Optical and Structural Analysis of GaN Microneedle Crystals Obtained via GaAs Substrates Decomposition and their Possible Growth Model Using the Volmer-Weber Mechanism

GaN microneedle crystals are grown via GaAs substrates decomposition, using ultrahigh-pure anhydrous ammonia as nitrogen precursor at 900 degrees C for 4 min. The X-ray diffraction pattern shows the possible cubic and hexagonal coexistence of phases for the GaN highest intensity peak. Scanning electron microscopy presents a seaflower-type growth for GaN microneedles, which can be related to factors such as lattice mismatch and substrate roughness due to the cleaning process. On the other hand, energy-dispersive spectroscopy and X-ray photoelectron spectroscopy characterizations demonstrate the elemental contributions of gallium and nitrogen for the GaN microneedle. Transmission electron microscopy shows uniform growth with an interplanar spacing of 2.76 angstrom. In addition, a possible growth model by hexagonal crystals stacking is proposed for obtaining GaN microneedles using the mechanism of Volmer-Weber growth. Photoluminescence spectrum presents an energy emission peak in the ultraviolet band with a value of 3.40 eV (364 nm), which is related to the band-to-band transition, and Raman scattering shows stress in the GaN microneedles due to the presence of different vibration modes for hexagonal GaN, indicating that several microneedles break.