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We fabricated p-Si/n-Ga2O3 and p+-Si/n-Ga2O3 heterostructures by surface-activated bonding (SAB) and investigated their electrical properties. Current density–voltage measurement was performed before and after thermal annealing at 450 °C. The current density substantially increased after annealing, which was attributed to thinning of an intermediate layer formed by the bonding process. Distinctive two-stage capacitance–voltage characteristics were observed for p-Si/n-Ga2O3 heterostructures, which were well reproduced by numerical calculation considering the effect of two-dimensional electron gas formed at the heterointerface. These results indicate that Ga2O3-based p–n heterostructures with good interface properties and large-area uniformity can be fabricated using SAB. [ABSTRACT FROM AUTHOR]

Frequency-domain probe beam deflection (FD-PBD) is an experimental technique for measuring thermal properties that combines heating by a modulated pump laser and measurement of the temperature field via thermoelastic displacement of the sample surface. In the conventional implementation of FD-PBD, the data are mostly sensitive to the in-plane thermal diffusivity. We describe an extension of FD-PBD that introduces sensitivity to through-plane thermal conductance by immersing the sample in a dielectric liquid and measuring the beam deflection created by the temperature field of the liquid. We demonstrate the accuracy of the method by measuring (1) the thermal conductivity of a 310 nm thick thermally grown oxide on Si, (2) the thermal boundary conductance of bonded interface between a 3C-SiC film and a single crystal diamond substrate, and (3) the thermal conductivities of several bulk materials. We map the thermal boundary conductance of a 3C-SiC/diamond interface with a precision of 1% using a lock-in time constant of 3 ms and dwell time of 15 ms. The spatial resolution and maximum probing depth are proportional to the radius of the focused laser beams and can be varied over the range of 1–20 μm and 4–80 μm, respectively, by varying the 1/e2 intensity radius of the focused laser beams from 2 to 40 μm. FD-PBD with liquid immersion thus enables fast mapping of spatial variations in thermal boundary conductance of deeply buried interfaces. [ABSTRACT FROM AUTHOR]

We studied electrical properties of n-Si/n-Ga2O3 heterojunctions fabricated by surface-activated bonding. The energy barrier heights (qϕb) at the Si/Ga2O3 interface for different reverse voltages (Vrev) were derived from temperature-dependent current density–voltage (J–V–T) characteristics. With shifting Vrev to the negative direction, qϕb gradually decreased and reached a constant value due to negatively charged interface states. The conduction band offset at the heterointerface was estimated to be 0.18 eV from the Vrev dependence of qϕb. The qϕb calculated from a capacitance of the heterojunction at thermal equilibrium was larger than those derived from the J–V–T characteristics, attributing to spatially inhomogeneous qϕb caused by the non-uniform distribution of the charged interface states. The density of shallow interface states was also extracted from the reverse J–V–T characteristics, which was estimated to be about 6 × 1012 cm−2 eV−1. [ABSTRACT FROM AUTHOR]

The direct integration of GaN with Si can boost great potential for low-cost, large-scale, and high-power device applications. However, it is still challengeable to directly grow GaN on Si without using thick strain relief buffer layers due to their large lattice and thermal-expansion-coefficient mismatches. In this work, a GaN/Si heterointerface without any buffer layer is fabricated at room temperature via surface activated bonding (SAB). The residual stress states and interfacial microstructures of GaN/Si heterostructures were systematically investigated through micro-Raman spectroscopy and transmission electron microscopy. Compared to the large compressive stress that existed in GaN layers grown on Si by metalorganic chemical vapor deposition, a significantly relaxed and uniform small tensile stress was observed in GaN layers bonded to Si by SAB; this is mainly ascribed to the amorphous layer formed at the bonding interface. In addition, the interfacial microstructure and stress states of bonded GaN/Si heterointerfaces was found to be significantly tuned by appropriate thermal annealing. With increasing annealing temperature, the amorphous interlayer formed at the as-bonded interface gradually transforms into a thin crystallized interlayer without any observable defects even after annealing at 1000 °C, while the interlayer stresses at both GaN layer and Si monotonically change due to the interfacial re-crystallization. This work moves an important step forward directly integrating GaN to the present Si CMOS technology with high quality thin interfaces and brings great promises for wafer-scale low-cost fabrication of GaN electronics. [ABSTRACT FROM AUTHOR]