Deep-level transient spectroscopy (DLTS) and Laplace-DLTS were used to investigate electrically active defects in (010)-oriented beta-Ga2O3 epilayers grown via metal-organic chemical vapor deposition and doped with Si during growth. The impact of isochronal rapid thermal annealing in N-2 on the electrical characteristics of Pt Schottky barrier diodes and on defect concentrations was examined by annealing at temperatures from 150 to 450 degrees C with 100 degrees C increments. Four deep levels were detected, with concentrations in the range of 10(13)-10(14) cm(-3) and activation energies of electron emission to the conduction band (Delta E-c) of 0.06, 0.40, 0.55, and 0.62 eV. The E-c-0.06 eV trap was no longer observed in DLTS measurements after heating to 400 K, and the E-c-0.62 eV trap was suppressed after annealing at 350 degrees C. In contrast, the E-c-0.40 eV trap progressively reduced in concentration, while the trap density of the E-c-0.55 eV level increased with each rapid thermal annealing step, suggesting defect redistribution along the [010] direction. The electric field dependence of the electron emission rates indicates acceptor-like behavior for the E-c-0.55 eV state and donor-like behavior for the E-c-0.62 eV state. As both states exhibit activation energies consistent with the commonly reported E1 defect, we propose the following labelling conventions: E1a (E-c-0.55 eV) and E1b (E-c-0.62 eV). The nature and potential origins for each of the observed defects are discussed.

A combined microanalysis and optical study of β-(AlxGa1-x)2O3 films grown on sapphire via metalorganic chemical vapour deposition, with thickness 350-1000 nm and Al fraction (x) from 0% to 45%, is presented. Al incorporation in the films showed a linear relation with nominal Al composition calculated from precursor flow rate, and the optical bandgap increased from 4.96 eV to 5.44 eV with a bowing parameter of 1.7 ± 0.5 eV. A high Al fraction led to reduced crystallinity, increased surface roughness, and diminished cathodoluminescence intensity. The topography revealed elongated surface features that evolved with Al content, and luminescence spectra exhibited a blueshift in peak emission attributed to the widening of the bandgap. These findings highlight the trade-off between bandgap tuning and material quality, informing future growth strategies for future electronic and optical devices.

Orthorhombic κ-phase Ga2O3 is a metastable, ferroelectric polymorph of Ga2O3 with a large spontaneous polarization, offering a pathway to polarization-induced high-mobility 2D electron gases via κ-Ga2O3/Al x Ga1-x N heterostructures. Here, we map the metal-organic chemical vapor deposition (MOCVD) growth window of κ-Ga2O3 on Al-rich Al x Ga1-x N-on-sapphire template layers (x = 0.5 and 0.75) by systematically varying the gallium and oxygen precursor flow rates and benchmark these results against cogrown films on c-plane sapphire. On Al0.5Ga0.5N, κ-Ga2O3 can be grown over a wide range of conditions extending to low growth rates and high VI/III regions, whereas on sapphire substrates the κ-phase favorable window is restricted to the high growth rate and low VI/III regime only. Microstructural and phase evolution analyses by X-ray diffraction (XRD) and transmission electron microscopy (TEM) of the κ-Ga2O3 films grown on Al0.5Ga0.5N confirms that growth initiates as a phase-pure monoclinic β-Ga2O3 layer; κ-Ga2O3 nucleation starts between 20 and 45 nm of layer thickness and becomes the only phase growing around ∼100-250 nm thick, resulting in a phase-pure κ-Ga2O3 top surface. A similar progression was observed for growth on x = 0.75% Al x Ga1-x N template layers.

Epitaxial.-Ga2O3 films grown on (001) diamond substrates with a.-(Al/Ga)2O3 buffer layer exhibit strong texture with multiple rotational domain variants sharing a common growth axis. This texture is attributed to two interrelated structural and geometrical factors: (1) pseudo-symmetry about the growth direction due to the high symmetry of the oxygen sublattice which results in close interplanar spacings of different lattice planes that determine the inplane lattice mismatch, and hence two different crystallographic relationships and types of domain variants; (2) the lack of higher-order symmetry in the C2/m monoclinic structure of.-Ga2O3 and the higher symmetry of the diamond substrate that leads to various subvariants. The microstructure of the films consists predominantly of domain clusters, with domains rotated by either.60. or 120. (.10.) relative to each other about the growth axis.[102]. Some domain boundaries (DBs), visible near edge-on in cross-sectional and plan-view projections, exhibit a high degree of coherency. These highly coherent DBs with small lattice rotation and/or distortion near the DB are observed where small inplane and off-plane DB lattice mismatch is expected. Larger lattice mismatch between domains is accommodated by relatively large lattice rotation and/or distortion near the DB, as well as changes in DB structure and shape. Understanding the origin of texture and the characteristics of common planar defects in.-Ga2O3 will offer insights into their impact on thermal and electrical transport properties and enable effective microstructural optimization for successful integration into future power electronics.

