The origin of negative charging in amorphous Al₂O₃ films: the role of native defects

Abstract

Amorphous aluminum oxide Al 2 O 3 (a-Al 2 O 3 ) layers grown by various deposition techniques contain a significant density of negative charges. In spite of several experimental and theoretical studies, the origin of these charges still remains unclear. We report the results of extensive Density Functional Theory (DFT) calculations of native defects -O and Al vacancies and interstitials, as well as H interstitial centers -in different charge states in both crystalline α-Al 2 O 3 and in a-Al 2 O 3 . The results demonstrate that both the charging process and the energy distribution of traps responsible for negative charging of a-Al 2 O 3 films [M. B. Zahid et al., IEEE Trans. Electron Devices 57, 2907 (2010)] can be understood assuming that the negatively charged O i and V Al defects are nearly compensated by the positively charged H i , V O and Al i defects in as prepared samples. Following electron injection, the states of Al i , V O or H i in the band gap become occupied by electrons and sample becomes negatively charged. The optical excitation energies from these states into the oxide conduction band agree with the results of exhaustive photo-depopulation spectroscopy (EPDS) measurements [M. B. Zahid et al., IEEE Trans. Electron Devices 57, 2907 (2010)]. This new understanding of the origin of negative charging of a-Al 2 O 3 films is important for further development of nanoelectronic devices and solar cells.

Hybrid‐Functional Study of Native Point Defects and Ti/Fe Impurities in α‐Al2O3

“…It has been reported that the dominant native point defects in α-Al 2 O 3 are vacancy and interstitial defects. [14,18,30,35] Here, we revisit all dominant native defects to investigate their effect on the electrical and optical properties of α-Al 2 O 3 . i defect is a multicharged deep acceptor defect with two defect transition levels at ε(0/À1) ¼ 2.99 eV and ε(À1/À2) ¼ 4.30 eV, whereas O split i defect acts as a double donor defect with two defect transition levels at ε(þ2/þ1) ¼ 0.35 eV and ε(þ1/0) ¼ 1.44 eV.…”

“…[12,13] Although several theoretical works have been carried out to study the effect of native point defects on the electronic property of Al 2 O 3 , they have not yet related them to describe the color in blue sapphire. [14][15][16][17][18][19][20][21][22] Based on the absorption spectroscopy analysis, it is concluded that there are two possible mechanisms, which is responsible for the blue coloring in sapphire: 1) the intervalence charge transfer (IVCT) of Ti-Fe pairs and 2) the transitions of intra-atomic d-d electrons in metal impurities. [12,23] Recently, Bristow et al performed the calculations using analytical force fields to study the Ti and Fe impurities in α-Al 2 O 3 and revealed that the IVCT mechanism between the Fe III -Ti III pairs is the lowest energy configuration and indeed the cause of blue coloring in sapphire.…”

“…Nowadays, the first-principles density functional calculations within the framework of hybrid functional are widely accepted to provide more accurate results than traditional local density approximation (LDA)/generalized gradient approximation (GGA) or LDA/GGA þ U. [26][27][28][29] Although several theoretical works based on DFT with hybrid functional have been carried to investigate the native point defects in α-Al 2 O 3 , [14,18,30] there is no relation between the defect and its optical property, which can help understanding the coloring of corundum at atomic scale. Therefore, we believe that the calculations with more accurate hybrid functional can help identify the actual ground-state configuration responsible for the blue coloring in sapphire.…”

Wet Chemical Oxidation to Improve Interfacial Properties of Al2O3/Si and Interface Analysis of Al2O3/SiOx/Si Structure Using Surface Carrier Lifetime Simulation and Capacitance–Voltage Measurement

“…The surface passivation of crystalline silicon (c-Si) solar cells can be improved using various materials such as SiO 2 [1][2][3][4][5][6], SiN x [7][8][9], Al 2 O 3 [10][11][12][13], TiO x [14][15][16], MoO x [17,18], and poly-Si [19][20][21][22]. In particular, Al 2 O 3 thin films are most widely used for boron-doped Si surfaces (or p + emitter surfaces) owing to the low surface recombination velocity (SRV) [10,11].…”

Edge-Etched Al2O3 Dielectric as Charge Storage Region in a Coupled MIS Tunnel Diode Sensor

“…Besides, a high density of these traps also introduces a pathway for leakage current [14]. The Al2O3 can be negatively charged by electron injection which causes the states of Ali or VO in the band gap to be occupied by electrons [15]. Hole trapping phenomenon is also observed in Al2O3 as a source of positive charging [16], [17].…”