Electron beam techniques have been used to analyze the impact of substrate choice and growth parameters on the compositional and optical properties of tin gallium oxide [(SnxGa1−x)2O3] thin films grown by plasma‐assisted molecular beam epitaxy. Sn incorporation and film quality are found to be highly dependent on growth temperature and substrate material (silicon, sapphire, and bulk Ga2O3) with alloy concentrations varying up to an x value of 0.11. Room temperature cathodoluminescence spectra show the Sn alloying suppressing UV (3.3–3.0 eV), enhancing blue (2.8–2.4 eV), and generating green (2.4–2.0 eV) emission, indicative of the introduction of a high density of gallium vacancies (VGa) and subsequent VGa–Sn complexes. This behavior was further analyzed by mapping composition and luminescence across a cross section. Compared to Ga2O3, the spectral bands show a clear redshift due to bandgap reduction, confirmed by optical transmission measurements. The results show promise that the bandgap of gallium oxide can successfully be reduced through Sn alloying and used for bandgap engineering within UV optoelectronic devices.

We have developed a superlattice structure (SLS) of HfO $_{\text{2}}$ and Al $_{\text{2}}$ O $_{\text{3}}$ high- k dielectrics by high-volume batch atomic layer deposition on a 200 mm platform. The SLS forms a hafnium aluminate (Hf $_{\text{1-x}}$ Al $_{\text{x}}$ O) alloy at deposition temperature and presents superior electrical properties as a metal-insulator-metal (MIM) capacitor. Among the samples, an Al mole fraction of $\sim$ 0.31 demonstrates the highest capacitance density ( C $_{\textit{p}}$ D ) of 12.46 fF/ $\mu $ m $^{\text{2}}$ and dielectric constant, $\kappa $ $>$ 22, 2% better than HfO $_{\text{2}}$ . A higher Al mole fraction of 0.56 shows a superior quadratic component ( $\alpha $ ) of voltage-coefficient of capacitance and 68% higher- $\kappa $ than an Al $_{\text{2}}$ O $_{\text{3}}$ capacitor. Electrical measurement before and after annealing at 650 $^{\circ}$ C for 30 s illustrates the thermal stability of capacitors. The present research indicates a small amount of Al incorporation in HfO $_{\text{2}}$ extends its quantization temperature by stabilizing the crystal phase by reducing oxygen vacancies and traps. It remarkably improved electrical characteristics under thermal stress compared to broken-down HfO $_{\text{2}}$ capacitors under annealing. Besides, the alloy also shows improved linearity over a broad frequency range, lower leakage current, and a breakdown electric field ( E $_{\text{BV}}$ ) in the order of 4 MV/cm. At the same time, higher Al incorporation provides the highest E $_{\text{BV}}$ of $\sim$ 8 MV/cm, low leakage, and near principle $\alpha $ of 210 ppm/V $^{\text{2}}$ with better thermal stability. These thin multilayer SLS alloys show excellent relative capacitance variation over the voltage with high C $_{\textit{p}}$ D , $\kappa $ , low leakage of 10 nA/cm $^{\text{2}}$ at 3 MV/cm, suitable for higher thermal budget and interposer process integration for various high bandwidth RF and low-cost memory applications with smaller chip area.

A highly uniform aluminum nitride thin film has been developed by thermal atomic layer deposition (ALD), which is designed to handle high volume of 200 mm wafers. A three-sigma thickness variation of <0.5 Å resulted from repeatable batch depositions of over 500 Å, while wafer-within-wafer (WinW) and wafer-to-wafer (WtoW) remained <5% by the optimized recipe in a 100+ wafer reactor. Various ALD deposition temperatures, film thicknesses, and substrate types of Si, quartz, and GaN/Si(111) templates have been examined for material and optical properties of an AlN film. A narrow temperature window of 300–350 °C was identified as the most suitable for the deposition process with 350 °C as the optimized one. Substrate-inhibited growth and nonlinearity in deposition rate have been observed for AlN which is possibly related to the available reaction sites at the time of nucleation on foreign substrate surfaces. A special set of experiments with a thorough exploration of XPS individual peaks such as Al2p, N1s, C1s, and O1s reveals negligible carbon and oxygen contamination with cent-percent Al–N bonding. An amorphous AlN film is evident on Si by cross-sectional TEM while a trace of polycrystalline film on GaN templates with smooth heterointerfaces to AlGaN/GaN structures. The optical bandgap is estimated to be 5.8 eV from the transmittance experiment. An in-depth refractive-index investigation shows high-density AlN by TEL Alpha-8SEiTM batch ALD which also exhibits excellent uniformity over composition and thickness with run-to-run (RtoR), WtoW, and WinW uniformity under 0.5%, highlighting the reliability and precision of the process while having high throughput.

