Enhanced light sensing characteristics of nanostructured gallium nitride/silicon heterojunctions: Interface matters

We report on the growth of highly pure and single crystalline gallium nitride (GaN) nanostructures on different silicon (Si) substrates by thermal vapor deposition via the direct reaction of gallium with volatile ammonia solution. The structural and optical characteristics of the as-grown GaN/Si nanostructured heterojunctions are investigated. The morphology of the formed GaN nanostructures is strongly dependent on the crystal orientation of the Si substrate. The X-ray diffraction and Raman analysis reveal that the fabricated GaN nanostructures have a hexagonal wurtzite structure. The photoluminescence spectra of all GaN nanostructures exhibit a strong near-band-edge ultraviolet (UV) emission peak (365-372 nm), which illustrates their potential in optoelectronic applications. The current-voltage measurements under dark, visible, and UV illumination conditions are performed to study the light sensing ability of the fabricated heterojunctions. Under reverse bias (5 V), the photocurrent of the GaN/n-Si (111) photodetector was comparably much higher than that of the GaN/n-Si (100) photodetector, probably due to the better quality of the GaN formed on Si (111) compared with those formed on Si (100), resulting in a higher photoresponse. The calculated rectification ratio revealed that the sensitivity of the GaN/n-Si (111) photodiode is higher than that of the GaN/n-Si (100), indicating the importance of the interface architecture. The fabricated photodiodes showed photoresponse toward UV and visible wavelengths, demonstrating shorter rise and decay times compared with other materials used to fabricate UV and visible light photodetectors. The prototype device shows a simple method for GaN synthesis and demonstrates the possibility of constructing nanoscale photodetectors for nano-optics applications. (C) 2013 AIP Publishing LLC.