Energy-band alignment of stacked single-crystalline Si/ α -Ga 2 O 3 p–n heterojunctions

A stacked single-crystalline Si/ α -Ga 2 O 3 p–n heterojunction was formed by transferring a 100 nm p-Si nanomembrane onto an α -Ga 2 O 3 epiwafer. The α -Ga 2 O 3 layer exhibited a (110) x-ray diffraction reflection, and the epi-layer at the Si/ α -Ga 2 O 3 interface had a valence-band maximum located 4.29 ± 0.10 eV below the Fermi-level. X-ray photoelectron spectroscopy depth profiling revealed decreases of 0.11 eV in the Si 2p binding energy and 0.35 eV in the Ga 3d binding energy from the bulk-like regions to the interface, consistent with upward band bending on both sides at the junction interface. Applying the Kraut method with the valence-band offset defined as E V (Si) − E V ( α -Ga 2 O 3 ) gave 3.93 eV; the corresponding conduction-band offset was 0.25 eV. The enhanced Si–O and Ga–O components indicate an ultrathin oxide-containing bonding region formed during heterojunction integration. Rather than being treated as a thick parasitic oxide, this region is interpreted as a thin passivating interlayer that does not preclude reliable extraction of the effective band alignment of the as-fabricated junction. Energy band profiles in equilibrium and under forward and reverse bias were calculated using technology-computer-aided design. The fabricated p–n heterojunction diode exhibited rectifying current density–voltage characteristics with an ideality factor of 1.47. These results provide an experimentally constrained band alignment for stacked Si/ α -Ga 2 O 3 p–n heterojunctions and support their development for bipolar electronic devices.