Electron Dynamics of TiN Thin Films and InGaN/GaN Dot-in-Nanowires

time- resolved pump-probe;InGaN/GaN nanowires;TiN thin films;electron dynamics;Electrical Engineering;Engineering;Electrical Engineering

George, HeatherMi, Zetian ;

University of Michigan

关键词: time- resolved pump-probe;    InGaN/GaN nanowires;    TiN thin films;    electron dynamics;    Electrical Engineering;    Engineering;    Electrical Engineering;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/147619/hthrfrg_1.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

The invention of ultrafast lasers revolutionized our capacity to examine the fundamental physics of the materials used in optoelectronics on a femtosecond timescale. Pump-probe is a powerful optical technique which measures the changes in the absorption; the transient data can inform the theory of carrier-carrier scattering, phonon interaction, and state lifetimes in the sample. This work explores the ultrafast electron dynamics of two materials of emerging importance to optoelectronics: Titanium Nitride (TiN) and InGaN dot-in-nanowire structures.TiN is a refractory conductive ceramic that has many uses in plasmonics, CMOS electronics, and hot carrier devices. Its optical properties as revealed by ellipsometry are very similar to those of noble metals, which are the most important traditional plasmonic materials; however, its thermal properties and electron-phonon coupling are quite different. Using pump-probe experiments, the transient carrier dynamics are explored. The results are interpreted using a two temperature model which reveals important contrasts to the noble metals; in particular, the electron-phonon coupling constant is on the order of 1018, which approximately two orders of magnitude greater than the coupling in gold. This is significant because heat is efficiently transferred to the substrate, leading to a large substrate contribution to the measured signal.Selective area samples of InGaN/GaN dot-in-nanowires grown on GaN/sapphire were investigated. This work shows the first time-resolved differential reflection measurements on green InGaN/GaN quantum dots. This type of growth is very controlled and slow compared to self-assembled structures, but this also allows the wires to be more homogenous. Even with this type of growth, defects and trap states play a major role in determining the performance of optoelectronic devices such as LEDs, lasers, and detectors. The lifetimes captured give an understanding of the states in the interaction, as well as energy loss to phonons. Two decay times were extracted; a fast decay 20-35 ps, which is attributed to decay into non-radiative states and a slower decay 330-830 ps, which we believe is mostly radiative recombination. This work can inform future growth and optimization for nanowire LED and laser applications.