The effects of nitride-based plasma pretreatment on the output characteristics of AlGaN/GaN high-electron-mobility transistors (HEMTs) on silicon substrates are investigated. N2 and NH3 plasma pre-treatment methods are studied to overcome the RF dispersion phenomenon caused by nitrogen-vacancy (VN)-related defect reduction. It is found that the nitride-based plasma pretreatment is effective to overcome the RF dispersion in AlGaN/GaN HEMTs on Si. The NH3 plasma pretreatment markedly reduced RF dispersion from 63 to 1%. This is considered to be attributable to the reduction of the effective VN-related defect density and elimination of carbon/oxide residuals on the surface of AlGaN/GaN HEMTs. A NH3 plasma pretreatment prior to SiN
x
100 nm passivation in the AlGaN/GaN HEMTs on Si markedly improves the total output power from 15 to 18.1 dBm under the operating conditions of V
DS = 15 V/V
GS = -1 V.
InAs/GaAs multistacked quantum dot (QD) layers were grown by using molecular beam epitaxy with various numbers of stacking cycles to investigate the shape and the interband transition in the InAs QDs. The appearance of another photoluminescence (PL) peak on InAs/GaAs QDs with more than six stacking cycles originated from the change of the QDs from an isotropic pyramidal shape to an elongated anisotropic pyramidal shape. Dislocation lines along the [1 1 10] direction existing on the InAs/GaAs QDs with more than six stacking cycles were attributed to the existence of excessive strain fields. Scanning transmission electron microscope and atomic force microscope images showed that the QD shape in the [1 1 10] direction was elongated without any remarkable change in the volume of the QDs. These results indicate that the shape of the InAs/GaAs QDs was strongly affected by the number of the stacking cycles and that the appearance of another PL peak is related to the change of the QD shape.
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