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UBC Theses and Dissertations

Electronic states and transport in GaNAs and GaAsBi Beaton, Daniel A.


ct: This thesis explores the effect of incorporation of nitrogen or bismuth in GaAs on electronic states and transport, namely shallow in-gap states associated with nitrogen clusters in GaNAs and the hole mobility in GaAsBi. Lowered in-gap emission intensity in GaNAs epi-layers grown in under atomically rich operation of the plasma source indicates that atomic nitrogen results in more optically efficient GaNxAs1-x films. Two significant additions made to the growth procedure of GaAsBi allowed for growth of thick, doped epi-layers: reduced growth rate and growth interrupt prior to the GaAsBi epi-layer. Hole mobility is found to decrease with increasing Bi concentration. This decrease is smaller than the analogous decrease of electron mobility in GaNAs. The temperature dependence of the hole mobility is modelled using terms for scattering from phonons, ionized impurities and a temperature independent bismuth related term. There is an increasing effect from the bismuth related term with increasing bismuth content. Calculation of the scattering cross-section based on the fitted coefficient for the 1% GaAsBi sample is in good agreement with a theoretically predicted value. For samples above 4.4% the hole mobility was found to be temperature independent and scattering cross-sections are more than an order of magnitude larger. These are indications that bismuth clusters play a significant role in reducing the hole mobility at high concentrations. GaAs, GaNAs and GaAsBi were incorporated in to device structures: Schottky diodes and p-i-n LEDs. Several defects were detected using DLTS and an increasing trend of defects for decreasing growth temperature found. Two hole traps were found to be related to growth of GaNAs, where only one was related to nitrogen incorporation. The device structure of the LEDs prevented an in-depth analysis and poor surface morphology of GaAsBi epi-layers resulted in leaky devices. While further work is required, it was found that the inclusion of a growth interrupt introduced many shallow traps. Optical measurements on the LEDs showed that the electroluminescence from the GaAsBi layer was temperature insensitive, while the emission from the GaAs layers followed the expected Varshni relation.

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