Band Offset Values Research Articles

How is graphene influencing the electronic properties of NiO–TiO2 heterojunction?

Abstract We synthesized a new nanocomposite bearing nitrogen-doped graphene as a carbon additive to the nickel oxide nanoparticles-titanium dioxide nanotubes heterojunction. The main purpose was the comparison of its structural and electronic properties, hence potential applications, with its undoped, reduced graphene oxide (GO) homolog. The beneficial effect of graphene on TiO2 heterojunctions is an accepted fact in the materials science field, mainly in favor of the nitrogen-doped one. Our data show that both graphenes have little influence on the band offset values of the NiO–TiO2 heterojunction. Still, the presence of reduced, undoped GO allows an improved electron transfer process from titania, causing a better charge carriers’ separation. This correlates well with their observed photocatalytic activity under visible light exposure, for the degradation of four emerging contaminant pollutants (amoxicillin, acetaminophen, ibuprofen, and β-estradiol). In addition, the band alignment of the NiO–TiO2 heterojunction with graphenes, and the corrected thermodynamic potentials of the organic pollutants explain well the observed photocatalytic behavior.

Microwave-Assisted Synthesis of CdS-MOF MIL-101 (Fe) Composite: Characterization and Photocatalytic Performance.

The present study outlines the synthesis of cadmium sulfide-metal-organic framework (CdS-MOF) MIL-101 (Fe) heterojunctions achieved via fast microwave-assisted reactions. Thus, different CdS-MOF MIL-101 (Fe) ratios were prepared to study their effectiveness as photocatalysts. These compounds were employed in the photocatalytic degradation of methylene blue (MB) under UV and visible irradiation. Structural, morphological, textural, compositional, and optical properties of the synthesized compounds determined by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), UV-vis spectroscopy, Raman spectroscopy, and Fourier transform infrared (FTIR) spectroscopy were utilized to characterize the structural, morphological, textural, compositional, and optical properties. Electrochemical impedance spectroscopy (EIS) was also employed to determine photovoltage and photocurrent densities. The resulting valence band offset (Vfb) and band gap energy values were utilized to construct an energy band scheme. Our research revealed that the CdS-MOF MIL-101 (Fe) heterojunction enhances the efficiency of electron-hole pair separation, thereby mitigating charge carrier recombination effects. Moreover, the type I electronic band structure established an efficient reaction mechanism, effectively suppressing the recombination of photogenerated electron-hole pairs. The photocatalytic system demonstrated exceptional behavior, achieving complete MB removal within 30 min of reaction time and exhibiting outstanding stability and reusability after four reaction cycles. These findings highlight the potential of the synthesized compounds in the field of wastewater treatment for organic pollutants, offering a promising alternative to current environmental issues.

WSe2/n-GaN and WSe2/p-GaN heterojunction band alignment

Abstract In this work, we measured the band alignment of 2D/3D heterostructures of WSe2 on n-doped, pdoped, and intrinsic GaN by X-ray photoelectron spectroscopy (XPS). The WSe2/n-GaN heterojunction exhibits type-II band alignment, with measured valence band offset (VBO) and conduction band offset (CBO) values of 2.28±0.15 eV and 0.96±0.15 eV, respectively. On the other hand, the WSe2/p-GaN heterojunction shows type-I band alignment, with measured VBO and CBO values of 0.1±0.15 eV and 1.22±0.15 eV, respectively. The results show that doping has a significant effect on the arrangement of the energy bands of the heterostructure, and provides a reference for device applications based on heterojunctions.

Structural and interface band alignment properties of transparent p-type α-GaCrO3:Ni/α-Al2O3 heterojunction

Herein, we report epitaxial growth of p-type Ni doped gallium chromium oxide thin film on Al2O3 substrates and studied its band alignment properties with that of the substrate. Thin films are grown using the magnetron-sputtering technique. Synchrotron-based XRD measurements, performed in the coplanar and non-coplanar geometries, confirm high-quality single domain epitaxial growth of p-type α-GaCrO3:Ni. Pendellosung oscillations around the Bragg peak and transmission electron microscopy reveal the high interfacial quality of p-type α-GaCrO3:Ni films with the substrate. Thin film, thickness ∼200 nm, shows around 70% average transmission. The values of valence band and conduction band offsets are determined to be 2.79 ± 0.2 and 0.51 ± 0.2 eV, respectively, which confirm straddling gap band alignment at the heterojunction. This type of alignment creates a threshold barrier for the selective charge carriers and is useful in enhancing the performance of a wide range of devices, including UV photodetectors, metal oxide semiconductor high electron mobility transistors, and light emitters.

