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In this work, we report a simplified method to measure thermal conductivity from the typical Raman thermometry method by employing a much simpler dispersion relationship equation and the Debye function, instead of solving the heat equation. Unlike the typical Raman thermometry method, our new method only requires monitoring of the temperature-dependent Raman mode shifting without considering laser power-dependent Raman mode shifting. Thus, this new calculation method offers a simpler way to calculate the thermal conductivity of materials with great precision. As a model system, theβ-Ga₂O₃nanomembrane (NM) on a diamond substrate was prepared to measure thermal conductivity ofβ-Ga₂O₃NMs at different thicknesses (100 nm, 1000 nm, and 4000 nm). Furthermore, the phonon penetration depth was investigated to understand how deep phonons can be dispersed in the sample so as to guide the dimensional design parameter of the device from the thermal management perspective.

 

In this study, Si/β‐Ga₂O₃solar‐blind photodetectors (PDs) have been demonstrated via micro‐transfer printing of a single crystalline Si pillar on β‐Ga₂O₃. Unlike other previous approaches for β‐Ga₂O₃based heterojunction, this new single crystalline p‐n Si/β‐Ga₂O₃heterojunction has a particle‐free heterointerface and does not show any sign of internal strain after the heterogeneous integration that is confirmed by Raman spectroscopy. As a result, PDs exhibit extremely high photoresponsivity (748 A W⁻¹), quantum efficiency (3.67 × 10⁵%), and UV/visible rejection ratio (≈10⁵) under UV light illumination. This result is believed to provide a viable route for the realization of high‐performance solar‐blind photodetection systems, which form some of the most indispensable and important components in high‐performance next‐generation security, biomedical, and environmental monitoring systems. Also, the unique heterogeneous integration method allows us to realize a variety of β‐Ga₂O₃based heterostructures that can further enhance the optical performances of β‐Ga₂O₃based PDs.

 

A free‐standing β‐Ga₂O₃, also called β‐Ga₂O₃nanomembrane (NM), is an important next‐generation wide bandgap semiconductor that can be used for myriad high‐performance future flexible electronics. However, details of structure‐property relationships of β‐Ga₂O₃NM under strain conditions have not yet investigated. In this paper, the electrical properties of β‐Ga₂O₃NM under different uniaxial strain conditions using various surface analysis methods are systematically investigated and layer‐delamination and fractures are revealed. The electrical characterization shows that the presence of nanometer‐sized gaps between fractured pieces in β‐Ga₂O₃NM causes a severe property degradation due to higher resistance and uneven charge distribution in β‐Ga₂O₃NM which is also confirmed by the multiphysics simulation. Interestingly, the degraded performance in β‐Ga₂O₃NM is substantially recovered by introducing excessive OH‐bonds in fractured β‐Ga₂O₃NM via the water vapor treatment. The X‐ray photoelectron spectroscopy study reveals that a formation of OH‐bonds by the water vapor treatment chemically connects nano‐gaps. Thus, the treated β‐Ga₂O₃samples exhibit reliable and stable recovered electrical properties up to ≈90% of their initial values. Therefore, this result offers a viable route for utilizing β‐Ga₂O₃NMs as a next‐generation material for a myriad of high‐performance flexible electronics and optoelectronic applications.

 

Here, high power flexible Schottky barrier diodes (SBDs) are demonstrated on a plastic substrate using single crystalline β‐Ga₂O₃nanomembranes (NMs). In order to realize flexible high power β‐Ga₂O₃SBDs, sub‐micron thick freestanding β‐Ga₂O₃NMs are created from a bulk β‐Ga₂O₃substrate and transfer‐printed onto the plastic substrate via a microtransfer printing method. It is revealed that the material property of β‐Ga₂O₃NMs such as crystal structure, electron affinity, and bandgap remains unchanged compared with its bulk properties. Flexible β‐Ga₂O₃SBDs exhibit the record high critical breakdown field strength (E_c) of 1.2 MV cm⁻¹in the flat condition and 1.07 MV cm⁻¹ofE_cunder the bending condition. Overall, flexible β‐Ga₂O₃SBDs offer great promise for future flexible energy convergence systems and are expected to provide a much larger and more versatile platform to address a broader range of high‐performance flexible applications.

 

Abstract In this paper, transient delayed rise and fall times for beta gallium oxide ( β -Ga 2 O 3 ) nanomembrane (NM) Schottky barrier diodes (SBDs) formed on four different substrates (diamond, Si, sapphire, and polyimide) were measured using a sub-micron second resolution time-resolved electrical measurement system under different temperature conditions. The devices exhibited noticeably less-delayed turn on/turn off transient time when β -Ga 2 O 3 NM SBDs were built on a high thermal conductive (high- k ) substrate. Furthermore, a relationship between the β -Ga 2 O 3 NM thicknesses under different temperature conditions and their transient characteristics were systematically investigated and verified it using a multiphysics simulator. Overall, our results revealed the impact of various substrates with different thermal properties and different β -Ga 2 O 3 NM thicknesses on the performance of β -Ga 2 O 3 NM-based devices. Thus, the high- k substrate integration strategy will help design future β -Ga 2 O 3 -based devices by maximizing heat dissipation from the β -Ga 2 O 3 layer. 

