Atomic and electronic structures of amorphous Al2O3

Creation of a Short-Range Ordered Two-Dimensional Electron Gas Channel in Al2O3/In2O3 Interfaces

The tuning of electrical properties in oxides via surface and interfacial two-dimensional electron gas (2DEG) channels is of great interest, as they reveal the extraordinary transition from insulating or semiconducting characteristics to metallic conduction or superconductivity enabled by the ballistic transport of spatially confined electrons. However, realizing the practical aspects of this exotic phenomenon toward short-range ordered and air-stable 2DEG channels remains a great challenge. At the heterointerface formed after deposition of an Al₂O₃ layer on a nanocrystalline In₂O₃ layer, a dramatic improvement in carrier conduction equivalent to metallic conduction is obtained. A conductivity increase by a factor of 10¹³ times that in raw In₂O₃, a sheet resistance of 850 Ω/cm², and a room temperature Hall mobility of 20.5 cm² V^-1 s^-1 are obtained, which are impossible to achieve by tuning each layer individually. The physicochemical origin of metallic conduction is mainly ascribed to the 2D interfacially confined O-vacancies and semimetallic nanocrystalline InO_x (x < 2) phases by the clustered self-doping effect caused by O-extraction from In₂O₃ to the Al₂O₃ phase during ALD. Unlike other submetallic oxides, this 2D channel is air-stable by complete Al₂O₃ passivation and thereby promises applicability for implementation in devices.

Passivation mechanism of thermal atomic layer-deposited Al2O3 films on silicon at different annealing temperatures

Thermal atomic layer-deposited (ALD) aluminum oxide (Al2O3) acquires high negative fixed charge density (Qf) and sufficiently low interface trap density after annealing, which enables excellent surface passivation for crystalline silicon. Qf can be controlled by varying the annealing temperatures. In this study, the effect of the annealing temperature of thermal ALD Al2O3 films on p-type Czochralski silicon wafers was investigated. Corona charging measurements revealed that the Qf obtained at 300°C did not significantly affect passivation. The interface-trapping density markedly increased at high annealing temperature (>600°C) and degraded the surface passivation even at a high Qf. Negatively charged or neutral vacancies were found in the samples annealed at 300°C, 500°C, and 750°C using positron annihilation techniques. The Al defect density in the bulk film and the vacancy density near the SiOx/Si interface region decreased with increased temperature. Measurement results of Qf proved that the Al vacancy of the bulk film may not be related to Qf. The defect density in the SiOx region affected the chemical passivation, but other factors may dominantly influence chemical passivation at 750°C.