This PDF file contains the front matter associated with SPIE Proceedings Volume 6473, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.

In the application of nitride semiconductors for electronic and optical devices, spontaneous and piezoelectric polarizations have been discussed recently. On the contrary, in light emitting devices, polarization is expected to be absent. To suppress the polarization effect, GaN growth on A-plane and R-plane sapphire substrates has been attempted. A-plane sapphire has crystallographical symmetry different from GaN. R-plane sapphire has large lattice-mismatch from GaN. In this paper, GaN grown on an M-plane sapphire substrate which has been focused in 1990 is reviewed. M-plane sapphire has a lattice-mismatched to GaN by less than 3%. Single-phase GaN was grown on sapphire tilted 15 degrees from an M-plane and its inclination of c-axis to the nominal axis of a substrate was by 32 degree. This number is much attractive to suppress the polarization effect in light emitting devices. This paper also describes N-polar GaN grown by MOVPE. Differently from the reported data about N-polar GaN this N-polar GaN with a surface as smooth as Ga-polar one was obtained and the density of threading dislocations was in order of 10¹⁸/cm². p-type doping was also possible. This N-polar is very suitable for the growth of InN, which has the high equilibrium-vapor-pressure of nitrogen, because N polarity has the advantage in the capture of nitrogen. The growth and the properties of N-polar InN on N-polar GaN templates are reviewed. Finally, the perspectives of InN in device applications are introduced.

We report on growth and characterization of epitaxial lateral overgrown (ELO) (11₂^-0) a-plane GaN by metalorganic chemical vapor deposition (MOCVD). The ELO samples were grown using a SiO₂ striped mask pattern consisting of 4 &mgr;m wide open windows and 10 &mgr;m or 20 &mgr;m wide SiO₂ stripes. Different growth rates in Ga- and N-wings along with the wing tilt create a major obstacle for achieving a fully coalesced flat surface in ELO-GaN. To address this problem we have employed a two-step growth method that is able to provide a high height to width aspect ratio in the first growth step followed by enhanced lateral growth in the second step by controlling the growth temperature. Depending on the growth conditions, lateral growth rate of the wings with Ga-polarity were from 2 to 5 times larger than that of the N-polarity wings. We investigated the effects of growth parameters on wing tilt, which was observed to be ~0.25° from the Kikuchi lines using large angle convergent beam electron diffraction (LACBED) and accompanied by some twist (0.09°) between the two opposite wings. Transmission electron microscopy (TEM) results showed that the threading dislocation density in the resulting fully coalesced overgrown GaN was reduced from 4.2×10¹⁰ cm^-2 in the window area to 1.0×10⁸ cm^-2 in the wing area, and that the wing areas contained relatively high density of basal stacking faults, 1.2×10⁴ cm^-1. The recombination of carriers/excitons localized at stacking faults was evident in far-field near bandedge photoluminescence (PL) measured at 10 K. Moreover, atomic force microscopy (AFM) measurements revealed two orders of magnitude higher density of surface pits in window than in wing regions, which could be decorating dislocation termination on surface. Time-resolved PL measurements for the a-plane ELO-GaN samples revealed biexponential decays. The recombination times were significantly increased ( &tgr;₁ =80 ps and &tgr;₂ =250 ps) compared to the standard a-plane epitaxial layers (<45 ps), and ratio of the slow decaying component magnitude to the fast decaying one was more than 1.5, showing considerable reduction of nonradiative centers by lateral overgrowth. In addition, room temperature near-field optical microscopy studies revealed the improved optical quality in the wing regions of the overgrown GaN. As revealed from far-field PL, the band edge luminescence at room temperature was more than two orders of magnitude weaker than the yellow luminescence. Therefore, the overall spectrally integrated near field PL was collected, and its intensity was noticeably stronger in the wing areas with both Ga and N polarity. The much weaker emission at the windows and meeting fronts of the two opposite wings were consistent with the observations of high density of dislocations in the window regions and new defects originating at the meeting boundaries from TEM.

GaN epitaxial layers grown on SiC and sapphire suffer from high density of line and point defects. To address this problem, new growth methods using in situ or ex situ nano-network masks as dislocation filters have been introduced recently. In this work, we report on metalorganic chemical vapor deposition (MOCVD) of GaN layers on 2-inch sapphire substrates using in situ SiN_x nano-networks intended for defect reduction. SiN_x interlayers with different deposition times were employed after ~2 &mgr;m GaN grown on sapphire, which was followed by ~3.5 &mgr;m GaN overgrowth. With increasing SiN_x coverage, full width at hall maximum (FWHM) values of (0002) and (10₁^-2) X-Ray diffraction (XRD) peaks monotonously decrease from 252 arc sec to 217 arc sec and from 405 ar csec to 211 arc sec, respectively for a 5.5 &mgr;m thick film. Similarly, transmission electron microscopy (TEM) revealed that screw and edge type dislocation densities as low as 4.4x10⁷ cm^-2 and 1.7x10⁷ cm^-2 were achieved. The use of SiN_x nanonetwork also increases the radiative recombination lifetimes measured by time-resolved photoluminescence to 2.5 ns from less than 0.5 ns in control GaN. We have also fabricated Ni/Au Schottky diodes on the overgrown GaN layers and the diode performance was found to depend critically on SiN_x coverage, consistent with TEM, XRD and TRPL results. A 1.13eV barrier height was achieved when SiN_x layer was used compared to 0.78 eV without any SiN_x nanonetwork. Furthermore, the breakdown voltage was improved from 76 V to 250 V with SiN_x nanonetwork.

Growth and polarity control of GaN and AlN on carbon-face SiC (C-SiC) by metalorganic vapor phase epitaxy (MOVPE) are reported. The polarities of GaN and AlN layers were found to be strongly dependent on the pre-growth treatment of C-SiC substrates. A pre-flow of trimethyaluminum (TMAl) or a very low NH₃/TMAl ratio resulted in Al(Ga)-polarity layers on C-SiC. Otherwise, N-polarity layers resulted. The polarities of AlN and GaN layers were conveniently determined by their etching rate in KOH or H₃PO₄, namely the etching rate on N-polarity is substantial larger, a method reported earlier. We suggest that the Al adatoms form several Al adlayers on C-SiC and change the incorporation sequence of Ga(Al) and N leading to a metal polarity surface. In addition, the hexagonal pyramids, typical on N-polarity GaN surface, are absent on N-polarity GaN grown on off-axis C-SiC owing to high density of terraces on the substrate surface. The properties of GaN layers grown on C-SiC have been studied by X-ray diffraction and are reported in this paper.

We report the structural and optical properties of Al_xGa_1-xN/Al_yGa_1-yN quantum wells (QWs) structures grown by gas source molecular beam epitaxy with ammonia on sapphire (0001) substrates. QWs structures consist of five pairs of Al_yGa_1-yN, 0.3xGa_1-xN, 0.55