Growth optimization, optical, and dielectric properties of heteroepitaxially grown ultrawide-bandgap ZnGa₂O₄ (111) thin film

Three generations of semiconductor materials have emerged since the invention of the transistor in 1947 and are currently empowering our modern society: first-generation semiconductors such as Si and Ge, second-generation semiconductors such as GaAs and InP, and most recently, third-generation wide bandgap (WBG) materials such as GaN and SiC.^1,2 Third-generation semiconductors, such as SiC (E_g∼ 3.2 eV) and GaN (E_g∼ 3.4 eV), are rapidly gaining demand due to potential applications toward the advancement of small area, high power, high-frequency switching, with low energy consumption compared to conventional Si (E_g∼ 1.1 eV).^3,4 While major manufacturers are showing tremendous interest in GaN and SiC power devices, these technologies still have limitations due to their high cost, low thermal conductivity, and high melting points (for GaN ∼ 2220 °C and for SiC ∼ 2730 °C). SiC is a very hard material that is challenging to cut, grind, and polish. It grows slowly, melts at a very high energy cost, and requires very high working pressures for bulk manufacturing.^3,5 Therefore, a renaissance in ultrawide bandgap (UWBG) semiconductor technology is currently under way, as evidenced by new device designs, new applications, and breakthroughs in understanding the fundamental properties of these materials. As a result, UWBG semiconductors are an emerging new area of research due to their high breakdown electric field, control of electrical conductivity, chemical composition, insensitivity to high temperature, and wide range of materials, physics, devices, and applications, such as power devices, 5G communication, fast chargers, deep-ultraviolet (DUV) optoelectronics, and Industry 4.0 technologies.^6,7 Currently, Ga₂O₃ (gallium oxide) is gaining popularity among ultrawide bandgap semiconductors due to its critical breakdown field and high Baliga's figure of merit (B_FOM), which has the potential for next-generation power device applications. Due to high material cost and purity, structural instability, low electron mobility, and device scaling and fabrication complexity, research has broadened to focus on alternative UWBG semiconductors that can resolve those issues to some extent.^8–10 

Ga-based spinels with the general formula AGa₂O₄, where A is a divalent metal atom, are an example of ternary systems that can provide UWBG (E_g > 3.5 eV) semiconducting behavior.¹¹ The semiconducting behavior of bulk and thin films MgGa₂O₄ crystals with an energy gap of 4.9 eV has been studied but possesses very low carrier mobility.^12,13 Another spinel zinc gallate (ZnGa₂O₄) exhibits excellent optical and electrical characteristics with an extremely wide energy gap between 4.6 and 5.2 eV. The ZnGa₂O₄ (ZGO) has a conventional cubic spinel structure of space group $Fd 3 ¯m$⁠, and the cations of Zn²⁺ and Ga³⁺ are arranged in tetrahedral and octahedral lattice positions, respectively. Because of its UWBG and proven ability to adjust electrical conductivity, ZGO may have similar potential to β-Ga₂O₃ and, due to its isotropic spinel structure, is considered a better option for device design than the monoclinic β-Ga₂O₃, which has a complex anisotropic structure–property relationship. ZGO is also a promising long-lasting brilliant phosphor that can be used for in vivo imaging by thermally driven luminescence and x-ray phosphorescence when doped with transition metal elements.^14–16 ZGO is frequently studied in polycrystalline and nanopowder materials, and Galazka et al. discovered its easily adjustable electrical conductivity and reported the successful development of a single crystal high-quality bulk material.¹⁷ With a free electron concentration of ∼10²⁰/cm³ and a Hall electron mobility of ∼107 cm²/V s at such high carrier concentrations, melt-grown ZGO crystals can be either conductive or made electrically insulating by Al doping. Studies of its inherent optical and electrical properties are limited in the literature even though these qualities are important for prospective usage for the aforementioned applications.¹⁸ Various diffuse reflectance spectroscopy (DRS) and transmittance spectroscopy techniques of ZGO samples have determined that it has a UWBG of 4.6–5 eV. The bandgap energy of a single crystal ZGO sample was observed to be 4.6 eV by Galazka et al.,¹⁸ using transmittance and reflectance spectroscopy and a calculated refractive index of 1.90 and 1.97 for wavelengths of 2 and 1 μm, respectively.¹⁹ Recently, Hilfiker et. al. have shown the variation in the dielectric function in the near-infrared to the deep-ultraviolet region with the critical point (CP) structures within the dielectric function, which are known to be caused by band-to-band transitions and associated exciton contributions.¹⁹ However, the effect of growth temperature and oxygen pressure during the fabrication of the ZGO thin film has a significant effect on the optical properties, bandgap, and dielectric function. The bandgap, dielectric constant, and carrier mobility have a significant role in Baliga's figure of merit (B_FOM), which represents a very important parameter in determining the properties of (UWBG) semiconductors in optoelectronic and power electronics applications.²⁰ Therefore, the enhancement of these parameters, i.e., bandgap and dielectric constant of UWBG ZGO, is very important for the evaluation/improvement of the performance of power semiconductor devices.

