The 8 μm thick single-crystalline α-Ga2O3 epilayers have been heteroepitaxially grown on sapphire (0001) substrates via mist chemical vapor deposition technique. High resolution X-ray diffraction measurements show that the full-widths-at-half-maximum (FWHM) of rocking curves for the (0006) and (10-14) planes are 0.024° and 0.24°, and the corresponding densities of screw and edge dislocations are 2.24 × 106 and 1.63 × 109 cm−2, respectively, indicative of high single crystallinity. The out-of-plane and in-plane epitaxial relationships are [0001] α-Ga2O3//[0001] α-Al2O3 and [11-20] α-Ga2O3//[11-20] α-Al2O3, respectively. The lateral domain size is in micron scale and the indirect bandgap is determined as 5.03 eV by transmittance spectra. Raman measurement indicates that the lattice-mismatch induced compressive residual strain cannot be ruled out despite the large thickness of the α-Ga2O3 epilayer. The achieved high quality α-Ga2O3 may provide an alternative material platform for developing high performance power devices and solar-blind photodetectors.

FIG. 5. Bandgap versus composition of b-(Al x Ga 1Àx) 2 O 3 plots obtained from our experiment and HSE simulation, and recent experimental studies. Reproduced with permission from Appl.

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In this work, nanoplasmonically enhanced α-Ga2O3 solar-blind photodetectors with an interdigital structure were fabricated on sapphire. By introducing Al nanoparticles (NPs) onto the device surface, the photodetector obtained a significant increase in responsivity at the solar-blind region, and the response peak located at 244 nm reached 3.36 A/W under an applied voltage of 5 V. Compared with the responsivity at 320 nm, the response ratio exceeds 240, demonstrating a superior solar-blind cut-off edge. It also presents that the photocurrent was dramatically increased under 254 nm ultraviolet irradiation for the enhanced device while the dark current remains below 1 pA at 20 V. To explicitly elucidate the enhancement effects by Al NPs under ultraviolet illumination, Kelvin probe force microscopy was employed and directly revealed the physical mechanism of surface plasmon oscillation, which promoted the formation of localized electric fields on α-Ga2O3. In addition, we illustrated the effects of interdigital spacing on device performances through experimental measurements and theoretical calculations. These results not only provide direct evidences for Al nanoplasmonic enhancement on the α-Ga2O3 device but also facilitate design and fabrication of solar-blind photodetectors.

Abstract