Deposition of a polycrystalline GaN layer on a porous Si/Si substrate by an electron beam evaporator with a successive ammonia annealing treatment

• The size of the Si pores increases with etching time.
• Polycrystalline GaN was formed when the samples were subjected to the NH3 annealing.
• 30 min-etched porous Si gives the best properties to the polycrystalline GaN.

This work begins with the deposition of a GaN layer on a porous Si/Si substrate using an electron beam evaporator. A few micrometres of porous Si were fabricated on the Si substrate for 10 and 30 min, and different porosities were obtained. For comparison, a GaN layer was also deposited directly on a Si substrate and a TiN buffer layer/Si substrate. The FESEM measurement revealed that the GaN layers turned into rough and distinguished hexagonal-facetted grains after the post-annealing treatment, especially the GaN layer on the 30 min-etched porous Si substrate. The XRD ω-scan revealed that the FWHM of the GaN peak was found to be the narrowest in the GaN layer on the 30 min-etched porous Si/Si substrate compared with those of the others. However, all of the samples exhibit very poor optical quality because no luminescence signal from GaN can be detected, as measured by photoluminescence (PL). The post-annealing treatment prompted the GaN layer to form a polycrystalline structure, as confirmed by the XRD measurement. Interestingly, the optical properties of the polycrystalline GaN greatly improved with a significant near band edge emission (NBE) and a GaN E2 (high) peak at 3.42 eV and 568 cm−1, respectively, as measured by PL and Raman measurements.

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