Study of hydrogen desorption from gallium nitride(0001)

Earlier work from this lab investigated interaction of hydrogen with GaN(0001) by surface science techniques such as low energy electron diffraction (LEED), Auger electron spectroscopy (AES), electron energy loss spectroscopy (ELS or EELS) and high resolution electron energy loss spectroscopy (HREELS). Based on these, we perform temperature programmed desorption (TPD) and electron stimulated desorption (ESD) studies on the surface.; A significant part of this dissertation work has been the design and construction of an ultra-high vacuum (UHV) apparatus, gas manifold system, sample mount, e-beam heater, wide spot electron gun, ion gun and differentially-pumped mass spectrometry system. Therefore, this dissertation also includes a description of the state of the art apparatus which was constructed to perform the experiments described in this work.; TPD of deuterium on GaN(0001) from Ga sites has been performed to measure the desorption kinetic parameters and to further understand the desorption mechanism. For a heating rate of 1°C/s, the main feature peaks at ∼410°C while the smaller feature occurs as a shoulder near 320°C. The ratio between the intensity of the main desorption peak and shoulder gets larger after more sputtering and annealing cycles. Heating rate variation analysis indicates a pseudo-first-order pre-exponential factor of 1 × 106 s−1 and desorption activation energy of 1.1 eV. The values are believed to be too low and attributed to multiple surface sites. Assuming a pre-exponential factor of 1 × 1013 s−1 yields an activation energy of 2.0 eV which implies a value for the molecular hydrogen adsorption barrier of ∼0.9 eV. After the deuterated sample being exposed to various doses of 90-eV electrons, TPD shows a decrease in the flux of desorbing deuterium centers at 400°C. This reduction in deuterium desorption is attributed to removal of surface D via electron stimulated desorption (ESD). The peak desorption temperature does not shift as hydrogen is removed by ESD indicating first order desorption and a diffusion mechanism is proposed. From the area under the TPD curves, an ESD cross-section of ∼9 × 10−19 cm2 is estimated. (Abstract shortened by UMI.)...