O-poor Conditions Research Articles

Molecular dynamics study of the effect of composition on elastic properties of silicon oxynitride films

Abstract Understanding mechanical properties of silicon oxynitride (a-SiON), a key insulating material, is vital for electronic device design and reliability. Though the effects of fabrication conditions on a-SiON have been studied, the underlying relationship between its atomic-scale structure and mechanical properties remains unclear. This study investigates the relationship between elasticity and atomic-scale structures in a-SiON by molecular dynamics simulations with a universal graph neural network interatomic potential. The bulk modulus increases from 49 to 140 GPa with higher N content. N atoms form N2 molecules under O-rich conditions, hindering bulk modulus increase, and form an Si3N4-like network under O-poor conditions, enhancing bulk modulus. Formation energy calculations indicate N2 formation is preferable under O-rich conditions. Meanwhile, under O-poor conditions, Si-N bond formation is preferable, which reinforces a-SiON by increasing bond density. The findings suggest realizing O-poor conditions is crucial for highly elastic insulating films.

First-principles study of oxygen vacancy defects in β-quartz SiO2/Si interfaces

Abstract Understanding the electronic structures of gate oxides in Si-based devices is significant for improving device performance. We investigate the electronic properties of the oxygen vacancy defects in β-quartz SiO2/Si interface structure using first-principles calculations. The results indicate that the constructed (SiO2)4/(Si)4 structure is an indirect-gap semiconductor, with its band edges contributed by Si side and a large band-edge energy difference ( > 1.780 eV). Our study reveals that the presence of oxygen vacancy defects reduces the band gap, and V O 1 is transformed from indirect into direct band gap. The Si dangling bonds in V O 1 cause charge localization around the O vacancy, while the formation of Si–Si bonds in V O 2 and V O 3 lead to electron delocalization. In the calculation of defect formation energies, we find that V O 1 maintains the lowest formation energy across different states, making it more likely to form and structurally stable. Compared to O-rich environments, the formation energy in O-poor environments is overall reduced by approximately 4.5 eV, indicating that oxygen vacancy defects are more likely to form and be controlled under O-poor conditions. Our study emphasizes the importance of interface structure and defect characteristics in semiconductor research, providing insights for the development of Si-based devices.

First-principles study of defects and doping limits in CaO

Calcium oxide (CaO) is a promising host for quantum defects because of its ultrawide bandgap and potential for long spin coherence times. Using hybrid functional calculations, we investigate the intrinsic point defects and how they limit Fermi-level positions and doping in CaO. We find calcium and oxygen vacancies to be the most common intrinsic defects, acting as compensating acceptors and donors, respectively. Oxygen interstitials are also prevailing under O-rich conditions and act as compensating donors. Due to compensation by these defects, O-poor conditions are required to dope CaO n-type, while O-rich conditions are required for p-type doping. We find that, at room temperature, intrinsic CaO can only achieve Fermi-level positions between 1.76 eV above the valence-band maximum (VBM) and 1.73 eV below the conduction-band minimum (CBM). If suitable shallow dopants are found, the allowed range of Fermi levels would increase to between VBM + 0.53 eV and CBM − 0.27 eV and is set by the compensating intrinsic defects. Additionally, we study hydrogen impurities, and show that hydrogen will not only limit p-type doping but can also act as shallow donor when substituting oxygen (HO defects).

Hydrogen passivation of acceptor defects in delafossite CuMO2 (M = Al, Ga, In): Insights for enhanced p-type conductivity

Transparent conducting oxides with p-type conductivity hold immense potential for various electronic applications. The role of native point defects in delafossite CuMO2 (M = Al, Ga, In) as the source of p-type conductivity has been widely acknowledged. However, understanding the primary defects governing the electrical properties and devising strategies for improvement remains a critical challenge. In this study, we employ range-separated hybrid density functional calculations to elucidate the impact of acceptor defects and their interactions with hydrogen on electrical conductivity. Our findings demonstrate that hydrogen plays a pivotal role in controlling p-type conductivity in these oxides. Our investigation reveals that the interactions between hydrogen interstitial Hi and copper vacancy VCu lead to the formation of stable complexes that are electrically inactive. Considerable binding energies are observed for Hi–VCu complexes, indicating that they are highly bound complexes with low formation energy and, thus, high concentrations under both O-rich and O-poor conditions. A second hydrogen can be bound to VCu to form 2Hi–VCu complexes, which are thermodynamically stable and function as a single donor. Furthermore, hydrogen can bind with the antisite acceptor defects, CuM, forming Hi–CuM complexes. However, the lower binding energies associated with these complexes suggest likely dissociation into isolated Hi and CuM at relatively low temperatures. By shedding light on the strong influence of hydrogen passivation of acceptor defects, this study offers valuable insights into p-type conductivity in delafossite CuMO2.

