Petr Vacek

It is shown that for zincblende InGaN/GaN quantum wells (QWs) produced by metal–organic vapour phase epitaxy, reducing the growth temperature from 740 °C to 684 °C tunes the emission from the blue to the orange region of the visible spectrum. The emission spectrum was found to be independent of the excitation density at each growth temperature, consistent with the QWs being free of significant internal polarisation fields. The spectrally integrated emission intensity at 300 K grows from 22% to 34% of its value at 11 K as the peak emission energy decreases from 2.75 eV to 2.0 eV; this reduction in thermal quenching as the emission energy decreases is attributed to a significant lessening of thermionic emission.

Epitaxial growth of wurtzite AlN films on Si {111} results in 19% lattice misfit, which gives rise to a large density of threading dislocations with different recombination rates of electron–hole pairs. Here, we investigate types and distributions of threading dislocations of the MOVPE-grown 200 nm AlN/Si {111} film, whereby the dislocations are visualized using the technique of wet chemical etching. Atomic force microscopy suggests the existence of four different types of etch pits without any topological differences. Cross-sectional transmission electron microscope studies on etched samples are employed to associate the types of dislocations with the shapes of their etch pits. The recombination activity of individual dislocations was quantified by measuring the electron beam induced current and by correlative measurement of topography, secondary electron imaging, and the electron beam absorbed current. The strongest recombination activity was obtained for the m + c-type (mixed), c-type (screw), and a + c-type (mixed) threading dislocations, whereas the a-type (edge) threading dislocations were nearly recombination-inactive.

The defect structure of zincblende GaN nucleation layers grown by metalorganic vapor-phase epitaxy on 3C-SiC/Si (001) was investigated by high-resolution scanning transmission electron microscopy. Perfect dislocations, partial dislocations, and stacking faults are present in the layers. Perfect dislocations are identified as 60° mixed-type and act as misfit dislocations to relieve the compressive lattice mismatch strain in GaN. Stacking faults are mainly bounded by 30° Shockley partial dislocations and rarely by Lomer–Cottrell partial dislocations, both of which are able to relieve the compressive lattice mismatch strain in the layer. We propose that the stacking faults and their partial dislocations originate from the dissociation of perfect dislocations present in the zincblende GaN layer and by direct nucleation of partial dislocations loops from the surface. These are the two main mechanisms that lead to the final defect structure of the zincblende GaN nucleation layers.

X-ray diffraction and bright-field transmission electron microscopy are used to investigate the distribution and density of {111}-type stacking faults (SFs) present in a heteroepitaxial zincblende GaN epilayer with high phase purity, grown on a 3C-SiC/Si (001) substrate by metalorganic vapour-phase epitaxy. It is found that the 4° miscut towards the [110] direction of the substrate, which prevents the formation of undesirable antiphase domains, has a profound effect on the relative densities of SFs occurring on the different {111} planes. The two orientations of SFs in the [−110] zone, where the SF inclination angle with the GaN/SiC interface is altered by the 4° miscut, show a significant difference in density, with the steeper (111) SFs being more numerous than the shallower (−1−11) SFs by a factor of ∼5 at 380 nm from the GaN/SiC interface. In contrast, the two orientations of SFs in the [110] zone, which is unaffected by the miscut, have densities comparable with the (−1−11) SFs in the [−110] zone. A simple model, simulating the propagation and annihilation of SFs in zincblende GaN epilayers, reproduces the presence of local SF bunches observed in TEM data. The model also verifies that a difference in the starting density at the GaN/SiC interface of the two orientations of intersecting {111} SFs in the same zone reduces the efficiency of SF annihilation. Hence, (111) SFs have a higher density compared with SFs on the other three {111} planes, due to their preferential formation at the GaN/SiC interface caused by the miscut.