Unpassivated AlGaN/GaN high-electron-mobility transistors show significant gate lag effects due to the presence of surface states in the region between the gate and drain contact. Low-temperature (100 °C) layers of MgO or Sc2O3 deposited by plasma-assisted molecular-beam epitaxy are shown to effectively mitigate the collapse in drain current through passivation of the surface traps. These dielectrics may have advantages over the more conventional SiNX passivation in terms of long-term device stability.

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A brief review is given of recent progress in fabrication of high voltage GaN and AIGaN rectifiers. GaN/AIGaN heterojunction bipolar transistors and GaN metal-oxide semiconductor field effect transistors. Improvements in epitaxial layer quality and in fabrication techniques have led to significant advances in device performance.

The collection efficiency of carrier photogenerated in the intrinsic region of strained InAsxP1−x/InP multiquantum well p-i-n structures is analyzed. The existence of a critical threshold built-in electric field value above which total carrier collection becomes possible is demonstrated. Maximized carrier collection and high output voltage are systematically reached for built-in electric field exceeding the critical value while similar structures operating with a substantially lower built-in electric field (e.g., identical well characteristics but thicker i region) yields nonoptimized collection of carrier in this area and altered voltage output. The slight dependence of the critical electric field with the carrier confinement level is revealed, stressing out the importance of thermally activated escape energy. Finally, the results are discussed in the context of photovoltaic devices showing substantial efficiency improvement for devices designed with built-in electric fields in excess of the threshold value.

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Indium segregation in In x Ga 1Ϫx As/GaAs ͑0.3Ͻxр0.5͒ quantum wells grown by molecular-beam epitaxy and its influence on their electronic properties are investigated using thermally detected optical absorption. A kinetic model is used to derive concentration profiles and applied to interpret experimental data. The dependence of the In surface segregation on growth temperature and growth rate is studied. It is shown that a decrease of the substrate temperature is the best method to limit the segregation process kinetically. From a fit of the kinetic model to experimental data, the conduction-band offset ratio Q c is found to be independent of indium composition x between 0.2 and 0.5 ͑Q c ϭ0.64Ϯ0.01͒. The exciton wave function is calculated using a variational technique involving a transfer-matrix formalism to study the influence of potential shape on excitonic properties. Only a slight increase in oscillator strength with In segregation is observed for the fundamental excitonic transition.

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