In the present work, ZGO thin-film samples are grown heteroepitaxially on the sapphire substrate by pulsed laser deposition (PLD) under varying growth temperatures at an optimized oxygen pressure. Sapphire substrates have excellent mechanical and thermal stability, chemical inertness, and higher resistance to chemical corrosion than MgO and spinel substrates. It is possible to grow thin films on sapphire substrates with low defect density and high crystal quality. The performance of electronic and optoelectronic devices depends on the epitaxial growth of superior semiconductor layers, which is dependent on the high structural perfection of sapphire crystals.²¹ The structural and optical properties in terms of the bandgap, refractive index, and complex dielectric function of ZnGa₂O₄ thin films are investigated. Furthermore, PLD represents a more efficient deposition method to build complex metal oxide thin films with different metal dopants in a relatively extensive doping range than other epitaxial thin-film development techniques such as metalorganic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), and atomic layer deposition (ALD).²² For basic research on the characteristics of ZnGa₂O₄-based epitaxial thin films and heterostructures for prospective device applications, PLD is considered one of the most cost-effective techniques. Recently, heteroepitaxial ZnGa₂O₄ thin films have been deposited on cubic spinel MgAl₂O₄ (MAO) as well as on cubic MgO substrates for thin-film transistors (TFTs) applications²³ and sapphire substrates for deep-ultraviolet applications^24,25 employing PLD techniques. An in-depth analysis of the structural order and crystalline quality of ZGO thin films is carried out by x-ray diffraction (XRD), φ-scan, and ω-scan. X-ray photoelectron spectroscopy (XPS) allows for the determination of the elemental composition of Zn and Ga atomic ratios, cation oxidation states, etc. The cross-sectional images, interfacial characteristics, crystalline nature, and fast-Fourier transform (FFT) images are visualized using high-resolution transmission electron microscopy (HRTEM). The optical absorbance spectra of ZGO thin films are carried out by UV–vis spectroscopy, and the bandgaps are determined using the Kubelka–Munk equation and Tauc’s plot. By performing a regression analysis on the optical model and measured ellipsometry data, a multiple-sample analysis (MSA)-based method was used to assess their thickness, dielectric function, and other optical properties.

The ZGO thin films are grown on c-plane sapphire (Al₂O₃) substrates using the PLD technique at varying substrate temperatures from 650 to 750 °C and an oxygen pressure of 1 × 10⁻²Torr. High incongruent decomposition and evaporation of the ZnO–Ga₂O₃ binary system, as well as the significantly higher vapor pressure of Zn compared to Ga, have resulted in a narrow growth window for single-phase and nearly stoichiometric ZnGa₂O₄ epitaxial thin films.^26,27 Therefore, the preparation of the PLD target is more important than the deposition parameters, and three targets taking ZnO and Ga₂O₃ with 50%–50%, 75%–25%, and 98%–2%, respectively, were prepared. The two metal oxides are mixed thoroughly by ball milling for 1 h and pelletized at room temperature and a mechanical pressure of 1.5 × 10⁴ psi. All three pelletized samples were calcined at 1150 °C in an ambient atmosphere for 24 h and used as the PLD target. The vapor pressure of Zn and Ga is 0.0127 and 0.0091 Torr at 750 °C, respectively.²⁸ Despite the use of mosaic targets containing 50% ZnO–50% Ga₂O₃ and 75% ZnO–25% Ga₂O₃, the evaporation of zinc on a heated substrate due to the relatively high vapor pressure results in severe Zn losses, which are already observed above 300 °C, and leads to significant Zn deficiency in the ZnGa₂O₄ films deposited above 700 °C. It is expected that the higher Zn (98%) containing target can effectively offset the significant Zn loss that occurs during thin-film deposition. The ZGO thin films were grown at varying growth temperatures from 650 to 750 °C with a constant oxygen partial pressure of ∼1 × 10⁻²Torr. A laser fluence of ∼3.33 J/cm² is used to ablate and deposit the thin film since it facilitates higher kinetic energies and larger flux for the incorporation of Zn into the growing ZnGa₂O₄ crystalline films with the target supplying additional Zn to partially compensate for the Zn loss. The number of laser pulses and laser frequency of 7500 and 5 Hz, respectively, were used for all depositions.

