Creation and Mechanisms of Two-dimensional Electron Gas in Metal Oxide Based Heterostructures by Atomic Layer Deposition

Abstract ?????? ????????? ???????????? ?????? ?????? ?????? ????????? ??????????????? 2?????? ???????????? ?????? ??? ??????????????? ?????? ?????? Yuhang Liu Dept. of Materials Science and Chemical Engineering The Graduate School, Hanyang University ????????? ????????? ???????????? ?????? ?????? ????????? ?????? ??????????????? AlGaAs/GaAs, Ge/SiGe ??? LaAlO3/SrTiO3 AlGaAs/GaAs, Ge/SiGe ??? LaAlO3/SrTiO3 ??? ????????? ?????? ?????? ???????????? ???????????? 2????????? ????????? ?????? ???????????????. ??? ?????? ?????? ?????? ????????? Field-Effect Transistor (FETs)??? ?????? ???????????? ????????? FETs ??? ????????? ????????? ?????? ??????????????? ??? ???????????? ????????? ??????. ??? ????????? ????????? ?????? ??????(ALD)??? ????????? ?????????????????? ?????? ?????? ???????????? ???????????? ????????? ?????? ??????(2DEG)??? ?????? ????????? ?????????. ALD ????????? ?????? ????????? Al2O3/TiO2 ?????? ?????? ????????? Epitaxial ???????????? ???????????? LaAlO3/SrTiO3 ?????? ?????? ????????? ????????? ????????? ????????? ????????? ???????????????. Al2O3/TiO2 ??????????????? 2DEG ?????? ?????? ????????? ?????? ???????????? Al2O3??? ALD ????????? ???????????? TiO2 ?????? ????????? ?????? ????????? 2DEG ????????? ????????? ????????? ???????????? ????????? ???????????????, ???????????? ????????? ?????? ???????????? ?????? ?????? ????????? ?????????????????? ??? carrier density??? ????????? ?????? ?????? ??? ??? ?????????. ????????? Al2O3/TiO2 ???????????? ????????? ???????????? ??? FETs??? ???????????? ????????? ????????? ????????? ?????? ????????? ?????? ????????? ?????? FETs ?????? On current, on/off ????????? ??? sub-threshold swing(SS)??? ?????? ????????? ????????? ????????? ???????????? ???????????????. ZnO ????????? ?????? ???????????? ??????(Al2O3/ZnO, HfO2/ZnO ??? ZnS/ZnO)????????? 2DEG ????????? ????????? ???????????? ???????????????. ZnO ?????? ???????????? ??????????????? 2DEG ???????????? ????????? ?????? photoluminescence spectroscopy (PL) ??? X-ray photoelectron spectroscopy (XPS) ????????? ?????????????????? Al2O3/ZnO ???????????? ????????? ?????? ????????? ???????????? oxygen vacancy??? electron donor ????????? ???????????? 2DEG??? ???????????? ???????????????. ZnS/ZnO ???????????? ????????? ?????? ?????? SiO2 ????????? ????????? ????????? ???????????? ?????? ?????????, ?????? Carrier density??? ?????? 2DEG??? ????????? ??? ??????. ??? ????????? ????????? ?????? ????????? ?????? ????????? ???????????? ?????? 2DEG ?????? ?????? ????????? ????????? ?????? ????????? ???????????? ????????? ???????????? ??????????????? ??????.Abstract Creation and Mechanisms of Two-dimensional Electron Gas in Metal Oxide Based Heterostructures by Atomic Layer Deposition Yuhang Liu Dept. of Materials Science and Chemical Engineering The Graduate School, Hanyang University In the early research, semiconductor heterostructures have been studied in a broad range of two-dimensional phenomena, such as AlGaAs/GaAs, Ge/SiGe and LaAlO3/SrTiO3. These heterostructures are bricks of field-effect transistors (FETs), and they have a great impact in FETs and other electronic applications. In this thesis, two-dimensional electron gas (2DEG) has been studied in metal oxide based heterostructures via atomic layer deposition film growth technique. The electrical properties of Al2O3/TiO2 heterostructures are comparable with those of LaAlO3/SrTiO3 heterostructure. The origin of 2DEG in Al2O3/TiO2 heterostructure has been studied, and it turns out that oxygen vacancy is the key to create 2DEG, which is formed during Al2O3 top-layer ALD deposition. It has also found that the thickness of TiO2 layers have an immense impact on the 2DEG formation, in other words, the crystallinity of TiO2 layers influences the carrier density and activation energy of oxygen vacancy. In addition, FETs have been fabricated using Al2O3/TiO2 heterostructure exhibiting high on/off current ratio and low sub-threshold swing, which outperform the oxide heterostructure-based FETs. Realization of 2DEG at the interfaces in ZnO-based heterostructures is demonstrated, i.e. Al2O3/ZnO, HfO2/ZnO and ZnS/ZnO heterostructures. Mechanism of 2DEG at the interface of ZnO-based bilayers has been studied by photoluminescence spectroscopy in conjunction with XPS analysis. By taking Al2O3/ZnO bilayer as an example, it revealed that oxygen vacancy plays a pivotal role by acting as electron donor at the interface of heterostructure. ZnS/ZnO heterostructure is investigated on thermal epitaxial SiO2 substrate. The low sheet resistance and high carrier density are obtained at room temperature. The ultra-thin bilayers make use of precise deposition method of ALD at low temperature, allowing technology integration in traditional semiconductor industry, and the results manifest new possibilities for electronic devices based on metal oxide heterostructures.Docto