Structural and morphological qualities of InGaN grown via elevated pressures in MOCVD on AlN/Si(111) substrates

• Published in: Journal of crystal growth 2013-11, Vol.383, p.1-8
• Main Authors: Ho, Jian Wei, Zhang, Li, Wee, Qixun, Tay, Andrew A.O., Heuken, Michael, Chua, Soo-Jin
• Format: Article
• Language: English
• Subjects: A1. AlN; A1. InGaN; A1. Suppression of phase separation; A3. Metal organic chemical vapour deposition; Aluminum nitride; B2. Semiconducting III–V materials; Chemical vapor deposition (including plasma-enhanced cvd, mocvd, etc.); Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Crystallography; Droplets; Elevated; Epitaxial growth; Equations of state, phase equilibria, and phase transitions; Exact sciences and technology; Indium; Indium gallium nitrides; Islands; Materials science; Methods of crystal growth; physics of crystal growth; Methods of deposition of films and coatings; film growth and epitaxy; Physics; Solubility, segregation, and mixing; phase separation; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; Theory and models of crystal growth; physics of crystal growth, crystal morphology and orientation
• ISSN: 0022-0248; 1873-5002
• DOI: 10.1016/j.jcrysgro.2013.08.016

We examine the structural and morphological qualities of InxGa1−xN grown directly on AlN/Si(111) substrates by MOCVD as a function of growth pressure and temperature. The use of elevated pressures (up to 300Torr) resulted in the suppression of InGaN phase separation and indium droplet formation allowing single phase, textured epitaxial (0002)-oriented InxGa1−xN to be grown on the highly mismatched substrates. Various indium compositions x, up to ~0.4, can subsequently be achieved by adjusting the growth temperature over the range of 655°C–795°C. Increase in growth temperature reduces the indium composition x but is accompanied by a decrease in the FWHM of the (002)-ω and asymmetric (105)-ω rocking curves indicating lower crystallographic tilt and improved crystal quality. The reduction in tilt saturates at ~705°C. This corroborates with room-temperature photoluminescence (PL) measurements where PL is not detectable below ~705°C but emerges above this temperature and narrows in FWHM with further temperature increase. SEM shows that films grown at low pressure are compositionally and morphologically non-uniform, while films grown at elevated pressure are homogeneous, single phase and composed of densely packed, interconnected epitaxial islands, with lower temperature favouring a smaller island size. We conclude that while lower temperatures favour increased indium incorporation, the ensuing smaller island size and greater extent of island boundaries, arising from larger lattice mismatch and lower surface mobility of species, degrades crystal quality appreciably. Above 705°C, improvement in crystallographic quality is limited by the AlN growth template and requires innovative MOCVD growth strategies. •We examine the qualities of InxGa1−xN grown directly on AlN/Si(111) by MOCVD.•Elevated pressures suppress phase separation and indium droplet formation.•Increase in temperature promotes coalescence of grains but reduces indium content.•Crystal quality improves markedly until ~705°C as shown in PL and XRD, and slows.•Epitaxial quality is limited by AlN template and requires innovative growth strategies.