Microstructure of non-polar GaN on LiGaO2 grown by plasma-assisted MBE
We have investigated the structure of non-polar GaN, both on the M - and A-plane, grown on LiGaO2 by plasma-assisted molecular beam epitaxy. The epitaxial relationship and the microstructure of the GaN films are investigated by transmission electron microscopy (TEM). The already reported epi-taxial relationship and for M -plane GaN is confirmed. The main defects are threading dislocations and stacking faults in both samples. For the M -plane sample, the density of threading dislocations is around 1 × 1011 cm-2 and the stacking fault density amounts to approximately 2 × 105 cm-1. In the A-plane sample, a threading dislocation density in the same order was found, while the stacking fault density is much lower than in the M -plane sample.
Epitaxial growth of nonpolar m-plane ZnO epilayers and ZnO/Zn0.55Mg0.45O multiple quantum wells on a LiGaO2 (100) substrate
Nonpolar m-plane ZnO epilayers and 5-period ZnO/Zn1−xMgxO (x = 0.45) multiple quantum wells (QWs) have been grown successfully on a LiGaO2 (100) substrate by plasma-assisted molecular beam epitaxy. The epilayer and QWs samples show different anisotropy of the X-ray rocking curves (RCs) and the surface stripes. The former exhibits a low FWHM value of 126 arcsec of the X-ray (100) RC along [110]ZnO, and its surface is composed of fine stripes along [0001]ZnO. The QW sample, in contrast, exhibits a low RC FWHM (169 arcsec) along [0001]ZnO with surface stripes oriented along [110]ZnO. These phenomena are attributed to an anisotropic stress relaxation. Moreover, combining the X-ray and TEM characterization techniques, both samples show an extremely low density of threading dislocations of less than 1 × 108 cm−2, but a high density of basal stacking faults of 1 × 106 cm−1. The room temperature cathodoluminescence spectrum of the ZnO/Zn1−xMgxO QWs shows a strong emission peak with an apparent blue shift to 3.56 eV, indicating the positive quantum confinement effect and hence the absence of induced polarization fields.
Formation mechanism and relative stability of the { 112 ¯ 0 } stacking fault atomic configurations in wurtzite (Al,Ga,In) nitrides
The formation of the ${12\ifmmode\bar\else\textasciimacron\fi{}10}$ stacking fault, which has two atomic configurations in wurtzite (Ga,Al,In)N, has been investigated by high-resolution electron microscopy and energetic calculations. It originates from steps at the SiC surface and it can form on a flat (0001) sapphire surface. A modified Stillinger-Weber potential is used in order to investigate the relative stability of the two atomic configurations which have comparable energy in AIN, whereas the $\frac{1}{2}〈101\ifmmode\bar\else\textasciimacron\fi{}1〉{12\ifmmode\bar\else\textasciimacron\fi{}10}$ atomic configuration should be more stable in GaN and InN. Experimental evidence is shown in the case of AIN and GaN from high-resolution electron microscopy. Observations carried out in plan-view show the $\frac{1}{2}〈101\ifmmode\bar\else\textasciimacron\fi{}1〉{12\ifmmode\bar\else\textasciimacron\fi{}10}$ atomic configuration in GaN layers. The $\frac{1}{6}〈202\ifmmode\bar\else\textasciimacron\fi{}3〉$ configuration was found in small areas inside the AIN buffer layer in cross-section observations. It folds rapidly to the basal plane, and when back in the prismatic plane it bears the $\frac{1}{2}〈101\ifmmode\bar\else\textasciimacron\fi{}1〉{12\ifmmode\bar\else\textasciimacron\fi{}10}$ atomic configuration.