Size-dependent photoconductivity and electroic transport in single GaN nanowire

The thesis corroborates the size-dependent photoconductivity and electronic transport in GaN single nanowire. By calculating GaN SNW (single nanowire) responsivity in different diameter, we find that single nanowire with smaller diameter has higher responsivity and higher gain. On the contrary, bigger nanowires have opposite results. On the other hand, the temperature-dependent result also reveals size-dependent in GaN SNW. Bigger nanowires show bulk GaN semiconductor properties and smaller ones (D<80nm) show temperature-independent
behavior.These phenomena imply size-effect in single GaN nanowire.

The size effect which reveals in photoconductivity and low temperature results could be explained by donor-type oxygen surface state on the nanowire surface. In order to illustrate how oxygen surface state affects electron transport, we propose three important suggestions to explain it. One is spatial separation, the other is that oxygen atom plays a role of donor type, which leads to convex band-bending, another is that oxygen surface state is above conduction band. These suggestions could completely interpret nanowire electronic transport in different diameter. And all suggestions that we proposed have been confirmed to be consistent with our experimental results.