Thermokinetic Study of Aluminum-Induced Crystallization of a-Si: The Effect of Al Layer Thickness

Abstract

The effect of the aluminum layer on the kinetics and mechanism of aluminum-induced crystallization (AIC) of amorphous silicon (a-Si) in (Al/a-Si)n multilayered films was studied using a complex of in situ methods (simultaneous thermal analysis, transmission electron microscopy, electron diffraction, and four-point probe resistance measurement) and ex situ methods (X-ray diffraction and optical microscopy). An increase in the thickness of the aluminum layer from 10 to 80 nm was found to result in a decrease in the value of the apparent activation energy Ea of silicon crystallization from 137 to 117 kJ/mol (as estimated by the Kissinger method) as well as an increase in the crystallization heat from 12.3 to 16.0 kJ/(mol Si). The detailed kinetic analysis showed that the change in the thickness of an individual Al layer could lead to a qualitative change in the mechanism of aluminum-induced silicon crystallization: with the thickness of Al ≤ 20 nm. The process followed two parallel routes described by the n-th order reaction equation with autocatalysis (Cn-X) and the Avrami–Erofeev equation (An): with an increase in the thickness of Al ≥ 40 nm, the process occurred in two consecutive steps. The first one can be described by the n-th order reaction equation with autocatalysis (Cn-X), and the second one can be described by the n-th order reaction equation (Fn). The change in the mechanism of amorphous silicon crystallization was assumed to be due to the influence of the degree of Al defects at the initial state on the kinetics of the crystallization process.

Thermal Stability and Crystallization Processes of Pd78Au4Si18 Thin Films Visualized via In Situ TEM

“…Interestingly, Figure 2i also shows the presence of 100 nm particles that are proved to be pure Au precipitating from the original Pd(Au)-Si crystalline film, which will be thoroughly described below.The whole process of thermal heating was recorded in Supplementary Video S1. Despite the fact that all of the crystallization processes can be visualized at the nanoscale via in situ TEM and the exact determination of the resultant crystalline phases, some key parameters regarding the crystallization kinetics [29][30][31] are difficult to estimate, which is in part due to the lack of fine control over the heating rate. Future studies of in situ TEM techniques with improved fine control over the heating rate will address these difficulties.…”