Tin-gallium oxide (TGO) epilayers have been characterized through the electron microscopy techniques of wavelength-dispersive X-ray spectroscopy (WDX) and cathodoluminescence. Tin incorporation was found to be highly dependent on growth conditions with (0001)-sapphire and (010)-Ga2O3 substrates enhancing tin incorporation. Cathodoluminescence measurements show that TGO luminescence consists of an enhanced blue emission and quenched UV when compared to Ga2O3.and the onset of new green emission originating from the TGO, further correlated through cross-sectional WDX and cathodoluminescence mapping. As well as luminescence intensity changes TGO films display redshifted luminescence bands associated with a bandgap reduction due to the alloying, confirmed through optical transmission measurements.

We demonstrate the versatile use of UV-ozone oxide (UVo) in surface cleaning, surface passivation, diffused junction passivation, and current tunneling applications of crystalline silicon (c-Si) solar cells. A UV-ozone generated oxide is used as a surface clean for random textured c-Si samples and the effectiveness of surface clean is determined by capping with a thin layer of aluminum oxide (AlO x ). Our developed UVo clean has resulted in a cleaning efficiency almost comparable to that of the benchmarked RCA clean, yielding a saturation current density of 12 fA/cm 2 . When planar and textured c-Si samples are capped by a stack of UVo and AlO x , a UV-ozone growth time of no more than 3 min is found to provide an optimum surface passivation. When tested on phosphorus and boron diffused junctions (with sheet resistance, R sh of 110–120 $\Omega\!/\!{\scriptstyle\square} $ ), the UVo and AlO x stack resulted in a J 0 of 11 fA/cm 2 or lower. The high-resolution transmission electron microscope imaging revealed that UVo structure is stable upon annealing for passivation activation. Last, when applied as a tunneling contact, the UVo realizes a contact resistivity ( ρc ) of ∼1 mΩ-cm 2 and ∼20 mΩ-cm 2 for boron and phosphorus doped metal-insulator-semiconductor contact structures, respectively, with moderately doped diffusions.

We report ultra-high responsivity of epitaxial (SnxGa1−x)2O3 (TGO) Schottky UV-C photodetectors and experimentally identified the source of gain as deep-level defects, supported by first principles calculations. Epitaxial TGO films were grown by plasma-assisted molecular beam epitaxy on (−201) oriented n-type β-Ga2O3 substrates. Fabricated vertical Schottky devices exhibited peak responsivities as high as 3.5 ×104 A/W at −5 V applied bias under 250 nm illumination with sharp cutoff shorter than 280 nm and fast rise/fall time in milliseconds order. Hyperspectral imaging cathodoluminescence (CL) spectra were examined to find the mid-bandgap defects, the source of this high gain. Irrespective of different tin mole fractions, the TGO epilayer exhibited extra CL peaks at the green band (∼2.20 eV) not seen in β-Ga2O3 along with enhancement of the blue emission-band (∼2.64 eV) and suppression of the UV emission-band. Based on hybrid functional calculations of the optical emission expected for defects involving Sn in β-Ga2O3, VGa–Sn complexes are proposed as potential defect origins of the observed green and blue emission-bands. Such complexes behave as acceptors that can efficiently trap photogenerated holes and are predicted to be predominantly responsible for the ultra-high photoconductive gain in the Sn-alloyed Ga2O3 devices by means of thermionic emission and electron tunneling. Regenerating the VGa–Sn defect complexes by optimizing the growth techniques, we have demonstrated a planar Schottky UV-C photodetector of the highest peak responsivity.

In this SBIR Phase I project, Qrona Technologies in collaboration with subcontractor research groups, at UCF and UM, fabricated both p-n-junction and MIS metal-oxide-based photodetectors, by performing device modeling and simulation, thin-film epitaxy using MBE and MSE, and device processing and characterization.

We experimentally proved an effective use of UV-ozone oxide layer in junction passivation and current tunneling applications of crystalline silicon (c-Si) solar cells. The UV-ozone generated oxide layer can improve the passivation quality of aluminum oxide(AlO x ) when inserted between the silicon wafer surface and atomic layer deposited(ALD) AlO x . When tested on junctions that moderately diffused by phosphorus and boron (sheet resistance R sh ~110 Ω/□), the UV-ozone oxide and AlO x stack resulted in a J 0 no more than 12fA/cm 2 . The same oxide layer is also considered as a passivating contact material. When applied as an interlayer between diffused silicon surface and aluminum contact, the passivated contact structure realized a contact resistivity (ρ c ) of ~ 1mΩ-cm 2 and ~ 25mΩ-cm 2 for boron and phosphorus passivating contact structures, respectively, with moderately doped diffusions.

