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.

GaN / Al 0.15 Ga 0.85 N multiple quantum wells (MQWs) have been grown by plasma-assisted molecular-beam epitaxy on R-plane (101̄2) sapphire substrates. The orientation relationship was found to be (112̄0) (Al)GaN∥(10 1̄2) Al2O3, resulting in nonpolar GaN/AlGaN heterostructures. Room-temperature photoluminescence studies were performed to compare the optical properties of the MQWs grown on (0001) and (101̄2) Al2O3 substrates. The peak transition energy, as a function of well width for the (112̄0) MQWs, followed the trend for rectangular potential profiles indicating the absence of built-in electrostatic fields. In comparison, the peak transition energies for the (0001) MQWs showed a significant redshift due to the quantum-confined Stark effect, consistent with a built-in field value of 750 kV/cm. In addition, the photoluminescence intensity was 20 to 30 times higher for the (112̄0) MQWs compared to the (0001) MQWs.

We experimentally demonstrate the formation of GaN nanotip pyramids by selective and anisotropic etching of N-polar GaN in KOH solution. For samples grown with adjacent Ga-and N-polar regions on the same wafer, the KOH solution was found to selectively etch only the N-polar surface while leaving the Ga-polar surface intact. An aggregation of hexagonal pyramids with well defined ͕10 1 1 ͖ facets and very sharp tips with diameters less than ϳ20 nm were formed. The density of the pyramids can be controlled by varying the KOH concentration, solution temperature or the etch duration. The GaN etching activation energy is estimated to be E a Ϸ0.587 eV. Dense GaN pyramids with sharp tips have applications in both electronic and photonic devices.