The structural characterizations of ZGO thin films including XRD, φ-scan, and x-ray rocking curve (XRC) were performed using a Rigaku SmartLab x-ray diffractometer. The XRD was performed at 2θ between 10° and 90°, a scan rate of 2°/min, and a step size of 0.0002° for all samples. The φ-scan and XRC (ω-scan) were accomplished between −10° and 360° (for 104 planes for sapphire and 220 planes for ZnGa₂O₄) and between 17° and 20°, respectively. XPS spectra were collected from a ThermoFisher Scientific Nexsa x-ray photoelectron spectrometer (XPS) using soft x-ray radiation (from Al sources). The HRTEM and fast-Fourier transform (FFT) images were obtained using a FEI Talos^™ f200i S/TEM with accelerating voltages between 120 and 200 kV. High-resolution scanning electron microscopy (HRSEM) images with energy-dispersive x-ray spectra (EDS) and mappings were collected using a FEI Helios NanoLab 400 DualBeam system in the field-free mode. The absorbance spectra and bandgap of ZGO thin films were examined from the data obtained from a Shimadzu UV-2600 UV–vis spectrophotometer in the range between 200 and 800 nm. The complex refractive index, extinction coefficient, and dielectric function of ZGO thin films at different growth temperatures were acquired by spectroscopic ellipsometry measurement (J.A. Woollam M2000X system).

To confirm the single-crystalline phase of the ZGO thin film for the three different targets on sapphire substrates, the XRD spectra at a growth temperature of 750 °C and a constant oxygen pressure of 1 × 10⁻²Torr are shown in Fig. 1(a). The ZGO thin film grown by the stoichiometrically balanced target (50%–50%) exhibits XRD peaks at 18.9°, 38.4°, 59.0°, and 81.9°, which are assigned to the single-crystalline XRD peaks of β-Ga₂O₃.²⁹ Even 75% ZnO−25% Ga₂O₃ targets displayed some secondary peaks with single crystalline XRD peaks of β-Ga₂O₃ indicating significant re-evaporation of Zn/ZnO. Finally, the XRD spectrum for the ZGO thin film deposited using the Zn-rich (98% ZnO–2% Ga₂O₃) target illustrates single-crystalline XRD peaks at 18.48°, 37.44°, 57.49°, and 79.76°, which corresponds to the cubic phase of the ZGO thin film (JCPDS-381240).³⁰ In order to view distinctly the difference between the XRD peaks of the β-Ga₂O₃ and ZGO thin film, an enlarged view of the (111) planes is shown in Fig. 1(b). There is a significant shift in the peaks for the (111) planes toward a lower diffraction angle due to the successful formation of a single-crystalline ZnGa₂O₄ at 750 °C. The peak shift and phase transition from β-Ga₂O₃ to ZnGa₂O₄ agree well with the MOCVD-grown ZnGa₂O₄ by Chikoidze et. al.^31, Figure 1(c) represents the XRD spectra of ZGO samples grown at various substrate temperatures from 650 to 750 °C and an oxygen pressure of 1 × 10⁻²Torr for the 98%–2% target. It exhibits highly oriented crystal growth with a series of reflection planes (111), (222), (333), and (444) associated with the cubic spinel structure of ZnGa₂O₄.³² All peaks of ZGO were calibrated and aligned using the sapphire (0006) planes at 41.72° (c = 1.297 nm). A number of secondary peaks are observed for the samples grown at temperatures lower than 700 °C due to unsuccessful incorporations of ZnO over Ga₂O₃. Consequently, a smaller FWHM of XRD for the sample grown at 750 °C indicates better crystalline quality and fewer imperfections, which is later confirmed by x-ray rocking curves. Figure 1(d) displays the single-crystalline XRD spectra of the ZGO sample at 750 °C in a log scale to view distinctly each peak. One very small additional peak at 2θ ∼ 85.9° is detected in the log scale, which is most likely due to the (62-4) plane and suggests the presence of a minor (<1%) polycrystalline nature of ZnGa₂O₄. The XRD φ-scans around the (220) out-of-plane peaks of the ZnGa₂O₄ thin film formed at temperature 750 °C and oxygen pressure 1 × 10⁻²Torr and the (104) out-of-plane peaks of the sapphire substrate were performed to estimate the in-plane orientation and epitaxial relationship between the films and substrates. The ZGO film has six peaks that are visible at 60° intervals (represented by the red line), suggesting that it is sixfold symmetric and that in-plane twinning is present in Fig. 1(e). The φ-scans by black lines exhibit three sharp peaks between 0° and 360°, which represents the threefold rotational symmetry of the c-plane sapphire. The in-plane epitaxial matching of the (111) oriented ZnGa₂O₄ thin film on the (0006) sapphire substrate is confirmed by the rotation of the six peaks of ZGO films by 30° with respect to the threefold peaks from the substrate. The crystalline quality of the as-grown ZGO samples for the three different temperatures 700°, 725°, and 750° at an oxygen partial pressure of 1 × 10⁻²Torr is examined by x-ray rocking curve (XRC) and shown in Fig. 1(f). The values of full width and half maxima (FWHM) of the rocking curves were determined to be 1.02°, 0.32°, and 0.098° of the (111) oriented ZGO thin film for 700, 725, and 750 °C, respectively, which indicates the excellent epitaxial crystal quality and relationship of the heteroepitaxial ZGO thin film on sapphire even with a lattice mismatch greater than 10% between the substrate and film. With the increase in the growth temperature, the FWHM of rocking curves decreases and indicates better crystalline quality for higher temperatures.³³ The FWHM value of ∼0.098° for the 750 °C grown ZGO thin film (222) indicates better crystalline quality than previously reported works of ZnGa₂O₄.