Exploration of the mechanical properties of carbon-incorporated amorphous silica using a universal neural network potential

C-incorporated amorphous silica (a-SiOC) is expected to be a significant dielectric film for miniaturized semiconductor devices. However, information on the relationship among its composition, atomic structures, and material properties remains insufficient. This study investigated the dependence of the elastic modulus on the C content in a-SiOC, employing a universal neural network interatomic potential to realize a high-accuracy and high-speed simulation of multicomponent systems. The relationship between elastic modulus and atomic network structures was explored by fabricating 480 amorphous structures through the melt-quenching method without predetermined structure assumptions. The bulk modulus increased from 45 to 60 GPa by incorporating 10% C atoms under O-poor conditions and 20% C atoms under O-rich conditions, respectively. This result is attributed to the formation of denser crosslinking atomic network structures. In particular, the C atoms bonded with the Si atoms with higher coordination under O-poor conditions, whereas they tend to bond with O atoms under O-rich conditions, breaking the SiO2 network. Large C clusters precipitated as the C fraction was increased under O-rich conditions. Gas molecules, such as CO and CO2, were also generated. These results are consistent with reported ab initio calculation results of the formation energies of C defects and gas molecules in SiO2. The findings suggest that realizing O-poor conditions during deposition is crucial for fabricating stronger dielectric films. Therefore, this work contributes to understanding the fabrication of stronger dielectric films and elucidating the underlying mechanism of C cluster formation.

First-principles investigates on the electronic structure and magnetic properties of V-, Cr-, Mn-doped two-dimensional Ga2O3

In this paper, the electronic and magnetic properties of transition metals (TM) doped two-dimensional (2D) Ga2O3 are investigated based on first-principles calculations. The formation energies under O-rich conditions are significantly lower than those under O-poor conditions, making it easier to synthesize the TM-doped 2D Ga2O3 systems under O-rich conditions. The introduction of V, Cr, and Mn has successfully introduced magnetism into 2D Ga2O3. The V3+, Cr3+, and Mn3+ ions are left with 2, 3, and 4 unpaired electrons occupying different d orbitals, further leading to magnetic moments of 2, 3, and 4 μB in the three doped systems, respectively. Biaxial strain can effectively manage the bandgap of the TM-doped Ga2O3 systems. This work proves that doping V, Cr, and Mn into 2D Ga2O3 is an effective way to broaden the application of 2D Ga2O3 in dilute magnetic semiconductor (DMS)-based devices.

Comparative study on structure and electronic properties of Al0.5Ga0.5N thin film and nanowire photocathode under surface oxidation

Oxidation will generate higher surface barriers and new surface states, resulting in declined electron escape probability and electron emission performance, which seriously affects surface activation effect of the photocathode. In order to explore the effects of oxidation on Al0.5Ga0.5N thin film photocathodes and nanowire photocathodes, we have analyzed structure and electronic properties of Al0.5Ga0.5N thin film and nanowire under oxidation. The results show that formation energies of Al0.5Ga0.5N film oxidation surface is negative in both O-rich and O-poor conditions under O adsorption, indicating that surface of Al0.5Ga0.5N film is easily oxidized. However, Al0.5Ga0.5N nanowires are easily oxidized only when O concentration is higher. The formation energies of oxygen substitution model are all positive, indicating that this form of oxide is not easy to form on the surface. The results of band structure and PDOS indicate that pristine Al0.5Ga0.5N film has abundant surface states near the Fermi level. After oxygen adsorption, Ga atoms form stable Ga–O bonds with O atoms and the surface states are weakened. For oxygen substitutional oxidation, compared to Al0.5Ga0.5N thin film, conduction band of Al0.5Ga0.5N nanowire splits to form more energy levels and CBM moves downward, forming an n-type surface, which is not conducive to photoelectric emission.

