Optical Properties of Manganese Doped Amorphous and Crystalline Aluminum Nitride Films
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ABSTRACT An aluminum nitride (AlN) film deposited on silicon (100) was used as the substrate for growing manganese (Mn) doped AlN film by metal organic chemical vapor deposition (MOVCD). The (15.78 µm) under layer of AlN was grown at 615°C at a pressure of 10-4 Torr. The (2.1 µm) top layer of Mn-AlN was grown at the same temperature and pressure but doped with pulse valve introduction of the manganese decacarbonyl (100 ms on, 100 ms off). The film was then characterized ex situ with IR reflectance microscopy, X-ray diffraction, scanning electron microscopy imaging, cathodoluminescence, and X-ray fluorescence. The IR reflectance measurements showed a strong (A1) LO mode for AlN at 920 cm-1 and 900 cm-1 with a shoulder at 849 cm-1. X-ray Diffraction yielded three diffraction peaks at a 2θ position of 33, 36 and 38 degrees corresponding to 100, 002, and 101 lattice planes respectively. Cathodoluminescence results show strong visible emitted light from incorporated manganese. The relative percentage of manganese to aluminum was below the detection limit (0.01 %) of the Xray fluorescence spectrometer. Amorphous Mn doped AlN films have also been grown using a low temperature atomically abrupt sputter epitaxial system. The amorphous Mn doped AlN showed no cathodoluminescence. INTRODUCTION Crystalline aluminum nitride (AlN) films have attracted considerable interest because they possess a very large band gap compared to the rest of the group III nitrides (6.2 eV) [1]. In addition, it has a high heat conductivity, excellent chemical and thermal stability; it will decompose rather than melt at 2400°C [2]. Amorphous AlN films have also attracted some interest because the band gaps of these semiconductors are close to those of the corresponding crystalline materials (5.6 eV vs 6.2 eV), with localized electronic states that do not extend into the bandgap. The amorphous AlN films have many of the desirable qualities of the crystalline materials, most importantly, they are not easily recrystallized. Recently, rare earth doped III-V semiconductors have been the subject of great interest because of their strong visible luminescence [3,4]. The films have been doped with rare earth elements, and light emission from doped crystalline and amorphous AlN in both the visible and infrared has been confirmed [5,6]. Manganese has been incorporated in powder samples of AlN [7-9], with the tetravalent manganese ion, Mn4+, occupying tetrahedral sites. The incorporation of manganese into semiconductor hosts is of interest because the manganese activated AlN exhibits a maximum in the
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emission spectrum in the red region (~600 nm). EXPERIMENTAL Crystalline aluminum nitride (AlN) films were grown by metal organic chemical vapor deposition (MOCVD) in a high vacuum stainless steel reaction chamber. This system consists of a growth chamber, pumping unit, and a gas inlet. An Alcatel corrosive resistant turbo pump evacuates the chamber into the 10-5 Torr range. The source gases for the AlN were ammonia (NH3) and trimethylaluminum (TMA). Th
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