Abstract
We have successfully grown wurtzite-phase InN epitaxial layers on Si(111) substrates using atomically flat AlN intermediate layers. Both hetero-interfaces were found to be abrupt based on the field emission scanning electron microscopy and transmission electron microscopy observations. Compositional analysis and the crystal structures for the best InN grown on the AlN/Si(111) has been intensively studied using scanning electron microscopy, field emission electron probe microanalysis, high resolution x-ray diffractometer (HR-XRD), and transmission electron microscopy. Cs and O2 sputtering secondary ion mass spectroscopy have also been used to study the depth profile of the epitaxial InN in order to probe the oxygen content precisely. For the photoluminescence obtaining at 77 K, two peaks which the energy difference is around 82 meV has been detected. According to the transmission electron microscopy microanalysis, two distinct heterostructures, such as InN/AlN/Si(111) and InN/AlN/SiOx/Si(111), are found. It is believed that the structure induced energy shift is the origin of this abnormal phenomenon. This structure induced strain energy is estimated to be around 2.6 GPa based on the hydrostatic photoluminescence reported from the literature and the low temperature photoluminescence taken in this study. Meanwhile, this sample is possessed of high electron mobility even though the carrier concentration is as high as ~ 10^19 /cm^3. The room temperature result is higher than 1100 cm^2/(V．s) via the van der Pauw method. In the second part of this report, unidirectional self-formation and self-apex selective InN nanotips have been successfully fabricated by using the top-down technique on the molecular beam epitaxy (MBE) grown InN/AlN/Si(111) template. Field emission measurement shows that this novel material has very low turn-on field (0.90+/-0.34 V/um at 1 uA/cm^2 and 2.08+/-0.53V/um at 10 uA/cm^2) with very high current density (~180 mA/cm^2) under the field ~ 7 V/um. Possible formation mechanism is discussed based on the cross-sentional analysis using transmission electron microscopy after field emission characterization. The angle dependent experiment further confirmed the proposed mechanism. The extra low turn-on characteristics of electron emission is attributed to the double enhancement of (i) the geometrical factor of the spherical InN nanostructures with suitable tip density, and (ii) the inherently high carrier concentration of the degenerate InN semiconductor with surface electron accumulation layer induced downward band bending effect that significantly reducing the effective electron tunneling barrier.