Synthesis, photoluminescence and field emission properties of well aligned/well patterned conical shape GaN nanorods

Vertically well aligned, well patterned and high density conical shaped GaN nanorods have been synthesized on a Si substrate by pre-treating the GaN powder with aqueous NH₃via a facile chemical vapor deposition method without any catalyst. The nanorods obtained have been characterized by XRD, EDX, TEM, HRTEM and SAED. The observed diameter of the nanorods is 80-100 nm whereas their sharp tip angle measured is 55°. The calculated number of sharp nanorod tips in 1 mm² is approximately 1.56 × 10⁸, indicating high growth density of nanorods which is crucial for field emission properties. The GaN nanorods have exhibited impressive field emission properties and high stability with a lower turn-on field of 3.35 V μm^-1 (0.01 mA cm^-2) at room temperature which is sufficient for electron emission devices, field emission displays and vacuum nano-electronic devices. Moreover, uniform, well-aligned, well-patterned and high-density growth of GaN nanorods also make them promising candidates for nano-device design and integration in the future. The room-temperature PL emission with a strong peak at 370 nm (3.35 eV) indicates that GaN nanorods have potential application in light-emitting nano-devices. A vapor-solid growth mechanism for GaN nanorods has also been discussed briefly.