Influence of Al _x Ga_1−x N nucleation layers on MOVPE-grown zincblende GaN epilayers on 3C-SiC/Si(001)

Abstract

The suitability of AlxGa1-xN nucleation layers with varying Al fraction x for the metal organic vapour phase epitaxy of zincblende GaN on (001) 3C-SiC was investigated, using X-ray photoelectron spectroscopy, atomic force microscopy, and x-ray diffraction. The as-grown nucleation layers exhibited elongated island structures on their surface, which reduce laterally into smaller, more equiaxed islands with increasing AlN composition. During high-temperature annealing in a mixture of NH3 and H2 the nucleation islands with low Al fraction ripened and increased in size, whereas this effect was less pronounced in samples with higher Al fraction. The compressive biaxial in-plane strain of the nucleation layers increases with increasing AlN composition up to x=0.29. GaN epilayers grown over nucleation layers that have low Al fraction have high cubic zincblende phase purity and are slightly compressively strained relative to 3C-SiC. However, those samples with a measured Al fraction in the nucleation layer higher than 0.29 were predominantly of the hexagonal wurtzite phase, due to formation of wurtzite inclusions on various {111} facets of zb-GaN, thus indicating the optimal Al composition for phase-pure zb-GaN epilayer growth.

Compositional Mapping of the AlGaN Alloy Composition in Graded Buffer Structures Using Cathodoluminescence

“…This behavior is expected since the species obtained from pyrolysis of TMAl are reactive and undergo parasitic prereactions slowing down the effective growth rate of the AlGaN layer and reducing the incorporation efficiency of AlN leading to a lower AlGaN composition when compared to the composition that would be suggested by the input group III precursor flow ratio into the reactor. [ 35,36 ]…”

“…Value at 10 K Value at RT E g;AlN 6.28 eV [38] 6.20 eV [39] E g;GaN 3.47 eV [40] 3.39 eV [41] b 0.9 eV [29] leading to a lower AlGaN composition when compared to the composition that would be suggested by the input group III precursor flow ratio into the reactor. [35,36]…”

AlN Buffer Enhances the Layer Quality of MBE-Grown Cubic GaN on 3C-SiC

“…Decreasing XRD-Δω of GaN layers with increasing layer thicknesses. The samples of this work are represented by dark gray symbols, while green squares and blue circles refer to other c-GaN layers grown by MOVPE , and MBE ,,, on comparable 3C-SiC substrates, respectively.…”

“…The virtues of such AlN as a buffer layer are barely explored for the epitaxy of cubic GaN, even though the growth of cubic AlN on 3C-SiC has already been established. ,− Few works report the sporadic use of AlN as a buffer − or as an interlayer yet without explicitly investigating neither the AlN layer itself nor its impact on a subsequent GaN layer. Only very recently, a systematic study of cubic Al x Ga (1– x ) N nucleation layers for the growth of c-GaN by metalorganic vapor-phase epitaxy (MOVPE) was reported and may be indicative of an increasing interest on the impact of the buffer layer …”

Cathodoluminescence studies of the optical properties of a zincblende InGaN/GaN single quantum well

“…One reason for this may be the presence of high defect densities, in particular {111}-type stacking faults (SFs) and wz inclusions [16,17]. While high phase purities with low or no wz inclusions can be achieved by optimizing the growth conditions [17][18][19], SFs are formed right at the beginning of the heteroepitaxial growth at an angle of about 55 • with respect to the (001) growth plane. As they are also inclined with respect to each other these SFs reduce in density with increasing film thickness by defect reactions, but they might not be completely avoidable [16] and hence some of the SFs might reach and intersect the QWs.…”