Revealing microstructure and dislocation behavior in BAlN/AlGaN heterostructures

We reveal the microstructure and dislocation behavior in 20-pair B0.14Al0.86N/Al0.70Ga0.30N multiple-stack heterostructures (MSHs) exhibiting an increasing dislocation density along the c-axis, which is attributed to the continuous generation of dislocations (edge and mixed-type) within the individual B0.14Al0.86N layers. At the MSH interfaces, the threading dislocations were accompanied by a string of V-shape pits extending to the surface, leading to interface roughening and the formation of surface columnar features. Strain maps indicated an approximately 1.5% tensile strain and 1% compressive strain in the B0.14Al0.86N and Al0.70Ga0.30N layers, respectively. Twin structures were observed, and the MSH eventually changed from monocrystalline to polycrystalline.Acknowledgments The KAUST authors acknowledge the support of the GCC Research Program REP=1=3189-01-01, Baseline BAS=1=1664-01-01, and Equipment BAS=1=1664-01-07. The work at QU was supported by the GCC Research Program GCC-2017-007. The work at the Georgia Institute of Technology was supported in part by DARPA under Grant No. W911NF-15-1-0026 and NSF under Grant No. DMR-1410874. R.D.D. acknowledges the additional support of the Steve W. Chaddick Endowed Chair in Electro-Optics and Georgia Research Alliance

Development of high power green light emitting diode dies in piezoelectric GaInN/GaN

ABSTRACT Increasing emission power and efficiency in green light emitting diodes is one of the big challenges towards all-solidstate lighting. The prime challenge lies in the combination of extension of wavelength from 470 nm blue to 525 nm green while maintaining the emission power level. Commonly a steep decrease in power is observed. In a broad development effort we have been able to ameliorate that decrease significantly and obtain bare die performance at 525 nm of 1.6 mW at 20 mA for 350x350 µm 2 dies. Here we discuss critical die performance and wafer yield aspects of our optimization approach to the active layer of the GaInN/GaN quantum wells

Structural properties, crystal quality and growth modes of MOCVD-grown AlN with TMAl pretreatment of sapphire substrate

The growth of high quality AlN epitaxial films relies on precise control of the initial growth stages. In this work, we examined the influence of the trimethylaluminum (TMAl) pretreatment of sapphire substrates on the structural properties, crystal quality and growth modes of heteroepitaxial AlN films on (0 0 0 1) sapphire substrates. Without the pretreatment, the AlN films nucleated on the smooth surface but exhibited mixed crystallographic Al- (N-) polarity, resulting in rough AlN film surfaces. With increasing the pretreatment time from 1 to 5 s, the N-polarity started to be impeded. However, small islands were formed on sapphire surface due to the decompostion of TMAl. As a result, small voids became noticeable at the nucleation layer (NL) because the growth started as quasi three-dimensional (3D) but transformed to 2D mode as the film grew thicker and got coalesced, leading to smoother and Al-polar films. On the other hand, longer pretreatment time of 40 s formed large 3D islands on sapphire, and thus initiated a 3D-growth mode of the AlN film, generating Al-polar AlN nanocolumns with different facets, which resulted into rougher film surfaces. The epitaxial growth modes and their correlation with the AlN film crystal quality under different TMAl pretreatments are also discussed.The KAUST authors would like to acknowledge the support of GCC Research Program REP/1/3189-01-01, Baseline BAS/1/1664-01-01, and Equipment BAS/1/1664-01-07. The work at QU was supported by GCC Research Program GCC-2017-007. The work at Georgia Institute of Technology was supported in part by DARPA under grant W911NF-15-1-0026 and NSF under grant DMR-1410874. RDD acknowledges the additional support of the Steve W Chaddick Endowed Chair in Electro-Optics and Georgia Research Alliance.Scopu

Influence of TMAl preflow on AlN epitaxy on sapphire

The trimethylaluminum (TMAl) preflow process has been widely applied on sapphire substrates prior to growing Al-polar AlN films by metalorganic chemical vapor deposition. However, it has been unclear how the TMAl preflow process really works. In this letter, we reported on carbon's significance in the polarity and growth mode of AlN films due to the TMAl preflow. Without the preflow, no trace of carbon was found at the AlN/sapphire interface and the films possessed mixed Al- and N-polarity. With the 5 s preflow, carbon started to precipitate due to the decomposition of TMAl, forming scattered carbon-rich clusters which were graphitic carbon. It was discovered that the carbon attracted surrounding oxygen impurity atoms and consequently suppressed the formation of AlxOyNz and thus N-polarity. With the 40 s preflow, the significant presence of carbon clusters at the AlN/sapphire interface was observed. While still attracting oxygen and preventing the N-polarity, the carbon clusters served as randomly distributed masks to further induce a 3D growth mode for the AlN growth. The corresponding epitaxial growth mode change is discussed.National Science Foundation,NSF: DMR-1410874, Defense Advanced Research Projects Agency, DARPA: W911NF-15-1-0026Scopu