The Fabrication And Characterization Of GaN One-Dimensional Nanomaterials And GaN Films

GaN is an excellent III- V semiconductor material with a direct and wide band gap and also one of the best advanced semiconductor materials. Having large direct energy band gap of 3.39 eV at room temperature, high melting temperature, high breakdown field, and high saturation drift velocity, it has been considered as a prime candidate for the applications in high-temperature, high-voltage and high-power optoelectronic-devices. Presently, much attention is being paid to GaN materials all over the world. MOCVD, MBE, and HVPE have become dominant methods for growing GaN films. Among these techniques, MOCVD has been widely used by researchers. However, GaN materials are not well prepared and applied in large scale because of the complicated fabrication technics and expensive equipments used by the above methods. Now, a many of scientific research institutions are exploring new technique to grow high quality GaN film on appropriate wafer. Si is an ideal substrate due to its high quality, high coefficient of heat conductivity, low price, easy cleavage and easily fabricating electrode and so on. In recent years, GaN one-dimensional nanomaterials have gained considerable attention for its potential applications in both visible light and ultraviolet light optoelectronic devices, therefore, GaN one-dimensional nanomaterials have become one of worldwide focus points.In this paper, high quality GaN one-dimensional nanomaterials and GaN films were synthesized on Si substrate by CVD. The composition and structure were analyzed, the growth mechanism and effect factors of GaN one-dimensional nanomaterials growth were discussed in detail.1. GaN nanowires were synthesized by a direct reaction of metallic gallium with flowing ammonia without any catalysts on Si(100) substrate via CVD at 950℃. The product was characterized using FESEM, EDS, XRD, HRTEM and PL. Results indicate that as-synthesized nanowires are single crystalline GaN with a hexagonal wurtzite structure. Their diameters are in the range of 20-120 nm, with lengths up to several tens of microns. Ga droplets deposited beforehand on Si play an important role in the GaN nanowires growth.2. Using oxide gallium as Ga source, ammonia as N source, and Pt as catalyst, GaN one-dimensional nanomaterials with different morphologies were synthesized on Si(100) substrate using different animating time (15mm/30min/45min). The results indicate the length and amount of GaN nanowires increase with increasing aminating time. Replacing oxide gallium with gallium as Ga source, GaN one-dimensional nanomaterials with different morphologies were synthesized on Si substrate at different aminating temperatures (900℃/925℃/950℃/975℃). The results show that with rising aminating temperature, GaN nanomaterials have a transformation process from nanowires to nanobelts, then from nanobelts to nanowires.3. Using oxide gallium as Ga source, ammonia as N source, Ni(Ac)₂ as catalyst, GaN nanobars were synthesized on Si(100) substrate at 1000℃, GaN nanobars have smooth surface. The diameter of GaN nanobars ranges from 20 to 200 nm, and the length varies from 2 to 10 micron. Replacing oxide gallium with gallium as Ga source, a large quantity of high quality GaN nanowires were synthesized on Si at 900℃. GaN nanowires have diameter ranging from 10 to 100 nm, with length up to 30μm. The growth of GaN nanowires or GaN nanobars was dominated by VLS mechanism.4. GaN film composed of crystalline microsheets was synthesized on Si(111) substrate by CVD using Ga₂O₃ and NH₃ as Ga and N sources, respectively. No buffer layer was used. The product was characterized using FESEM, EDS, XRD,HTEM and PL. The results show that the product is a high quality GaN film, which is composed of crystalline microsheets with less defects. GaN film deposited on Si substrate shows a smooth surface without cracking. A strong band-edge emission peak at 367nm is observed. It has been found that GaN nuclei firstly growed in island, and then formed the film two-dimensionally.