Study Of The Anomalous Transport Properties Observed In InN Nanowires

The III Nitride semiconductor system is an area of intense research because of its potential for opto-electronic devices and high speed transistors. Theoretical study have revealed InN posses the largest electron mobility and highest carrier saturation velocity among III Nitride semiconductor system, which indicates InN is a good candidate for high-performance transistors. This paper mainly illustrates the anomalous electronic transport properties in InN nanowires.It has a significant effect on understanding the physics of InN materials, mastering the applications in opto-electronic devices to study transport properties in InN nanowires.In chapter 1,we review the important properties, growth, electrical properties, optical properties and the applications of InN materials.In chapter 2,we introduce the resistance, conductivity anomaly observed in InN nanowires and the study about them. Chang et al. recently reported an interesting resistance anomaly in which the nanowire resistance decreases as cross section area is reduced for small diameter InN nanowires (less than 90nm). This observation is inconsistent with the classical Ohm's law. A recent study on InN nanocolumns by Calleja et al. found that the wire conductivity for small diameter nanowires was almost a linear function of the reciprocal of wire diameter. The transformation of conductivity indicates InN has a unique conduction mechanism. We examine possible theories presented in literature to explain the extraordinary observation and we find that the Scatter model and the Contact resistence Rc are not the accurate explanation to the resistance anomaly observed in nanowires. These theories don't refer the unique electronic property of InN-high density surface electron accumulation layer.In chapter 3,we study the effects of high density surface electron accumulation layer on the transport properties of InN nanowires. The presence of high density accumulation layer at the surface leads to two distinct conduction mechanisms in InN viz. surface and bulk. Firstly, we obtain the expression of average carriers concentration in InN nanowires from the expression of average carriers concentration in InN film. Then, we find the relationship between average carriers concentration and mobility. Due to the expression and relationship upwards, we obtain the expression of conductivity. We find that the conductivity increases with decreasing radius of InN nanowires. The Calleja's experiment result is proved by it. The special transport properties of InN nanowires which is different from other nanowires (For instance GaN nanowires) is induced by the unique electronic property of InN- high density surface electron accumulation layer. Secondly, we obtain the expression of conductance in small radius (<～50nm) InN nanowires and large radius (>～50nm) InN nanowires from the expression of conductivity. We find that the major conduction mechanism in large radius (>～50nm) is due to the bulk carrier transport. The expression of conductance in large radius (>～50nm) InN nanowires is consistent with the classical Ohm's law. However, for small radius nanowires (<～50nm) carrier transport is primarily due to surface conduction, thus, resistance should decrease with decreasing radius. The Chang's experiment result is proved by it. Therefore, with the study of anomalous electronic transport properties in InN nanowires, we indicate that the high density surface electron accumulation layer is very important for the transport properties of InN nanowires and it is the reason of the anomalous electronic transport properties in InN nanowires.