This article reports on the study of microstructure and dislocation of InN films using high resolution x-ray diffraction grown on sapphire (0001) both by metalorganic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE). The mosaic tilt, twist, and correlation lengths of InN films are determined by using symmetrical and asymmetrical reflections as well as reciprocal space mapping. Deducing from these results, MBE-grown InN film exhibits the edge-type dislocations of 4.0×109 cm−2, which is about ten times higher than the density of screw-type dislocations. In MOCVD-grown InN sample, the edge-type dislocations density is as high as 2.1×1010 cm−2, and the screw-type dislocations density is 1.3×109 cm−2. They indicate that edge type is the predominant dislocation type in the InN films. By comparing the reported transmission electron microscopy results, the accuracy of evaluation for the dislocation density using the mosaic model is proved.

The m-plane GaN films grown on LiAlO 2 ͑100͒ by metal-organic chemical vapor deposition exhibit anisotropic crystallographic properties. The Williamson-Hall plots point out they are due to the different tilts and lateral correlation lengths of mosaic blocks parallel and perpendicular to GaN͓0001͔ in the growth plane. The symmetric and asymmetric reciprocal space maps reveal the strain of m-plane GaN to be biaxial in-plane compress xx = −0.79% and zz = −0.14% with an out-of-plane dilatation yy = 0.38%. This anisotropic strain further separates the energy levels of top valence band at ⌫ point. The energy splitting as 37 meV as well as in-plane polarization anisotropy for transitions are found by the polarized photoluminescence spectra at room temperature. © 2008 American Institute of Physics. ͓DOI: 10.1063/1.2951618͔The wurtzite structure of III-nitrides leads to electrostatic fields along the ͓0001͔ direction due to spontaneous and piezoelectric polarization, when the film is grown on c-oriented substrates. 1 These built-in electric fields along the ͓0001͔ direction separate the electron and hole wave functions in a quantum well ͑QW͒ thereby reducing the recombination probability of electron-hole pairs. Consequently, it results in reduction of quantum efficiency of light-emitting diodes. 2 A way to overcome this deficiency is to grow GaNbased QWs along nonpolar orientations, for example, m plane 3,4 or a plane. 5,6 It has been shown that the electric field can be avoided in such nitride QWs. When ͓1100͔ or ͓1120͔ becomes the growth direction, the c axis of GaN lattice lies down in the growth plane. As a consequence, the C 6v hexagonal symmetry of the c growth plane is reduced to C 2v symmetry of the m growth plane. Firstly, it would show the anisotropic crystallographic characteristics. 7,8 Secondly, the nonpolar GaN films experience strong anisotropic deformation due to different in-plane lattice mismatches and thermalexpansion coefficients between GaN and underlying substrates. In the case of c-plane GaN films, isotropic strain in the c-plane preserves C 6v symmetry in the x-y plane so that no significant in-plane physical anisotropy occurs. The situation is quite different for nonpolar GaN films. Anisotropic in-plane strain components further lift the symmetry in the growth plane, which significantly modify the top three valence band ͑VB͒ states at ⌫ point. 9,10 Both the energy splitting and polarization selection of the transitions between conduction band ͑CB͒ and VB have been observed by absorption, reflectance, and photoreflectance spectroscopy. 11,12 Recently, transmission anisotropy spectroscopy has been utilized to obtain the energy splitting and polarization information of m-plane GaN films. 13 Although the in-plane strain components are important for the modifications in band structure of nonpolar GaN, it is still difficult to experimentally determine the full state of strain. In the case of m plane, GaN films are grown along GaN ͓1100͔ direction. The growth plane is the x-z plane, and the growth direc...

Ultraviolet GaN photodetectors on Si via oxide buffer heterostructures with integrated short period oxide-based distributed Bragg reflectors and leakage suppressing metal-oxide-semiconductor contactsWe report on the composition pulling effect and strain relief mechanism in AlGaN/AlN distributed Bragg reflectors (DBRs) grown on GaN template/a-Al 2 O 3 (0001) by metal organic chemical vapor deposition. The reciprocal space mapping contours reveal that these DBRs are coherently grown. Cross-section transmission electron microscopy image of the AlGaN/AlN DBRs and the energy-dispersive x-ray analysis indicate that an AlGaN layer with gradient Al composition is located between the Al 0.4 Ga 0.6 N and AlN layers along the [0001] direction. It is attributed to the fact that Ga atoms in AlGaN are pulled and segregated to the upper layer by the strain. The density of strain energy is estimated to reduce more than one order by forming this quasi-three-sublayer structure comparing to the designed bi-sublayer structure.