Thermodynamic Driving Force Activated Phonon Scattering in InN
Zaheer Ahmad, Osama A. Rana, Shakeel Ahmad, Mark Vernon, Brendan Cross, Alexander Kozhanov
TL;DR
This work addresses disorder in plasma-assisted MOCVD InN by introducing a single thermodynamic driving force, $\Delta\mu$, that correlates growth rate, defect-related Raman scattering, and structural coherence across diverse reactor conditions. A minimal framework combines an activated growth law $R(\Delta\mu) = A[\exp(\Delta\mu/E_g) - 1]$ with defect formation and Raman scattering that scale as $c_D(\Delta\mu) \propto \exp(\gamma_D\Delta\mu/(k_B T))$, all organized by $\Delta\mu$. Complementary kinetic Monte Carlo simulations bias surface events by $\Delta\mu$, reproducing the same exponential growth and defect activation trends and yielding consistent scales $E_g \approx 0.08$ eV and $E_d \approx 0.05$ eV. The results show that complex PA-MOCVD InN growth can be captured by a transferable coordinate, enabling defect-sparse growth control and providing a quantitative route to optimize material quality for devices.
Abstract
Defect related disorder during InN growth is a major challenge for making high performance electronic and optoelectronic devices. This is partly because film quality is often described using reactor specific settings instead of general physical variables. In this study, we show that plasma assisted MOCVD growth of InN can be described using a single thermodynamic driving force coordinate. This coordinate brings together growth kinetics, defect sensitive Raman response and structural coherence across different process conditions. When we use this coordinate, the incorporation rate follows a universal activated trend with a kinetic scale of about 0.08 eV. Raman measurements show a clear crossover between a defect sparse and a defect rich regime, a disorder activated Raman metric increases quickly after the crossover, while an A1-LO control metric stays mostly the same. This suggests that short range lattice disorder, not long range polar coupling, dominates the defect activation process. X-ray diffraction shows that the out of plane coherence length stays the same for samples with the same driving force, even if reactor settings are very different. This supports the idea that structural coherence is organized by thermodynamics in this growth window. Finally, a simple kinetic Monte Carlo model using driving force biased incorporation and defect activation events matches the observed exponential trends and the two regimes, supporting the driving force approach. These results show that a transferable driving force coordinate can be used for plasma assisted InN growth and offer a quantitative way to achieve defect sparse growth conditions.