In this study, we demonstrate a tolerant and durable Cr/Ni bilayer metal etch mask that allows us to realize approximately 150:1 etch selectivity to diamond. This result is achieved through the use of a very thin initial Cr layer of <10 nm thickness as part of the bilayer metal mask, which results in five to ten times improved selectivity than thick single metal layer masks or bilayer masks with thicker combinations. A finite element analysis was employed to design and understand the physics and working mechanism of the bilayer metal masks with different thicknesses. Raman spectroscopy and energy-dispersive x-ray spectroscopy on the diamond surface were also performed to investigate the changes in diamond quality before and after the deep diamond etching and found that no noticeable etch damage or defects were formed. Overall, this mask strategy offers a viable way to realize deep diamond etching using a high heat and chemistry tolerant and durable bilayer metal etching mask. It also offers several technological benefits and advantages, including various deposition method options, such as sputtering and physical vapor deposition, that can be used and the total thinness of the bilayer metal mask required given the higher selectivity allows us to realize fine diamond etching or high-aspect ratio etching, which is a critical fabrication process for future power, RF, MEMS, and quantum device applications.

 

In this paper, we demonstrated large-size free-standing single-crystal β-Ga 2 O 3 NMs fabricated by the hydrogen implantation and lift-off process directly from MOCVD grown β-Ga 2 O 3 epifilms on native substrates. The optimum implantation conditions were simulated with a Monte-Carlo simulation method to obtain a high hydrogen concentration with a narrow ion distribution at the desired depth. Two as grown β-Ga 2 O 3 samples with different orientations ([100] and [001]) were used to successfully create 1.2 μm thick β-Ga 2 O 3 NMs without any physical damage. These β-Ga 2 O 3 NMs were then transfer-printed onto rigid and flexible substrates such as SiC and polyimide substrates. Various material characterization studies were performed to investigate their crystal quality, surface morphologies, optical properties, mechanical properties, and bandgaps before and after the lift-off and revealed that the good material quality was maintained. This result offers several benefits in that the thickness, doping, and size of β-Ga 2 O 3 NMs can be fully controlled. Moreover, more advanced β-Ga 2 O 3 -based NM structures such as (Al x Ga 1−x ) 2 O 3 /Ga 2 O 3 heterostructure NMs can be directly created from their bulk epitaxy substrates; thus this study provides a viable route for the realization of high performance β-Ga 2 O 3 NM-based electronics and optoelectronics that can be built on various substrates and platforms. 

This paper reports the fabrication of β-Ga 2 O 3 nanomembrane (NM) based flexible photodetectors (PDs) and the investigation of their optoelectrical properties under bending conditions. Flexible β-Ga 2 O 3 NM PDs exhibited reliable solar-blind photo-detection under bending conditions. Interestingly, a slight shifting in wavelength of the maximum solar-blind photo-current was observed under the bending condition. To investigate the reason for this peak shifting, the optical properties of β-Ga 2 O 3 NMs under different strain conditions were measured, which revealed changes in the refractive index, extinction coefficient and bandgap of strained β-Ga 2 O 3 NMs due to the presence of nano-sized cracks in the β-Ga 2 O 3 NMs. The results of a multiphysics simulation and a density-functional theory calculation for strained β-Ga 2 O 3 NMs showed that the conduction band minimum and the valence band maximum states were shifted nearly linearly with the applied uniaxial strain, which caused changes in the optical properties of the β-Ga 2 O 3 NM. We also found that nano-gaps in the β-Ga 2 O 3 NM play a crucial role in enhancing the photoresponsivity of the β-Ga 2 O 3 NM PD under bending conditions due to the secondary light absorption caused by reflected light from the nano-gap surfaces. Therefore, this research provides a viable route to realize high-performance flexible photodetectors, which are one of the indispensable components in future flexible sensor systems. 

Theβ-Ga₂O₃nanomembrane (NM)/diamond heterostructure is one of the promising ultra-wide bandgap heterostructures that offers numerous complementary advantages from both materials. In this work, we have investigated the thermal properties of theβ-Ga₂O₃NM/diamond heterostructure with three different thicknesses ofβ-Ga₂O₃nanomembranes (NMs), namely 100 nm, 1000 nm, and 4000 nm thickβ-Ga₂O₃NMs using Raman thermometry. The thermal property—temperature relationships of theseβ-Ga₂O₃NM/diamond heterostructures, such as thermal conductivity and interfacial thermal boundary conductance were determined under different temperature conditions (from 100 K to 500 K with a 40 K interval). The result provides benchmark knowledge about the thermal conductivity ofβ-Ga₂O₃NMs over a wide temperature range for the design of novelβ-Ga₂O₃-based power electronics and optoelectronics.