The surface diffusion of Ga on an AlGaN/GaN stripe structure in the selective MOVPE

Abstract

The growth of GaN with an AlGaN/GaN heterostructure was attempted on a (111) Si substrate by selective area metal organic vapor phase epitaxy. The GaN obtained was a trapezoidal stripe with (1 1 01) facets on the sides and a (0001) facet on the top. The distribution of the Al composition on the facets was investigated by cathodeluminescence analyses as a function of the position. The surface diffusion of Ga on the (0001) AlGaN facet was studied under various growth conditions. It was found that the diffusion length is enhanced by elevating the growth temperature or lowering the Al composition. By the temperature dependence of the diffusion length, the activation energy of the Ga species was estimated. The results depended on the Al composition x; 1.23 ± 0.44 eV (x = 0.05), 1.84 ± 0.58 eV (x = 0.10) and 2.72 ± 0.73 eV (x = 0.15).

The surface diffusion of Ga species on an AlGaN facet structure in low pressure MOVPE

“…The surface diffusion length of the order of 0.7 µm was almost independent of the gas pressure. This value is in agreement with the previous results for an atmospheric pressure MOVPE, which has been estimated to be 0.62 µm for x = 0.13 at 1090 °C [4]. This shows that the surface diffusion length observed in the present paper is independent of the chemical process in the gas phase.…”

“…On the other hand, in the SAG of metalorganic vapor phase epitaxy (MOVPE), the growth behavior is determined by the diffusive transport of chemical species in the gas phase as well as on the sample surface [2]. Recently, the present authors investigated the non-uniform thickness and composition of an AlGaN alloy film in the atmospheric pressure SAG-MOVPE, and determined the apparent surface diffusion length of the order of 0.3-0.8 µm [3,4]. In those studies, however, the contribution of the diffusion phenomenon in the gas was not identified from that on the surface.…”

“…In all cases, the Al composition is high near the ridge on the (0001) facet while it is low near the top on the (1-101) facet. This suggests the escape out of the Ga chemical species at the corner of the trapezoid (reevaporation and/or inter-surface diffusion) [4]. Assuming a very short diffusion length of Al on the surface, we estimated the surface diffusion length of Ga species on the (0001) facet.…”

Topography of (202¯1) AlGaN, GaN and InGaN layers grown by metal-organic vapor phase epitaxy

“…The reduced undulation bunching distance in InGaN and AlGaN can be explained by a reduced adatom surface diffusion length. In the case of InGaN it is attributed to the lower growth temperature, and in the case of AlGaN it is attributed to the presence of Al-atoms on the surface, similar to the findings by Narita et al [15]. However since the number of data points is limited, further investigations are needed.…”

The role of surface kinetics on composition and quality of AlGaN

“…This is contrary to the common assumption that the Ga adatoms have a much longer diffusion length than the Al adatoms. 22 This work clearly shows that the control of the substrate misorientation and growth…”