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We reported the effect of the deposition time of barrier layers on optical and structural properties of high-efficiency green-light-emitting InGaN∕GaN multiple quantum wells (MQWs) by photoluminescence (PL) and high-resolution x-ray diffraction techniques. The MQW samples on (0001)-plane sapphire substrates were prepared with a ramping method by metalorganic chemical deposition. It was found that the structural or interface quality of the MQW system improved as the deposition time of barrier layers increased from 10 to 14min, but lattice relaxation was still observed. The relaxation degree decreases from 33% to 6% as the deposition time increases. Temperature-dependent PL measurements from 12 to 300K indicated that the integrated PL intensities start to decay rapidly as temperature rises above 50K for the sample with the shorter deposition time, and above 100K for the sample with the longer deposition time. The luminescence thermal quenching of the two samples suggests the two nonradiative recombination c...

The reverse bias current-voltage (I–V) characteristics of GaN-based light-emitting diodes (LEDs) were investigated. The leakage current exhibits exponential dependence on the bias voltage with different exponents for various voltage ranges. The leakage current is closely related to the density of dislocations. The number of dislocations in GaN was determined by atomic force microscopy combined with hot H3PO4 etching. Dislocations with a screw component in the GaN films were found to have a strong influence on the reverse leakage current of LEDs. The dislocation electrical activity in GaN grown on c-plane sapphire is different from that in GaN grown on a-plane sapphire.

Magnetically soft/hard exchange-coupled Ni80Fe20/Si3N4/Sm40Fe60 and Ni80Fe20/mixture/Sm40Fe60 layered structures with induced in-plane uniaxial anisotropy were deposited by sputtering on Si (100) substrates. The interfacial exchange coupling strength between the soft and hard layers was tailored by inserting a thin nonmagnetic insulating Si3N4 layer or by varying interfacial mixture of NiFe and SmFe. It was found that the reduction in the exchange coupling greatly reduces the nucleation field HN of the soft layer and increases the irreversible switching field Hirr of the hard layer. The simple formula used before to describe the nucleation field of the soft layer does not work in the case of the reduced interfacial exchange coupling.