UBC Theses and Dissertations
Passivation kinetics at semiconductor interfaces Gheorghita, Ligia
The interaction of atomic hydrogen with defects at a GaAs (100) surface was studied by continuously monitoring the photoluminescence of a GaAs wafer in a discharge-flow system at room temperature. It was found that there was an initial irreversible passivation of the surface in the presence of the hydrogen atoms, and this was followed by an improved (but reversible) passivation that occurred when the exposure to atomic hydrogen was discontinued. This reversible recovery of the passivation level was found to follow a non-exponential rate law. A kinetic study of the interaction of atomic hydrogen with the defects at a Si/Si0₂ interface was undertaken at temperatures between 23°C and 330°C. The concentration of defects at the interface was monitored continuously, in situ, with a remote radio frequency (RF) probe, which measured the steady-state photogenerated carrier concentration. The results were similar to those obtained with GaAs. The kinetics of the hydrogen atom loss from both semiconductors have been analyzed in terms of a distribution of trapping sites. A comparison of the GaAs and Si/Si02 systems leads us to conclude that hydrogen atoms can be trapped at interstitial sites near these interfaces. The reaction of molecular hydrogen with defects at the (111) Si/Si0₂ interface has been investigated in the 135°C to 300°C temperature range, using the RF-probe to continuously monitor the rate of removal of electrically active defects. The kinetic parameters calculated from these experiments are compared with earlier workers' electron paramagnetic resonance (EPR) studies of the so-called "P[sub b]" defect. Our results confirm the non-exponential nature of the reaction reported by one of these studies, and are consistent with the rate constants obtained earlier at high temperatures. This process has an activation energy of 1.5 eV. However, the new results indicate that there are other interfacial defects, which could not be detected by EPR, that react with H₂ in a process that has a much lower activation energy (0.5 eV). Similar experiments were conducted on intrinsic and p-type (100) Si/Si0₂ and the same non-exponential rate law was observed for the passivation of interfacial defects in the presence of H₂.
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