Analysis of Carrier Transport at Zn1-xSnxOy/Absorber Interface in Sb2(S,Se)3 Solar Cells.

This work explores the effect of a Zn1-xSnxOy (ZTO) layer as a potential replacement for CdS in Sb2(S,Se)3 devices. Through the use of Afors-het software v2.5, it was determined that the ZTO/Sb2(S,Se)3 interface exhibits a lower conduction band offset (CBO) value of 0.34 eV compared to the CdS/Sb2(S,Se)3 interface. Lower photo-generated carrier recombination can be obtained at the interface of the ZTO/Sb2(S,Se)3 heterojunction. In addition, the valence band offset (VBO) value at the ZTO/Sb2(S,Se)3 interface increases to 1.55 eV. The ZTO layer increases the efficiency of the device from 7.56% to 11.45%. To further investigate the beneficial effect of the ZTO layer on the efficiency of the device, this goal has been achieved by five methods: changing the S content of the absorber, changing the thickness of the absorber, changing the carrier concentration of ZTO, using various Sn/(Zn+Sn) ratios in ZTO, and altering the thickness of the ZTO layer. When the S content in Sb2(S,Se)3 is around 60% and the carrier concentration is about 1018 cm-3, the efficiency is optimal. The optimal thickness of the Sb2(S,Se)3 absorber layer is 260 nm. A ZTO/Sb2(S,Se)3 interface with a Sn/(Zn+Sn) ratio of 0.18 exhibits a better CBO value. It is also found that a ZTO thickness of 20 nm is needed for the best efficiency.

Accurate band alignment of sputtered Sc2O3 on GaN for high electron mobility transistor applications

Sc2O3 is a promising gate dielectric for surface passivation in GaN-based devices. However, the interface quality and band alignment of sputtered Sc2O3 on GaN has not been fully explored. In this work, x-ray photoelectron spectroscopy (XPS) and variable angle spectroscopic ellipsometry were performed to extract the discontinuities in the valence and conduction bands of the Sc2O3/GaN system. Sc2O3 films were deposited on GaN using radio frequency sputtering. The valence band offset of Sc2O3/GaN was determined to be 0.76 ± 0.1 eV using Kraut’s method. The Sc2O3 band gap of 6.03 ± 0.25 eV was measured using O 1s energy loss spectroscopy. The electron affinity measurements of GaN and Sc2O3 using XPS secondary electron cut-off spectra provided an additional degree of accuracy to the derived band line-up for the Sc2O3/GaN interface. The band alignment results were compared with literature values of band offsets determined experimentally and theoretically for differently grown Sc2O3 films on GaN.

Investigation of crystalline and band alignment properties of NiO/GaN and Ni0.5Co0.5O/GaN heterojunctions using synchrotron radiation based techniques

Epitaxial layers of NiO and Ni0.5Co0.5O have been deposited on GaN templates using RF magnetron sputtering deposition technique. The epitaxial relationship in out-of-plane and in-plane directions for NiO and Ni0.5Co0.5O layers with respect to GaN is [111]NiO(Ni0.5Co0.5O)∥[0001]GaN and [1̅10]NiO(Ni0.5Co0.5O)∥[1̅21̅0]GaN, respectively. The epi-layers are found to have two triangular domain structures oriented along [111] direction with an in-plane rotation of 60° with respect to each other. Photoelectron spectroscopy (PES) has been used to determine the valence band offset (∆EV) and the band alignment at the heterojunctions (HJs). The ∆EV at NiO/GaN and Ni0.5Co0.5O/GaN HJs are 1.2 ± 0.2 eV and 1.8 ± 0.2 eV, respectively. The conduction band offsets (∆EC) have also been estimated using the determined values of optical band gap (NiO: Eg = ∼ 3.5 eV; Ni0.5Co0.5O: Eg = ∼ 3.3 eV) from optical transmission measurements. The values of ∆EC are found to be 1.5 ± 0.2 eV and 1.9 ± 0.2 eV at NiO/GaN and Ni0.5Co0.5O/GaN HJs, respectively. A type-II band alignment is observed at both the HJs. Higher values of valence band and conduction band offsets are observed at Ni0.5Co0.5O/GaN HJ in comparison to NiO/GaN. These experimentally determined values of band offsets can be used to design wide band gap HJ based devices like photodetectors, where higher values of band off-set at the Ni0.5Co0.5O/GaN HJ can be utilized to confine the carriers.