Bismuth and oxygen vacancies induce (2 × 1) reconstructions in bismuth oxyhalide (BiOX, X = Cl, Br, I) (0 0 1) surfaces

The bismuth oxyhalides (BiOX, X = Cl, Br, I) are constantly investigated due to their efficient catalytic properties. Here we extend the exploration of the (001) BiOX surfaces, considering different possible surface terminations and defects through a comprehensive ab-initio approach. First-principles thermodynamics are used to analyze the models’ stability. Results show that the Bi-terminated BiOX (1 × 1) surfaces are the most stable at Bi-rich and O-rich chemical potential conditions; At Bi-rich and O-poor conditions, the halogen-terminated BiOX (1 × 1) surfaces become stable. Furthermore, as the Bismuth chemical potential decreases, Bismuth and Oxygen vacancies stabilize the BiOX (2 × 1) surface reconstructions. The BiOX (2 × 1) reconstructions present arrays of ordered Bi and O vacancies along the [010] direction. The models’ electronic properties are computed by the projected density of states, Thersoff-Hamann scanning tunneling microscopy (THSTM) images, and electrostatic potential isosurfaces. The proposed BiOX (2 × 1) surfaces could facilitate nucleophilic attacks at the O surface atoms; consequently, it could be key to promote surface catalytic reactions, such as water splitting.

The cationic interstitials induced resistive switching: a case study on Mn-doped SnO2

This work has explored the possible defects in Mn-doped SnO2 and compared the effects of interstitial Mn and oxygen vacancies on the electronic structure of SnO2. Combining the DFT calculations and experimental measurements, we found that when the Mn-doped SnO2 is synthesised under Sn-rich or O-poor conditions, the defect pair of Mn substitution and interstitial rather than oxygen vacancy will be formed, which induces energy band across the Fermi level and significantly affects the electronic structure of SnO2. With the Mn interstitials, stable intrinsic multi-level resistive states and optical SET can be achieved in the Mn-doped SnO2 memristors. This result can provide guidance in the fabrications of defective metal oxides and promote the investigations on cationic interstitial triggered multi-level resistive switching and optoelectronic memristors.

The role of native point defects and donor impurities in the electrical properties of ZnSb2O4: a hybrid density-functional study.

The ceramic material zinc antimony oxide ZnSb2O4 has promising electrical and magnetic properties, making it suitable for various applications such as electrochemical and energy storage. However, the effects of point defects and impurities on its electrical properties have never been revealed. Here, we employ hybrid density-functional calculations to investigate the energetics and electronic properties of native point defects and donor impurities in ZnSb2O4. The energetically favorable configurations of native point defects under selected growth conditions (O-rich and O-poor) are identified based on the calculated formation energies. The study finds no shallow donor and shallow acceptor defects with low formation energies. Still, the oxygen vacancy (VO) has the lowest formation energy among the donor-type defects under O-rich and O-poor conditions. However, it acts as a very deep acceptor, making it unlikely to provide free electron carriers to the conduction band. Moreover, electron carriers are likely to be compensated by the formation of zinc vacancies (VZn) and the zinc substituted for antimony (ZnSb), which behave as dominant acceptors. Our analysis of the charge neutrality conditions estimates that the Fermi level of undoped ZnSb2O4 would be pinned in a range that is 2.60 eV to 3.12 eV above the VBM for O-rich to O-poor growth conditions, respectively, suggesting that this material is semi-insulating. The possibility of enhancing free electron carriers by doping with Al, Ga, In, and F impurities is also investigated. Our results, however, indicate that high n-type conductivity is hindered by self-compensation in which the impurities additionally act as electron killers. Our results suggest that other impurity candidates and approaches may need to be considered to efficiently dope this material into n-type. Overall, this work paves the way for point defect engineering in this class of ternary oxides.

Defect physics of intrinsic point defects in BiPO4 photocatalysts: a hybrid functional study.

