Broad visible emission from GaN nanowires grown on n-Si (1 1 1) substrate by PVD for solar cell application

Nanostructured gallium nitrides (GaNs) were grown on a catalyst–free Si (1 1 1) substrates using physical vapor deposition via thermal evaporation of GaN powder at 1150 °C in the absence of NH3 gas for different deposition time. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometer (EDX) results indicated that the growth of GaN nanostructure varies with deposition time. Both X-ray diffraction (XRD) patterns and Raman spectra reveals a hexagonal GaN with wurtzite structure. Photoluminescence (PL) showed that the UV emission was suppressed, and the visible band emission was enhanced with increasing deposition time. Enhancement of visible band emission from the GaN NWs is due to the increasement of deep level states, which was resulted from growth process. Current–voltage (IV) characteristics of GaN/Si heterostructure were measured and good rectifying behavior was observed for this photodiode (PD). The forward current under illumination was almost three times than that in the dark current at +5 V. Responsivity of the photodetector was 10.5 A/W at range from 350 nm to 500 nm, which rapidly increased to 13.6 A/W at 700 nm. We found that the fabricated photodiode PD has an infra-red (IR) photoresponse behavior. The analysis of optical and electrical properties indications that the grown GaN in the absent of NH3 is a promising optical material and has potential applications in photo voltage solar cell.

► GaN NWs were grown on Si (1 1 1) using PVD at different deposition times in the absence of NH3.
► Increased deposition time resulted in increased diameter and density of NWs and NBs.
► Increased deposition times enhanced visible emission and suppression of UV emission.
► A broad visible-band emission of GaN NWs had a good photo response in the UV and visible region.
► The photodiode displayed a small response and recovery times.