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GaAs/Al0.3Ga0.7As quantum wells (QWs) grown on (411)A-oriented GaAs substrates by molecular beam epitaxy (MBE) showed extremely flat interfaces over a macroscopic area (about 200 µm φ) even for the case of no growth interruption, which is mainly due to the intrinsically large migration of Ga atoms and layer growth in the step-flow mode on the (411)A plane. Photoluminescence linewidths at 4.2K were almost the same as or better than the narrowest linewidths reported for GaAs/AlGaAs and GaAs/AlAs QWs grown on GaAs (100) substrates with growth interruption at each GaAs/AlGaAs(AlAs) interface. Only one sharp luminescence peak was observed for each QW on the (411)A substrates, in contrast with three luminescence peaks for the QWs on the (100) substrates, indicating that extremely flat and uniform interfaces over a macroscopic area of laser excitation (200 µm diameter) are realized in the GaAs/AlGaAs QWs grown on (411)A GaAs substrates.

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In this paper, UV photoconductivity of a transparent gate AlGaN/GaN high electron mobility transistor (HEMT) on a Si substrate is demonstrated. The transparent gate enables the HEMT to standby under pinch-off conditions for operation as a photodetector. Therefore, the device can overcome the drawback of high standby-current in conventional metal gate field-effect transistor (FET)-based photodetectors without sacrificing its high responsivity. A negative threshold-voltage shift of -0.25 V and a significant drain-current increase over two orders of magnitude were observed under UV-light irradiation condition from the surface-side. A high responsivity of 2.0×105 A/W at 360 nm with a low leakage current of 3×10-6 A/mm was simultaneously achieved. These experimental results were in agreement with the models for generation of a photo carrier and its transportation in a heterostructure.

The X-ray spectrometer used in high-energy-density plasma experiments generally requires both broad X-ray energy coverage and high temporal, spatial, and spectral resolutions for overcoming the difficulties imposed by the X-ray background, debris, and mechanical shocks. By using an elliptical crystal together with a streak camera, we resolve this issue at the SG-II laser facility. The carefully designed elliptical crystal has a broad spectral coverage with high resolution, strong rejection of the diffuse and/or fluorescent background radiation, and negligible source broadening for extended sources. The spectra that are Bragg reflected (23 • < θ < 38 • ) from the crystal are focused onto a streak camera slit 18 mm long and about 80 µm wide, to obtain a time-resolved spectrum. With experimental measurements, we demonstrate that the quartz(1011) elliptical analyzer at the SG-II laser facility has a single-shot spectral range of (4.64-6.45) keV, a typical spectral resolution of E/∆E = 560, and an enhanced focusing power in the spectral dimension. For titanium (Ti) data, the lines of interest show a distribution as a function of time and the temporal variations of the He-α and Li-like Ti satellite lines and their spatial profiles show intensity peak red shifts. The spectrometer sensitivity is illustrated with a temporal resolution of better than 25 ps, which satisfies the near-term requirements of high-energy-density physics experiments.

Off-state bias stress reliability studies were carried out on AlGaN/GaN high-electron-mobility transistors (HEMTs) on Si substrate with different buffer thicknesses. Critical voltage (Vcrit) and preferential electroluminescence (EL) emission were observed for HEMTs grown on 2.5-µm-thick buffer layer, which is believed to be due to nonuniform electric field at the gate–drain region. In contrast, HEMTs with a 4.0-µm-thick buffer layer did not show any sign of Vcrit, which was further accompanied by a uniform EL emission. This is due to the improved quality of GaN grown on thick buffer layer, which dispels the nonuniform electric field at the gate–drain region.

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