13:30 〜 15:30
▲ [19p-P5-23] Ionization potentials and electron affinities of amorphous Cd-In-Ga-O
キーワード：Amorphous oxide semiconductor, Band alignment, Ionization potential
Band alignment of semiconductor is one of the most significant parameters to design the semiconductor devices such as thin film transistor in flat panel displays, solar cells and laser diodes. When we fabricate semiconductor device, their device have to be designed based on the suitable band alignment, meaning that ionization potential (Ip) and electron affinity (χ) and band gap should be taking into account. Among various semiconductors, we are going to focus on the amorphous oxide semiconductors (AOSs) which have several advantages such as high carrier mobility compare with amorphous Si, low processing temperature, wide range tunability of their physical properties by varying their compositions, and etc.
In this study, we fabricate amorphous Cd-In-Ga-O films to demonstrate the tunability of Ip and χ, independently. The films were fabricated by radio frequency magnetron sputtering system connected with ultraviolet photoelectron spectroscopy (UPS) vacuum chamber: Ip can be measured by UPS without exposing samples to atmospheric contamination. Mixed powders of CdO, In2O3 and Ga2O3 were employed as sputtering targets. Electrical properties such as carrier type, carrier concentration (N), and electron mobility (μ) were evaluated by Hall measurement using the van der Pauw method.
Ip and χ are energy difference from the vacuum level to the valence band maximum (VBM) and the conduction band minimum (CBM), respectively. Ip values were increased by increasing Cd concentration. On the other hand, χ values were changed by tuning In:Ga ration but keeping Cd concentration. As a result, the energy positions of the VBMs and CBMs of amorphous Cd-In-Ga-O system, which are Ip and χ, respectively, could be independently controlled by tuning Cd:In:Ga ratios. Carrier concentrations of amorphous Cd-In-Ga-O films were decreased from ~1020 to ~1016 cm-3 by increasing Ga concentration because Ga could suppresses generation of oxygen vacancy, which might origin of carriers in this system.
In this study, we fabricate amorphous Cd-In-Ga-O films to demonstrate the tunability of Ip and χ, independently. The films were fabricated by radio frequency magnetron sputtering system connected with ultraviolet photoelectron spectroscopy (UPS) vacuum chamber: Ip can be measured by UPS without exposing samples to atmospheric contamination. Mixed powders of CdO, In2O3 and Ga2O3 were employed as sputtering targets. Electrical properties such as carrier type, carrier concentration (N), and electron mobility (μ) were evaluated by Hall measurement using the van der Pauw method.
Ip and χ are energy difference from the vacuum level to the valence band maximum (VBM) and the conduction band minimum (CBM), respectively. Ip values were increased by increasing Cd concentration. On the other hand, χ values were changed by tuning In:Ga ration but keeping Cd concentration. As a result, the energy positions of the VBMs and CBMs of amorphous Cd-In-Ga-O system, which are Ip and χ, respectively, could be independently controlled by tuning Cd:In:Ga ratios. Carrier concentrations of amorphous Cd-In-Ga-O films were decreased from ~1020 to ~1016 cm-3 by increasing Ga concentration because Ga could suppresses generation of oxygen vacancy, which might origin of carriers in this system.