A study of amorphous transition metal oxide films

We present an experimentally guided study of film layer structure and opto-electronic properties of transition metal oxide (TMO) films. The oxide material system studied comprised the metals silicon (Si), zinc (Zn), and indium (In). The films were deposited via radio frequency magnetron sputtering (RFMS) on room-temperature Corning Eagle XG Glass (CEXG) substrates. Distinct (bi-layer (BL) vs single-layer (SL)) layer structures manifest as a function of angular distribution or pressure distance product (Greek letter 'phi') of sputtered material flux sourcing film growth. The films are amorphous, transparent and semiconducting. Experimental determination of absolute temperature (T) dependence of resistivity (Greek letter 'rho') revealed that at temperatures close to room-temperature, ionized impurity scattering (IIS) is the dominant conduction electron scattering mechanism. Thence, application of the Brooks-Herring (BH) model of IIS permitted analysis of the electronic state of the films. Thereby, the electronic state was revealed to be highly compensated. The design of experiment (DOE) and (associated) response surface analysis (RSA) frameworks were recruited from the very first stage — namely, the stage of film fabrication — of this study. This provisioned a self-referencing set of (nine) films (the ‘samples’) that are the subject of this study. The two layers of the BL films are / will-be-referred-to-as the sub-plantation layer (SPL) and the thin-film layer (TFL). The SPL is situated mediate substrate and TFL, and constitutes thereby the film-substrate interface. For consistent nomenclature, the term ‘TFL’ will be used to refer to the sole (film) layer of SL films. The layer structures of the films were established via x-ray reflectometry (XRR). The films were interrogated optically via spectroscopic ellipsometry (SE) (at room-temperature), and electrically via AC Field Hall Effect (ACFHE) measurements (between T = 10.1 K to 300 K). An account of the understanding of the film layers — viz., SPL, and TFL — as has been achieved, is as follows: ~ The sub-plantation layer (SPL) ~ We report the controlled emergence of a bonafide nanoscale layer — the SPL — at (comprising) the film-substrate interface. The determination of presence of a SPL is direct — that is, sans any assumptions, or modeling — via Fourier analysis of XRR results. We present three independent — experimental, empirical, and theoretical — threads of analysis to rationalize emergence of the SPL, as follows: > In terms of deposition process conditions under which a SPL manifests. Our semi-quantitative analysis is in terms of angular distribution or phi of the material flux sourcing film growth. Evidently, this thread of analysis is beholden to the specific physics of the deposition process, namely, RFMS. > Via RSA of SPL physical properties (SPL thickness (dSPL), SPL density (DSPL), and SPL roughness (rSPL)). This analysis reveals the following two process factors to be relevant: RF power (PRF), and process gas pressure (p). While the analysis is on the basis of experimentally observed process factors dependence of the physical properties noted, it is not beholden to the physics of the deposition process (RFMS). > Via dimensional analysis (DA) of the physical properties noted previously, in light of RFMS process. The dimensionless group for PRF (PRF*) thus determined reveals precisely the two previously noted process factors to be relevant. This analysis is ab initio. We highlight implications of our results for the industrially important problem of sputtered-film-on-substrate adhesion. Thereby, our results bear commercial promise, particularly for research and development (R&D) of flexible electronics applications. ~ The thin-film layer (TFL) ~ We quantify the semiconducting nature of the films (TFLs) on basis of optical (via SE) and electrical (via ACFHE) measurements of their room-temperature electronic properties. We interrogate the film (material system) electronic state on basis of the experimentally determined T dependences of conduction electron concentration (n) and conduction electron mobility (Greek letter 'mu'). Presence of a T-range (in the vicinity of and including room-temperature) where IIS is the dominant conduction electron scattering mechanism is established. Application of the BH model of IIS then lead to the (quantitative) determination that the electronic state is (highly) compensated. This determination — consistent with the experimentally observed anomalous oxygen content dependence of — is consistent with trap limited conduction. Thereby, we relate the electronic state to the chemistry and physics of film microstructure and material system. ~ The ready-reckoner ~ Figure 7.1 presents another and visual walk through — a ‘ready-reckoner’ — of this study. ~ Epilogue ~ This study represents new lines of investigation for the Professor Peter P. Edwards FRS ML Group.

Keywords: Collimation
Glass
Corning Eagle XG Glass
Semiconducting film
Linear model
Subplantation Layer
Sputtering
Mott
Transparent conducting film
Transition metal oxide film
Amorphous film
Ionized Impurity Scattering
Semiconductor Metal Transition
Radio Frequency Magnetron Sputtering
Design of Experiment
Aerospace
Kurt J. Lesker
Transparent conducting oxide film
Thin film
Brooks Herring
Flexible electronics
Corning
Nanostructured film
RF Magnetron Sputtering
Surface roughness
RF Sputtering
Zinc
Interface roughness
Machine Learning
Collimator
Materials discovery
Indium
Metal Insulator Transition
Phonon Scattering
Transparent conductive oxide film
Ioffe Regel
Dimensional Analysis
Radio Frequency Sputtering
Physical Vapour Deposition
Response Surface Analysis
Transparent conductive film
Silicon
Substrate Stage
Advisor: Edwards, P
Bruce, P
Pepper, M