Abstract
The fabrication of high-quality InxAl1−xN alloys over the whole composition is very challenging. Controlling the In/(In + Al) beam flux ratio and the growth temperature, this paper reports the fabrication of single crystalline InxAl1−xN alloys over the whole In composition by radio-frequency plasma-assisted molecular beam epitaxy. A comprehensive systematic study on the structural and vibrational properties of the InxAl1−xN alloys for the whole In composition has been carried out experimentally by Raman spectroscopy and theoretically by the forced vibrational method. The InxAl1−xN alloys show broad Raman peaks in the intermediate range of In composition. The appearance of Raman inactive B1 (High) mode has been confirmed by the experimental and theoretical results. The B1 (High) and A1 (LO) modes show one-mode behavior, whereas the E2 (High) mode shows the two-mode behavior in the whole In composition range. The observed Raman modes from the grown InxAl1−xN alloys well match with the calculated phonon modes of the InxAl1−xN alloys. These results provide an in-depth understanding of the growth of whole compositional InxAl1−xN alloys and the fabrication of optoelectronic devices using these promising materials.
Highlights
In the last few years, interest in indium aluminum nitride (InxAl1−xN) alloys have been stimulated because of the revision of the indium nitride (InN) bandgap,1–5 which conveniently spreads the InxAl1-xN alloys over a broader spectral range, extending from the near infrared at ∼1.9 μm (0.64 eV for InN) through the visible spectrum area and into the deep ultraviolet at ∼0.2 μm (6.2 eV for AlN)
Considering that the Raman inactive B1 (High) mode appears due to the local lattice distortion introduced into the unit lattice inside the mixed crystal, the sample with metallic In has strong local lattice distortion. These results strongly indicate that the Raman spectroscopy is very useful for the investigation of the structural properties of the InxAl1−xN alloys to obtain the optimum growth conditions
The B1 (High) and A1 (LO) modes have shown one-mode behavior, whereas the E2 (High) mode has shown the two-mode behavior of the InN-like and the AlN-like E2 (High) modes in the whole In composition range of InxAl1−xN alloys
Summary
In the last few years, interest in indium aluminum nitride (InxAl1−xN) alloys have been stimulated because of the revision of the indium nitride (InN) bandgap, which conveniently spreads the InxAl1-xN alloys over a broader spectral range, extending from the near infrared at ∼1.9 μm (0.64 eV for InN) through the visible spectrum area and into the deep ultraviolet at ∼0.2 μm (6.2 eV for AlN). InxAl1−xN alloys have become very promising and potential materials for a variety of optoelectronic and electronic devices, which include high-electron mobility transistors and high-efficiency solar cells. A number of studies on the growth of InxAl1−xN alloys have been reported using MBE, MOVPE, and sputtering, where much of the effort has been carried out using MOVPE. InxAl1−xN alloys have become very promising and potential materials for a variety of optoelectronic and electronic devices, which include high-electron mobility transistors and high-efficiency solar cells.. A number of studies on the growth of InxAl1−xN alloys have been reported using MBE, MOVPE, and sputtering, where much of the effort has been carried out using MOVPE. Due to the large different natures of the mother materials (InN and AlN) as well as the optimum growth temperature, good-quality InxAl1−xN alloys throughout the whole composition are yet to be obtained. Because of the poor crystalline quality, the InxAl1−xN alloys are insufficiently understood, and there are many points that have not been clarified over the entire composition. The InxAl1−xN research over the entire composition is still struggling in the growth stage compared with the other III-nitride semiconductors alloys such as InGaN and AlGaN. For practical applications of InAlN devices, more studies toward the fabrication of a high-quality layer over the entire composition are indispensable
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