The elemental composition and bonding characteristics of the ZGO thin film grown at 750 °C were analyzed by XPS and are shown in Fig. 2. The XPS survey scan in Fig. 2(a) divulges various sharp peaks corresponding to Ga-3s, Ga-2p, Ga-3p, Ga-3d, Ga-LMM, Zn-2p, Zn-LMM, O-1s, and C-1s bonds and the obtained oxidation states +2 for Zn, +3 for Ga, and −2 for oxygen. The atomic percentages ratio of Zn/Ga was approximated at ∼0.48 from the intensity and area under the Zn-2p_3/2 and Ga-2p_3/2 curves. The atomic ratios of Zn:Ga:O obtained were 15.98%, 30.12%, and 53.9%, respectively, from the XPS analysis, which corresponds well to the energy dispersive x-ray (EDX) spectra shown in Fig. S1(g) in the supplementary material. The individual spectrum of Zn-2p in Fig. 2(b) reveals two broad and sharp peaks at 1021.5 and 1044.8 eV, representing Zn-2p_3/2 and Zn-2p_1/2, respectively. In addition, the XPS spectrum of Ga-3d in Fig. 2(c) is deconvoluted with three different contributions of O-2s, Ga³⁺, and Ga at 22.9, 20.2, and 18.5 eV, which originates due to an overlapping of O-2s states, Ga³⁺ lattice ions in Ga-3d states, and minor elemental gallium residue, respectively. The individual scan of O-1s peaks in Fig. 2(d) is deconvoluted to the two components, which are assigned to the lattice oxygen (O²⁻) (530.8 eV) and oxygen vacancies (532.5 eV), respectively. The broad symmetric peak at 530.8 eV corresponds to the lattice oxygen ions (O²⁻) in ZGO bonded with Ga and Zn, and the small peak at 532.5 eV is designated to the oxygen ions in the oxygen vacancy region. Interestingly, an oxygen vacancy in an oxygen-deficient interlayer functions as an electron trap, allowing oxide semiconductor conductivity to be regulated.³⁴ 

To observe the oxygen vacancies with growth temperatures, we have shown the O-1s spectra of ZGO grown at three different temperatures 700, 725, and 750 °C with Gaussian fitting as shown in Figs. 3(a)–3(c), respectively. Usually, high growth temperatures may cause the thin film to develop thermally induced minor defects and these defects can result in oxygen vacancies being created by the loss of oxygen atoms from the lattice structure.^35,36 From Figs. 3(a)–3(c), the peaks around 532.5 eV are associated with the oxygen vacancies and their value slightly increases with growth temperatures. The obtained area under the curves after fitting is used to calculate the ratios of oxygen vacancies (O_II) with lattice oxygen (O²⁻), and its values were determined to be 0.09, 0. 10, and 0.11 for 700, 725, and 750 °C, respectively.

