Fine structure of AlN∕AlGaN superlattice grown by pulsed atomic-layer epitaxy for dislocation filtering

Abstract

We report the detailed structure analysis of our AlN∕AlGaN superlattice (SL) grown by pulsed atomic-layer epitaxy (PALE) for dislocation filtering. Due to the nature of PALE, the AlGaN well material itself in the SL was found to be composed actually of an AlxGa1−xN∕AlyGa1−yN short-period superlattice (SPSL), with the periodicity of 15.5Å (≈6 monolayer), determined consistently from high-resolution x-ray diffraction and high-resolution transmission electron microscopy measurements. The SPSL nature of the AlGaN layers is believed to benefit from the AlN∕AlGaN SL’s coherent growth, which is important in exerting compressive strain for the thick upper n-AlGaN film, which serves to eliminate cracks. Direct evidence is presented which indicates that this SL can dramatically reduce the screw-type threading dislocation density.

Reducing dislocations of Al-rich AlGaN by combining AlN buffer and AlN/Al0.8Ga0.2N superlattices

“…Therefore, the partially relaxed SLs effectively assist in decreasing the edge TDs extending into upper Al-rich AlGaN. In comparison with the results reported by others [14], where fully strained SLs effectively reduce screw TDs but do nothing with the edge ones, it suggests that SLs' strain extent has a close relation with reducing screw or edge TDs. In our case, the function of SLs buffer on improving the crystalline quality of Al-rich AlGaN includes two aspects.…”

“…Taking the (1 1 2 4) RSM as an example, the tilt broadens the RLPs along the normal to [11][12][13][14][15][16][17][18][19][20][21][22][23][24] direction, whereas the lateral coherence length broadens along the [11][12][13][14][15][16][17][18][19][20] lateral direction [24]. Thus, both broadening extents of Al 0.69 Ga 0.31 N can be estimated from its (1 1 2 4) RSM in Fig.…”

“…However, techniques for fabricating highquality Al-rich AlGaN films are not mature up to now, due to lack of lattice and thermal matched substrates and inherent Al chemical activity. Therefore, many approaches are currently being pursued, such as using AlN buffers of different growth modes [9][10][11], AlN/AlGaN superlattices (SLs) [12][13][14], etc. Recently, Bai et al [15] reported the (0 0 0 2) AlN full-width at half-maximum (FWHM) of 68 arcsec, much narrower than that of current GaN typically between 250 and 300 arcsec.…”

“…3shows the triple-axis (1 1 2 4) RSM of sample A. The horizontal and vertical axes, Q x[11][12][13][14][15][16][17][18][19][20] and Q z [0 0 0 1], are components of the reciprocal lattice vector relative to the[11][12][13][14][15][16][17][18][19][20] and [0 0 0 1] directions, respectively. The measured AlGaN lattice constants (a x , c x ) are (3.1289 Å , 5.0511 Å ) according to the coordinates of its reciprocal lattice point (RLP).…”

Microstructure of interfacial HgTe/CdTe superlattice layers for growth of HgCdTe on CdZnTe (211)B substrates

“…Substantial research [17][18][19] has shown that the development of strained-layer SLs makes it possible to grow epitaxial layers of high quality on lattice-mismatched substrates, especially for III-V materials. The strained layers serve as a series of barriers that tend to bend any misfit dislocations into the growth plane, thus preventing the propagation of dislocations into the next layer.…”