Enhanced surface effects and optical property modulation of Ge₂Sb₂Te₅ by pulsed laser irradiation

Abstract

In this work, Ge2Sb2Te5 (GST) thin films are irradiated by a 1064 nm pulsed laser heat treatment system with different beam profiles. The surface effects induced by different laser conditions are studied systematically by atomic force microscope, spectroscopic ellipsometry, and Raman spectroscopy. It is found that a top-hat beam profile with uniform intensity distribution demonstrates the advantages of a non-destructive and homogeneous surface, which is critical for large-scale processing uniformity. The threshold laser fluence for the amorphization process is predicted by simulation and further proved by the laser irradiation experiment to be 27.9 mJ/cm2 at 1 ns pulse width. We further show that modulation of complex refractive indices of GST thin films can be achieved with different duty ratios (spatial ratio of amorphization part) from 0% to 100%. Our approach paves the way for the precise control of the optical properties of PCMs in emerging optical applications such as photonic switches, optical memories, and all-optical neural networks.

Optical and dispersion studies of thin S35-xGe15SnxTe50 films: Assessment of some physical parameters of samples

“…Therefore, it is crucial to investigate the chalcogenide glasses' optical properties to comprehend the films' optical behavior. Thin film samples interact with incident photons and absorb or scatter light, which determines the films' optical characteristics [25][26][27]91]. One can adjust light intensity, wavelength, film thickness, substrate morphology, temperature, the atomic proportion of elements, defects, and other variables to achieve the desired characteristics [27,28].…”

“…The average heat of atomization The average heat of atomization (H s ) is the energy needed to break apart 1 mole of a material into its constituent atoms. Pauling postulated that at standard temperature and pressure, a binary semiconductor system consisting of two atoms (A and B) would have a heat of atomization, H s (A-B), given by [18,26,44]:…”

“…The average coordination number, 〈r〉 is an important parameter, specifies the number of nearest (or the closest) neighbor atoms. 〈r〉 can be obtained for non-crystalline materials by using the following equation [26]:…”

“…Further, figure 11(a) was linearly fitted to get the following equation: < r 〉 = 2.300 + 0.020 x, where x is the fractional atomic percentage of Sn. This is because the Sn element replaces the S element, and Sn is of quadrant valence 4, which is greater than the valence of S, which is a divalent 2 [13,26]. This coordinated number, < r 〉 was also plotted versus the optical energy gap, as depicted in figure 12(b).…”

Multi‐Level Optical Switching by Amorphization in Single‐ and Multi‐Phase Change Material Structures

“…For PCMs on the GeTe-Sb 2 Te 3 pseudobinary tie-line, the nucleation time is on the order of a nanosecond, [38] hence sub-nanosecond laser or electrical heating pulses are typically required to achieve the quench rates that can lead to partially crystallized films with concomitantly different optical properties. [39] Note, some optical devices have been developed that achieve multi-level optical response by varying the length or area of the GST film that is crystallized within an optically probed region, [40] and we refer to this case as extrinsic crystallization. Herein, however, we aim to achieve multiple optical levels by controlling the size of nanocrystalites within an amorphous matrix.…”