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We investigated the electrical and optical properties of InGaAs self-assembled quantum dots grown using the atomic layer epitaxy (ALE) technique. Dots–in–a–well structures were grown by alternately supplying InAs and GaAs sources on an InGaAs layer and covering with another InGaAs layer. Three samples produced with different numbers of cycles of alternate InAs/GaAs supply were characterized by capacitance-voltage and photoluminescence (PL) measurements. For the ten cycle dots–in–a–well structure, a strong zero-dimensional electron confinement was observed even at room temperature. On the other hand, for the five-cycle structure, the PL results indicate that the InGaAs quantum well structure coexists unstably with premature quantum dots. By comparing the results for samples with different numbers of cycles, we suggest that an ALE dots–in–a–well structure can be formed by the aggregation of In and Ga atoms incorporated into the InGaAs quantum well layer when the number of cycles exceeds the critical number of seven cycles. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Electronic and optical devices fabricated from wide band gap semiconductors have many properties ideal for high temperature, high frequency, high power, and radiation hard applications. Progress in wide band gap semiconductor materials growth has been impressive and high quality epitaxial layers are becoming available. Useful devices, particularly those fabricated from SiC, are rapidly approaching the commercialization stage. In particular, MESFETs ( MEtal Semiconductor Field- Effect Transistors) fabricated from wide band gap semiconductors have the potential to be useful in microwave power amplifier and oscillator applications. In this work the microwave performance of MESFETs fabricated from SiC, GaN and semiconducting diamond is investigated with a theoretical simulator and the results compared to experimental measurements. Excellent agreement between the simulated and measured data is obtained. It is demonstrated that microwave power amplifiers fabricated from these semiconductors offer superior performance, particularly at elevated temperatures compared to similar components fabricated from the commonly employed GaAs MESFETs. [ABSTRACT FROM AUTHOR]

The thermal effect of GaN Schottky diode on the I–V characteristics was simulated with the application of the forward bias voltage. The simulated diode had the cylindrical structure with the Schottky and ohmic contacts at the same top surface. The Schottky contact of circular shape with 340 μm diameter was surrounded by the ring-type ohmic contact of the inner and the outer diameters of 440 and 740 μm, respectively. The diode was doped with four different concentrations: 1×1015, 5×1015, 5×1016 and 1×1017/cm3. The simulated currents were obtained by increasing the forward bias up to 30 V in these four diodes of different doping concentrations. At low level of forward bias, the thermal effect assisted the ionization of doped atoms and thus increased the currents flow. The current and the thermal effect increased with the doping concentration. The maximum temperature increase of the diode with 1×1017/cm3 doping concentration was as high as 140 K above room temperature. The induced heat did not seem to be high enough to ionize all the dopants but produced the thermally generated electron–hole pairs. With the increase of forward bias, especially at high doping concentration, the thermal effect on mobility slowed down the current increase. The various behaviors in I–V curves were resulted from the different thermal effect with different doping concentration levels. At low doping, the thermal effect was small but the inclusion of the thermal effect showed the increase of current through assisting the ionization process. At high doping, there seemed to be the decrease in mobility with the forward bias accompanied with enhanced ionization process. So it was concluded that the consideration of thermal effect in evaluating the precise I–V curve is very important irrespective of doping levels. [Copyright &y& Elsevier]