A Novel Method to Synthesize Blue-Luminescent Doped GaN Powders
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A Novel Method to Synthesize Blue-Luminescent Doped GaN Powders R. Garcia, A. Thomas1, A. Bell and F. A. Ponce Department of Physics and Astronomy, Arizona State University, Tempe, AZ 852811504 1 Rogers Corporation, Durel Division, Chandler, AZ 85224-6155 ABSTRACT A new method to synthesize highly luminescent GaN:Mg powders has been developed. This method has a high control over the concentration of magnesium in the final product. The method consists of reacting a high purity (99.999 %) galliummagnesium alloy with ultra-high purity ammonia in a horizontal quartz tube reactor at high temperatures for several hours. Electron microscopy showed that the light-gray powders produced by this method consist of at least two different shaped crystallites; large columnar crystals sized around 10 µm and small platelets crystals between 1 and 2 µm. X-ray diffraction showed that those crystallites have a well defined wurtzite structure. Room temperature photoluminescence (PL) and cathodoluminescence (CL) showed a high intensity blue emission around 2.94 eV (422 nm). At helium temperature the well known Mg-related donor-acceptor pair band was observed at 3.25 eV (380 nm) by PL and CL. INTRODUCTION Gallium nitride is an important material for optoelectronic devices because of its direct band gap at 3.45 eV, which corresponds to ultraviolet emission at 360 nm. With the introduction of suitable dopants such as Mg, Si, rare earths (Pr, Eu, Er, Tm) and the formation of solid solutions with indium nitride (InN), the full range of visible electromagnetic radiation (400 to 700 nm) may be obtained [1-5]. Until now, most research has focused on GaN thin films for the production of blue/UV LEDs and laser diodes. GaN powders have been largely overlooked despite having a huge potential for impact in the electroluminescent (EL) lighting industry. Current electroluminescence powders consist of ZnS:Cu,Cl and can be found in many applications including backlighting in cell phones, car dash board, watch lights etc. Current ZnS EL device efficiencies are not improving as fast as technology requires and so it is necessary to look at other semiconductors as possible alternatives. GaN is a very robust material with similar structural and electronic properties to ZnS, and therefore seems like a good candidate. An important step towards producing GaN EL powders is to achieve n- and ptype doping. In this study, we have achieved Mg- doping of high purity GaN powders using a new synthesis technique.
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EXPERIMENTAL DETAIL Magnesium doped gallium nitride powder was produced using a galliummagnesium alloy as a precursor. According to phase diagrams magnesium is very soluble in gallium and they form a liquid solution in all proportions at temperatures greater than 500ºC [6]. In order to measure how the magnesium concentration affects the luminescence intensity, different magnesium concentration (0.005, 0.007, 0.01 and 0.02) alloys were prepared by this method. The gallium-magnesium alloy is prepared using a mechanical shaker. Ultra-high purity
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