Abruptness Improvement of the Interfaces of AlGaN/GaN Superlattices by Cancelling Asymmetric Diffusion

973 program [2012CB619301, 2011CB925600]; "863" program [2011AA03A111]; FRFCU [2012121011, 2011121042]; National Natural Science Foundation [61204101, 61227009, 90921002]; Science and Technology Program of Fujian and Xiamen of ChinaInterfacial abruptness plays a critical role in affecting the quantum confinement effect in heterostructures. Here, we accurately determine the inter-diffusion depth across the AlGaN/GaN interfaces and propose a simple blocking scheme to effectively improve the superlattice abruptness. It is found that the Al diffusion depth at the upper and lower interfaces of the AlGaN barrier appears considerably asymmetric. Such difference leads to the gradient interfacial region and the asymmetric quantum well shape. A pair of ultra-thin blocking layers is introduced to the GaN/AlGaN interface to block the Al downward diffusion. After the blocking treatment, the interfacial abruptness is improved and the light emission intensity from the superlattice can be effectively enhanced. (C) 2013 The Japan Society of Applied Physic

Structural properties of InN films grown in different conditions by metalorganic vapor phase epitaxy

National Natural Science Foundation [60827004, 90921002]; Fujian and Xiamen projects of ChinaInN thin films were grown on GaN underlayer with sapphire substrate by metalorganic vapor phase epitaxy under different growth conditions, including growth temperature, reactor pressure, and V/III ratio. X-ray diffraction and Raman scattering measurements reveal that the samples grown at different temperatures are mixed with different phases, especially at higher temperature. The calculated phonon dispersion curves of wurtzite, zinc-blende, and rocksalt structures show that the samples mainly contain wurtzite structure and small amount of zinc-blende phase, while the samples grown at 600 degrees C and 650 degrees C include a new structural phase other than the three well-known ones. This analysis demonstrates that the InN epilayer grown at 550 degrees C has the highest phase purity and better crystalline quality. Besides the key role of growth temperature, a relatively higher reactor pressure and lower V/III ratio are found to be more conducive to the improvement of crystalline quality, though they have a modest effect on the InN microstructure

Origins and suppressions of parasitic emissions in ultraviolet light-emitting diode structures

863 program; National Nature Science Foundation [60827004, 90921002, 60776066]; Science & Technology Program of Fujian and Xiamen of ChinaThe AlGaN-based ultraviolet (UV) light-emitting diode (LED) structures with AlN as buffer were grown on sapphire substrate by metalorganic vapor-phase epitaxy (MOVPE). A series of cathodoluminescence (CL) spectra were measured from the cross section of the UV-LED structure using point-by-point sampling to investigate the origins of the broad parasitic emissions between 300 and 400 nm, and they were found to come from the n-type AlGaN and AlN layers rather than p-type AlGaN. The parasitic emissions were effectively suppressed by adding an n-type AlN as the hole-blocking layer. Electroluminescence (EL) and atomic force microscopy (AFM) measurements have revealed that the interface abruptness and crystalline quality of the UV-LED structure are essential for the achievement of the EL emissions from the multiple quantum wells (MQWs)