MBE Growth of Nitride-Arsenide Materials for long Wavelength Opto-electronics
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ABSTRACT Nitride-Arsenide materials were grown by molecular beam epitaxy (MBE) using a radio frequency (rf) nitrogen plasma. The plasma conditions that maximize the amount of atomic nitrogen versus molecular nitrogen were determined using the emission spectrum of the plasma. Under constant plasma source conditions and varying group III flux, the nitrogen concentration in the film is inversely proportional to the group III flux (i. e. the nitrogen sticking coefficient is unity). The relationship between nitrogen concentration in the film and lattice parameter of the film is not linear for nitrogen concentrations above 2.9 mole % GaN, indicating that some nitrogen is incorporated on other locations than the group V lattice sites. For films with these higher nitrogen concentrations, XPS indicates that the nitrogen exists in two configurations: a Gallium-Nitrogen bond and another type of nitrogen complex in which nitrogen is less strongly bonded to Gallium atoms. Annealing removes this nitrogen complex and allows some of the nitrogen to diffuse out of the film. Annealing also improves the crystal quality of GaAsN quantum wells.
INTRODUCTION Group III-Nitride-Arsenides are promising materials for 1.3µm and 1.55µm telecommunications optoelectronic devices grown on GaAs substrates1,2,3. The role of nitrogen is two fold: the nitrogen causes the bulk bandgap to decrease dramatically and the smaller lattice constant of GaN results in less strain in InGaNAs compared to InGaAs. However, the growth of such nitride-arsenides is complicated by the difficulty of generating a reactive nitrogen source and the divergent properties of nitride and arsenide materials. The luminescence properties of InGaNAs deteriorate rapidly with increasing nitrogen concentration4. It is common to increase the luminescence efficiency of these InGaNAs quantum wells by a short high temperature anneal3. In the present study, growth of nitride-arsenides was performed by elemental source MBE using a rf nitrogen plasma. We have investigated the incorporation of nitrogen using X-Ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy (SIMS), high resolution X-ray diffraction (HRXRD), and electron microprobe. The effect of thermal annealing on crystal quality and nitrogen incorporation was studied using XPS and HRXRD.
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DETAILS OF MBE NITRIDE-ARSENIDE GROWTH The growth of Nitride-Arsenides was performed in a Varian Gen II system by elemental source MBE. Group III fluxes are provided by thermal effusion cells, dimeric arsenic is provided by a thermal cracker, and reactive nitrogen is provided by an rf plasma cell. The plasma cell is operated at 250-350 W with a nitrogen gas flow of 0.1-0.5 sccm. Typical growth rates are 0.4-4 Å/s. These conditions allow to add up to 5 atomic percent nitrogen to III-V materials
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