A comprehensive diagram to grow InAlN alloys by plasma-assisted molecular beam epitaxy

Abstract

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...

High quality InAlN single layers lattice-matched to GaN grown by molecular beam epitaxy

“…The fast Fourier transformation (FFT) of the HRTEM image of the InAlN/GaN interface ( Fig. 3(b)) confirms that InAlN layer grows in-plane accommodated to the GaN substrate, with the expected epitaxial relationship (0001) [11][12][13][14][15][16][17][18][19][20]InAlNjj(0001) [11][12][13][14][15][16][17][18][19][20]GaN. High angle annular dark field (HAADF) observations (Fig.…”

“…[3][4][5][6] Reports concerning molecular beam epitaxy (MBE) growth are very scarce and have been mainly focused on HEMTs. [7][8][9][10][11][12][13][14] Difficulties to fabricate high quality LM InAlN/GaN heterostructures concern the following issues: high crystalline quality and good homogeneity of InAlN layers as well as flat and abrupt heterostructure interfaces. In general, MBE growth technique facilitates the formation of exceptionally flat and abrupt interfaces and, thus, offers potential for further improvements.…”

“…15 InAlN layers were grown at 535 C on the boundary between In-droplets and N-rich growth regimes (i.e., under effective III-N stoichiometry), yielding layers free of droplets with typically 17% 6 2% indium content. 12,14 Growth times were set to 20 6 2 min, which resulted in layers 50-60 nm thick. Let us note that these values correspond to the thickness of one InAlN semi-period, inserted into a DBR targeted for blue/green applications, respectively.…”

(V)EELS Characterization of InAlN/GaN Distributed Bragg Reflectors

“…The ELF is directly related to the joint density of states between the valence and conduction bands, a magnitude which can be modelled and calculated theoretically by ab-initio computer simulation. In this line, the analysis presented here has been extended to relate optoelectronic and structural properties presented in latter publications [1][2][3], through band-gap determination, plasmon peak related indium ratio and Cole-Cole plots of CDF. …”

“…The InAlN ternary compound, with 17-18% indium content, grows in-plane lattice-matched to GaN and opens the possibility for fabrication of strain-free III-nitride heterostructures. Still, several problems remain concerning the growth, crystalline quality and homogeneity of InAlN epitaxial films [1][2][3][4]. A precise knowledge of the InAlN 4 Also at: Paul-Drude-Institute for Solid State Electronics, Hausvogteiplatz 5-10117 Berlin, Germany 5 Fundación ARAID, 50004 Zaragoza, Spain 6 Also at: TEM-MAT, (SCT), Universitat de Barcelona, Solé I Sabarís 1, Barcelona, Spain band gap value and its dependence on In content is a critical issue.…”