2D Electron Gas at the Interface of Atomic-Layer-Deposited Al2O3/TiO2 on SrTiO3 Single Crystal Substrate

The presence of 2D electron gas (2DEG) at the interface between an amorphous Al2O3 (a-AO) thin film and an anatase TiO2 (TO) thin film is demonstrated. The a-AO and TO thin films are prepared via atomic layer deposition on a SrTiO3 (STO) single crystal substrate. The reduction of the TO surface during the a-AO deposition produces oxygen vacancies, which are effective electron donors. The systematic analysis of the physical properties of the TO layer reveals that the crystallinity of the TO layer affects the conductivity, carrier concentration and the mobility of the 2DEG, and also the critical a-AO thickness, which is the minimum thickness for exhibiting the apparent conductivity. The 2DEG between the a-AO and the sufficiently thick TO layer exhibits an almost two-orders-of-magnitude-higher carrier concentration (approximate to 10(14) cm(-2)) than the previously reported 2DEG at a-AO/STO, while the mobility (approximate to 10 degrees cm(2) V-1 s(-1)) is relatively low. Also, angle-resolved X-ray photoelectron spectroscopy elucidates the spatial distribution and atomic ratio of the reduced Ti ions. Due to the increasing fraction of the anatase phase in the TO layer, the oxygen vacancies are prone to ionize, and the carriers are better confined to the interface, making them more 2DEG-like.