Co-sputtering Preparation Of Mn-doped Gan Films And Nanostructures

Semiconductor material has experienced three generation with the develop of semiconductor industry. GaN is an excellent III-V wide-band gap semiconductor material, commonly used in blue or green light-emitting diodes or laser diodes, and all kinds of radioresistance, high-frequency, high-temperature and high-density integrated devices. Nanowires, nanobelts, and nanorods are a new class of one-dimensional materials that have been attracting a great deal of interest in research in the last few years. Doping semiconductor nanostructures with selected dopantions represents an effective means of imparting new electrical, optical, and magnetic properties into these promising materials. Due to its intriguing properties and technological applications, GaN alloys doped with various impurity elements, such as Si, Mg, Al, Mn, etc., have received tremendous attention. Manganese-doped GaN (Mn:GaN) is an attractive material for spintronics because of proposed high-temperature ferromagnetic ordering of Mn in the GaN lattice. So on the base of the growth of one-dimension GaN nanostructures, It is very interesting to investigate the growth of Mn-doped GaN nanostructures.In this paper, Mn-doped GaN one-dimensional nanosmaterials were synthesized by magnetron sputtering and ammoniating progress. The structure, elemental composition, morphology and photoluminescence properties of the GaN nanomaterials were determined by X-ray diffraction (XRD), Scanning electronic microscope (SEM), High-resolution transmission electronic microscope (HRTEM), Fourier transformed infrared spectroscopy (FTIR), X-ray photoelectron energy spectroscopy (XPS) and Photoluminescence spectroscopy(PL). The growth mechanism of GaN nanomaterials was proposed and discussed based on the investigation of the influence of the ammoniating temperature, ammoniating time and the flux of NH₃ on the properties of Mn-doped GaN nanostructure. 1. Synthesis of one-dimensional Mn-doped GaN nanostructures through co-sputtering and ammonification method.One-dimension Mn-doped GaN nanomaterials were fabricated by ammoniating Mn/Ga₂O₃ thin films deposited by direct current (DC) magnetron sputtering system and radio frequency (RF) magnetron sputtering system respectively. The influences on the growth of GaN nanostructures were investigated by changing the ammoniating temperature, ammoniating time or the flux of NH₃. The results reveal that different anneal temperature, different ammoniating time of Mn/Ga₂O₃ thin films and different flux of NH₃ have a great influence on the synthesis of GaN nanostructures. The synthesized nanostructures were of hexagonal wurtzite single-crystal GaN. There were 15 cycles in this process, the total thickness of the Mn/Ga₂O₃ thin films was about 900nm and the total sputtering time was 100 min. The single sputtering cycle is that: first a Mn layer was deposited for 10 s and the thickness of the Mn layer in every cycle is about 25 nm, and then an un-doped Ga₂O₃ film was deposited to a thickness of about 35 nm. In the second step, as-deposited Mn/Ga₂O₃ thin films were ammoniated in a conventional tube furnace.2. Optical properties of GaN nanostructures The samples show two emission bands with the well-defined peaks at 388 nm, and 409nm, respectively. The large distinct red-shift of the band gap emission from the 370 nm of bulk GaN to 409 nm of Mn-doped GaN nanobars can arising from Mn+2 acceptor level in the band gap. Additional the peak at 388 nm represents near-band edge emission of wide band gap.3. Exploration of the growth mechanism for GaN nanostructuresIn the ammoniating process, NH₃ decomposes into NH₂, NH, H₂, N₂ and N when the ammoniating temperature is above 800℃. The Ga₂O₃ particles are reduced to gaseous Ga₂O by H₂ and then GaN molecules are synthesized through the reaction between Ga₂O and NH₃. The formed GaN molecules diffuse and agglomerate into GaN crystalline nuclei, and then the very small GaN crystalline nuclei grow up gradually with the progress of the ammonification. When the microcrystalline grow along the same direction, they become nanowires, nanorods or nanograins. In the sputtering process, layered structure of the Ga₂O₃ films doped with Mn has been obtained. Thus, in the growth process, Mn has more opportunity to substitute the position of Ga. At that temperature, vapourized Mn was doped into the GaN particles to occupy the position of Ga vacancies.