Local Site Distribution of Oxygen in Silicon-Rich Oxide Thin Films: A Tool to Investigate Phase Separation

Abstract

Thin films of nonstoichiometric silicon oxide (SiO x with x < 2) have been studied extensively during the past few decades because of their importance in many electronic and optoelectronic applications, and particular attention has been paid to models that can better describe their global structure. Herein, we present a detailed study of SiO x films deposited on silicon(111) and silica substrates using the low-pressure chemical vapor deposition (LPCVD) method by thermal oxidation of silane in an oxygen atmosphere at a temperature of 570 °C. The oxygen and silane flows in the reactor were varied to obtain films with different values of oxygen content x. Ellipsometry and m-line measurements were used to determine the complex refractive index of the deposited films. The oxygen contents in the films were measured by infrared spectroscopy, energy-dispersive X-ray spectroscopy (EDX), and time-of-flight elastic recoil detection analysis (TOF-ERDA). The oxygen contents in the films were also estimated from the measured values of the complex refractive indices using Bruggeman's effective-medium aproximation (EMA). All of the results were in good agreement, except for those obtained from infrared spectroscopy, which corresponded to systematically higher oxygen contents. This effect was interpreted as being due to an inhomogeneous distribution of oxygen atoms in the films (phase separation). This issue was confirmed by X-ray photoelectron spectroscopy (XPS) analysis of the Si 2p core levels, which showed an almostcomplete phase separation of the silicon-rich oxides into amorphous silicon and silicon dioxide, indicating that the mixture model is the most appropriate for the present films.

On the interplay between Si-Er-O segregation and erbium silicate (Er2Si2O7) formation in Er-doped SiOx thin films

“…In addition, it has been also highlighted that, for high concentrations, rare earth ions may also exhibit inhomogeneity upon deposition [14]. Moreover, as proposed by the mixture model [15] and recently evidenced by XPS [16], oxygen can be in homogenously distributed in SRSO layers, thus leading to the formation of Oxygen-rich and Oxygen-poor network. Therefore, we can assume that both Si excess and Er content promote the separation of these two oxygen networks as highlighted in Fig.…”

Structural and optical properties of a‐SiOx:H thin films deposited by the GJ EBP CVD method

“…The obtained data are in clear contradiction with the data given above. Apparently, this contradiction can be resolved by assuming that synthesized films contain an oxygen rich regions SiO у ( y > x ), which determine the position of the centers of SiOSi group stretching modes and determine the presence of broad high‐frequency shoulder at ∼1150 cm −1 .Thus, the structure of the synthesized films describes with mixture model, according to which the material contains oxygen rich regions and silicon rich regions .…”

Correlated effects of preparation parameters and thickness on morphology and optical properties of ZnO very thin films

“…Granular materials can be viewed as a mixture of bulk ZnO and voids according to the effective medium approximation [37]. A decrease of void volume fraction means an increase of density or decrease of porosity induces an increase of the dielectric function over the whole considered spectrum [46,47]. The granular layers in fact evolve towards a system made of grains with larger size and denser packing.…”