Indium incorporation and surface morphology of InAlN layers grown on ͑0001͒ GaN by plasma-assisted molecular beam epitaxy were investigated as a function of the impinging In flux and the substrate temperature in the 450-610°C range. In incorporation was found to decrease with substrate temperature due to thermal decomposition of the growing layer, while for a given temperature it increased with the impinging In flux until stoichiometry was reached at the growth front. The InN losses during growth followed an Arrhenius behavior characterized by an activation energy of 2.0 eV. A growth diagram highly instrumental to identify optimum growth conditions was established. © 2008 American Institute of Physics. ͓DOI: 10.1063/1.3026541͔ InAlN alloys have a direct band gap tunable from 0.7 to 6.2 eV, and for a 17% In there is lattice match ͑in-plane͒ to GaN. Heterostructures and devices including InAlN layers, such as resonant cavities, multiquantum wells for high-speed intersubband devices, or high electron mobility transistors, have been recently reported. [1][2][3][4] Growth diagrams, useful to identify optimum conditions, have been established for binaries ͑AlN, GaN, InN͒, grown by plasma-assisted molecular beam epitaxy ͑PA-MBE͒, from the surface morphology dependence on growth temperature and impinging fluxes. [5][6][7][8] However, the growth of InAl͑Ga͒N alloys poses much more difficulties due to InN thermal decomposition 9-12 and strong differences between InN and AlN.This work reports on the growth and characterization of metal-face InAlN layers on GaN templates. Indium incorporation and surface morphology are analyzed as a function of growth temperature and metal fluxes to build up a growth diagram.InAlN thin layers ͑ϳ80 nm thick͒ were grown by PA-MBE on ͑0001͒ GaN templates ͑ϳ3.6 m thick͒ grown by metal-organic vapor phase epitaxy on sapphire ͑Lumilog͒. Growth temperature was measured with an Ircon Modline3 optical pyrometer. Metal fluxes ͑⌽ Ga , ⌽ Al , ⌽ In ͒, measured as beam equivalent pressure ͑Bayard Alpert͒, were calibrated in atoms/ s cm 2 using cross-sectional scanning electron microscopy ͑SEM͒ data from N-rich GaN, AlN, and InN thick layers grown at temperatures where thermal decomposition and adatom desorption are negligible. 5 Similarly, the active N flux ⌽ N was calibrated in atoms/ s cm 2 using cross-sectional SEM data from Ga-rich GaN thick layers grown at low temperatures ͑680°C͒. Prior to the InAlN growth, a 100 nm thick GaN buffer layer was grown at 700°C under intermediate Ga-rich conditions 5 to obtain a smooth and flat surface. Alloy compositions were assessed by high resolution x-ray diffraction ͑HR-XRD͒ and surface morphologies were characterized by SEM ͑JEOL JSM-5800͒ and by atomic force microscopy ͑AFM͒ ͑Digital Instruments MMAFM-2͒.To analyze separately the effects of growth temperature and impinging In flux on In incorporation, two sets of samples were grown. In a first set ͑series A͒ all impinging fluxes were kept constant and the growth temperature varied between 450 and 610°C, a range...