Plasma-enhanced Atomic Layer Deposition Research Articles

Plasma enhanced atomic layer deposition of crystallized gallium phosphide on Si with tri-Ethylgallium and tri-tert-Butylphosphine

25 ∼ 30 nm thick polycrystalline gallium phosphide (GaP) films with high P / Ga atomic ratios were deposited on Si (100) using a plasma enhanced atomic layer deposition (PE-ALD) process with triethyl gallium (TEG), tri-tertiary butyl phosphide (tri-TBP), and atomic hydrogen. The key is chemical functionalization of the Si (100) surface since the wet-cleaned Si surface is nearly inert to TEG and tri-TBP. In-situ Auger spectroscopy was employed to identify the most successful functionalization which employed a gas phase mixture of atomic hydrogen and tri-TBP consistent with formation of a surface phosphide layer on Si(100); this layer efficiently nucleated the PE-ALD of GaP. The crystallinity and surface roughness of GaP films were tuned by controlling the pulse length of atomic H plasma, showing the self-limiting ALD film growth with 2.7 Å/cycle. The optimal crystallized GaP thin film on 6°-miscut Si showed local epitaxy growth of homogeneous GaP epi-layers in transmission electron microscopy (TEM).

Influence of Rapid Thermal Annealing on the Characteristics of Sn-Doped Ga2O3 Films Fabricated Using Plasma-Enhanced Atomic Layer Deposition

In this work, Sn-doped Ga2O3 films fabricated using plasma-enhanced atomic layer deposition were treated by rapid thermal annealing (RTA). The RTA influence on the chemical state, surface morphology, energy band alignment, and electrical properties of Sn-doped Ga2O3 films were thoroughly investigated. The results of X-ray photoelectron spectroscopy (XPS) demonstrated that Sn atoms were successfully doped into these films. Moreover, energy band alignments were obtained by the energy-loss peak of the O 1s spectrum and valence band spectra and thoroughly discussed. X-ray reflectivity (XRR) and atomic force microscope (AFM) measurements indicated that the Sn-doping level affects the interfacial microstructure and surface morphology. As the Sn content increases, the film thickness decreases while the roughness increases. Finally, the leakage current-voltage (I-V) characteristics proved that the Sn-doped Ga2O3 films have a large breakdown field. In I-V tests, all metal oxide semiconductor (MOS) capacitors exhibited a hard breakdown. This research demonstrates a method for manufacturing high-performance optoelectronic devices with desired properties.

Exploration of Chemical Composition of In–Ga–Zn–O System via PEALD Technique for Optimal Physical and Electrical Properties

AbstractIn–Ga–Zn–O (IGZO) material has been researched due to its favorable electrical characteristics for application in thin‐film transistor (TFT) applications such as low off current and relatively high mobility. However, most recently, as the developing and expanding application fields, conventional IGZO is a challenging aspect because higher mobility and excellent step‐coverage are required to be applied to high‐resolution displays and 3D NAND. In this regard, atomic layer deposition (ALD) is suggested as a novel deposition method for tackling issues. Here, this work systematically synthesizes IGZO films with various compositions by the supercycle technique of plasma‐enhanced ALD (PEALD) to determine the optimum metal cation composition range of the IGZO system for high‐mobility TFTs. The trends in the metal composition dependent electrical properties of ALD processed IGZO films are comparable to the previously reported results, while the structural properties are exclusive. Since both microstructure and carrier concentration affect to device characteristics complexly, the optimal In–Ga–Zn region is newly demonstrated via PEALD (XIn: 0.56–0.63, XGa: 0.13–0.17, XZn: 0.17–0.34). In this region, the device exhibits a remarkably high µFE of 41.4–43.7 cm2 V−1 s−1, a low subthreshold swing (SS) of 0.24–0.25 V decade−1, an initial threshold voltage (Vth) of −0.9 to −1.0 V, and a slight Vth shift (0.01 V) under the positive bias temperature stability (PBTS).

