氮化銦奈米柱陣列之載子動力學

Abstract

Indium nitride (InN) with a narrow direct band gap has superior electronic transport properties over other group-III nitrides and it makes InN attractive for applications such as high-frequency electronic devices, near-infrared optoelectronics, and high-efficiency solar cells. With the rapid down-sizing of electronic and photonic device dimensions, understanding of the carrier transportation in nanoscale materials becomes crucial. In this thesis, we report the ultrafast carrier dynamics of vertically aligned InN nanorod arrays grown by molecular-beam epitaxy on Si (111) substrates. We employ ultrafast optical spectroscopy at a wide range of probe wavelengths (800 nm – 1600 nm) to understand the absorption/relaxation process of nanorods with different rod height, diameter, and rod density. The band-filling effect dominant absorption process is observed for nanorods, while the band-gap renormalization effect is dominant in epilayer. Typically, band-gap renormalization is significant in high carrier density and then band-filling dominant absorption in InN nanorods indicates smaller carrier density than in epilayer, due to less efficient absorption limited by the size of nanorods. Polarization-dependent transient reflectivity responses in nanorods shows that carrier lifetimes along parallel and perpendicular directions to the axis of nanorods are different only for small-diameter nanorods, implying that the carrier confinement can occur in the nanorods with the diameter comparable to theirs diffusion length.

Indium nitride (InN) with a narrow direct band gap has superior electronic transport properties over other group-III nitrides and it makes InN attractive for applications such as high-frequency electronic devices, near-infrared optoelectronics, and high-efficiency solar cells. With the rapid down-sizing of electronic and photonic device dimensions, understanding of the carrier transportation in nanoscale materials becomes crucial. In this thesis, we report the ultrafast carrier dynamics of vertically aligned InN nanorod arrays grown by molecular-beam epitaxy on Si (111) substrates. We employ ultrafast optical spectroscopy at a wide range of probe wavelengths (800 nm – 1600 nm) to understand the absorption/relaxation process of nanorods with different rod height, diameter, and rod density. The band-filling effect dominant absorption process is observed for nanorods, while the band-gap renormalization effect is dominant in epilayer. Typically, band-gap renormalization is significant in high carrier density and then band-filling dominant absorption in InN nanorods indicates smaller carrier density than in epilayer, due to less efficient absorption limited by the size of nanorods. Polarization-dependent transient reflectivity responses in nanorods shows that carrier lifetimes along parallel and perpendicular directions to the axis of nanorods are different only for small-diameter nanorods, implying that the carrier confinement can occur in the nanorods with the diameter comparable to theirs diffusion length.