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Ultrafast carrier thermalization in n-type indium nitride (InN) with an electron concentration of 3.8×1018 cm-3 was investigated by femtosecond transient transmission measurements at room temperature with different wavelengths. An extremely fast carrier external thermalization time on the order of 400 fs was observed, which is much faster than all previous reports. This observed femtosecond thermalization time is consistent with a prediction based on a Coulomb screening effect. Through wavelength dependent and power dependent studies, even with a 400 fs thermalization time, we did not observe any evidence of the existence of the hot phonon effect, which agrees with a recent report that a longitudinal optical phonon lifetime could be shorter than 300 fs in specific InN samples. [ABSTRACT FROM AUTHOR]

We demonstrate that formation of p-n junction in gallium nitride (GaN) can be directly visualized on cleavage surfaces in a cross-sectional geometry, where the focused synchrotron radiation (soft x-ray) images the different doping layers on the nonpolar a-plane surface perpendicular to the polar growth direction. In contrast to the as-grown GaN polar surface, the in situ cleaved GaN a-plane surface is shown by using photoelectron spectroscopy to be under the flatband conditions. This unique surface property opens up the way to image and identify p-n junctions in III-nitride semiconductors. [ABSTRACT FROM AUTHOR]

InN/AlN metal-insulator-semiconductor heterojunction field-effect transistors with a gate-modulated drain current and a clear pinch-off characteristic have been demonstrated. The devices were fabricated using high-quality InN (26 nm)/AlN (100 nm) epifilms grown by plasma-assisted molecular-beam epitaxy on Si (111) substrates. The devices exhibited a current density higher than ∼530 mA/mm with a 5 μm gate length. The pinch-off voltage was at ∼-7 V with an associated drain leakage current less than 10 μA/mm. The observed high current density may be attributed to the high sheet carrier density due to the large spontaneous polarization difference between InN and AlN. [ABSTRACT FROM AUTHOR]

Surface biochemical functionalization of group-III nitride semiconductors has recently attracted much interest because of their biocompatibility, nontoxicity, and long-term chemical stability under demanding physiochemical conditions for chemical and biological sensing. Among III-nitrides, aluminum nitride (AlN) and aluminum gallium nitride (AlGaN) are particularly important because they are often used as the sensing surfaces for sensors based on field-effect transistor or surface acoustic wave (SAW) sensor structures. To demonstrate the possibility of site-selective biofunctionalization on AlN surfaces, we have fabricated two-dimensional antibody micropatterns on AlN surfaces by using patterned self-assembled monolayer (SAM) templates. Patterned SAM templates are composed of two types of organosilane molecules terminated with different functional groups (amino and methyl), which were fabricated on AlN/sapphire substrates by combining photolithography, lift-off process, and self-assembly technique. Because the patterned SAM templates have different surface properties on the same surface, clear imaging contrast of SAM micropatterns can be observed by field-emission scanning electron microscopy (FE-SEM) operating at a low accelerating voltage in the range of 0.5-1.5 kV. Furthermore, the contrast in surface potential of the binary SAM microstructures was confirmed by selective adsorption of negatively charged colloidal gold nanoparticles (AuNPs). The immobilization of AuNPs was limited on the positively charged amino-terminated regions, while they were scarcely found on the surface regions terminated by methyl groups. In this work, selective immobilization of green fluorescent protein (GFP) antibodies was demonstrated by the specific protein binding of enhanced GFP (EGFP) labeling. The observed strong fluorescent signal from antibody functionalized regions on the SAM-patterned AlN surface indicates the retained biological activity of specific molecular recognition resulting from the antibody-EGFP interaction. The results reported here show that micropatterning of organosilane SAMs by the combination of photolithographic process and lift-off technique is a practical approach for the fabrication of reaction regions on AlN-based bioanalytical microdevices.