Abstract Two complementary localised density of states spectroscopies, Modulated Photo-Conductivity (MPC) and the Constant Photocurrent Method (CPM) are applied to Ga2O3 thin films and are shown to be sensitive to carrier traps above and below the Fermi level, respectively. These techniques measure the film directly, without requiring a Schottky or p-n junction, which may offer advantages over conventional techniques in the study of high-resistivity or semi-insulating materials. The benefits of a higher-resolution MPC analysis are demonstrated.

GaN high electron mobility transistors (HEMTs) on SiC substrates are the highest performing commercially available transistors for high-power, high-frequency applications. However, Joule self-heating limits the maximum areal power density, i.e., operating power is derated to ensure the lifetime of GaN-based devices. Diamond is attractive as a heat sink due to its record-high thermal conductivity combined with its high electrical resistivity. GaN-on-diamond devices have been demonstrated, bringing the diamond as close as possible to the active device area. The GaN/diamond interface, close to the channel heat source, needs to efficiently conduct high heat fluxes, but it can present a significant thermal boundary resistance (TBR). In this work, we implement nanoscale trenches between GaN and diamond to explore new strategies for reducing the effective GaN/diamond TBR (TBReff). A 3× reduction in GaN/diamond TBReff was achieved using this approach, which is consistent with the increased contact area; thermal properties were measured using nanosecond transient thermoreflectance (ns-TTR). In addition, the SiN x dielectric interlayer between the GaN and diamond increased its thermal conductivity by 2× through annealing, further reducing the TBR. This work demonstrates that the thermal resistance of heterogeneous interfaces can be optimized by nanostructured patterning and high-temperature annealing, which paves the way for enhanced thermal management in future device applications.

Thermal management is the main technological challenge for next generation electronic devices. Recently, several groups successfully demonstrated boron arsenide (BAs) microcrystals with an ultrahigh thermal conductivity approaching that of diamond. The development of scalable epitaxial BAs growth techniques is urgently required to enable a transition of BAs material to real applications. We have grown boron arsenide layers on 3C-SiC/Si and sapphire substrates over a wide temperature range using molecular beam epitaxy (MBE). We have confirmed the incorporation of arsenic by a wide range of characterization techniques. The best quality of the boron arsenide layers was achieved at high growth temperatures of around 750 °C. We have demonstrated that high temperatures nucleation of the boron arsenide layer started with deposition of boron-rich monolayers on the substrate surface. For the epitaxy on sapphire during the initial growth phase, the cubic boron arsenide layers align with the hexagonal structure of the sapphire substrate and grow in the ⟨111⟩ direction for a few crystalline monolayers; however, currently, we are not able to sustain that, and the boron arsenide layer becomes amorphous. For boron arsenide layers grown at high temperatures, we have observed an increase in the thermal conductivity and cathodoluminescence optical response with a reproducible peak centered at ∼1.67 eV. The experimental results are explained by increased chemical interaction between arsenic and boron at growth temperatures above ∼600 °C. Our experimental data show that MBE growth conditions need to be further optimized first to improve stoichiometry and after that to decrease point-defect densities in boron arsenide layers to achieve an increase in the thermal conductivity.

Diamond is an attractive substrate choice for the growth of gallium oxide for high-power device applications due to its high thermal conductivity. However, the cubic crystal structure of diamond is very different from that of monoclinic β-Ga2O3. Adding to the complexity, there is a large surface energy difference between the two materials, and a high-temperature oxide environment is required for Ga2O3 growth. Here, we demonstrate a viable pathway that enables thick adherent Ga2O3 layers to be grown epitaxially on diamond (001) substrates, using metal–organic chemical vapor deposition. This growth is achieved using an intermediary (Al0.06Ga0.94)2O3 (AGO6) buffer layer. Omission of the strain management buffer results in Ga2O3 films that exfoliate into membranes for thicknesses greater than about 500 nm. Implementation of the buffer layer allows for the alleviation of the excess strain energy developed within the grown film and assists in improving film quality, increasing grain size, reducing dislocations, and providing epitaxially textured thin films relative to layers without the buffer. Adherent 750-nm-thick β-Ga2O3 epitaxial layers have been achieved using the AGO6 buffer, with a full-width at half-maximum of 1.36° and a root-mean-square roughness of 6.24 nm. The thermal conductivity of the β-Ga2O3 thin films with and without the AGO6 buffer was measured to be 6.0–6.5 W/mK. Thus, integration of the monoclinic gallium oxide with the diamond cubic substrate using the intermediary buffer layer improves the crystal quality but does not impact the thermal conductivity, suggesting the future feasibility of using diamond substrates for a wide range of Ga2O3 device applications.

