Phase separation and ordering in InGaN alloys grown by molecular beam epitaxy

Abstract

In this study, we investigated phase separation and long-range atomic ordering phenomena in InGaN alloys produced by molecular beam epitaxy. Films grown at substrate temperatures of 700-750°C with indium concentration higher than 35% showed phase separation, in good agreement with thermodynamic predictions for spinodal decomposition. Films grown at lower substrate temperatures ͑650-675°C͒ revealed compositional inhomogeneity when the indium content was larger than 25%. These films, upon annealing to 725°C, underwent phase separation, similar to those grown at the same temperature. The InGaN films also exhibited long-range atomic ordering. The ordering parameter was found to increase with the growth rate of the films, consistent with the notion that ordering is induced at the growth surface. The ordered phase was found to be stable up to annealing temperatures of 725°C. A competition between ordering and phase separation has been observed, suggesting that the driving force for both phenomena is lattice strain in the alloy.

Defects, strain relaxation, and compositional grading in high indium content InGaN epilayers grown by molecular beam epitaxy

“…1,2 However, due to the immiscibility of alloy constituents, chemically induced phenomena, such as phase separation and compositional pulling, may take place, resulting in complex defect microstructures that are sensitive to the growth conditions. [3][4][5][6] The fluctuations in the indium concentration can be either long-or short-range in character. Short-range ones cause the local depletion of indium around regions that exhibit higher InN molar fraction.…”

High efficiency, radiation-hard solar cells

“…Growth of In 1-x Ga x N over the entire composition range has proven to be challenging due the presence of a significant miscibility gap at the growth temperatures required to maintain the stability of In-rich material [Ho and Stringfellow, 1996]. To our knowledge, all reported attempts to grow In 1-x Ga x N with 0.2 < x < 0.6 and with a thickness useful for solar cells (i.e., > 200 nm) by either MOCVD [Wakahara et al, 1997;El-Masry et al, 1998;Rao et al, 2004] or MBE [Doppalapudi et al, 1998] techniques resulted in phase separated material. We thus consider growth of uniform material in this composition range to be a significant achievement of the DII project.…”

High Al-Content AlInGaN Devices for Next Generation Electronic and Optoelectronic Applications

“…We have also examined the effect of chemical ordering on the band gaps of strained wurtzite InGaN. This work was motivated by experimental studies showing evidence of cation ordering along the [0001] direction in wurtzite alloys [30]. Furthermore, a recent theoretical study by Northrup et al [31] reported that indium atoms have a 0.5 eV bias to incorporate at one of the two possible sites at a step edge in wurtzite InGaN, thereby providing a mechanism for ordering along the [0001] direction.…”