Charge transport and trapping in InN nanowires investigated by scanning probe microscopy

Abstract

Charge transport and trapping in InN nanowires (NWs) and their networks have been investigated using scanning current voltage microscopy (SIVM) and scanning gate microscopy (SGM). SIVM maps indicate highly conducting NWs and nanojunctions as well as significant variation in surface barrier height along the NWs, which are strongly affected by deformations. SIVM measurements were used to determine the electrical conductivity and carrier mobility of individual NWs exploiting the unusually large probe current under reverse bias, arising out of possible type II heterostructure band alignment. Strong correlation between surface barrier change and electrical conductivity of the NW was observed, which can be explained by considering a high density of electron accumulation at the NW surface. SGM measurements performed on NW field effect transistors reveal large scale trapping of carriers under reverse bias, while cyclic drain current-probe voltage measurements indicate both trapping and detrapping rates to be strongly dependent on the magnitude of the reverse bias. Application of a negative probe bias pulse resulted in a drain current recovery transient with time constant of tens of seconds indicating large activation energy for the traps whose density is estimated to be in excess of 2×1013 cm−2.