Gallium Oxide has a high Baliga Figure of Merit but it is challenging to fully exploit its potential for power electronics because of its limited thermal conductivity and lack of usable p-doping. We report integration of Gallium Oxide with diamond and SiC, using growth and bonding based approaches, for mitigation.

Gallium oxide (Ga2O3) based phototransistor can be used as a switch and an amplifier in typical digital and analog UV photonic applications, respectively. The light detection capability in Ga2O3 is very high, but these phototransistors suffer from poor drain current saturation with bias. Furthermore, the transistor switching action generally necessitates a gate terminal voltage, where a faulty gate power supply can lead to a high current flow in the transistor and subsequently damage the control driver circuit. An alternative is a two-terminal device with pure optical coupling at gate terminal, termed as a light effect transistor (LET). The LET has the field effect transistor (FET)-like current–voltage output characteristics, where the controlling mode is light instead of voltage, and being a two-terminal device, the fabrication processes are straightforward and cost-effective in contrast to the traditional FET. The fabricated LET device comprised an n-Ga2O3/p-GaN heterojunction with a planar metal–semiconductor–metal structure. This unique device can operate in two modes, linear (photodetector) within 1–2.5 V and saturation [depletion width modulated light effect transistor (DM-LET)] within 2.5–5 V. Under the DM-LET mode, the structure exhibits transistor-like action, the drain current saturates with the variation in drain voltage and is only controlled by the change in optical intensity. The transistor-like action has been attributed to the pinch-off effect near the drain electrode due to modulation in the heterojunction depletion width and has been explained using detailed numerical simulation. Such devices have the potential to be used in UV photonic integrated circuits and UV-non-line-of-sight communication technologies.

Heteroepitaxy of gallium oxide (Ga2O3) is gaining popularity to address the absence of p-type doping, limited thermal conductivity of Ga2O3 epilayers, and toward realizing high-quality p-n heterojunction. During the growth of beta-Ga2O3 on 4H-SiC (0001) substrates using metal-organic chemical vapor deposition, we observed formation of incomplete, misoriented particles when the layer was grown at a temperature between 650 degrees C and 750 degrees C. We propose a thermodynamic model for Ga2O3 heteroepitaxy on foreign substrates which shows that the energy cost of growing beta-Ga2O3 on 4H-SiC is slightly lower as compared to sapphire substrates, suggesting similar high-temperature growth as sapphire, typically in the range of 850 degrees C-950 degrees C, that can be used for the growth of beta-Ga2O3 on SiC. A two-step modified growth method was developed where the nucleation layer was grown at 750 degrees C followed by a buffer layer grown at various temperatures from 920 degrees C to 950 degrees C. 2 theta-omega scan of X-ray diffraction (XRD) and transmission electron microscope images confirm the beta-polymorph of Ga2O3 with dominant peaks in the (-201) direction. The buffer layer grown at 950 degrees C using a "ramp-growth" technique exhibits root-mean-square surface roughness of 3 nm and full width of half maxima of XRD rocking curve as low as 0.79 degrees, comparable to the most mature beta-Ga2O3 heteroepitaxy on sapphire, as predicted by the thermodynamic model. Finally, the interface energy of an average Ga2O3 island grown on 4H-SiC is calculated to be 0.2 J/m(2) from the cross-section scanning transmission electron microscope image, following the Wulff-Kaishew theorem of the equilibrium island shape.

We discuss the potential of heterogenous integration of Ga2O3 with diamond for enabling energy-efficient kV-class power devices. The integration alleviates Ga2O3 material drawbacks such as its low thermal conductivity and inefficient hole conductivity. The benefits of heterogeneous integration are demonstrated through electrical and thermal simulations of a Ga2O3-Al2O3-diamond superjunction based Schottky barrier diode. The simulation studies show that the novel device has potential to break the RON-breakdown voltage limit of Ga2O3, while showing relatively low rise in temperature compared to conventional devices. First steps for the actual materials integration are taken with the epitaxial growth of Ga2O3 on single crystal diamond substrates.

