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Register a new userWafer-scale Heterogeneous Integration of Monocrystalline b{eta}-Ga2O3 Thin Films on SiC for Thermal Management by Ion-Cutting Technique
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The ultra-wide bandgap, high breakdown electric field, and large-area affordable substrates make b{eta}-Ga2O3 promising for applications of next-generation power electronics while its thermal conductivity is at least one order of magnitude lower than other wide/ultrawide bandgap semiconductors. To avoid the degradation of device performance and reliability induced by the localized Joule-heating, aggressive thermal management strategies are essential, especially for high-power high-frequency applications. This work reports a scalable thermal management strategy to heterogeneously integrate wafer-scale monocrystalline b{eta}-Ga2O3 thin films on high thermal conductivity SiC substrates by ion-cutting technique. The thermal boundary conductance (TBC) of the b{eta}-Ga2O3-SiC interfaces and thermal conductivity of the b{eta}-Ga2O3 thin films were measured by Time-domain Thermoreflectance (TDTR) to evaluate the effects of interlayer thickness and thermal annealing. Materials characterizations were performed to understand the mechanisms of thermal transport in these structures. The results show that the b{eta}-Ga2O3-SiC TBC values increase with decreasing interlayer thickness and the b{eta}-Ga2O3 thermal conductivity increases more than twice after annealing at 800 oC due to the removal of implantation-induced strain in the films. A Callaway model is built to understand the measured thermal conductivity. Small spot-to-spot variations of both TBC and Ga2O3 thermal conductivity confirm the uniformity and high-quality of the bonding and exfoliation. Our work paves the way for thermal management of power electronics and b{eta}-Ga2O3 related semiconductor devices.
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We report on low-temperature MOVPE growth of silicon delta-doped b{eta}-Ga2O3 films with low FWHM. The as-grown films are characterized using Secondary-ion mass spectroscopy, Capacitance-Voltage and Hall techniques. SIMS measurements show that surface segregation is the chief cause of large FWHM in MOVPE-grown films. The surface segregation coefficient (R) is observed to reduce with reduction in the growth temperature. Films grown at 600 {deg}C show an electron concentration of 9.7 x 1012 cm-2 and a FWHM of 3.2 nm. High resolution scanning/transmission electron microscopy of the epitaxial film did not reveal any significant observable degradation in crystal quality of the delta sheet and surrounding regions. Hall measurements of delta-doped film on Fe-doped substrate showed a sheet charge density of 6.1 x 1012 cm-2 and carrier mobility of 83 cm2/V. s. Realization of sharp delta doping profiles in MOVPE-grown b{eta}-Ga2O3 is promising for high performance device applications.
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We demonstrate that the confocal laser scanning microscopy (CLSM) provides a non-destructive, highly-efficient characterization method for large-area epitaxial graphene and graphene nanostructures on SiC substrates, which can be applied in ambient air without sample preparation and is insusceptible to surface charging or surface contamination. Based on the variation of reflected intensity from regions covered by interfacial layer, single layer, bilayer, or few layer graphene, and through the correlation to the results from Raman spectroscopy and SPM, CLSM images with a high resolution (around 150 nm) reveal that the intensity contrast has distinct feature for undergrown graphene (mixing of dense, parallel graphene nanoribbons and interfacial layer), continuous graphene, and overgrown graphene. Moreover, CLSM has a real acquisition time hundreds of times faster per unit area than the supplementary characterization methods. We believe that the confocal laser scanning microscope will be an indispensable tool for mass-produced epitaxial graphene or applicable 2D materials.
We report on the growth and characterization of metalorganic vapor-phase epitaxy-grown b{eta}-(AlxGa1-x)2O3/b{eta}-Ga2O3 modulation-doped heterostructures. Electron channel is realized in the heterostructure by utilizing a delta-doped b{eta}-(AlxGa1-x)2O3 barrier. Electron channel characteristics are studied using transfer length method, capacitance-voltage and Hall measurements. Hall sheet charge density of 1.06 x 1013 cm-2 and mobility of 111 cm2/Vs is measured at room temperature. Fabricated transistor showed peak current of 22 mA/mm and on-off ratio of 8 x 106. Sheet resistance of 5.3 k{Omega}/Square is measured at room temperature, which includes contribution from a parallel channel in b{eta}-(AlxGa1-x)2O3.
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