Improving the Stability of Polymer Electrolyte Membrane Fuel Cells via Atomic Layer-Deposited Cerium Oxide

In this study, to enhance the stability of the cathode platinum (Pt) catalyst in polymer electrolyte membrane fuel cells, cerium oxide (CeOx) was deposited by plasma-enhanced atomic layer deposition (PEALD) process on the Pt catalyst sputtered on the cathode. A change in the peak power density loss after an accelerated stress test (AST) during I-V measurement of the membrane-electrode assembly according to the number of cycles was observed, which confirmed stability improvement. In polymer electrode membrane fuel cells (PEMFCs), free radicals lead to degradation of the performance and stability of catalysts; we used CeOx to prevent these problems. CeOx acts as a free radical scavenger through the redox reaction of Ce3+/4+ ions in the cell test and prevents oxidative hydroxyl and hydroperoxyl radical attack created in the reaction between hydrogen peroxide and released cations. By preventing oxidation, the stability was improved without decreasing the performance. Therefore, the improvement of stability through plasma-enhanced atomic layer deposition CeOx encapsulation can be considered a promising strategy for PEMFC catalysts.

Interface-independent sound speed and thermal conductivity of atomic-layer-deposition-grown amorphous AlN/Al2O3 multilayers with varying oxygen composition

Dielectric amorphous multilayers (AMLs) play a critical role in a wide array of technologies such as optical coatings, nanoelectronics, energy harvesting, and recovery devices. However, despite their wide applications, a robust understanding of the effect of the interplay between chemical and structural disorder on the thermal properties of AMLs is still lacking. Therefore, in this paper, we experimentally and numerically investigate the effects of composition and interface density on the sound speed and thermal conductivity of a series of amorphous aluminum nitride and aluminum oxide multilayers grown via plasma-enhanced atomic layer deposition. To systematically change the composition, the oxygen content of the AMLs is proportionally varied with interface density during growth. We find that the longitudinal sound speed of these AMLs is dictated by the oxygen content instead of the number of interfaces. The thermal conductivity, in contrast, is dictated by both interface density and oxygen content. The interfaces act to decrease the thermal conductivity, whereas the oxygen content increases the thermal conductivity. Due to the competing influence of the interfaces and oxygen content, the thermal conductivity of the AMLs remains nearly constant as a function of interface density. Our study provides crucial insights into the effect of the interplay of composition and interfaces on the sound speed and thermal conductivity of AMLs.

InOx Doped SnO2 Nanostructure Deposited on MEMS Device by PE-ALD Process for Detection of NO2

The micro-electro-mechanical systems (MEMS) method makes the gas sensing element. The sensing layer uses RF Sputter and plasma-enhanced atomic layer deposition (PE-ALD) technology to deposit indium oxide (InOx) thin films on Tin oxide (SnO2) to form an n-n type double-layer structure. The results show that the response of SnO2-InOx and monolayer SnO2 is 153% and 55%, respectively, which is an improvement of 98% under exposure to 0.6 ppm NO2, and the sensor can obtain the best sensing at 200 °C (∼14 mW). In response, the lowest NO2 concentration was 0.2 ppm, and the selectivity test was carried out with four other gases, such as SO2, H2, CO, and NH3, and the test results showed the specificity for NO2.

Photovoltaics literature survey (No. 181)

Photovoltaics literature survey (No. 181)

Heterostructure Films of SiO2 and HfO2 for High-Power Laser Optics Prepared by Plasma-Enhanced Atomic Layer Deposition

Absorption losses and laser-induced damage threshold (LIDT) are considered to be the major constraints for development of optical coatings for high-power laser optics. Such coatings require paramount properties, such as low losses due to optical absorption, high mechanical stability, and enhanced damage resistance, to withstand high-intensity laser pulses. In this work, heterostructures were developed by sub-nanometer thin films of SiO2 and HfO2 using the plasma-enhanced atomic layer deposition (PEALD) technique. Thin-film characterization techniques, such as spectroscopic ellipsometry, spectrophotometry, substrate curvature measurements, X-ray reflectivity, and Fourier transform infrared spectroscopy, were employed for extracting optical constants, residual stress, layer formation, and functional groups present in the heterostructures, respectively. These heterostructures demonstrate tunable refractive index, bandgap, and improved optical losses and LIDT properties. The films were incorporated into antireflection coatings (multilayer stacks and graded-index coatings) and the LIDT was determined at 355 nm wavelength by the R-on-1 method. Optical absorptions at the reported wavelengths were characterized using photothermal common-path interferometry and laser-induced deflection techniques.

