Silicon oxide (SiO x ) films grown by plasma-enhanced chemical-vapor deposition (PECVD) were investigated for applications in a course wavelength-division multiplexing (CWDM) network. The SiO x films were deposited on 4-in. silicon wafers based on the reaction of N 2 O/SiH 4 precursors. After postdeposition annealing at 1,150°C, the transmission spectra of the films prepared at different flow rates of the precursor were compared. We found that the transmission spectrum of the films deposited at the low-flow conditions can be flattened to a ripple of less than 0.5 dB ranging from visible up to 1,470 nm. In addition, the material losses at wavelengths around 1,500 nm caused by absorption of Si-H and N-H bonds were significantly reduced.

An InCaP/lnGaAsN/GaAs NpN double-heterojunction bipolar transistor (DHBT) structure has been characterised using the techniques of photoreflectance (PR), including the dependence of the signals on the polarisation ([I 1 01 and [ I 1 O ] } of the incident radiation, and surface photovoltage spectroscopy (SPS). The ordering parameter of the InGaP is deduced from the polarisation dependence of the PR signals from the emitter region. The observed Franz-Keldysh oscillations have been used to evaluate the electric fields in the collector and emitter regions. The field in the collector region agrees well with the theoretical value, while the ficld in the emitter region is found to be about 25 kV/cm smaller than the theoretical value not taking into account the possible ordering-induced screening effect. The difference is ascribed to the influence of the piezoelectric field related to ordering. In addition, the InGaAsN hand gap is determined to be 1.196eV by analysing thc PR and SPS spectra in the base region. The narrower band gap of InGaAsN has led to a lower turn-on voltage, which shows grcat potential for the application of InGaAsN in low-power electronics.

We have measured the photoreflectance (PR) spectra at 300 K and dc current gain for GaInP/GaAs heterojunction bipolar transistors (HBTs) grown by metalorganic chemical vapor deposition with different growth conditions. From the observed Franz–Keldysh oscillations, we have evaluated the built-in dc electric fields and associated band gaps in the GaInP emitter and GaAs collector regions. The observed increase in current gain with the low GaInP band gap is in agreement with band alignment between partially ordered GaInP and GaAs, but the observed current gain is not strongly dependent on electric field. For samples with comparable GaInP band gaps we have thereby detected a limiting factor, base bulk recombination, governing the current gain of HBTs from Gummel plots.

InGaP/GaAs double heterojunction bipolar transistors (DHBTs) with composite collector has been proposed, simulated and fabricated to obtain the suitable heterojunction bipolar transistor (HBT) performance for power amplifiers in wireless communication. The composite collector combines both wide-bandgap (InGaP) and narrow-bandgap (GaAs) materials. In the composite collector, InGaP material provides high breakdown field and thus is able to be employed to reduce thickness of collector while keeping the same breakdown voltage; GaAs material provides high electron mobility and thus is able to be used to reduce on-resistance and transit time. Three InGaPIGaAs HBTs with different structures in collector have been grown, fabricated and characterized. The Gumme1 plots from simulation and measurement for the proposed DHBT show the negligible difference in current gains, which is due to the identical structures in base/emitter regions and effectively reduced conduction spike in base-collector junction. Overall, the DHBT with composite collector remains the advantages of DHBT with improved performance in on-resistance and knee voltage.

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