Kardar-Parisi-Zhang Universality, Anomalous Scaling and Crossover Effects in the Growth of Cdte Thin Films

TL;DR

This study investigates the growth dynamics of CdTe thin films across various temperatures, demonstrating the universality of KPZ scaling and revealing temperature-dependent crossover effects and surface fluctuation behaviors.

Contribution

It provides the first experimental verification of KPZ universality in CdTe thin film growth and explores how temperature influences the scaling and fluctuation regimes.

Findings

KPZ universality class confirmed at 250°C.

Temperature-dependent crossover from Poissonian to KPZ growth.

Different KPZ parameters ($ u$, $ extlambda$) observed at various temperatures.

Abstract

We report on the growth dynamic of CdTe thin films for deposition temperatures ($T$) in the range of $150\,^{\circ}\mathrm{C}$ to $300\,^{\circ}\mathrm{C}$. A relation between mound evolution and large-wavelength fluctuations at CdTe surface has been established. One finds that short-length scales are dictated by an interplay between the effects of the formation of defects at boundaries of neighbouring grains and a relaxation process which stems from the diffusion and deposition of particles (CdTe molecules) torward these regions. A Kinetic Monte Carlo model corroborates these reasonings. As $T$ is increased, the competition gives rise to different scenarios in the roughening scaling such as: uncorrelated growth, a crossover from random to correlated growth and transient anomalous scaling. In particular, for $T = 250\,^{\circ}\mathrm{C}$, one shows that surface fluctuations are described by the celebrated Kardar-Parisi-Zhang (KPZ) equation, in the meantime that, the universality of height, local roughness and maximal height distributions for the KPZ class is, finally, experimentally demonstrated. The dynamic of fluctuations at the CdTe surface for other temperatures still is described by the KPZ equation, but with different values for the superficial tension ($\nu$) and excess of velocity ($\lambda$). Namely, for $T = 150\,^{\circ}\mathrm{C}$ one finds a Poissonian growth that indicates $\nu = \lambda = 0$. For $T = 200\,^{\circ}\mathrm{C}$, however, a Random-to-KPZ crossover is found, with $\lambda > 0$ in the second regime. Finally, for films grown at $T = 300\,^{\circ}\mathrm{C}$, one demonstrates that a KPZ growth with $\lambda < 0$ takes place. We discuss the different mechanisms leading to KPZ scaling which depend on $T$, and conjecture the behavior of the phenomenological parameter $\lambda$ as function of the deposition temperature.