Effects of plasma power on ferroelectric properties of HfO2-ZrO2 nanolaminates produced by plasma enhanced atomic layer deposition

This study introduces the use of plasma-enhanced atomic layer deposition (PEALD) for growing ultrathin Zr-doped hafnium oxide (HfO2-ZrO2 or HZO) nanolaminates and the effect of radio frequency (RF) plasma power on the electrical properties of these fluorite-structure oxide films, which were employed in ferroelectric devices. The effect of the PEALD plasma power in a range of 50∼200 W on the degree of the orthorhombic phase and the number of oxygen vacancies in the crystallized films can be found more clearly after the additional heat treatment by rapid thermal annealing (RTA). Our measurement results reveal the notable effect of plasma power in using PEALD on the growth and properties of ferroelectric oxide films. Particularly, the increased plasma power can decrease the crystallized films' remnant polarization (Pr) from 12.68 to 4.29 μC/cm2. Besides, a relationship between the leakage current and the electronic structure causing the films’ polarization is revealed. The spectroscopically resolved band-edge electronic revealed the conversion of orthorhombic HfO2 in the laminar stacking with ZrO2 to the homogeneous HfZrxOy compounds as increasing RF power. In general, these findings show the opportunity to utilize our developed HZO nanolaminates grown by PEALD for many trending applications, particularly polarization-driven memory and ferroelectric-based advanced transistors.

Graphene-assisted low temperature growth of nearly single-crystalline GaN thin films via plasma-enhanced atomic layer deposition

Direct growth of gallium nitride (GaN) thin films is performed using plasma-enhanced atomic layer deposition (PEALD) at 300 °C on a sapphire with a graphene interlayer. The x-ray diffraction and spherical aberration corrected transmission microscope results confirm that the GaN thin films are nearly single-crystalline. Additionally, the interfacial properties and nucleation behaviors of the GaN thin films deposited on graphene are investigated in detail. Therefore, this study offers a perspective on PEALD growth of high-quality nanoscale GaN epilayers and broadens the choice for low-temperature fabrication of GaN based-devices.

Tailoring the performance of the LiNi0.8Mn0.1Co0.1O2 cathode using Al2O3 and MoO3 artificial cathode electrolyte interphase (CEI) layers through plasma-enhanced atomic layer deposition (PEALD) coating.

The Ni-rich layered oxide cathode has shown high energy density, proper rate capability, and longevity of the rechargeable battery, while poor stability and capacity fading are assumed to be its common cons. To address this obstacle, prospective cathode materials are synthesized by integrating the lithium transition metal oxides with an artificial cathode electrolyte interphase (CEI) layer. Herein, plasma-enhanced atomic layer deposition (PEALD) is employed to coat the LiNi0.8Mn0.1Co0.1O2 (NMC811) electrode with Al2O3 and MoO3. The combined results from morphological examinations revealed the formation of uniform Al2O3 and MoO3 sheets after 200 cycles of PEALD coating. Consistent results from the XRD analysis demonstrate that Al2O3 and MoO3 artificial CEIs can reduce Li-Ni mixing. The cyclic voltammetry tests show the oxidation-reduction kinetic. The modified NMC811 structures with Al2O3 and MoO3 represent a remarkable improvement in terms of capacity retention. The coated cathode with Al2O3 clearly outperforms the modified configuration with MoO3 concerning ionic conductivity, charge/discharge reversibility, and capacity retention. The promising results obtained in this study open the possibility of synthesizing Ni-rich cathodes with enhanced electrochemical performance.

Influence of deposition temperature on microstructure and gas-barrier properties of Al2O3 prepared by plasma-enhanced atomic layer deposition on a polycarbonate substrate.

