Diameter-dependent surface photovoltage and surface state density in single semiconductor nanowires

Area of Science:

• Materials Science
• Nanotechnology
• Semiconductor Physics

Background:

• Surface properties significantly influence the electronic behavior of semiconductor nanowires.
• The relationship between nanowire diameter and surface characteristics is crucial for device performance.
• Previous studies noted diameter-dependent surface recombination velocity in nanowires, but its origin was unclear.

Purpose of the Study:

• To determine the surface state density (N(s)) in individual n-type zinc oxide (ZnO) nanowires.
• To investigate the influence of nanowire diameter on N(s).
• To elucidate the role of N(s) in the diameter dependence of surface recombination and carrier transport.

Main Methods:

• Single-nanowire surface photovoltage measurements.
• Finite-element electrostatic simulations.
• Determination of surface carrier lifetime.
• Measurement of minority carrier diffusion lengths.

Main Results:

• Surface state density (N(s)) in n-type ZnO nanowires generally increases with decreasing diameter.
• The determined N(s) explains the observed diameter dependence of surface recombination velocity.
• Surface carrier lifetime measurements suggest N(s) drives the transition from bulk-limited to surface-limited transport around 30-40 nm diameter.

Conclusions:

• The diameter dependence of surface state density is a key factor in the electronic properties of ZnO nanowires.
• Understanding N(s) is critical for controlling carrier transport and device behavior in nanostructures.
• These findings provide insights into optimizing nanowire-based electronic and optoelectronic devices.