This article reports a nonpolar GaN metal−semiconductor− metal (MSM) photodetector (PD) with an ultrahigh responsivity and an ultrafast response speed in the ultraviolet spectral region, which was fabricated on nonpolar (112̅ 0) GaN stripe arrays with a major improvement in crystal quality grown on patterned (110) silicon substrates by means of using our twostep processes. Our nonpolar GaN MSM-PD exhibits a responsivity of 695.3 A/W at 1 V bias and 12628.3 A/W at 5 V bias, both under 360 nm ultraviolet illumination, which are more than 20 times higher and 4 orders of magnitude higher compared to the current state-of-the-art photodetector, respectively. The nonpolar GaN MSM-PD displays a rise time and a fall time of 66 and 43 μs, respectively, which are 3 orders of magnitude faster compared to the current state-of-the-art photodetector.

A prototype photoelectrode has been fabricated using a GaN nano-pyramid array structure grown on a cost-effective Si (111) substrate, demonstrating a significant improvement in performance of solar-powered water splitting compared with any planar GaN photoelectrode. Such a nano-pyramid structure leads to enhanced optical absorption as a result of a multi-scattering process which can effectively produce a reduction in reflectance. A simulation based on a finite-difference time-domain approach indicates that the nano-pyramid architecture enables incident light to be concentrated within the nano-pyramids as a result of micro-cavity effects, further enhancing optical absorption. Furthermore, the shape of the nano-pyramid further facilitates the photo-generated carrier transportation by enhancing a hole-transfer efficiency. All these features as a result of the nano-pyramid configuration lead to a large photocurrent of 1 mA cm under an illumination density of 200 mW cm, with a peak incident photon-to-current conversion efficiency of 46.5% at ∼365 nm, around the band edge emission wavelength of GaN. The results presented are expected to pave the way for the fabrication of GaN based photoelectrodes with a high energy conversion efficiency of solar powered water splitting.

An epitaxial growth technic has been developed to synthesize semi‐polar (11‐22) GaN on (113) Si substrate with inverted‐pyramid patterns. The reaction between Ga and Si substrate has been successfully solved by simply depositing a thin SiO2 layer on selective regions of the substrate before growth. High quality semi‐polar (11‐22) GaN‐on‐Si with a smooth surface has been obtained after delicately tuning growth conditions. Based on the scanning electron microscopy and x‐ray diffraction characterizations, a model has been well established to illuminate the growth process. Due to the very low density of defects confirmed by transmission electron microscopy, our sample demonstrates an excellent optical property, which is promising for efficient optoelectronic devices using GaN‐on‐Si configuration. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

To fully exploit the advantages of GaN for electronic devices, a critical electric field that approaches its theoretical value (3 MV/cm) is desirable but has not yet been achieved. It is necessary to explore a new approach toward the intrinsic limits of GaN electronics from the perspective of epitaxial growth. By using a novel two-dimensional growth mode benefiting from our high-temperature AlN buffer technology, which is different from the classic two-step growth approach, our high-electron-mobility transistors (HEMTs) demonstrate an extremely high breakdown field of 2.5 MV/cm approaching the theoretical limit of GaN and an extremely low off-state buffer leakage of 1 nA/mm at a bias of up to 1000 V. Furthermore, our HEMTs also exhibit an excellent figure-of-merit (V br 2/R on,sp) of 5.13 × 108 V2/Ω·cm2.

High‐quality semi‐polar (11‐22) GaN is obtained by means of growth on patterned (113) silicon substrates featured with stripy grooves and extra periodic gaps which are perpendicular to the grooves. Ga melting‐back during the GaN growth at a high temperature is eliminated as a result of special patterning design. On‐axis X‐ray rocking curve measurements show that the linewidth is significantly reduced down to 339 arcsec. Photoluminescence (PL) measurements at 10 K show strong GaN band‐edge emission only, meaning that any basal stacking fault‐related emission is not observed. Furthermore, green InGaN/GaN light‐emitting diodes (LEDs) with an emission wavelength of around 530 nm are achieved on the semi‐polar GaN grown on the patterned Si substrates. Excitation power‐dependent PL measurements do not show a shift in wavelength, meaning a significant reduction in polarization‐induced piezoelectric fields. Electroluminescence (EL) measurements exhibit that the output power of the semi‐polar LED increases linearly with increasing injection current. It is worth highlighting that the overgrowth technology on designed patterned (113) silicon is a potential approach to manufacturing high‐performance semi‐polar GaN emitters on Si substrates in a long wavelength region.