We prepared polymer-based encapsulation films by plasma-enhanced atomic layer deposition (PEALD) of Al2O3 film on a polycarbonate (PC) substrate at 80-160 °C to fabricate Al2O3/PC barrier films. The thermal and dynamic mechanical properties of the PC substrate, the structural evolution of PEALD Al2O3 films, the optical transmission, surface morphology, and gas-barrier properties of Al2O3/PC film are all studied in this work as a function of temperature. The glass transition temperature T g of the PC substrate is about 140 °C, and the coefficient of thermal expansion increases significantly when the temperature exceeds T g. Increasing the deposition temperature from 80 to 160 °C for Al2O3 film deposited over 300 cycles increases the density from 3.24 to 3.45 g cm-3, decreases the thickness from 44 to 40 nm, and decreases the O/Al content ratio from 1.525 to 1.406. Al2O3/PC films deposited at 80-120 °C have no surface cracks, whereas surface cracks appear in samples deposited near or above 140 °C. Upon increasing the deposition temperature, the water vapor transmission rate (WVTR) and oxygen transmission rate (OTR) of Al2O3/PC films decrease significantly at temperatures below T g, and then increase at temperatures near to or above T g due to cracks in the films. The optimal deposition temperature is 120 °C, and the minimum WVTR and OTR of Al2O3/PC film are 0.00132 g per (m2 24 h) and 0.11 cm3 per (m2 24 h 0.1 MPa), respectively. The gas-barrier properties of the Al2O3/PC films are attributed to both the densification of the Al2O3 film and the cracks, which are caused by the shrinkage of the PC substrate.

Thin V2O5 films synthesized by plasma-enhanced atomic layer deposition for memristive applications.

In the present study, the V2O5 films synthesized by plasma-enhanced atomic layer deposition on p-Si and fluorinated graphene on Si (or FG/Si) substrates were analyzed for memristive applications. A number of samples were grown with V2O5 films with an average thickness of 1.0-10.0 nm, as determined by ellipsometric measurements. The study of surface morphology by atomic force microscopy showed that an island growth occurs in the initial stages of the film growth. The Raman spectra of the synthesized V2O5 films with an average thickness of more than 2.0 nm on the SiO2/Si substrates exhibit six distinct modes typical of the orthorhombic V2O5 phase. A large hysteresis was found in the C-V characteristics of the V2O5 films with a thickness of 1.0-4.2 nm. In general, the built-in charge in the V2O5 layers with an average thickness of 1.0-4.0 nm is positive and has a value of about ∼(2-8) × 1011 cm-2 at the 1 MHz frequency. Increasing the V2O5 film thickness leads to the accumulation of negative built-in charge up to -(1.7 to 2.3) × 1011 cm-2 at the 1 MHz frequency. The temperature dependence of the conductivity exhibits different electrically active states in V2O5/Si and V2O5/FG/Si structures. Thus, the FG layer can modify these states. V2O5 layers with an average film thickness of 1.0-3.6 nm demonstrate the memristive switching with an ON/OFF ratio of ∼1-4 orders of magnitude. At film thicknesses above 5.0 nm, the memristive switching practically vanishes. V2O5 films with an average thickness of 3.6 nm were found to be particularly stable and promising for memristive switching applications.

Stable chemical enhancement of passivating nanolayer structures grown by atomic layer deposition on silicon.

Incorporation of carrier-selective passivating contacts is on the critical path for approaching the theoretical power conversion efficiency limit in silicon solar cells. We have used plasma-enhanced atomic layer deposition (ALD) to create ultra-thin films at the single nanometre-scale which can be subsequently chemically enhanced to have properties suitable for high-performance contacts. Negatively charged 1 nm thick HfO2 films exhibit very promising passivation properties - exceeding those of SiO2 and Al2O3 at an equivalent thickness - providing a surface recombination velocity (SRV) of 19 cm s-1 on n-type silicon. Applying an Al2O3 capping layer to form Si/HfO2/Al2O3 stacks gives additional passivation, resulting in an SRV of 3.5 cm s-1. Passivation quality can be further improved via simple immersion in hydrofluoric acid, which results in SRVs < 2 cm s-1 that are stable over time (tested for ∼50 days). Based on corona charging analysis, Kelvin probe measurements and X-ray photoelectron spectroscopy, the chemically induced enhancement is consistent with changes at the dielectric surface and not the Si/dielectric interface, with fluorination of the Al2O3 and underlying HfO2 films occurring after just 5 s HF immersion. Our results show that passivation is enhanced when the oxides are fluorinated. The Al2O3 top layer of the stack can be thinned down by etching, offering a new route for fabrication of ultra-thin highly passivating HfO2-containing nanoscale thin films.

