Self-formed compositional superlattices triggered by cation orderings in m-plane Al1−xInxN on GaN

Abstract

Immiscible semiconductors are of premier importance since the source of lighting has been replaced by white light-emitting-diodes (LEDs) composed of thermodynamically immiscible InxGa1−xN blue LEDs and yellow phosphors. For realizing versatile deep-ultraviolet to near-infrared light-emitters, Al1−xInxN alloys are one of the desirable candidates. Here we exemplify the appearance and self-formation sequence of compositional superlattices in compressively strained m-plane Al1−xInxN films. On each terrace of atomically-flat m-plane GaN, In- and Al-species diffuse toward a monolayer (ML) step edge, and the first and second uppermost < $$\stackrel{-}{1}\stackrel{-}{1}20$$ 1 - 1 - 20 > cation-rows are preferentially occupied by Al and In atoms, respectively, because the configuration of one In-N and two Al-N bonds is more stable than that of one Al-N and two In-N bonds. Subsequent coverage by next < $$\stackrel{-}{1}\stackrel{-}{1}20$$ 1 - 1 - 20 > Al-row buries the < $$\stackrel{-}{1}\stackrel{-}{1}20$$ 1 - 1 - 20 > In-row, producing nearly Al0.5In0.5N cation-stripe ordering along [0001]-axis on GaN. At the second Al0.72In0.28N layer, this ordinality suddenly lessens but In-rich and In-poor < $$\stackrel{-}{1}\stackrel{-}{1}20$$ 1 - 1 - 20 >-rows are alternately formed, which grow into respective {0001}-planes. Simultaneously, approximately 5-nm-period Al0.70In0.30N/Al0.74In0.26N ordering is formed to mitigate the lattice mismatch along [0001], which grow into approximately 5-nm-period Al0.70In0.30N/Al0.74In0.26N {$$10\stackrel{-}{1}2$$ 10 1 - 2 } superlattices as step-flow growth progresses. Spatially resolved cathodoluminescence spectra identify the emissions from particular structures.

Composition Inhomogeneity in Nonpolar (101̅0) and Semipolar (202̅1) InAlN Layers Grown by Plasma-Assisted Molecular Beam Epitaxy

“…Last but not least, the structural quality of thick nonpolar (101̅0) InAlN layers grown on bulk GaN has been studied. Severe composition instability and cation ordering process were reported to take place in order to mitigate the lattice mismatch along the [0001] direction . Note that degradation of the InAlN quality was also reported earlier for thick c -plane InAlN layers grown by MOVPE …”

“…Fundamental property studies as well as device demonstrations are reported. − However, despite numerous studies on nonpolar and semipolar structures, there has been only a very limited number of them presenting InAlN grown on non- c -plane substrate orientations. Moreover, all of these studies describe layers and structures grown by metal–organic vapor-phase epitaxy (MOVPE) − with no studies on semipolar or nonpolar InAlN layers grown by plasma-assisted molecular beam epitaxy (PAMBE). Therefore, it is very important to undertake experimental efforts toward a comprehensive understanding of InAlN growth mechanisms and controlling the resulting layer properties on non- c -plane GaN substrates using PAMBE.…”

“…The epitaxy of high-quality InAlN is difficult due to extreme differences in optimum growth conditions for its binary constituents. Typical growth temperatures used for InN and AlN in PAMBE are ≈450 °C and ≈800 °C, while in MOVPE, they are <400 and >1600 °C, respectively. c -plane (0001) InAlN layers are usually grown by PAMBE at ≈550 °C , due to low indium incorporation efficiency, , much lower than in InGaN .…”

“…23 cation ordering process were reported to take place in order to mitigate the lattice mismatch along the [0001] direction. 20 Note that degradation of the InAlN quality was also reported earlier for thick c-plane InAlN layers grown by MOVPE. 24 The epitaxy of high-quality InAlN is difficult due to extreme differences in optimum growth conditions for its binary constituents.…”

Growth and Microstructure Analyses of Semipolar AlInN Epitaxial Layers on a Fully Relaxed Semipolar {112¯2} GaInN/GaN/m‐plane Sapphire Template

“…layers can be formed on the fully relaxed semipolar GaInN layers, they will become highly promising structural components for long-wavelength visible GaN LDs. On the other hand, although some researchers have reported the growth of nonpolar [7,8,[24][25][26][27] and semipolar [26][27][28][29] AlInN layers, there have been no reports focusing on the growth of thick and flat-surface AlInN epitaxial layers with high-InN mole fraction. Therefore, in this study, we attempted to grow AlInN layers with submicrometer thicknesses and high-InN mole fractions using a fully relaxed semipolar GaInN template and to evaluate their crystal qualities including the surface flatness.…”