Dislocation behaviour in III‐nitride epitaxial films grown on vicinal sapphire (0001) substrates

Abstract

Dislocation behaviour in AlN and GaN films grown on vicinal sapphire (0001) substrates are investigated using transmission electron microscopy. It is found that the dislocation behaviours strongly depend on the vicinal angle of the substrates. When the vicinal angle is 0.5 o , the dislocation lines propagate along the caxis and no bending of the dislocation line is found. On the other hand, dislocation bending occurs in the films grown on the 2.0 o -off substrates, which results in the great reduction of the dislocation density in the films. The dislocation loop formation and the combination of two dislocations into one are the main mechanisms for this reduction. The surface morphology (mono-layer and multilayer step formations) plays an important role in determining the different dislocation behaviours.1 Introduction III-nitride materials have attracted great attentions due to their potential applications in optical and electronic devices [1][2][3]. It is strongly required to realize high-quality epitaxial films with low dislocation density, because high-density dislocations, due to the lack of proper substrates for the epitaxial growth, greatly influence the properties of device operations. To solve this problem, many growth techniques have been proposed [4][5][6][7][8]. Among them, epitaxial lateral overgrowth (ELO) is the most successful technique, which has been applied to the commercialised optical devices such as LDs. However, the present techniques are still difficult to obtain the satisfied quality of epitaxial films for the purpose of electronics devices, because uniformly low dislocation density on the whole wafer is strictly required for the electronics device application. Furthermore, the processes of the present techniques are very complicated, such as additional patterning, re-growth and etc. We have proposed a new approach to uniformly reduce the dislocation density [9]. This technique is simply to use vicinal substrates for the epitaxial growth without any additional processes. In order to promote this technique to the practical application, understanding of the dislocation behaviours in the films grown on such vicinal substrates is necessary.In this study, we systematically investigate the dislocation behaviours in the ALN and the GaN films grown on the vicinal sapphire (0001) substrates observed by transmission electron microscopy (TEM). Both cross-sectional and plan-view observations were carried out to characterize the dislocation behaviours in the epitaxial films. Based on the observation results, the mechanism of the dislocation density reduction is discussed.

AlxGa1−xN‐Based Quantum Wells Fabricated on Macrosteps Effectively Suppressing Nonradiative Recombination

“…Although the threading dislocation densities differ significantly, it may not lead to the lifetime difference, as suggested by the above comparison between the planar QWs on sapphire and AlN. This assertion is supported by previous reports, in which macrosteps bend threading dislocations and decrease their density, thereby reducing influences from threading dislocations. Rather, impurity concentrations should be considered.…”

Infrared stimulated emission with an ultralow threshold from low-dislocation-density InN films grown on a vicinal GaN substrate

“…1 b, c. When InN was grown on the 1°-off vicinal substrate, the macro-steps were approximately 1 nm in height and 200 nm in width, whereas when the InN was grown on the 2°-off vicinal substrate, much larger macro-steps were observed with a height and width of 5.4 nm and 350 nm, respectively. The formation of macro-steps implies that the reduction in TD density occurred, as reported in previous studies [ 20 , 21 , 25 ] which is supported by the X-ray diffraction (XRD) measurements shown in Fig. 1 d. The full width at half maximum (FWHM) values for the (102) diffraction peaks decreased from 1200 to 750 arcsec as the vicinal angle increased from 0.35° to 2°, which indicates an improvement in the twisting feature of the InN film grain structure.…”

Low-Defect-Density Aluminum Nitride (AlN) Thin Films Realized by Zigzag Macrostep-Induced Dislocation Redirection

“…These phenomena are quite different from the previous finding that the projections of inclined dislocations on the (0001) plane mainly gather near the step edges and arrange in parallel. 38,39 Based on the above results, we can infer the physical mechanism behind different dislocation behaviors. To explain it clearly, we schematically drew dislocation propagation paths under the influence of different step movements, as shown in Figure 6.…”

“…Some of them formed half-loops (Figure d), and some of them changed the propagation direction within the (0001) plane (Figure e,f). These phenomena are quite different from the previous finding that the projections of inclined dislocations on the (0001) plane mainly gather near the step edges and arrange in parallel. , …”