A high figure‐of‐merit UV‐C solar‐blind photodetector (PD) fabricated from thin‐film beta‐gallium oxide (β‐Ga2O3) grown on n‐Si substrates by plasma‐assisted molecular beam epitaxy is demonstrated. Film growth sequences for nucleation of Ga2O3 on (100)‐ and (111)‐oriented Si substrates are developed, and the influence of crucial growth parameters is systematically investigated, namely, substrate temperature, oxygen flow rate, and plasma power on the functional properties of the PDs. The PDs show an ultra‐high responsivity of 837 A W−1 and a fast ON/OFF time below 4 ms at −5 V. In addition, they display strong rectifying properties and a sharp cutoff below 280 nm with the average responsivities between 10 and 80 A W−1, a detectivity on the order of 1010 Jones, and rise/fall times between 4 and 500 ms. High photoconductive gain is likely to be due to the mid‐bandgap donor/acceptor defect levels, including oxygen vacancies in the form of self‐trapped holes. It is demonstrated that these defect levels can be modified by controlling the growth conditions, thereby allowing for tailoring of the PD characteristics for specific applications. The methodology represents a cost‐effective solution over homoepitaxial approaches, with characteristics that meet or exceed those reported previously, offering new possibilities for on‐wafer integration with Si opto‐electronics.

Heterogeneous integration of β-(SnxGa1−x)2O3 (TGO) UV-C photodetectors on silicon substrates by molecular beam epitaxy is demonstrated. Multimodal electron microscopy and spectroscopy techniques reveal a direct correlation between structural, compositional, and optical properties of TGO and the functional properties of the photodetectors. Wavelength dispersive x-ray spectroscopy results accurately determine Sn concentrations (x) in the region of 0.020, and room temperature cathodoluminescence (CL) hyperspectral imaging shows changes in the CL emission intensity in TGO compared with a Ga2O3 sample with no Sn. Alloying Ga2O3 with Sn is shown to quench the red emission and enhance the blue emission. The increase in blue emission corresponds to the rise in VGa-related deep acceptors responsible for the high gain observed in the TGO detectors. A Ga2O3 nucleation layer is shown to improve the TGO surface quality and give better device properties compared to TGO grown directly onto the Si substrate, including a higher specific detectivity on the order of 1012 Jones.

The authors report on high spectral responsivity (SnxGa1 − x)2O3 Schottky UV photodetectors grown by plasma-assisted molecular beam epitaxy on β-Ga2O3 substrates. Schottky devices exhibited peak responsivities ranging from 49 to 194 A/W, with peak responsivity and wavelength position increasing systematically for higher Sn concentration from x = 0.01 to 0.18. Dark currents for the devices ranged from <1 nA to 3 μA with rise and fall times in the 0.21–3 s time range, with slower response times likely due to photoconductive gain caused by trapped holes. Incorporation of up to 18% Sn into the tin gallium oxide (TGO) devices resulted in a redshift in the peak responsivity position, ranging from 5.19 to 4.86 eV, demonstrating tunability within the UV-C spectral region through Sn concentration adjustment. The authors believe this to be the highest reported responsivity for a planar Ga2O3-based Schottky photodetector to date, suggesting that TGO based UV-C Schottky detectors are an attractive approach toward deep-UV sensing applications.

Surface passivation is a key process to achieve high-efficiency in silicon solar cells. In this paper we applied UV-ozone treatment to achieve high-quality passivation on both planar and textured, n-type and p-type wafers.

We report on the fabrication and characterization of solar-blind photodetectors based on metal organic chemical vapor deposition grown polycrystalline monoclinic indium gallium oxide (InxGa1-x)(2)O-3 alloys on sapphire using N2O for oxidation. The effects of growth conditions on indium incorporation efficiency and oxygen vacancies of the (InxGa1-x)(2)O-3 alloy, photo-to-dark current ratio (PDR), gain and responsivity of the fabricated photodetectors were investigated. The optical bandgap of the films was found to decrease due to the indium incorporation (x = 20.3%, 17.7%, 10.6% for samples A, B, and C, respectively) into the lattice of gallium oxide. By increasing the indium content incorporated into the lattice of Ga2O3, we demonstrated solar-blind photodetectors whose peak responsivity increased from 0.79 A/W (Ga2O3) to 319.1 A/W, 66.1 A/W and 27.7 A/W for samples A, B and C, respectively at 5 V applied bias with the cut off wavelength below 280 nm. Increasing in content resulted in a higher concentration of oxygen vacancies in as-grown films. Increased oxygen vacancies as a result of the change in growth conditions lead to higher photoconductive gain, higher responsivities, and lower PDR, demonstrating a trade-off between responsivity and the PDR. To the best of our knowledge, the peak responsivity value reported in this work is the highest for (InxGa1-x)(2)O-3 based solar-blind photodetectors. Fast rise and fall times in the order of 100 ms have been measured for the photodetectors.

