The oxidation of single crystal gallium nitride in dry air has been investigated. X-ray photoelectron spectroscopy (XPS) revealed minimal oxide growth at 450 and 750 °C for up to 25 h. However, at 900 °C the growth of an oxide approximately 5000 Å thick was observed after 25 h. This oxide was determined to be the monoclinic β-Ga2O3 using glancing angle x-ray diffraction. XPS spectra of the Ga 3d and Ga 2p core levels indicated peak shifts of 1.2 and 1.3 eV, respectively, from Ga–O to Ga–N bonding. The Ga L3M45M45 core level binding energy was also investigated and β-Ga2O3 and GaN each presented a characteristic peak shape.

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We report on a study of Al and Ti/Al contacts to n-type GaN. Al contacts on n-GaN (7 ϫ10 17 cm Ϫ3) annealed in forming gas at 600°C reached a minimum contact resistivity of 8 ϫ10 Ϫ6 ⍀ cm 2 and had much better thermal stability than reported by previous researchers. Ti/Al ͑35/115 nm͒ contacts on n-GaN (5ϫ10 17 cm Ϫ3) had resistivities of 7ϫ10 Ϫ6 and 5 ϫ10 Ϫ6 ⍀ cm 2 after annealing in Ar at 400°C for 5 min and 600°C for 15 s, respectively. Depth profiles of Ti/Al contacts annealed at 400°C showed that low contact resistance was only achieved after Al diffused to the GaN interface. We propose that the mechanism for Ohmic contact formation in Ti/Al contacts annealed in the 400-600°C range includes Ti reducing the GaN native oxide and an Al-Ti intermetallic coming into intimate contact with the GaN.

We report in this communication the design and fabrication of solutionprocessed white light-emitting diodes (LEDs) containing a bilayer of heavy metal-free colloidal quantum dots (QDs) and polymer in the device active region. White electroluminescence was obtained in the LEDs by mixing the red emission of ZnCuInS/ZnS core/shell QDs and the blue-green emission of poly(N,N 0 -bis(4-butylphenyl)-N,N 0bis(phenyl)benzidine). A high color rendering index of 92 was achieved as compared to a 5310 K blackbody reference by virtue of broadband emission of the QDs. The Commission Internationale de l'Eclairage chromaticity coordinates of the white LED output exhibit a distinctive bias dependence. Finally, aging of the white LEDs was studied, revealing the difference between the photochemical stabilities of the QDs and polymer molecules and the consequent effect on the color evolution of the LEDs.