Study on fabrication of heterostructures based on InN, GaN and alloys and applications for HFET

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In this research project, our aim is to develop fundamental technologies for fabrication of HFET based on InN, GaN and their alloys. We have studied the crystal growth of high quality InN and InGaN using plasma-excited molecular beam epitaxy and the fabrication of heterostructure based on these materials. Principal results obtained in this project are summarized as follows ;1. For the InN growth on sapphire by RF-MBE, single crystalline InN with high quality crystalliniy and excellent electrical properties were successfully grown by optimizing growth condition such as nitridation, low-temperature grown buffer layer, growth temperature etc.2. Based on systematic studies on structural and optical characterizations using TEM, XRD, Raman scattering, EXAFS, PL and optical absorption, true bandgap energy of InN with ideal wurtzite structure is found to be approximately 0.65 eV.3. Single-crystalline InN was successfully grown on Si by introducing brief nitridation and AIN buffer.4. High quality In-rich InGaN without phase separation was obtained by using low-temperature grown InN buffer. It was also found that insertion of the InN template was very effective in improving the crystalline quality and surface morphology of In-rich InGaN.5. InN/InGaN quantum well structures were successfully fabricated on the InN template grown on sapphire, and PL emissions from the InN well layers were observed for the first time.6. Influences of thermal oxidation of InN on the chemical properties of InN surface and structural and optical properties were studied. The oxidation of InN was confirmed to promote the formation of In_2O_3, which had a remarkable influence on optical properties of the InN.7. Monte Carlo simulation of electrical properties of InN with narrow bandgap showed that InN has higher mobility and saturation velocity than GaN, indication excellent potential for HFET application.