Porous GaN on Si(1 1 1) and its application to hydrogen gas sensor

The growth of heterostructure of n-type GaN/AlN/Si(1 1 1) is carried out using the molecular beam epitaxy (MBE) Veeco model Gen II system. The surface morphology of the as-grown GaN sample showed pits on the GaN surface in a ratio small than those found by other research groups. Porous GaN samples were synthesized by an electrochemical etching technique combined with increasing the current density to 75 mA/cm2. The formation of pore structures are of different sizes, the etched surface became hexagonal, and pore structures are confined to a smaller size. The PL results showed greater blue shift luminescence in comparison to results found by other research groups. The reduction in crystallite size is confirmed by an increase in the broadening of XRD spectra. Raman spectra also displayed a strong band at 522 cm−1 from the Si(1 1 1) substrate, and a small band at 301 cm−1. These are due to the acoustic phonons of Si. Two Raman active optical phonons are assigned to h-GaN at 139 cm−1 and 568 cm−1, due to E2 (low) and E2 (high) respectively. The sensitivity of the gas sensor is increased as a function of the hydrogen flow rate and they became much higher compared to the as-grown sample.