This work elucidates the two-stage growth of GaN on V-grooved (001)Si substrates using metal-organic chemical vapor deposition. The first growth stage proceeds on the {111}Si sidewalls until GaN fills the V grooves. Then the second stage continues and leads to a semipolar surface with the {1-101}GaN facets. GaN films with thickness of over 1μm can be obtained without cracks by this two stage-growth. Excitation-power-dependent and time-resolved photoluminescence measurements confirm that the internal electric field in the InGaN∕GaN multiple-quantum well (MQW) grown on this GaN template is indeed smaller than that of the MQW grown on (0001)GaN.

The authors report on the growth of GaN on AlGaN∕(111)Si micropillar array by metal-organic chemical vapor deposition. Using the substrates with micropillar array, 2-μm-thick GaN films without cracks can be achieved. Transmission electron microscopy, atomic force microscopy, and micro-Raman studies indicate that the dislocation density and residual stress of the GaN grown on micropillar array are also reduced. The results reveal the potential of this type of substrates for growing GaN-based devices as well as preparing GaN freestanding substrates.

h i g h l i g h t sHere observational characteristics of 12 solar neutron events are presented. Different calculation methods of neutron energy spectrum are compared. It can be parameterized in the acceleration parameters and physical parameters of one specific solar neutron event.a b s t r a c t Solar neutron events provide important opportunities to explore particle acceleration mechanisms using data from ground-based detectors and spacecrafts. Energetic neutrons carry crucial physics information of the acceleration site, such as energy spectrum, atmospheric elements of solar flare, scale height, convergence of the magnetic field and magnetohydrodynamic turbulence. Here 12 representative solar neutron events observed on the Earth, together with X and c-ray observations from spacecrafts are presented. Theoretical approaches on solar neutrons that are carried out mainly through the Monte Carlo simulation are compared with the observation data, and the constraints of different theoretical models on the observations are to be summarized.

Thermal stability, optical reflectivity, and contact resistivity of Pd∕Ni∕Al∕Ti∕Au ohmic contacts to p-type GaN were investigated. In contrast to its Pd∕Al∕Ti∕Au counterparts, Pd∕Ni∕Al∕Ti∕Au contacts retained their specific contact resistivity (<2×10−2Ωcm2) and reflectivity (>76%) after long-term annealing at 150 °C in nitrogen ambient. According to the results of the secondary ion mass spectroscopy study, it is suggested that the Ni layer prevents the penetration of Ti into GaN during thermal treatment.

Two emission peaks with different behaviors are observed from the electroluminescence spectrum of AlIn-GaN laser diode structure. A significant blueshift and a linewidth broadening are measured for the low-energy peak with an injection current, while a slight blueshift and a moderate linewidth narrowing occur for the high-energy peak. Accordingly, these two peaks are assigned to be from localized state and quantum well state emissions, respectively. The quantum well state emission exhibits a biexciton feature in contrast to the localized excitons. Based on the injection current dependent thermal quenching behavior of the localized state, a multiple carrier escaping mechanism is proposed.