Band-offsets scaling of low-index Ge/native-oxide heterostructures

We investigate, through XPS and AFM, the pseudo layer-by-layer growth of Ge native oxide across Ge(001), (110) and (111) surfaces in ambient environment. More significantly, our study reveals a universal set of valence and conduction band offset (VBO and CBO) values observed for Ge(001), Ge(110), and Ge(111) surfaces as a function of Ge-oxide concentration. We find that the band offsets appear to be the same across these low-index Ge surfaces i.e., for Ge-oxide/Ge heterostructures with the same Ge-oxide overlayer concentration or thickness. In contrast, different oxidation rates for Ge(001), Ge(110), and Ge(111) surfaces were observed, where the oxidation rate is fastest for Ge(001), compared to Ge(110) and Ge(111). This can be attributed to the different number of unsatisfied Ge dangling bonds (2 vs 1) associated to the respective ideal Ge surface in forming Ge-oxide. Thus, at any given oxidation time, the oxide concentration or thickness for each type of low index Ge surface will be different. This in turn will lead to different band offset value observed for each type of Ge surface. More significantly, we show that while oxidation rates can differ from different Ge surface-types, the band offset values can be estimated simply based on the Ge-oxide concentration regardless of Ge surface type.

Correlation between defect properties and the performance of eco-friendly CsSnI3-based perovskite solar cells

This study investigates the potential use of eco-friendly, all-inorganic cesium tin iodide (CsSnI3) perovskite (PVK) as an absorber layer. Despite having higher temperature stability of CsSnI3, the challenge is to get a uniform and defect-free film that hinders the performance. To accomplish this goal, we investigated several performance-related variables for perovskite solar cells (PSCs), including material defect density (Nt ), transport materials, layer thickness, temperature impacts, and back contact work functions. Negative valence band or conduction band offset values indicate no barrier preventing photogenerated carriers from flowing into the charge transport layers. The simulation result shows that hole transport layer thickness shows a higher impact than electron transport layer thickness. For the PVK thickness of 500 nm and a carrier density of 1018 cm−3, the device offers an optimum power conversion efficiency of 20.1%. The performance is more significantly affected by the defects in the PVK material compared to the defects present at the interface. Higher recombination (Re−h+) occurs at the TiO2–CsSnI3 interface. Defects located within the deep-level trap positioned at the mid-point of the band gap energy (E g) have a negative impact on the performance. The temperature coefficient (C T) is approximately ‒0.367% K‒1, indicating excellent thermal stability in an open environment. The selection of ‘A’ cation, the addition of additives, or carefully controlled fabrication techniques can mitigate the defect. This research shows the strategy for creating defects-free PSC devices, ultimately enhancing performance and the stability.

Enhanced photodetection through a perovskite BaTiO3 dielectric in a Si-MoS2 heterojunction.

The present investigation deals with the effect of a BaTiO3 (BTO) dielectric layer on the performance of MoS2/p-Si heterojunction photodetectors. The MoS2/p-Si junction demonstrates a responsivity of ∼80 A W-1 and detectivity of ∼1012 Jones. The inclusion of a dielectric BTO layer significantly enhances the performance of MoS2/p-Si photodetectors, leading to a remarkable improvement with a very high responsivity of ∼603 A W-1 and detectivity of ∼1013 Jones. The I-V characteristics of the MoS2/p-Si and MoS2/BTO/p-Si junctions under illumination can be understood by considering their respective energy band diagrams. This addition alters the energy band alignment, leading to higher conduction band offset and valence band offset values. The large photocurrent in forward bias in the MoS2/BTO/p-Si junction may be attributed to the presence of photogenerated electrons in the depletion region of BTO. BTO exhibits characteristics such as a long carrier diffusion length and low recombination rates, contributing to a reduction in carrier recombination within the photodetector for which the photocurrent of the MoS2/BTO/p-Si heterojunction can be improved significantly. The enhanced performance of the MoS2/BTO/p-Si junction, characterized by higher responsivity and detectivity, underscores the potential of this heterojunction for advanced photodetection applications, suggesting promising avenues for further research and development in the field of photodetectors. A comparative study with the available literature reveals that the excellent responsivity of ∼603 A W-1 and detectivity of ∼1013 Jones of the presently studied MoS2/BTO/p-Si heterojunction appear highly promising for various futuristic device applications.

