A model to explain the observed low transverse mobility in GaN by scattering of electrons at charged dislocation lines is proposed. Filled traps along threading dislocation lines act as Coulomb scattering centers. The statistics of trap occupancy at different doping levels are investigated. The theoretical transverse mobility from Coulomb scattering at charged traps is compared to experimental data. Due to the repulsive potential around the charged dislocation lines, electron transport parallel to the dislocations is unaffected by the scattering at charged dislocation lines.
The lateral transport in GaN films produced by electron cyclotron resonance plasma-assisted molecular beam epitaxy doped n type with Si to the levels of 1015–1020 cm−3 was investigated. The room temperature electron mobility versus carrier concentration was found to follow a family of bell-shaped curves consistent with a recently proposed model of scattering by charged dislocations. The mechanism of this scattering was investigated by studying the temperature dependence of the carrier concentration and electron mobility. It was found that in the low carrier concentration region (<1017 cm−3), the electron mobility is thermally activated with an activation energy half of that of carrier concentration. This is in agreement with the prediction of the dislocation model.
Nanopores can be used to detect and analyse biomolecules. However, controlling and tuning the translocation speed of molecules through a pore is difficult, limiting the wider application of these sensors. Here we show that low-power visible light can be used to control surface charge in solid-state nanopores and can influence the translocation dynamics of DNA and proteins. We find that laser light precisely focused at a nanopore can induce reversible negative surface charge densities as high as 1 C/m2, and that the effect is tuneable on sub-millisecond timescales by adjusting the photon density. By modulating surface charge, we can control the amount of electro-osmotic flow through the nanopore, which affects the speed of translocating biomolecules. In particular, a few mW of green light can reduce the translocation speed of double-stranded DNA by more than an order of magnitude and the translocation speed of small globular proteins such as ubiquitin by more than two orders of magnitude. The laser light can also be used to unclog blocked pores. Finally, we discuss a mechanism to account for the observed optoelectronic phenomenon.
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