Heteroepitaxial growth of β-Ga2O3 on (001) diamond by metal–organic chemical vapor deposition (MOCVD) is reported. A detailed study was performed with Transmission Electron Microscopy (TEM) elucidating the epitaxial relation of (−201) β-Ga2O3||(001) diamond and [010]/[−13–2] β-Ga2O3 ||[110]/[1–10] diamond, with the presence of different crystallographically related epitaxial variants apparent from selected area diffraction patterns. A model explaining the arrangement of atoms along ⟨110⟩ diamond is demonstrated with a lattice mismatch of 1.03–3.66% in the perpendicular direction. Dark field imaging showed evidence of arrays of discrete defects at the boundaries between different grains. Strategies to reduce the density of defects are discussed.

The harmful UV radiation leaking out of the ozone hole can have a detrimental effect on mother nature. To monitor any UV rays leaking out of the ozone hole requires an electronic device such as deep UV photodetectors. In this context, Sn-doped Ga2O3 incorporated with SnO2 nanostructures has been grown on a c-plane sapphire substrate using low-pressure chemical vapor deposition (LPCVD) followed by the fabrication of metal-semiconductor-metal (MSM) based deep ultraviolet (UV) photodetector (PD) using Pt as electrodes with interdigitated geometry. The PD possesses a low dark current of 21 nA even at 50 V bias with a very high photo-to-dark current ratio of 9 × 104 and exceptionally large responsivity of 1532 and 262 A/W under 254 nm and 302 nm UV-illumination respectively. Consequently, an extremely high detectivity of 1.7 × 1015 Jones and external quantum efficiency of 7.4 × 105% has been recorded under 254 nm illumination with a fast fall time of 0.2 sec. The PD works well in UV-B range with high responsivity and is attributed to the long wavelength absorption by the SnO2 nanostructures accompanied by a charge transfer from SnO2 to the Ga2O3 layer. The high gain has been attributed to the photoconductive gain due to interface trapped charges and self-trapped holes, along with light trapping on the textured Ga2O3 surface.

This article proposes a new junction barrier Schottky diode (JBSD) design based on P-GaN/N-Ga2O3 heterojunction with faster switching characteristics and higher breakdown ability than the traditional two-terminal power switches. Calibrated models have been used for technology computer-aided design (TCAD) simulations of the proposed JBSD after a comprehensive review of various physical models and model parameters in the present literature. Analysis in terms of static and transient behavior for a varying proportion of PN area to the Schottky contact area (PN:SBD ratio) was looked upon for the JBSD. With the increase of PN:SBD ratio, the reverse voltage handling capability increased as expected, but the reverse recovery time and maximum reverse recovery current decreased. This might be counterintuitive initially, as with an increase in PN:SBD ratio, the PN behavior would dominate over SBD, and slower transient behavior is expected. However, due to redistribution of electric field and the reduction in depletion capacitance across the JBSD with increase in PN:SBD ratio, JBSD with PN:SBD ratio of 8 gives us a breakdown at 1890 V and a switching time of 9.72 ns. Furthermore, a comparison of the transient response with state-of-the-art SiC Schottky diode reveals the efficiency of the proposed structure in terms of reverse recovery parameters to be significantly better, translating to 7.4 times lower power losses at higher frequencies. Overall, the design and analysis presented here suggest the promising potential of P-GaN/N-Ga2O3 vertical devices for high-voltage and fast switching applications.

Reduction of high dark current has been a challenge for high responsivity photodetector (PD). In this context, the present article demonstrates an ultralow dark current of Ga 2 O 3 -based deep ultraviolet (UV)photodetectors (UV-PDs) with enhanced photoresponses by tailoring a p/n heterojunction. An n-Ga 2 O 3 /p-CuO quasi-heterostructure-based deep UV-PDs has been fabricated on a sapphire (0001) substrate using an inexpensive electrospraying technique. After Ga 2 O 3 deposition, platinum (Pt) electrodes (~50 nm) are fabricated as a metal-semiconductor-metal (MSM) device using sputtering. The device exhibits a very low dark current in the order of few fA (6.94 × 10 -14 A) at 5 V because of the enhanced depletion width at p/n heterojunction and Pt/Ga 2 O 3 metal-semiconductor contacts, which provides a narrow path for free carriers to travel from one metal contact to other under dark condition. The depletion layers get thinner due to the absorption of UV-photons in the UV-illumination condition. Hence, the photogenerated carriers get a wider channel to get collected at Pt-electrodes. Thus, in addition to ultralow dark current, the device exhibits an extraordinary photodetection characteristics, such as a high responsivity (~6.33 × 10 3 AW -1 ), remarkable phototo-dark current ratio (~2.99 × 10 6 ), very high detectivity (~4.44 × 10 14 mHz 0.5 W -1 ), and exceptional external quantum efficiency of ~3.1 × 10 6 % at 5 V.