On the surface of as-grown β-Ga2O3 single crystals that are cut and polished, we found nanometer-sized grooves elongated in the [001] direction. We confirmed that these grooves terminate within the crystals in the [010] direction. This proves that the grooves are different from micropipes penetrating crystals. Their typical length and width are 50–1200 nm in the [001] direction and ∼40 nm in the [100] direction, respectively. The grooves tend to form an array in the [001] direction. The type of nanometer-sized grooves should be essentially different from etch pits.

Diamond/Si junctions have been achieved by surface activated bonding method without any chemical and heating treatments. Bonded interfaces were obtained that were free from voids and mechanical cracks. Observations by using transmission electron microscopy indicated that an amorphous layer with a thickness of ∼20 nm across the bonded interface was formed, and no structural defects were observed at the interface. The amorphous layer of the diamond side was confirmed to be the mixture of sp2 and sp3 carbons by electron energy loss spectroscopy analyzation. The sp3/(sp2 + sp3) ratio estimated from the X-ray photoemission spectra decreased from 53.8% to 27.5%, while the relative intensity of sp2 increased from 26.8% to 72.5% after the irradiation with Ar fast beam which should be predominantly attributable to the diamond-graphite conversion.

Here, we investigate the dislocations in β-Ga 2 O 3 single crystals grown by edge-defined film-fed growth (EFG) and halide vapor-phase epitaxy (HVPE) using synchrotron X-ray topography. The (001)-and (201)-oriented crystals grown in the [010] direction by EFG exhibited dislocations along the 〈010〉 direction with some dislocations oriented in a line; in addition, wandering dislocations were observed on the (001) surface. Based on the invisibility criterion, the Burgers vector of some dislocations was determined to be 〈010〉. On the other hand, in the (001) film grown by HVPE over the EFG substrate, threading dislocations propagating in the [001] direction were observed. Furthermore, it was found that the dislocations on the substrate grown by EFG were inherited by the film formed by HVPE: a dislocation was generated in the film grown by HVPE at both ends of the void defects in the substrate grown by EFG.

Diamond/Si bonding interface with an entire contact area and high thermal stability is achieved by surface activated bonding method. The fabrication of diamond field-effect transistors (FETs) on the diamond bonded to Si is demonstrated. The FET exhibits clear saturation and pinch-off characteristics. A 5-nm-thick SixCx-1 layer was formed at the

Highlights•Diamond/Si bonding interface could withstand a load of high temperature as high as 800 °C.•The amorphous layer observed at the bonding interface decreased with annealing temperature.•The residual stress released in the diamond of the bonding interface decreased with annealing temperature.•The residual stress formed in the bonding interface annealed at 1000˚C is much smaller than that of diamond grown on Si.