Energy Band Alignment at p–n Heterojunction Interface in CZTSSe Solar Cells with Novel ZnMgO Buffer Layer

By substituting Zn1−xMgxO (ZMO) for the conventional CdS buffer layer, the CZTSSe solar cells with the efficiency of 11.2% are obtained herein, which can be attributed to the conduction band regulation in the heterojunction. An appropriate conduction band offset (CBO) value can effectively reduce nonradiative recombination loss of charge carriers at the interface, thereby improving the open‐circuit voltage (Voc). Herein, ZMO buffer layer with the optical bandgap ranging from 3.34 to 3.90 eV is applied to enhance the CBO in the heterojunction from 0.14 to 0.72 eV. The ZMO‐buffered solar cells exhibit higher Voc and short‐current density (Jsc) compared to CdS‐buffered cells. The optimal efficiency of 11.2% is obtained in CZTSSe solar cell with the CBO of 0.27 eV, Jsc of 39.0 mA cm−2, fill factor of 69.6%, and Voc of 412 mV.

Simulation study of single solar cell structures based on the compositionally variable perovskite material CsSn(I1−xBrx)3 for tandem configured solar cells

This work involves simulating the performance of a single solar cell configured TiO2/CsSn(I1−xBrx)3/Cu2O, based on the lead-free, metallic CsSn(I1−xBrx)3 perovskite absorber, whose bandgap energy is tunable as a function of its bromine content. The simulation model used takes into account the variation of the physical parameters of the absorber as a function of its composition, represented by the ratio x, and also makes it possible to obtain the photovoltaic performance of the device studied as a function of x. The state of the front interface between the ETL electron-transport layer and the perovskite absorber was evaluated as a function of (x), by calculating the conduction bandgap offset and the misfit strain. Different electron transport layers were considered. The simulation results showed that the absorber composition influences all photovoltaic parameters, and that the choice of electron transport layer is important to achieve a compromise between device performance and the correct state of the front interface. The results indicate that CdZnS and CdS ETL materials correspond to bromine absorption ratios of x = 0 and x = 0.35 for which the conduction band offset values are − 0.03 eV and 0 eV respectively and the misfit strain 0.09 and 0.057, while ZnSe and ZnS correspond to ratios of x = 0.75 and x = 1 for which the conduction band offsets are 0 eV and 0.38 eV respectively and the strain 0.056 and 0.08. Based on these results, we determined the following optimal structures: CdZnS/CsSnI3/Cu2O and CdS/CsSn(I0.65Br0.35)3/Cu2O, which achieved yields of 18.1% and 18.5% respectively, as suitable for lower subcells with narrow bandgap energies, while the structures: ZnSe/CsSn(I0.25Br0.75)3/Cu2O and ZnS/CsSnBr3/Cu2O, which achieved efficiencies of 17.5% and 18% respectively, as top sub-cells with wide bandgap energies, in a tandem solar cell device. The aim is to develop highly efficient, non-toxic and stable single and tandem perovskite cells.

High‐Efficiency Cd‐Free CZTSSe Solar Cells with Organic Semiconductor PCBM as a Buffer Layer

Replacing the traditional CdS buffer layer with more environmentally friendly materials is an urgent issue for environment‐friendly CZTSSe solar cells. Herein, a nontoxic, flexible, and conductive organic molecular semiconductor PCBM to replace CdS is used and a Cd‐free CZTSSe solar cell is obtained. By introducing mild spin‐coated ZnO window layers, the damage of PCBM in conventional sputtering ZnO process is effectively avoided, and a higher efficiency than previously reported organic semiconductor buffer layer systems and comparable to CdS buffer layer devices are achieved. The flexible PCBM covers the surface of the CZTSSe absorber layer densely and forms a flatter film surface, which is beneficial for the following ZnO deposition. The CZTSSe/PCBM interface exhibits a typical “spike‐like” energy band alignment with a conduction band offset value of only 0.1 eV. Compared with CZTSSe/CdS interface, the CZTSSe/PCBM heterojunction possesses larger interfacial recombination resistance and a longer carrier lifetime. The ideal coating ability, suitable energy band alignment, as well as the better interface carriers transfer behavior suggest that the organic molecular semiconductors can be used instead of the CdS buffer layer to pave the way for truly environment‐friendly kesterite photovoltaic devices.