The structure and characteristics of epitaxial thin films can be effectively characterized at the nanoscale level using transmission electron microscopy (TEM). The high-resolution TEM analysis of the ZGO thin film grown at 750 °C was performed to investigate the microstructure as well as the interface between the sapphire/ZGO thin film as shown in Fig. 4. An ultrathin cross-sectional specimen of the epitaxial thin film was prepared using a focused ion beam (FIB) to mill and thin the samples to electron transparent thickness. The cross-sectional TEM images in Fig. 4(a) are demonstrated to evaluate the film thickness, which was found to be ∼265 nm (indicated by the green line), considering the small sample volume and likely outermost surface amorphization following the focused ion beam (FIB) thinning process. The interface between the sapphire and ZGO film is clearly visible in Fig. 4(b), and it confirms the epitaxial relationship of nearly 30° obtained from XRD analysis. The interface between the substrate and film appears very sharp and distinct, and there is no sign of a minor secondary phase from unreacted residue elements. The quasi-single-crystalline structure of the transparent crystal lattice stripes of cubic ZnGa₂O₄ with the preferred (111) orientation perpendicular to the film surface illustrates the d-spacing value of 4.82 Å in Fig. 4(c). Minor contributions of ZnO and Ga₂O₃ crystal stripes were observed on a large scale near interfaces, which arises due to rapid thermal annealing during growth and bond rearrangement at the interface between the amorphous and crystalline phases.^37,38 The FFT pattern from the region of Fig. 4(d) contains the film and substrate with several reflection planes of the ZGO film such as (111), (011), and (002) and gives an out-of-plane orientation relationship with the substrate. The scanning electron microscopy (SEM) micrographs with EDS and mappings of the ZGO thin film grown at 750 °C are also displayed in Fig. S1 in the supplementary material. The uniform distribution of Zn, Ga, and O with thickness ∼247 nm was confirmed by the elemental mappings and EDX spectra with stoichiometrically balanced atomic distributions of 14.37%, 28.28%, and 57.35%, respectively.

Here, h represents the Planck constant, $ν$ is the frequency of vibrations, $n=2$ for direct bandgap transitions and ½ for indirect bandgap transitions, and A and t denote the absorbance and thickness of the film. The Tauc’s plots in Fig. 5(b) show an optical bandgap of 5.08, 5.11, and 5.14 eV for growth temperatures of 700, 725, and 750 °C, respectively. The practical bandgap of the high crystalline ZGO thin film grown at 750 °C gives a real bandgap that is affected by changes in the carrier concentration at higher growth temperatures. Bandgap renormalization, a variety of many-body interactions between the carriers in the conduction band and valence band, is known to be associated with the bandgap narrowing in the ZGO thin film at lower growth temperatures.⁴³ Additionally, the electronic energy bands may become more widely spaced as a result of these thermally assisted vibrations, which would facilitate the movement of electrons from the valence to the conduction bands and narrow the bandgap.

The A, B, and C are the fitting parameters that control the line shape of the refractive index and $k 0$ and $E g$ represent the amplitude of absorption and band edges, respectively. The variation in the refractive index (n) and extinction coefficient (k) with a wavelength between 200 and 1000 nm is shown in Figs. 5(c) and 5(d), respectively, with their corresponding values. The near-infrared refractive index (n) was determined to be ∼1.94 for ZGO (750 °C) from the extrapolation, which is in very good agreement with recently published ZnGa₂O₄ results.^19,46 Similarly, the extinction coefficient (k), which is an indication of the amount of light absorbed or transmitted in any medium, was obtained to be ∼0.023, representing potential optical applications for optical filters, coatings, fiber optics, and microscopy, among others. The dispersion of the refractive index with longer wavelengths, i.e., infrared or radio waves experiences relatively lower bending (sometimes called refraction) when they pass through the ZGO samples and, consequently, the refractive index slightly decreases.

The experimental real (ɛ_r) and imaginary (ɛ_i) dielectric functions are calculated using Eqs. (8) and (9), respectively, and their variation with photon energy further is emphasized in Figs. 5(e) and 5(f), respectively. The real dielectric function of two ZGO samples grown at 700 and 725 °C follows an unalike trend and decreases after a maximum near 3.5 eV. However, the ɛ_r of 750 °C grown ZGO increases with photon energy producing a relaxation plateau near 5 eV and giving the highest value of ∼6.8. The variation in ɛ_r with energy well corresponds to the theoretical data by the density functional theory (DFT) of ZnGa₂O₄ by Hilfiker et. al.,¹⁹ and the obtained value of the dielectric function is slightly higher than their value (∼6.2) near the relaxation anomaly region. We observed that anharmonic coupling causes the imaginary component of the dielectric function to be slightly negative from the exciton model contribution throughout a small spectral region of the 750 °C grown ZGO sample. Anharmonic coupling of two resonant processes results in a phase shift between their oscillatory characteristics because of the exchange of excitation energy. An identical observation was reported by α-phase cubic Ga₂O₃ by Hilfiker et.al.¹⁹ The roughness of ZGO samples grown between 700 and 750 °C was obtained between ∼18 and 25 nm, respectively. We have compared the growth and optical parameters of some recent studies of ZnGa₂O₄ grown on sapphire in Table I.

