A modified Schottky-contact gated-four-probe structure was applied to study the stability of the hydrogenated and deuterated amorphous silicon (a-Si:D) thin-film transistors under various bias conditions. It was found that after 10 V bias stress, the density of gap states generated in both the upper and lower part of the mobility gap of deuterated amorphous silicon is two to twenty times less than those of hydrogenated silicon. Besides, less density of states at the lower part of mobility gap of a-Si:D is generated after 20, −10, and −20 V bias stress.
Atomic force microscopy (AFM) is typically used to measure the quantum dot shape and density formed by lattice mismatched epitaxial growth such as InAs on GaAs. However, AFM images are distorted when two dots are situated in juxtaposition with a distance less than the AFM tip width. Scanning electron Microscope (SEM) is much better in distinguishing the dot density but not the dot height. Through these measurements of the growth of In x Ga 1)x As cap layer on InAs quantum dots, it was observed that the InGaAs layer neither covered the InAs quantum dots and wetting layer uniformly nor 100% phase separates into InAs and GaAs grown on InAs quantum dots and wetting layer, respectively.
Photoluminescence ͑PL͒ of self-assembled InAs quantum dots ͑QDs͒ on GaAs substrate with different In͑Al͒GaAs cap layer are studied. It is now well known that the peak position of the InAs QDs covered with InGaAs layer shifts to longer wavelength than those covered with GaAs and AlGaAs. The theoretical simulations are developed to distinguish various contributions to the wavelength shift from the dot height, strain, and barrier height of different cap layers. It reveals that most of the stress in the InAs QDs comes from the upper GaAs cap layer.
The mechanisms responsible for the shift of the photoluminescence spectrum to longer wavelength by depositing an InCaAs cap layer on InAs/GaAs quantum dots are studied in detail. It is demonstrated that the phase separation growth of InAs and GaAs rather than the stress in the lnAs quantum dots is the main reason for the wavelength shifts. Also, AFM image of single lnAs quantum dot is observed. The reason for the differences between AFM and SEM images is discussed.
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