Synchronously Measuring The Barrier Structure And Electrical Transport Of Nanowire Schottky Barrier

There are two types of contact between metal and semiconductor: ohmic contact and Schottky contact.When the Schottky barrier is formed,the transport properties of the device are mainly controlled by the Schottky barrier.Schottky barrier devices based on nanowires have the advantages of high sensitivity,fast response,and large on/off ratio,and have received extensive attention and research.In recent years,a variety of high-performance devices have been developed using nanowire Schottky barriers,such as rectifier diodes,photodetectors,gas sensors,and resistance switch.The establishment of a barrier structure model is the basis for the analysis of Schottky barrier's electrical transport properties.For the traditional planar contact with infinite size,the one-dimensional barrier structure model is obtained by solving the Poisson equation.At present,the electrical analysis of most nanowire Schottky barriers still use the one-dimensional barrier structure model of the traditional planar barrier.However,the nanowire Schottky barrier has a significant structural difference from the traditional planar Schottky barrier.The size of the nanowire Schottky barrier contact area is not infinite but is confined to the nanometer range.Moreover,most nanowire devices use lateral contact electrodes rather than longitudinal contacts.Therefore,using the traditional one-dimensional barrier structure model to analyze the nanowire Schottky barrier has limitations in many cases,and the accuracy of the obtained electrical parameters needs to be discriminated carefully.For these reasons,the structure of the nanowire Schottky barrier need to be analyzed and detected,its barrier structure model need to be established,and the regulation effect of the barrier structure on the electrical transmission need to be explored.These researches are favorable for understanding the electrical transport mechanism of the nanowire Schottky barrier.The atomic force microscopy can be used to measure the barrier structure of the nanowire Schottky barrier in nanoscale,but this method is costly and complicated,which is difficult to achieve in-situ measurement in an actual device.At present,there is still lack of effective methods for the synchronous measurement of the electrical transport and barrier structure of the nanowire Schottky barrier.Establishing novel method to synchronously measure barrier structure and electrical transport is of great significance for revealing the regulation effect of the barrier structure on the electrical transport properties.In this paper,we firstly use the simulation method based on finite element analysis to calculate the barrier structure and electrical transport properties of ZnO nanowire Schottky barrier.The simulation results show that the barrier structure is similar to the traditional barrier structure model when the barrier width is smaller than the diameter of the ZnO nanowires,and the barrier is pinched off when the barrier width is larger than the diameter of the ZnO nanowires.After the nanowire Schottky barrier being pinched off,the depletion layer will expand along the long axis of the nanowires,and the interface electric field will increase slowly with the voltage and reach saturation.Since the interface electric field is the main factor of the Schottky barrier,the electrical transport properties should have significant differences before and after the barrier being pinched off.Based on these simulation results,a novel measurement method,measuring the voltage of the external electrode in three-electrode nanowire device(VEE-TED),has been developed to synchronously measure the structure and electrical transport properties of nanowire Schottky barriers.We applied the VEE-TED method to a resistive switch device based on a ZnO nanowire Schottky barrier to analyze its mechanism.It is found that during the transition from the high resistance state to the low resistance state,the nanowire Schottky barrier is partially depleted and a strong electric field exists at the interface.This provides direct experimental evidence for the resistive switch mechanism related to the interface strong electric field.The VEE-TED method provides an experimental method for synchronously measuring the structure and electrical transport properties of the nanowire Schottky barrier.However,through the simulation it is found that this method has limitations in determining the structure of the nanowire Schottky barrier.For example,although this method can identify the partially depleted barrier structure,it cannot distinguish between ohmic contact and Schottky barrier's pinched-off state.In order to solve this problem,we have introduced a traditional three-electrode method to measure the voltage of the intermediate electrode,which can distinguish these two conditions.Combining these two different three-electrode-based measurement methods,we propose a measurement method based on four-electrode system.Using this four-electrode measurement method,it is possible to distinguish between three types of barrier structures: the Ohmic contact,the partially depleted barrier,and the pinched-off barrier.Moreover,this four-electrode method can identify the changes in the barrier structure with voltage,for example,the transition from Ohmic contact to the partially depleted barrier,the transition from partially depleted barrier to the Ohmic contact,and the transition from partially depleted barrier to the pinched-off barrier.Using the four-electrode measurement method,we actually measured the barrier structure of multiple ZnO nanowire devices and their variation with voltage,which verifies the effectiveness of this method in determining the barrier structure.In addition,we measured the barrier structure and the current synchronously based on the four-electrode method.The measurement results show that when the nanowire Schottky barrier changes from partially depleted to pinched-off,the current-voltage curve also changes from linear state to saturated state.Through the study of this paper,we proposed a method for synchronous measurement of the barrier structure and electrical transport of nanowire Schottky barrier based on three-electrode and four-electrode systems.This method provides a powerful experimental method and technology for revealing the unique barrier structure and the novel electrical transport properties of the nanowire Schottky barrier.