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The effects of negative polarization charge at the n -InGaN/p -GaN interface on the performance of hydride vapour phase epitaxy-deposited single heterostructure n -In0.17Ga0.83N/p -GaN light emitting diodes with p -side down are investigated. The negative polarization charge at the interface leads to the formation of a two-dimensional hole gas within the InGaN near the n -InGaN/p -GaN interface, as well as reducing the barrier for hole injection. In addition, electrons encounter experience a significant barrier for injection across the heterointerface. As a result, superlinear increase in light output as injection current increases below 20 A/cm2 and peak emission wavelength shift from 495 nm to 470 nm are observed. We show that the combination of two-dimensional hole-gas formation on the n -InGaN side of the hetero-interface and enhancement of the electron barrier to transport across this interface may reduce efficiency droop at high current density without the need for an AlGaN electron blocking layer. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In this paper, we demonstrate new results on controllable HVPE growth of nitride materials with a deposition rate below 0.02 microns per minute and the first quantum size structures fabricated by HVPE. The nm-scale layer thicknesses were verified by transmision electron microscopy (TEM) and photoluminescence (PL). Quantum well (QW) GaN/AlGaN and AlN/AlGaN structures have been grown by HVPE for the first time. Properties of the HVPE grown QWs are reported. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

This paper contains results on InN and InGaN growth by Hydride Vapor Phase Epitaxy (HVPE) on various substrates including sapphire and GaN/sapphire, AlGaN/sapphire, and AlN/sapphire templates. The growth processes are carried out at atmospheric pressure in a hot wall reactor in the temperature range from 500 to 750 oC. Continuous InN layers are grown on GaN/sapphire template substrates. Textured InN layers are deposited on AlN/sapphire and AlGaN/sapphire templates. Arrays of nano-crystalline InN rods with various shapes are grown directly on sapphire substrates. X-ray diffraction rocking curves for the (002) InN reflection have the full width at half maximum (FWHM) as narrow as 270 arcsec for the nano-rods and 460 arcsec for the continuous layers. InxGa1–xN layers with InN content up to 10 mol.% are grown on GaN/sapphire templates. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

AlGaN epilayers grown by plasma-assisted molecular beam epitaxy and exhibiting high internal quantum efficiency (up to 30%) are incorporated into double-heterostructure devices grown on base layers of varying defect density. Growth of these AlGaN active layers, having increased emission from localization of carriers in regions of nanoscale compositional inhomogeneities, is found to benefit from base layers of reduced defect density, including thick AlGaN templates grown by hydride vapor phase epitaxy. Nonlinear radiative processes are observed at high optical excitation for layers grown on lower defect base layers. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In this paper we report on first InGaN-based light emitting structures grown by hydride vapour phase epitaxy (HVPE). InGaN layers and multi layer InGaN/InGaN epitaxial structures were grown on GaN/sapphire template substrates and characterized. InN content in the InGaN layers was varied from 5 to 35 mol.%. Thickness of InGaN layers was controlled from 10 nm to 2 microns. Density of treading dislocations in the InGaN layers was estimated to be in the 109 cm–2 range. X-ray diffraction measurements and transmission electron microscopy data confirmed a formation of InGaN/InGaN superlattice structures. Light emitting diode epitaxial wafers were fabricated by HVPE deposition of n-type InGaN layers and multi layer structures on p-type GaN template substrates. Depending on InN content in the InGaN light emitting regions, peak electroluminescence wavelength varied from 450 to 510 nm. Results of material characterization are reported. Advantages of the proposed upside down LED configuration and future applications of HVPE to grow InGaN layers and structures are discussed. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We probe the electric field in In-face and N-face InN/InGaN multiple quantum wells (MQWs) using low temperature intensity-dependent photoluminescence (PL) under continuous-wave laser excitation at 900 nm. The In-face structure consists of 30 periods of 2.5 nm thick InN wells and 24 nm thick In0.92Ga0.08N barriers. The N-face sample consists of 25 periods of 1.5 nm InN wells and 15 nm thick In0.88Ga0.12N barriers. At low excitation power, the PL peak energy from both In-face and N-face MQWs is redshifted relative to that from bulk InN. As excitation power increases, we observe a 50 and 44 meV blueshift of the PL peak energy from the In-face and N-face MQWs, respectively. The blueshift is a result of the optically induced screening of the built-in electric field. From the measured blueshift, we calculate a minimum change of the electric field to be ∼0.4 MV/cm and ∼0.6 MV/cm in the In-face and N-face well regions, respectively. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We report on the fabrication and evaluation of flip-chipped double heterostructure UVLEDs operating at 320 nm that employ a bulk (80nm) AlGaN active region containing nanoscale compositional inhomogeneities (NCI), deposited by plasma-assisted molecular beam epitaxy. The devices were deposited on AlGaN templates grown by hydride vapor phase epitaxy and contain electron and hole injection layers grown by metalorganic chemical vapor deposition. A packaged, 300 μm x 300 μm device with 3% internal quantum efficiency has a peak output power of 0.56 mW at 90 mA DC current that corresponds to an external quantum efficiency of 0.15%. Nearly constant external quantum efficiency is observed for DC current density up to 100 A/cm2, suggesting that the NCI regions effectively suppress the deleterious effects of polarization fields at low injection currents that should inhibit radiative recombination in double heterostructure devices. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We report the Stark energy sublevels of Nd3+ ions in GaN grown by plasma-assisted molecular beam epitaxy as determined by luminescence spectra. The photoluminescence spectra is correlated with transitions from the 4F3/2 doublet state to the 4I9/2, 4I11/2, and 4I13/2 multiplets of the Nd3+ ion for above and below bandgap excitation, with the strongest emission occurring at 1.12 eV (1106 nm). A splitting of the 4F3/2 excited state is determined to be 4.1 meV. From photoluminescence excitation spectra, we also identify the Stark sub-levels of the excited states 4F5/2, 2H9/2, 4F7/2, 4S3/2, 2G7/2, and 4G5/2. Photoluminescence excitation spectra exhibit an optimal excitation energy of 1.48 eV (836 nm). Site-selective spectroscopy studies using combined excitation-emission spectroscopy with confocal microscopy imply enhanced substantial doping at the Ga site. In addition, optical loss and gain measurements of a GaN:Nd waveguide excited above bandgap indicate an internal loss coefficient of ∼6.5 +/– 2 cm–1 and a net gain of ∼ –2 +/– 2 cm–1. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)