Mechanisms of Silicon Surface Passivation by Negatively Charged Hafnium Oxide Thin Films

We have studied the mechanisms underpinning effective surface passivation of silicon with hafnium oxide (HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) thin films grown <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">via</i> atomic layer deposition (ALD). Plasma-enhanced ALD with O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> plasma and a tetrakis(dimethylamido)hafnium precursor was used to deposit 12 nm thick HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> films at 200 °C on high-lifetime 5 Ωcm <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> -type Czochralski silicon wafers. The passivation was activated by postdeposition annealing, with 30 min in air at 475 °C found to be the most effective. High-resolution grazing incidence X-ray diffraction measurements revealed the film crystallized between 325 and 375 °C, and this coincided with the onset of good passivation. Once crystallized, the level of passivation continued to increase with higher annealing temperatures, exhibiting a peak at 475 °C and yielding surface recombination velocities of <5 cm s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> at 5 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> injection. A steady decrease in effective lifetime was then observed for activation temperatures >475 °C. By superacid repassivation, we demonstrated this reduction in lifetime was not because of a decrease in the bulk lifetime, but rather because of changes in the passivating films themselves. Kelvin probe measurements showed the films are negatively charged. Corona charging experiments showed the charge magnitude is of order 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> qcm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−2</sup> and that the reduced passivation above 475 °C was mainly because of a loss of chemical passivation. Our study, therefore, demonstrates the development of highly charged HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> films and quantifies their benefits as a standalone passivating film for silicon-based solar cells.

Atomic layer deposition of AlGaN alloy and its application in quantum dot sensitized solar cells

The role of plasma-enhanced atomic layer deposition growth of AlGaN ternary alloys on &lt;i&gt;c&lt;/i&gt;-planar sapphire substrates and the preparation of quantum dot-sensitized solar cells are explored in this work. The interface between the film and the substrate as well as the band gap of AlGaN ternary alloys during atomic layer deposition is dependent on Al component. At high Al fraction, there appears a good interface between the AlGaN alloy film and the substrate, however, the interface becomes rough when the Al fraction is reduced. The AlGaN alloy prepared by atomic layer deposition has a high band gap, which is related to the oxygen content within the film. Subsequently, CdSe/AlGaN/ZnS and CdSe/ZnS/AlGaN structured cells are prepared and analyzed for quantum dot solar cells from AlGaN films with an AlN/GaN cycle ratio of 1∶1. It is found that AlGaN can modify and passivate quantum dots and TiO&lt;sub&gt;2&lt;/sub&gt;, which can wrap and protect the structure of TiO&lt;sub&gt;2&lt;/sub&gt; and CdSe quantum dot, thus avoiding the recombination of photo-generated carriers. This modification effect is also reflected in the improvement of open-circuit voltage, short-circuit current, filling factor and photovoltaic conversion efficiency of quantum dot solar cells. These factors are discussed in this work, trying to modify carrier transport characteristics of AlGaN films prepared by atomic layer deposition.

Uniformity of HfO2 Thin Films Prepared on Trench Structures via Plasma-Enhanced Atomic Layer Deposition.

In this study, we assessed the physical and chemical properties of HfO2 thin films deposited by plasma-enhanced atomic layer deposition (PEALD). We confirmed the self-limiting nature of the surface reactions involved in the HfO2 thin film's growth by tracing the changes in the growth rate and refractive index with respect to the different dose times of the Hf precursor and O2 plasma. The PEALD conditions were optimized with consideration of the lowest surface roughness of the films, which was measured by atomic force microscopy (AFM). High-resolution X-ray photoelectron spectroscopy (XPS) was utilized to characterize the chemical compositions, and the local chemical environments of the HfO2 thin films were characterized based on their surface roughness and chemical compositions. The surface roughness and chemical bonding states were significantly influenced by the flow rate and plasma power of the O2 plasma. We also examined the uniformity of the films on an 8″ Si wafer and analyzed the step coverage on a trench structure of 1:13 aspect ratio. In addition, the crystallinity and crystalline phases of the thin films prepared under different annealing conditions and underlying layers were analyzed.

