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Evidence is presented that π-bonding is present in the surface dimers on clean Si(100)–(2×1) and, as a consequence, that hydrogen atoms preferentially pair on surface dimer atoms even at low coverage. We propose a simple lattice gas model in order to calculate the equilibrium distribution of doubly- and singly-occupied dimers as a function of coverage and temperature, and show that even a very conservative estimate of the enthalpy difference between hydrogen on doubly- and singly-occupied dimers can explain the observed first-order desorption kinetics.

We report on the electrical characteristics of InGaN∕GaN multiple-quantum-well light-emitting diodes (LEDs) grown on sapphire and free-standing GaN substrates. As a result of defect reduction, the tunneling current in the homoepitaxially grown LED was remarkably suppressed and diffusion-recombination current dominated at intermediate forward bias. Temperature-dependent measurements showed that the remaining reverse current originated from carrier generation and tunneling associated with deep-level traps. In contrast, the LED on sapphire exhibited dominant tunneling characteristics over a wide range of applied bias. Nanoscale electrical characterization using conductive atomic force microscopy revealed highly localized currents at V-defects, indicating that the associated dislocations are electrically active and likely responsible for the high leakage current in the heteroepitaxially grown LED.

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