Surface morphology of InGaN layers
|Robert Czernecki 1,3, Mike Leszczynski 1,3, Jaroslaw Domagala 2, Stanisław Krukowski 1, Marcin Krysko 1, Piotr Perlin 1, Paweł Prystawko , Tadeusz Suski 1, Grzegorz Targowski 1|
1. Polish Academy of Sciences, Institute of High Pressure Physics (UNIPRESS), Sokolowska 29/37, Warszawa 01-142, Poland
The aim of this work was to give new experimental information on how the growth conditions in metalorganic chemical vapour phase epitaxy (MOVPE) influence the morphology and microstructure of InGaN layers in order to find optimum growth conditions of light emitting diodes and laser diodes.
InGaN (In content up to 25%) and GaN layers (up to 30 nm) grown on GaN bulk substrates (with ultra-low dislocation density) were examined using the atomic force microscopy (AFM), X-ray diffraction (XRD) in order to learn about the atomic step morphology and microstructure influenced by the substrate misorientation (up to 2 degrees with respect to c-axis), flow of indium, of hydrogen and by growth temperatures. Concerning the step morphology, the following observations were made:
i) at low growth temperatures, when N2 is used as a carrier gas, GaN layers contain pinholes,
ii) the pinholes disappear when hydrogen is added to the carrier gas and then the step-flow-like morphology of the surface is observed (Fig. 1),
iii) when InGaN layers are grown using N2 carrier gas, no pinholes were observed, but the steps become jaggy,
iv) when adding hydrogen, the steps become linear, but the incorporation of indium is much smaller, as observed in previous papers.
The explanation of the experimental results is proposed based on higher oxygen incorporation (without hydrogen in the carrier gas) at low temperatures causing jaggy steps and pinholes, however, in all cases the oxygen content was below the detection limit in secondary ion mass spectroscopy (SIMS).
Concerning microstructure, the following new data were obtained:
i) the substrate misorientation is accompanied by smaller indium incorporation into InGaN layers caused by a smaller step velocity in the step-flow growth mode (Fig. 2).
ii) This phenomenon gives rise to an additional surface roughening as the length of the terraces is not uniform.
iii) the indium content increases with the layer thickness.
Presentation: Poster at E-MRS Fall Meeting 2009, Symposium C, by Mike Leszczynski
See On-line Journal of E-MRS Fall Meeting 2009
Submitted: 2009-05-25 15:20 Revised: 2009-06-07 00:48