Improved performance of Cd-free CZTS thin-film solar cells by using CZTS0.4Se0.6 BSF layer

Cu2ZnSnS4 (CZTS) thin film solar cells (TFSCs) have received great attention from the solar cell industry for their environment, price, high absorption coefficient and great electronic properties. This work provides a strategy to prompt the photoelectric conversion efficiency (η) of CdS/CZTS-based TFSCs via introducing the back surface field (BSF) layer and wxAMPS to simulate the results. Meanwhile, the optimum ratio of sulfur to selenium in the BSF layer material CZTSSe has been also studied, and a new device structure has been constructed. Beneficial from the introduction of CZTSSe as a BSF layer, the interface recombination is suppressed and leads to an enhanced Voc. Subsequently, MoO3, ZnS, WO3, TiO2 and In2S3 as candidates to substitute for the toxic Cd buffer layer are investigated. The results demonstrate that In2S3/CZTSSe exhibits the best performance with 28.59 % and 0.99 V, ascribed to a superior spike-like value. It was found that the presence of a spike-like conduction band (CB) at the In2S3/CZTSSe interface and a more suitable conduction band offset (CBO) value could suppress the interfacial complexation. Therefore, In2S3 performs best as a buffer layer material. However, due to the cost of indium, this paper recommends the utilization of wide bandgap semiconductor materials MoO3 and ZnS, which also have good stability and conversion efficiencies that can reach 28.38% and 28.41%, respectively. The work of this paper provides important guidance for researchers to manufacture CZTS TFSCs.

Electronic, Thermodynamic Stability, and Band Alignment Behavior of the CoVSi/NaCl Heterojunction

We report the band discontinuity of the CoVSi/NaCl heterointerface. First principle calculations based on density functional theory using GGA, GGA + U, and GGA + mbJ approximations were applied to study the structural, electronic, and band alignment properties. Structural and thermodynamic stability studies indicate that this semiconductor - dielectric heterojunction can be synthesized experimentally in thermodynamic equilibrium conditions. The valence and conduction band offset values (VBO and CBO) were 0.74 and 3.02 eV, respectively. Also, the effective electron affinity parameter (χ e) for both CoVSi and NaCl were calculated as ∼1.51 and ∼0.769 eV, respectively, using Anderson’s law. The study of the electronic structure expresses the occurrence of half-metallic ferromagnetic behavior with a narrow band gap of about 0.09 eV. In this heterojunction, electrons and holes were confined to the CoVSi layers, and conduction band minimum and valence band minimum were replaced in the CoVSi layers. This restriction, applied to load carriers on one side of the interface, significantly increases the light-material interaction in light-emission programs. Therefore, this heterojunction can be recommended for light-emitting applications and thin atomic layer materials with quantum confinement of charge carriers.

Photoelectric characteristics of Al-doped ZnO/p-Si diode prepared by radio frequency magnetron sputtering

Al-doped ZnO (AZO) thin films were deposited on p-type silicon (p-Si) substrates by radio frequency magnetron sputtering technology. The crystal structure, morphology characterization and elemental analysis show that AZO film grows along the c-axis (002) orientation without other impurities. The current–voltage and current-time characteristics under different illumination conditions demonstrate that the Au/AZO/p-Si diode has typical rectification behavior, excellent stability and repeatability. The photocurrent is proportional to the intensity of ultraviolet (UV) irradiation, and the photocurrent reaches 110 μA at a bias voltage of 5 V under 11.75 mW cm−2 UV light irradiation. By calculating the conduction band and valence band offset values of AZO/p-Si heterojunction, the energy band diagrams at different bias states are constructed to explain the photoelectric response behavior. These results will be helpful for the design of high-performance photodiodes.

Natural band alignment of BAlN and BGaN alloys

The natural band alignment of BAlN and BGaN alloys was investigated using the atomic solid-state energy scale approach. The band edge positions relative to the vacuum level were determined for BAlN and BGaN alloys, and the band offset values for each heterostructure were estimated. The results suggest that the natural band alignment of BAlN and BGaN alloys behaves according to the common anion rule. Further, the Schottky barrier height (SBH) was calculated based on the results of band alignment for BAlN and BGaN alloys. The predicted SBH values are expected to be an important guideline for boron nitride and its related alloy device design.

