The electrical properties of p-Si/n-GaAs heterojunctions fabricated by using surface-activated bonding (SAB) were investigated by measuring their current-voltage (I-V) and capacitance-voltage (C-V) characteristics. The I-V characteristics showed rectifying properties. Their flat-band voltage obtained from C-V measurements was around 1.6 V. Observation by using field-emission-scanning electron microscopy and energy dispersive X-ray spectroscopy revealed neither structural deficits nor oxide layers at the interfaces. These results suggest that the SAB-based Si/ GaAs heterojunctions are applicable for fabricating novel devices.

The effects of thermal annealing process on the interface in p þ-Si/n-SiC heterojunctions fabricated by using surface-activated bonding are investigated. It is found by measuring their current-voltage (I-V) characteristics that the reverse-bias current and the ideality factor decreased to 2.98 Â 10 À6 mA/cm 2 and 1.03, respectively, by annealing the junctions at 1000 C. Observation by using transmission electron microscopy indicates that an amorphous layer with a thickness of $6 nm is formed at the unannealed interface, which vanishes after annealing at 1000 C. No structural defects at the interface are observed even after annealing at such a high temperature.

The valence band offsets, ⌬E V , of In 0.17 Al 0.83 N / GaN, In 0.25 Al 0.75 N / GaN, and In 0.30 Al 0.70 N / GaN heterostructures grown by metal-organic vapor phase epitaxy were evaluated by using x-ray photoelectron spectroscopy ͑XPS͒. The dependence of the energy position and the full width at half maximum of the Al 2p spectrum on the exit angle indicated that there was sharp band bending caused by the polarization-induced electric field combined with surface Fermi-level pinning in each ultrathin InAlN layer. The ⌬E V values evaluated without taking into account band bending indicated large discrepancies from the theoretical estimates for all samples. Erroneous results due to band bending were corrected by applying numerical calculations, which led to acceptable results. The evaluated ⌬E V values were 0.2Ϯ 0.2 eV for In 0.17 Al 0.83 N / GaN, 0.1Ϯ 0.2 eV for In 0.25 Al 0.75 N / GaN, and 0.0Ϯ 0.2 eV for In 0.30 Al 0.70 N / GaN. Despite the large decrease of around 1.0 eV in the band gap of InAlN layers according to the increase in the In molar fraction, the decrease in ⌬E V was as small as 0.2 eV. Therefore, the change in band-gap discontinuity was mainly distributed to that in conduction band offset.

Microscopic electroluminescence (EL) and photoluminescence (PL) measurements of high-biased AlGaN/GaN high-electron-mobility transistors are reported. We observed that the EL intensity reveals peaks around the edge of the channel and the electron temperature there is higher than the electron temperature at the center of the channel. These EL features were found to be consistent with the change in the junction temperature, which we locally estimated by comparing the PL data with measurements in raised ambient temperatures.

junctions fabricated by surface-activated bonding (SAB) were investigated. An amorphous layer with a thickness of 3 nm was found across the bonding interface without annealing. The current-voltage (I-V) characteristics of p +-GaAs/n +-Si, p +-Si/n +-GaAs, n +-Si/n +-GaAs, and p +-Si/p +-GaAs junctions showed excellent linearity. The interface resistance of n +-Si/n +-GaAs junctions was found to be 0.112 Ω&cm 2 , which is the smallest value observed in all the samples. The resistance decreased with increasing annealing temperature and decreased to 0.074 Ω&cm 2 after the junction annealing at 400°C. These results demonstrate that n +-Si/n +-GaAs junctions are suitable for the connection of subcells in the fabrication of tandem solar cells.