Herein, tunneling aluminum oxide (Al2O3) passivation layers are demonstrated to be a candidate for hole collecting, passivating contacts when coupled with a boron‐doped surface. These very thin Al2O3 films (1.5–3 nm) are deposited using spatial atomic layer deposition (ALD) on boron diffused (110–115 Ω □−1) hydrophilic surfaces operating as metal–insulator–semiconductor (MIS) contacts. The emitter saturation current density values of ≈57 fA cm−2 are achieved for the Al2O3 film thicknesses of 2 nm before metallization. At this same thickness, the contact resistivity values of 33 mΩ cm2 are obtained after metallization. Most importantly, the boron diffusion, wet chemical surface preparation, and spatial ALD of Al2O3 used to create these MIS structures are all performed with industrially relevant equipment on Cz wafers.

In this study, substochiometric hole-selective molybdenum oxide (MoOx) contacts in crystalline silicon (c-Si) solar cells were investigated by a combination of transmission electron microscopy (TEM) and spatially resolved electron energy-loss spectroscopy (SR-EELS). It was observed that a ≈ 4 nm SiOx interlayer grows at the MoOx/c-Si interface during the evaporation of MoOx over a c-Si substrate. SR-EELS analyses revealed the presence of a 1.5 nm diffused MoOx/indium tin oxide (ITO) interface in both as-deposited and annealed samples. Moreover, the presence of a 1 nm thin layer with a lower oxidation state of Mo was detected at the SiOx/MoOx interface in an as-deposited state, which disappears upon annealing. Overall, it was evident that no hole-blocking interlayer is formed at the MoOx/ITO interface during annealing and homogenization of the MoOx layer takes place during the annealing process. Furthermore, device simulations revealed that efficient hole collection is dependent on MoOx work function and that reduction in the work function of MoOx results in loss of band bending and negatively impacts hole selectivity.

We report on a high performance Pt/n−Ga2O3/n+Ga2O3 solar blind Schottky photodiode that has been grown by metalorganic chemical vapor deposition. The active area of the photodiode was fabricated using ∼30 Å thick semi-transparent Pt that has up to 90% transparency to UV radiation with wavelengths < 260 nm. The fabricated photodiode exhibited Schottky characteristics with a turn-on voltage of ∼1 V and a rectification ratio of ∼108 at ±2 V and showed deep UV solar blind detection at 0 V. The Schottky photodiode exhibited good device characteristics such as an ideality factor of 1.23 and a breakdown voltage of ∼110 V. The spectral response showed a maximum absolute responsivity of 0.16 A/W at 222 nm at zero bias corresponding to an external quantum efficiency of ∼87.5%. The cutoff wavelength and the out of band rejection ratio of the devices were ∼260 nm and ∼104, respectively, showing a true solar blind operation with an excellent selectivity. The time response is in the millisecond range and has no long-time decay component which is common in photoconductive wide bandgap devices.

The focus of this work is on the characterization of passivated crystalline Si (c-Si) surfaces subjected to various cleaning sequences involving UV ozone (UVo) treatment and HF-dip. A combination of photoconductance decay (PCD) measurements and high-resolution transmission electron microscopy (HRTEM) studies were used to obtain a deeper insight into passivation mechanisms of UVo and its origin at the nano-scale.

We report on the growth of epitaxial Co3O4 (1 1 1) thin films by close injection showerhead (CIS)-MOCVD on sapphire substrates (c-, a- and r- planes). The deposition was carried out by using tri-dipivaloylmethanato-cobalt (Co(dpm)3) as precursor for Co and pure O2 or H2O vapor as oxidant. The effects of growth conditions, including Co(dpm)3 vaporization temperature, substrate temperature, O2/H2O flow rates, growth pressure and substrate orientation on the growth of the Co3O4 thin films were investigated. The crystallinity, phase purity and surface morphology of the films were studied by XRD, Raman and UV-visible spectroscopies, RHEED, SEM, and AFM. The as-grown films were found to be pure (1 1 1) oriented normal spinel type epitaxial Co3O4 thin films. The morphology of the films was strongly dependent on the identity of oxygen source used. Films grown using pure oxygen showed strongly faceted structures while those grown using H2O were dominated by porous interwoven and nanostructured films. The size and density of the faceted surface are strongly dependent on the growth rate of the films, controlled by adjustment of growth parameters. High growth rates resulted in small and dense grains. The growth of Co3O4 (1 1 1) was only successful on the a- and c-plane sapphire substrates, with no indication of nucleation and growth on r-plane sapphire substrates. Under otherwise identical growth conditions, the growth rate of films grown using H2O vapor was found to be 5 times higher than when using pure oxygen. These results demonstrate that Co(dpm)3 is a viable source for Co3O4 thin film growth by MOCVD, with resultant film morphology being highly dependent on the oxygen source and growth parameters.