Defect reduction in GaN epilayers grown by metal-organic chemical vapor deposition with in situ SiNx nanonetwork

Line and point defect reductions in thin GaN epilayers with single and double in situ SiNxnanonetworks on sapphire substrates grown by metal-organic chemical vapor deposition were studied by deep-level transient spectroscopy(DLTS), augmented by x-ray diffraction(XRD), and low temperature photoluminescence(PL). All samples measured by DLTS in the temperature range from 80to400K exhibited trap A (peak at ∼325K) with an activation energy of 0.55–0.58eV, and trap B (peak at ∼155K) with an activation energy of 0.21–0.28eV. The concentrations of both traps were much lower for layers with SiNx nanonetwork compared to the reference sample. The lowest concentration was achieved for the sample with 6mindeposition SiNx nanonetwork, which was also lower than that for a sample prepared by conventional epitaxial lateral overgrowth. In concert with the DLTS results, PL and XRD linewidths were reduced for the samples with SiNx network indicating improved material quality. Consistent trend among optical, structural, and DLTS results suggests that SiNxnetwork can effectively reduce both point and line defects

GaN resistive hydrogen gas sensors

GaN epilayers grown by organometallic vapor phase epitaxy have been used to fabricate resistivegas sensors with a pair of planar ohmic contacts. Detectible sensitivity to H2 gas for a wide range of gas mixtures in an Ar ambient has been realized; the lowest concentration tested is ∼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. Real-time response to H2 shows a clear and sharp response with no memory effects during the ramping cycles of H2 concentration. The change in current at a fixed voltage to hydrogen was found to change with sensor geometry. This appears to be consistent with a surface-adsorption-induced change of conductivity; a detailed picture of the gas sensing mechanism requires further systematic studies

Structural and electrical properties of Pb(Zr,Ti)O3 films grown by molecular beam epitaxy

Single-crystal, single-phase Pb(ZrxTi1−x)O3 films (x=0–0.4) were grown on (001)SrTiO3 and SrTiO3:Nb substrates by molecular beam epitaxy. Layer-by-layer growth of thePb(Zr,Ti)O3 films was achieved by using PbTiO3 buffer layers between the SrTiO3substrates and the Pb(Zr,Ti)O3 films. The layers with low Zr content showed high crystallinity with full width at half maximum of ω -rocking curves as low as 4arcmin , whereas increase in Zr concentration led to pronounced angular broadening. The PbZr0.07Ti0.93O3 filmsexhibited remanent polarization as high as 83μC/cm2 , but local areas suffered from nonuniform leakage current

A High-Sensitivity AlGaN/GaN HEMT Terahertz Detector with Integrated Broadband Bow-Tie Antenna

Many emerging applications in the terahertz (THz)frequency range demand highly sensitive, broadband detectorsfor room-temperature operation. Field-effect transistors with in-tegrated antennas for THz detection (TeraFETs) have proven tomeet these requirements, at the same time offering great potentialfor scalability, high-speed operation, and functional integrability