Papers by Author: Y.T. Moon

Abstract: Improved structural quality and radiative efficiency were observed in GaN thin films grown by metalorganic chemical vapor deposition on in situ-formed SiN and TiN porous network templates. The room temperature carrier decay time of 1.86 ns measured for a TiN network sample is slightly longer than that for a 200 μm-thick high quality freestanding GaN (1.73 ns). The linewidth of the asymmetric X-Ray diffraction (XRD) (1012) peak decreases considerably with the use of SiN and TiN layers, indicating the reduction in threading dislocation density. However, no direct correlation is yet found between the decay times and the XRD linewidths, suggesting that point defect and impurity related nonradiative centers are the main parameters affecting the lifetime.

Abstract: Carrier transport properties of AlGaN/GaN heterostructures have been analyzed with the quantitative mobility spectrum analysis (QMSA) technique. The nominally-undoped Al0.15Ga0.85N/GaN sample was grown by metal-organic vapor phase epitaxy. Variable-magneticfield Hall measurements were carried out in the temperature range of 4-160 K and magnetic field range of 0-6.6 T. QMSA was applied to the experimental variable-field data to extract the concentrations and mobilities associated with the high-mobility 2DEG and the relatively lowmobility bulk electrons for the temperature range investigated. For temperatures below 100 K the calculated mobility and carrier density values were close to the experimental results. No bulk conduction was observed in this temperature range. At 160 K, QMSA results show that parallel conduction in 3 mm thick GaN layer started to affect the average electron mobility.

Abstract: We report on the fabrication and testing of GaN resistive gas sensors for hydrogen detection. The Si-doped n-type GaN was grown by organometallic vapor phase epitaxy (OMVPE) on c-plane sapphire substrates. The device structure is simply a pair of metal ohmic contact pads. The sensors are sensitive to H2 gas over a wide range of concentration: the lowest concentration tested being ~0.1% H2 (in Ar), well below the lower combustion limit in air. No saturation of the signal is observed up to 100% H2 flow. In the continuous operation mode with varying H2 concentration, a clear and sharp response was recorded with no memory effects during ramping up and down cycles of H2 concentration. The change in current at a fixed voltage to hydrogen was found to change with sensor geometry. The possible gas sensing mechanisms are still under investigation.