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AlN homoepitaxial films were grown by metalorganic chemical vapor deposition on chemomechanically polished (1100)-oriented single crystalline AlN substrates. The dependence of the surface morphology, structural quality, and unintentional impurity concentrations on the growth temperature was studied in order to determine the most appropriate growth conditions for high quality (1100) AlN epitaxial layers. Optically smooth surfaces (RMS roughness of 0.4 nm) and high crystalline quality, as demonstrated by the presence of FWHM values for (1010) rocking curves along [0001] of less than 25 arc-sec, were achieved for films grown above 1350 °C. Furthermore, sharp and intense near band edge luminescence was observed in these high quality films. A reduction in unintentional oxygen impurity levels was seen with an increase in growth temperature. These high crystalline quality films are suitable for device applications and hold great potential for providing an ideal platform for deep UV emitters with high Al content AlGaN without polarization related effects. [ABSTRACT FROM AUTHOR]

High-resolution photoluminescence studies on m-plane (1-100) homoepitaxial films grown by metalorganic chemical vapor deposition on AlN revealed several sharp donor-bound exciton (DBX) peaks with a full width at half maximum as narrow as 550 μeV. Power dependent hotoluminescence distinguished DBXs tied to the Γ5 free exciton (FX) from those tied to the 1Γ FX. Both the n=2 and n=1 excited states of the Γ5 and Γ1 were resolved, giving binding energies of 52meV and 55 meV, respectively. The DBX transition at 6.006 eV was identified as originating from the neutral-donor-oxygen (O0X). This assignment was based on secondary ion mass spectroscopy measurements, peak position with respect to the Si0X, and deep defect luminescence peaks located at 3.25 eV and 3.58 eV.VC 2014 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4870284] [ABSTRACT FROM AUTHOR]

Optical gain spectra for ~250 nm stimulated emission were compared in three different AlGaN-based structures grown on single crystalline AlN substrates: a single AlGaN film, a double heterostructure (DH), and a Multiple Quantum Well (MQW) structure; respective threshold pumping power densities of 700, 250, and 150 kW/cm2 were observed. Above threshold, the emission was transverse-electric polarized and as narrow as 1.8 nm without a cavity. The DH and MQW structures showed gain values of 50–60 cm–1 when pumped at 1MW/cm2. The results demonstrated the excellent optical quality of the AlGaN-based heterostructures grown on AlN substrates and their potential for realizing electrically pumped sub-280 nm laser diodes. [ABSTRACT FROM AUTHOR]

AlGaN lateral polarity structures (LPS) with varying Al composition, have been fabricated by metalorganic chemical vapour deposition on LPS templates containing µm size domains. III-metal and N-polar AlGaN domains have been grown on LT-AlN and c-sapphire domains, respectively. LPS characterization by SEM and AFM reveals two major effects when the Al composition has been varied: (a) A high Al content leads to columnar growth within N-polar domains and (b) a height difference between the polar domains can be observed for low Al compositions towards III-polarity. The surface quality of the III-polar domains is not effected by the Al composition. The surface roughness of N-polar domains decreases for lower Al compositions. The high periodicity of the polar domains and the high quality of the boundary between domains suggest a high potential of AlGaN LPS to be used as lateral wave guides for quasi phase matching. [ABSTRACT FROM AUTHOR]