Nucleation and growth of germanium islands during layer exchange metal-induced crystallization

TL;DR

This paper investigates the nucleation and growth mechanisms of germanium islands during Al-induced layer exchange crystallization, extending phase transformation theory to nanoscale growth and demonstrating control via bias-voltage stressing.

Contribution

It introduces a model for nanoscale Ge island growth during layer exchange, incorporating a transition from atomic-attachment to surface diffusion kinetics, and shows control of island density through bias-voltage.

Findings

Growth switches from atomic-attachment to surface diffusion-limited

Transition depends on nucleation site density and temperature

Bias-voltage controls Ge island density

Abstract

Al-induced layer exchange crystallization of amorphous Ge thin films has been demonstrated recently, and provides a suitable system to characterize, model and control Ge crystal growth on non-crystalline substrates. Direct observation of Ge transfer to the surface of Al through an interposed GeOx interfacial layer allows independent measurement of the density and average area of crystalline Ge islands formed on the surface. Based on these experimental observations, the Johnson-Mehl-Avrami-Kologoromov phase transformation theory is extended to model nanoscale nucleation and growth of Ge islands in two dimensions. The Ge island growth mechanism switches from atomic-attachment-limited to surface diffusion-limited kinetics with increasing time. The transition point between these regimes depends on the Ge nucleation site density and the annealing temperature. Finally, we show that local bias-voltage stressing of the interfacial layer controls the areal density of nucleated Ge islands on the film surface.