RESUMEN
Electrical and interfacial properties of metal-oxide-semiconductor (MOS) capacitors fabricated using atomic layer deposited bilayer TiO2/Al2O3 films on In0.53Ga0.47As/InP substrates are reported. Vacuum annealing at 350 °C is shown to improve the interface quality. Capacitance-voltage (C-V) characteristics with higher accumulation capacitance, negligible frequency dispersion, small hysteresis and low interface state density (â¼1.5 × 10(11) cm(-2) eV(-1)) have been observed for MOS capacitors. Low frequency (1/f) noise characterization and inelastic electron tunneling spectroscopy (IETS) studies have been performed to determine defects and interface traps and explain the lattice dynamics and trap state generation mechanisms. Both the IETS and 1/f noise studies reveal the spatial locations of the traps near the interface and also the nature of the traps. The IETS study further revealed the dynamic evolution of trap states related to low frequency noise sources in the deposited TiO2/Al2O3 stacks. It is shown that deposition of an ultrathin layer of TiO2 on Al2O3 can effectively control the diffusion of As in the dielectric and the oxidation states of In and Ga at the In0.53Ga0.47As surface.
RESUMEN
High quality surface passivation on bulk-GaAs substrates and epitaxial-GaAs/Ge (epi-GaAs) layers were achieved by using atomic layer deposited (ALD) titanium aluminum oxide (TiAlO) alloy dielectric. The TiAlO alloy dielectric suppresses the formation of defective native oxide on GaAs layers. X-ray photoelectron spectroscopy (XPS) analysis shows interfacial arsenic oxide (As(x)O(y)) and elemental arsenic (As) were completely removed from the GaAs surface. Energy dispersive X-ray diffraction (EDX) analysis and secondary ion mass spectroscopy (SIMS) analysis showed that TiAlO dielectric is an effective barrier layer for reducing the out-diffusion of elemental atoms, enhancing the electrical properties of bulk-GaAs based metal-oxide-semiconductor (MOS) devices. Moreover, ALD TiAlO alloy dielectric on epi-GaAs with AlGaAs buffer layer realized smooth interface between epi-GaAs layers and TiAlO dielectric, yielding a high quality surface passivation on epi-GaAs layers, much sought-after for high-speed transistor applications on a silicon platform. Presence of a thin AlGaAs buffer layer between epi-GaAs and Ge substrates improved interface quality and gate dielectric quality through the reduction of interfacial layer formation (Ga(x)O(y)) and suppression of elemental out-diffusion (Ga and As). The AlGaAs buffer layer and TiAlO dielectric play a key role to suppress the roughening, interfacial layer formation, and impurity diffusion into the dielectric, which in turn largely enhances the electrical property of the epi-GaAs MOS devices.
RESUMEN
Apparatus and method for the in situ control of photonic device intermixing processes are described. The setup utilises an optical fiber splitter which delivers photons to selectively anneal the photonic device and simultaneously measures the emission spectra from the device to monitor the intermixing process in real time. The in situ monitoring of a laser annealing process for the modification of a semiconductor laser diode facet is demonstrated using the instrumentation. A progressive blueshift in the emission wavelength of the device can clearly be observed in real time while high energy photons are delivered to anneal the device facet, hence enabling the control on the degree of intermixing required. This instrumentation is also ideal for broadening of emission spectra in quantum dot and quantum well based light emitting devices such as superluminescent diodes and broadband laser.
RESUMEN
INTRODUCTION: Data on safety issues and therapeutic outcomes of endoscopy in pregnancy remains limited especially in the local context. The concerns are that of safety in sedation and radiation to the foetus, effects on the pregnancy, the need for special precautions on mother and foetus during the procedure and long-term foetal outcome. We report a case series on four pregnant women to address these concerns and outline their therapeutic approaches. METHODS: We reviewed four patients who underwent oral gastroduodenoscopy (OGD) or endoscopic retrograde cholangiopancreatography (ERCP) during their pregnancies. Lead aprons were used to shield the foetuses in all patients that underwent ERCP. Sedation was given when necessary, and an anaesthetist was employed in one case for close patient monitoring. Fluoroscopy was minimised and radiographs were taken only when essential. RESULTS: The mean patient age was 27.8 years (range 23-35 years). The mean gestation was 21.5 weeks (range 14-32 weeks), with two patients each being in their second and third trimesters. The indications for ERCP were cholangitis and pancreatitis (one), choledocholithiasis on ultrasonography (two), and that for OGD was persistent vomiting (one). Two patients underwent sphincterotomy and one had a biliary stent inserted. One patient was lost to follow-up. The other three had a full-term normal delivery and all babies were healthy at birth with good birth weight and normal Apgar scores. CONCLUSION: Our series showed that endoscopic procedures in pregnancy are safe for both mother and foetus. However, these procedures should be restricted to cases with definite. indications and radiation exposure should be minimised with additional safety precautions such as minimal radiation exposure and the use of lead shield when applicable.