Plasma-enhanced atomic layer deposition of WO3-SiO2 films using a heteronuclear precursor

Tungsten oxide–silicon dioxide (WOx–SiOy) composite thin films were deposited for the first time via the remote oxygen plasma-enhanced atomic layer deposition (ALD) process using a novel metal-organic heteronuclear and heteroleptic precursor, bis(tert-butylimido)bis(trimethylsilylmethyl)tungsten. Self-limiting ALD growth was demonstrated over a wide temperature window of 203–328 °C with growth per cycle decreasing with increasing temperature from 0.75 to 0.4 Å/cycle, respectively. Residual gas analysis revealed ligand competition and showed that ligand reaction during ALD nucleation and growth was a function of deposition temperature, thereby affecting the film composition. As the temperature increased from 203 to 328 °C, the film composition [W/(Si + W)] ranged from 0.45 to 0.53. In addition, the carbon impurity content was reduced and the refractive index increased from 1.73 to 1.96, the density increased from 4.63 to 5.6 g/cm3, and the optical bandgap decreased from 3.45 to 3.27 eV. Grazing angle x-ray diffraction indicated that as-deposited films were amorphous. Upon annealing in O2 at 500 °C or higher, depending on deposition temperature, films are crystalized into the triclinic WO3 phase. At the same time, WO3 is sublimed from the surface and films are reduced in thickness.

Reducing the β-Ga2O3 Epitaxy Temperature to 240 °C via Atomic Layer Plasma Processing

In this work, we report on low-temperature as-grown single-phase epitaxial beta-gallium oxide (β-Ga2O3) films on c-plane sapphire at the substrate temperature of 240 °C using plasma-enhanced atomic layer deposition (PEALD). The films were deposited using triethylgallium (TEG) and Ar/O2 plasma as the metal precursor and oxygen co-reactant, respectively. Growth experiments were performed with an rf-power level of 50 W. Additionally, each unit ALD cycle was followed by in situ Ar-plasma annealing treatment, which consisted of Ar-plasma exposure for 20 s at 250 W rf power. X-ray diffraction (XRD) of the sample on sapphire revealed epitaxial Ga2O3 film signature with the monoclinic β-phase. On the other hand, GIXRD of the samples grown on Si and glass displayed polycrystalline β-Ga2O3 films. High-resolution transmission electron microscopy (HR-TEM) confirmed the epitaxial relationship of the Ga2O3 layers grown on sapphire substrates. X-ray photoelectron spectroscopy (XPS) shed light on the chemical bonding states of pure β-Ga2O3 layers outlining the Ga–O bonding states. STEM-EDX measurements confirmed the pristine nature of the β-Ga2O3 film with carbon atomic composition falling below the tool’s detection levels.

Thickness dependent optical properties of amorphous/polycrystalline Ga2O3 thin films grown by plasma-enhanced atomic layer deposition

Amorphous/polycrystalline Ga2O3 is attracting considerable attention because its low cost and convenience of use make it a promising material for applications of solar blind ultraviolet detectors and power electronics, except for the widely investigated α/β phase Ga2O3. Spectroscopic ellipsometry (SE) is the preferred technique for determining optical constants that are vital for device design. The bandgap energy of Ga2O3 is close to the upper energy limit of commercial ellipsometers, making it challenging to determine the optical constants of Ga2O3 films. Considering the results obtained using the point-by-point method, we developed a strategy using 2 Tauc-Lorentz (2TL) oscillators that reasonably describes the optical behavior of the amorphous/polycrystalline Ga2O3 films deposited by plasma-enhanced atomic layer deposition on Si, sapphire, and Si/SiO2 substrates. The refractive index of the Ga2O3 films increases after annealing due to the reduced thickness and polycrystalline structure of the films. The polycrystalline samples have larger bandgaps than amorphous samples. The optical constants of Ga2O3 films with thicknesses ranging from ∼ 3 to ∼ 28 nm were extracted through SE fitting by the developed 2TL method. For both the as-deposited and annealed films, the bandgap increases as the film thickness decreases. The obtained results are useful for the design of photodetectors and power devices.