Effects of Growth Sequence on Optical and Structural Properties of InAs/GaAs Quantum Dots Grown by Atomic Layer Molecula
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Effects of Growth Sequence on Optical and Structural Properties of InAs/GaAs Quantum Dots Grown by Atomic Layer Molecular Beam Epitaxy J. D. Song*, Y. M. Park, J. C. Shin, J. G. Lim, Y. J. Park, W. J. Choi, I. K. Han, W. J. Cho, J. I. Lee, H. S. Kim1, and C. G. Park1 Nano-device Research Center, KIST, Seoul 136-791, Korea 1 Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang 790-784, Korea *Email: [email protected] ABSTRACT The influence of growth sequence on optical and structural properties of InAs/GaAs quantum dots (QD) grown by atomic layer epitaxy was investigated systematically. It is found that growth interruption (GI) after In is more effective than non-GI after In in reducing the density of coalescent dots, and reducing the dot width distribution of the QDs. Meanwhile, dot densities are approximately doubled by non-GI after In. GI after As reduces dot height distribution compared with non-GI after As. Generally, GI after In plays a more critical role than GI after As does in formation of the QDs. The sample grown with In/GI/As/GI sequence shows the lowest 300 K-photoluminescence (PL) linewidth (~30 meV), high PL peak separation between ground and 1st excited level (~80 meV). From the result, it is known that In/GI/As/GI is the favorable growth sequence among the sample sets. Temperature dependence of PL linewidth shows that the In/GI/As/GI sample is insensitive to cryostat temperature and it is attributed to weak wetting effect. Thinner wetting layers shown in a cross-sectional TEM image supports this. INTRODUCTION Three-dimensionally confined electrons, holes, and excitons induced by semiconductor quantum dots (QD) have attracted much attention due to the introduction of new physical phenomena and, as a result of it, improvement of performance in optoelectronic devices such as low threshold current density, large characteristic temperature, and so on. Therefore, many researchers have focused on this topic and developed QD laser diodes (LD) that can be operated at room temperature [1,2]. For more practical application to QD LDs, however, more uniform formation of QDs and weaker wetting layer effects are required, because the effective gain volume of QDs for a specified spectrum will be increased by uniform QDs and the wetting layer
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is suspected to be a source of non-zero-dimensional phenomena in QDs [3]. Although QDs formed by migration enhanced epitaxy (MEE) – atomic layer molecular beam epitaxy (ALMBE) have attracted attentions to solve the uniformity problems [4-6], relatively few articles are reported on this topic compared to those on the QDs grown by conventional molecular beam epitaxy (MBE). Furthermore, parametric researches on the relation between the physical properties and the various growth factors during ALMBE such as deposition sequence, and growth interruption method and so on, are required to decrease non-zero-dimensional effects and to let the QDs grown by ALMBE technology prevail. In this presentation, the role
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