In this work, the intrinsic point defect properties of bulk BiPO4 under different growth conditions are intensively investigated and explored using first-principles hybrid functional calculations. It is found that Bi vacancies and O vacancies are the primary native defects in BiPO4. Under O-poor conditions, BiPO4 acts as an intrinsic insulator because the O vacancy defects (donor) and the Bi vacancy defects (acceptor) compensate for each other. Under Bi-poor conditions, good p-type conductivity is observed in BiPO4, which affirms the observed p-type conductivity behavior in experiments. Bi vacancies in BiPO4 are very shallow, which make it an excellent acceptor and are mostly responsible for the p-type character. In addition, it is found that the primary Bi vacancy defects of BiPO4 hardly affect its electronic structure and optical absorption spectrum regardless of the charge states. In contrast, the neutral O vacancy defects in BiPO4 introduce an impurity energy level near the VBM and induce a new optical absorption peak at around 370 nm. Furthermore, the O vacancies should be favorable for enhancing the production and separation efficiencies of the photo-generated electrons and holes in BiPO4. While Bi vacancies easily provide p-type carriers, simultaneously, they could become the active sites for the photocatalytic reactions because of their dominant -3 charge state. Therefore, understanding the defect physics in BiPO4 photocatalysts is believed to be beneficial for more research in developing BiPO4 or BiPO4-based photocatalysts.

Insight into the Effect of Anionic–Anionic Co-Doping on BaTiO3 for Visible Light Photocatalytic Water Splitting: A First-Principles Hybrid Computational Study

In this research, we thoroughly studied the electronic properties and optical absorption characteristics with double-hole coupling of anions–anion combinations for designing effective photocatalysts for water redox using first-principles methods within the hybrid Heyd–Scuseria–Ernzerhof (HSE06) exchange–correlation formalisms. The findings reveal that the values of formation energy of both the anion mono- and co-doped configurations increase monotonically as the chemical potential of oxygen decreases. The N–N co-doped BaTiO3 exhibits a more favorable formation energy under an O-poor condition compared with other configurations, indicating that N and N pairs are more likely to be synthesized successfully. Interestingly, all the co-doping configurations give a band gap reduction with suitable position for oxygen production and hydrogen evolution. The obtained results demonstrate that all the co-doped systems constitute a promising candidate for photocatalytic water-splitting reactions. Furthermore, the enhanced ability of the anionic-anionic co-doped BaTiO3 to absorb visible light and the positions of band edges that closely match the oxidation-reduction potentials of water suggest that these configurations are viable photocatalysts for visible-light water splitting. Therefore, the wide-band gap semiconductor band structures can be tuned by double-hole doping through anionic combinations, and high-efficiency catalysts for water splitting using solar energy can be created as a result.

Opto-electronic properties of carbon doped NiO

Hybrid functional first principles calculations reveal the effects of substitutional carbon on electronic and optical properties in the anti-ferromagnetic configuration of NiO. Spin polarized projected density of states and unfolded band structures show electronic band edge modification and magnetic anisotropy due to carbon substituting both at nickel and oxygen sites; only carbon substituted at an oxygen site, however results in the emergence of inter-band gap impurity states. This is due in part to the steric differences between carbon substituting nickel vs oxygen as well as the difference in valence between carbon and oxygen. Carbon substituting nickel is more stable than substituting oxygen, with a lower formation energy both in O-rich and O-poor conditions. Charge density isosurface plots reveal that carbon substituting nickel does not result in any appreciable modification to the bonding profile around the substitution, while oxygen substitution results in the formation of covalent bonds between the carbon and the nearest nickel atoms. Substitutional carbon at either the nickel or oxygen site causes a red shift in all optical properties towards the visible light region. The anisotropy in the optical and electronic properties for both carbon substitution at nickel and oxygen sites implies that these properties may be tuned through carbon doping and oxygen growth control for transparent conducting oxide and optoelectronic device applications.

Role of vacancies in tuning the electronic and magnetic properties of BiCoO3

Effect of vacancies on structural, electronic and magnetic properties of BiCoO3 (BCO) have been studied using first principles calculations. Formation energy calculation suggest that VBi is stabilized in −2 charge state with no net change in magnetization and is likely to be formed spontaneously. VCo is stabilized in −1 state under O-poor conditions and exhibits various transition levels under O-rich conditions leads to a net magnetization. VO are formed readily under O-poor conditions with 0 and +2 charge state. Under O-rich conditions, VO(1) is stabilized in 0 and +1 states with a change in magnetization and leads to a net magnetization of 2 μ B (0.25 μB per formula unit), and VO(2) is stabilized as 0 and +2 charge states with no change in net magnetization. DOS shows that VBi leads to the formation of acceptor levels which may be responsible for p-type conduction, on the other hand, VO(2) leads to the formation of deep traps in BCO.

