Indium distribution inside quantum wells: The effect of growth interruption in MBE
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Indium distribution inside quantum wells: The effect of growth interruption in MBE A.M. Sanchez1, P. Ruterana1 S. Kret2, P. Dłużewski3, G. Maciejewski3, N. Grandjean4, B. Damilano4 1
ESCTM-CRISMAT, UMR6508-CNRS, ISMRA. 6, Boulevard Maréchal Juin, 14050 Caen Cedex, France 2 Institute of Physics, PAS , Al. Lotników 32/46, 02-668 WARSAW, Poland 3 IFTR PAS, Świętokrzyska 21, 00-049 WARSAW, Poland 4 CRHEA, UPR 10 CNRS, 1 rue Bernard Gregory, 06560 VALBONNE, France
ABSTRACT Quantitative analysis of high resolution electron microscopy image has been carried out to measure the indium distribution inside InGaN/GaN quantum well. The analyzed samples were nominally grown with 15% indium composition by molecular beam epitaxy with interruptions during the InxGa1-xN layer growth. The strain distribution is not homogeneous inside the quantum wells, and indium rich clusters can be observed. Areas with almost no indium concentration were observed corresponding to the growth interruption. A comparison with samples grown by metalorganic chemical vapor deposition is attempted. INTRODUCTION The III-N semiconductor materials technology is progressing rapidly with many practical applications in optoelectronic. GaN and related materials have been intensively used in recent years for super-bright blue and green light emission diodes and laser diodes. InGaN/GaN quantum wells constitute the active structures in these devices. They exhibit better efficiency than GaAs-based devices in spite of the huge densities of defects observed in the layers (108-1010 cm-2 dislocations). The first explanation implied that the emission takes place inside InGaN quantum dots due to indium segregation in melatorganic chemical vapor deposition (MOCVD) grown devices1. The recombination of localized excitons in In rich nanometers islands play an important role in the strong emission from InGaN/GaN multiple quantum wells (MQW). The presence of In rich regions could be related to the poor miscibility between InN and GaN at the growth temperature. At 800°C the alloy is unstable in a wide composition range (0.04 zone axis showing the alternated contrasts inside the InGaN quantum well, (a) N2 and (b) N4. Quantum wells are shown by white arrows.
Mat. Res. Soc. Symp. Proc. Vol. 743 © 2003 Materials Research Society
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In order to analyze the strain distribution in the InGaN quantum wells, we performed lattice distortion measurements from high resolution images. Only areas with relatively slow rise of thickness were considered for quantitative evaluation.
Figure 3. (a) Superposition of the experimental HRTEM image and strain map in sample N2. A non-homogeneous indium distribution can be determined. (b) Surface plot with the indium concentration inside the quantum well.
Figure 3a shows the superposition of the experimental HRTEM image and the strain distribution calculated in this area corresponding to the N2 sample. This image is in good agreement with the previous one shown in Figure 2a. As can be observed, the InGaN quantum well is not continuous alo
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