Determination of local density of states in amorphous oxide semiconductors with Kelvin Probe Force Microscopy

Fabbri, Luca (2022) Determination of local density of states in amorphous oxide semiconductors with Kelvin Probe Force Microscopy. [Laurea magistrale], Università di Bologna, Corso di Studio in Physics [LM-DM270], Documento ad accesso riservato.
Documenti full-text disponibili:
[img] Documento PDF (Thesis)
Full-text non accessibile fino al 1 Settembre 2025.
Disponibile con Licenza: Creative Commons: Attribuzione - Non commerciale - Non opere derivate 4.0 (CC BY-NC-ND 4.0)

Download (11MB) | Contatta l'autore


Amorphous semiconductors are important materials as they can be deposited by physical deposition techniques on large areas and even on plastic substrates. Therefore, they are crucial for transistors in large active matrices for imaging and transparent wearable electronics. The most widely applied candidate for amorphous thin film transistors production is Indium Gallium Zinc Oxide (IGZO). It is attracting much interest because of its optical transparency, facile processing by sputtering deposition and notable improved charge carrier mobility with respect to hydrogenated amorphous silicon a-Si:H. Degradation of the device and long-term performance issues have been observed if IGZO thin film transistors are subjected to electrical stress, leading to a modification of IGZO channel properties and subthreshold slope. Therefore, it is of great interest to have a reliable and precise method to study the conduction band tail, and the density of states in amorphous semiconductors. The aim of this thesis is to develop a local technique using Kelvin Probe Force Microscopy to study the evolution of IGZO DOS properties. The work is divided into three main parts. First, solutions to the non-linear Poisson-Boltzmann equation of a metal-insulator-semiconductor junction describing the charge accumulation and its relation to DOS properties are elaborated. Second macroscopic techniques such as capacitance voltage (CV) measurements and photocurrent spectroscopy are applied to obtain a non-local estimate of band-tail DOS properties in thin film transistor samples. The third part of my my thesis is dedicated to the KPFM measurements. By fitting the data to the developed numerical model, important parameters describing the amorphous conduction band tail are obtained. The results are in excellent agreement with the macroscopic characterizations. KPFM result is comparable also with non-local optoelectronic characterizations, such as photocurrent spectroscopy.

Tipologia del documento
Tesi di laurea (Laurea magistrale)
Autore della tesi
Fabbri, Luca
Relatore della tesi
Correlatore della tesi
Corso di studio
Ordinamento Cds
Parole chiave
atomic force microscopy,kelvin probe force microscopy,IGZO,thin film transistors,capacitance - voltage,CV,photocurrent
Data di discussione della Tesi
23 Settembre 2022

Altri metadati

Gestione del documento: Visualizza il documento