First-principles study of SrSnO<sub>3</sub> as transparent conductive oxide

As a wide band gap semiconductor with perovskite structure, SnSnO<sub>3</sub> is regarded as a promising candidate of transparent conductive oxides due to its superior properties like high transparency, non-toxicity and low price. In this work, the electronic structure of SrSnO<sub>3</sub> is obtained through first-principles calculations based on HSE06 hybrid functional. Especially, we investigate the defect formation energy and transition levels of the intrinsic and external defects in SrSnO<sub>3</sub>. The intrinsic defects including the anti-site defects (Sr<sub>Sn</sub> and Sn<sub>Sr</sub>), the vacancy defects (V<sub>Sr</sub>, V<sub>Sn</sub>, and V<sub>O</sub>), and the interstitial defects (Sr<sub>i</sub>, Sn<sub>i</sub> and O<sub>i</sub>) are considered while the external doping defects are taken into account, including the substitution of Li, Na, K, Al, Ga, In for Sr site, Al, Ga, In, P, As, Sb for Sn site, and N, P at O site. Subsequently, the suitable doping elements and the corresponding experimental preparation environments are pointed out. Furthermore, we discuss the mechanism of its conductance according to the energy positions of the band edges. Our calculation results demonstrate that SrSnO<sub>3</sub> is an indirect-type semiconductor with a fundamental band gap of 3.55 eV and an optical band gap of 4.10 eV and then has a good visible light transmittance. Its valence band maximum (VBM) comes from O-2p state while its conduction band minimum (CBM) mainly originates from Sn-5s state. In consistent with the delocalized Sn-5s state at CBM, the electron effective mass is light and isotropic, which is beneficial to n-type conductance. The n-type intrinsic defects Sn<sub>Sr</sub> and V<sub>o</sub> have lower defect formation energy than the p-type intrinsic defects under O-poor condition while the n-type and p-type defects with low defect formation energy are almost equal under O-rich condition. Moreover, the transition levels of Sn<sub>Sr</sub> and V<sub>O</sub> are both deep. Therefore, SrSnO<sub>3</sub> cannot have a good conductance without external doping. Our calculations also demonstrate that it is hard to produce an efficient p-type external doping due to the compensation effect by V<sub>O</sub>. On the other hand, substitution of As or Sb for Sn site can result in an effective n-type external doping due to their low defect formation energy and shallow transition levels. According to the low energy positions of VBM (–7.5 eV) and CBM (–4.0 eV) of SrSnO<sub>3</sub>, we explain the reason why it is easy to realize an n-type conductance but hard to produce a high-performance p-type conductance, which follows the doping rules for wide band gap semiconductors. Finally, Sb-doped SrSnO<sub>3</sub> is proposed as a promising candidate for n-type transparent conductive materials.

First-principles study of configurations, electronic and photocatalytic properties of carbon-doped anatase TiO2

C-Doping TiO2 could significantly enhance the photocatalytic activity, as found in experiments, but the mechanism behind is elusive. We systematically investigated the configurations, electronic and photocatalytic properties of C-doped anatase TiO2 by first-principles calculation. The results show that the structures for the C-anion (Ca) and C-cation (Cc) doped TiO2 could exist in different form, and the Ca and substitutional Cc doping are favored under O-poor and O-poor conditions, respectively. The calculated electric and optical properties demonstrate that the substitutional Cc doping play the vital role in narrowing the bandgap, responsible for enhanced visible-light absorption of the TiO2. Finally, the calculated band edges using the hybrid functional of Heyd, Scuseria and Ernzerhof (HSE) suggested that substitutional Cc doped TiO2 could exhibit the small band gap and appropriate band edges for visible-light photocatalytic water splitting. The findings could not only give new insights into atomistic origin of visible-light response and photocatalysis of the C-doped TiO2.

Effect of oxygen vacancies on the electronic structure and dielectric properties of SrAl2O4: A first-principles study

In this study, both the generalized gradient approximation (GGA) and the GGA-1/2 methods were applied to examine the effect of oxygen vacancies on the electronic and optical properties of bulk monoclinic SrAl2O4. Since the monoclinic structure of SrAl2O4 has two non-equivalent sites for oxygen atoms, we can distinguish between two kinds of oxygen vacancies (VO) in this material. These two kinds of VO are labeled VOI and VOII. Our results show that although these two types of vacancies have comparable formation energies, their electronic and optical properties are significantly different. The formation energy of the VO defect under Sr-rich, Al-rich, and O-poor conditions was less than 1 eV, which means that it could exist at high concentrations. Moreover, the results of density of states (DOS) analysis show that the oxygen vacancy had a deep donor defect featuring a fully occupied electronic level located deep in the band gap of SrAl2O4. This electronic level was located at Ev+2.9eV in case of VOI and at Ev+3.3eV in case of VOII. This defect induced a noticeable change in the spectrum of optical absorption of SrAl2O4. Our results show that the formation of oxygen vacancies can significantly enhance the UV absorption-related properties of this material.