Combining advanced photoelectron spectroscopy approaches to analyse deeply buried GaP(As)/Si(1 0 0) interfaces: Interfacial chemical states and complete band energy diagrams

The epitaxial growth of the polar GaP(100) on the nonpolar Si(100) substrate suffers from inevitable defects at the antiphase domain boundaries (APDs), resulting from mono-atomic steps on the Si(100) surface. Stabilization of Si(100) substrate surfaces with As is a promising technological step enabling the preparation of Si substrates with double atomic steps and reduced density of the APDs. In this paper, 4–50-nm-thick GaP epitaxial films were grown on As-terminated Si(100) substrates with different types of doping, miscuts, and As-surface termination by metalorganic vapor phase epitaxy (MOVPE). The GaP(As)/Si(100) heterostructures were investigated by X-ray photoelectron spectroscopy (XPS) combined with gas cluster ion beam (GCIB) sputtering and by hard X-ray photoelectron spectroscopy (HAXPES). We found residuals of As atoms in the GaP lattice (∼0.2–0.3 at.%) and a localization of As atoms at the GaP(As)/Si(100) interface (∼1 at.%). Deconvolution of core level peaks revealed interface core level shifts. In As core levels, chemical shifts between 0.5 and 0.8 eV were measured and identified by angle-resolved XPS measurements. Similar valence band offset (VBO) values of 0.6 eV were obtained, regardless of the doping type of Si substrate, Si substrate miscut or type of As-terminated Si substrate surface. The band alignment diagram of the GaP(As)/Si(1 0 0) heterostructure was deduced.

Investigation of a vertical 2D/3D semiconductor heterostructure based on GaSe and Ga2O3

Mixed-dimensional heterostructures are emerging to be very promising for future electronic and optoelectronic applications. Here, we report on the fabrication and characterization of a 2D/3D vertical van der Waals p–n heterojunction based on p-type gallium selenide (GaSe) and n-type gallium oxide (). Kelvin Probe Force Microscopic (KPFM) measurements have been conducted to estimate the difference in the surface potential values between GaSe and , which is further used to find out the conduction band offset value at the GaSe/ hetero-interface to design the band diagrams. The current–voltage measurements on the device display a diode-like behavior which is attributed to the type-II band alignment, present at the p–n junction interface as per the electron affinities and bandgap values of GaSe and . The device exhibits a high current rectification ratio of ∼2500 extracted at V. The photoresponse properties of the heterostructure are also studied and the figure of merit parameters of the photodetector such as photoresponsivity and specific detectivity have been evaluated for the fabricated device. Since the GaSe/ heterojunction holds a great potential in the field of efficient optoelectronic devices, we believe our study could pave the way to designing innovative optoelectronic devices by integrating low-dimensional materials with conventional 3D semiconducting materials.

Structural and electronic properties of HfO2 films on Si through H2O2 wet oxidation with improved thermal stability

The thermal stability and material properties of HfO2 thin films on Si substrates with and without H2O2 wet chemical oxidation were investigated. The HfO2 samples were deposited through plasma‐enhanced atomic layer deposition and subjected to thermal annealing. They were then examined using X‐ray diffraction, transmission electron microscopy, X‐ray photoelectron spectroscopy, reflection electron energy loss spectroscopy, and conductive atomic force microscopy. For the Si substrate without H2O2 wet chemical oxidation, a native oxide (~1.8 nm) was formed on the substrate before HfO2 deposition. After the annealing process at 600°C, the band gap (Eg) of the HfO2 films increased from 6.0 to 6.2 eV due to the diffusion of Si into HfO2. Furthermore, the conduction and valence band offsets (ΔEc and ΔEv, respectively) between HfO2 and Si changed from 1.02 to 1.42 and 3.86 to 3.66 eV, respectively. After the H2O2 wet oxidation of the Si substrate, a 1.5‐nm chemical oxide was formed instead of a native oxide. The band offset and Eg values of HfO2 were similar before and after 600°C annealing (ΔEv = 3.86 eV, ΔEc = 1.02 eV, and Eg = 6.0 eV), implying the high thermal stability of the HfO2 films. Accordingly, wet oxidation not only prevents diffusion from chemical oxide but also markedly improves the oxide leakage current, which is useful for developing highly efficient and thermally stable HfO2 gate oxides in Si‐based integrated circuit devices.