In summary, our present work demonstrates the high-quality heteroepitaxial growth of the ZnGa₂O₄ (111) thin film on sapphire (c-plane) by PLD techniques using a zinc-rich target Zn_0.98Ga_0.02O and observes their epitaxial relationship, chemical state, structural insight, and optical properties. The ZnGa₂O₄ thin film was grown at different temperatures ranging from 650 to 750 °C with ΔT = 25 °C after optimizing the oxygen pressure 1 × 10⁻² Torr. Due to the mismatch of the vapor pressure between Zn and Ga, the zinc-rich target Zn_0.98Ga_0.02O gives a balanced pulsed laser ablation of both elements than the stoichiometrically balanced target. The epitaxial relationship between the ZnGa₂O₄ (111) and sapphire (0001) substrates was established by the φ scan, and nearly 30° out-of-plane relationship was found. The x-ray rocking curve displayed a narrow FWHM of ∼0.098° for the ZGO sample grown at 750 °C. The chemical state of Zn, Ga, and O from the XPS curve provides sound information about the elemental composition, atomic percentages, and the minor oxygen vacancies compared to lattice oxygen (∼0.098 for 750 °C), which slightly increases with the rise of growth temperatures. The HRTEM micrographs with the FFT pattern of the ZGO (111) sample confirm the quasi-single-crystalline nature with minor additional phase and crystal lattice spacings of 4.82 Å. The Tauc plot from UV–vis spectra helped us to determine the UWBG gap of ∼5.08 eV for 750 °C grown samples, and an indicative effect of growth temperature on the bandgap was observed. The utmost refractive index of ∼1.94 and low extinction coefficient of ∼0.023 were obtained for the 750 °C grown ZGO sample from the ellipsometric data using the Cauchy dispersion formula. The variation in the real dielectric function with energy exhibits one relaxation plateau near 5 eV with a maximum value of ∼6.8, which is higher than the previously reported value. The UWBG gap and obtained dielectric function of epitaxially grown ZnGa₂O₄ recommend its probable applications in high-power electronics and DUV sensors.

See the supplementary material for the high-resolution field emission scanning electron microscopy (FESEM) micrographs of the top surface, cross-sectional SEM images, and EDX elemental mapping of the ZGO thin film (Fig. S1), and the experimental and fitted ellipsometric angles (a) ψ and (b) δ with a wavelength between 200 and 1000 nm (Fig. S2).

We want to acknowledge the project funding from the Office of Research and Sponsored Programs (ORSP) of Texas State University awarded to PI Haque and the instrumentation facilities at Shared Research Operation (SRO). The first author, SK, would also like to thank his colleagues from the advanced UWBG materials and device lab of the Ingram School of Engineering, Texas State University.

The authors have no conflicts to disclose.

Subrata Karmakar: Conceptualization (equal); Data curation (equal); Formal analysis (equal); Funding acquisition (equal); Investigation (equal); Methodology (equal); Project administration (equal); Resources (equal); Software (equal); Supervision (equal); Validation (equal); Visualization (equal); Writing – original draft (equal); Writing – review & editing (equal). Injamamul Hoque Emu: Data curation (supporting); Formal analysis (supporting); Investigation (supporting). Md Abdul Halim: Data curation (supporting); Investigation (supporting). Pallab Kumar Sarkar: Data curation (supporting). Maria Sultana: Data curation (supporting). Ayesha Tasnim: Data curation (supporting). Md Abdul Hamid: Data curation (supporting). Istiaq Firoz Shiam: Data curation (supporting). Ravi Droopad: Formal analysis (supporting); Project administration (supporting); Resources (equal); Supervision (supporting); Writing – original draft (supporting); Writing – review & editing (equal). Ariful Haque: Funding acquisition (equal); Project administration (equal); Resources (equal); Writing – review & editing (equal).

The data that support the findings of this study are available within the article and its supplementary material.