Intrinsic point defects and charge carrier trapping in monolayer BiOX (X = I, Br, and Cl)

Two-dimensional (2D) layered bismuth oxyhalides, BiOX (X = I, Br, and Cl), have great potential in optoelectronics and photocatalysis applications. The intrinsic point defects are crucial for carrier conductivity and transport. However, the understanding for defect physics of 2D atomic-scale BiOX are still unclear. Herein, through the first-principles calculations, we investigate the formation of intrinsic point defects and their effect on charge carrier trapping in 2D monolayer BiOX. Under a O-poor condition, the donor defects, such as the Biad, BiX, VO, and VX, can form spontaneously and induce a high n-type conductivity. The VX shows a shallow transition level and has no defect states. In contrast, the Biad, BiX, and VO display deep transition levels and obvious localized defect states that are responsible for the charge carrier trapping. As O becomes richer, the concentration of acceptor defects increases. Nevertheless, the donor and the acceptor defects can strongly compensate each other, pinning the Fermi energy in the band gap. The dominant acceptor defects, such as the BrBi, OBr, and OCl, show the deep transition levels and serve as carrier traps due to the charge localized around the defect sites. Our work gives an insight into the defect physics of atomic-scale 2D BiOX and provides a guidance for their optoelectronics and photocatalysis applications.

Electronic structure and optical properties of Ge- and F-doped α-Ga2O3: First-principles investigations* *Project supported by the National Natural Science Foundation of China (Grant No. 51302215) and the Natural Science Basic Research Program of Shaanxi Province, China (Grant Nos. 2018JQ6084 and 2019JQ-860).

The prospect of α-Ga2O3 in optical and electrical devices application is fascinating. In order to obtain better performance, Ge and F elements with similar electronegativity and atomic size are selected as dopants. Based on density functional theory (DFT), we systematically research the electronic structure and optical properties of doped α-Ga2O3 by GGA+U calculation method. The results show that Ge atoms and F atoms are effective n-type dopants. For Ge-doped α-Ga2O3, it is probably obtained under O-poor conditions. However, for F-doped α-Ga2O3, it is probably obtained under O-rich conditions. The doping system of F element is more stable due to the lower formation energy. In this investigation, it is found that two kinds of doping can reduce the α-Ga2O3 band gap and improve the conductivity. What is more, it is observed that the absorption edge after doping has a blue shift and causes certain absorption effect on the visible region. Through the whole scale of comparison, Ge doping is more suitable for the application of transmittance materials, yet F doping is more appropriate for the application of deep ultraviolet devices. We expect that our research can provide guidance and reference for preparation of α-Ga2O3 thin films and photoelectric devices.

Tuning conduction mechanism via surface termination and point defects in n-type LaAlO3/SrTiO3 interfaces

Based on first-principles calculations, the electronic properties of n-type LaAlO3/SrTiO3 (LAO/STO) interfaces with LaO and AlO2 terminations were investigated. Thermodynamic analysis shows that the AlO2-terminated and LaO-terminated LaAlO3 surfaces are preferably formed under O-rich and O-poor conditions, respectively. We found that there are two polarization fields in heterostrucutres: one is the build-in polarization field induced by alternating LaO+1 and AlO2−1 layers and another is the strain-induced additional polarization field only existing in relaxed structures. The two polarization fields have a distinct influence on the electronic structures of interfaces. In this work, the influences of oxygen vacancies and cation defects at different sites on the conduction mechanism were analyzed in detail. The results indicate that point defects affect the electronic states of interfaces by two ways: providing or accepting electrons, and disturbing the internal polarization field. Approaching the interface, the defects tend to play the former role. Moreover, the calculations show that under O-rich condition, the reduced oxygen vacancies and the improved cation vacancies spontaneously formed at the interface deteriorate the n-type conductivity. The present results provide a theoretical guidance to utilize the effects of surface termination and point defects to tune the conductivity of perovskite heterostructures.