modulation.And with an optimized channel length,we obtain high-voltage transfer gain.Furthermore,we have fabricated 12 BP–MoS₂ CMOS inverters,and most of them exhibit high gain larger than 60 with the highest gain of 152 at V_dd=3 V,which is among the best reported in all inverters made from 2D materials.The ternary inverter contains one short channel black phosphorus transistor,one long channel black phosphorus transistor and one MoS₂ transistor.Interestingly,the device shows three steady output voltage states,in which the high voltage state“logic 1”comes from the off state of MoS₂ transistor,the low voltage state“logic 0”comes from the off state of long channel BP transistor,and the novel state“logic 1/2”comes from voltage drop distribution between the two BP transistors.Furthermore,the device shows high tunability that the mid value state can be well controlled by simply tuning the channel length of the components.Secondy,we study various electronic devices based on black phosphorus heterostructures.In the vertical BP-MoS₂ heterostructures device,we obtain high current rectification ratio,high on–off ratio and large output current simultaneously.In the lateral BP-MoS₂ heterostructures device,we observe both positive and negative differential transconductance in the transfer characteristic curves,which can be used in logic applications.By connecting the heterojunction in-series with a black phosphorus transistor,we demonstrate the first ternary inverter with tunable logic states by electric field,that is,the device shows classical binary logic under small driving voltage V_dd<1V and novel ternary logic under V_dd>1 V.In summary,our ternary device is compatible to classical binary device and also shows high tunability:the range and output voltage of the middle logic state,and even its emergence can all be well controlled.Thus unique and high performance makes black phosphorus devices promising in future electronic and circuit applications.Thirdly,we focus our attenetion on the optoelectronic applications based on black phosphorus.By systematically study of photodetection in terms of wavelength,incident power,device scaling and biasing voltage,we conclude the photoresponsivity of the phototransistor is inversely proportional to the of channel length squared.And we obtain ultra-high photoresponsivity up to 10⁶ A/W at room temperature for the ultra-scaled channel length of 100 nm device.Next,we performed low temperature photo detection on BP transistors.As expected,the photoresponsivity shows a huge increase at low temperatures.At T=20 K,broadband photodetection from 400 nm to 900 nm with a large photoresponsivity of more than 10⁷ A/W is achieved.In BP-MoS₂ heterostructure based photovoltaic device,we obtain high photocurrent to dark current ratio up to 10⁵ for the low dark current under zero biasing and large photocurrent driven by the build potential in the pn junction.Benefited from the narrow bandgap of black phosphorus,the device shows broadband photodetection up to 2?m at room temperature.In addition,we have focused great attention on the encapsulation of black phosphorus devices.We find the thin film of Al seeding layer by physical vapor deposition largely enhances the air stability of black phosphorus devices.