Real-time Observation of Nucleation and Evolution of InAs Quantum Dots on GaAs(001) During MBE
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Real-time Observation of Nucleation and Evolution of InAs Quantum Dots on GaAs(001) During MBE Itaru Kamiya, Kohtaro Matsuura, and Tsuyoshi Higashinakagawa Toyota Technological Institute, 2-12-1 Hisakata, Tempaku, Nagoya, 468-8511, Japan ABSTRACT Real-time observation of self-assembled (SA) InAs quantum dot (QD) growth on GaAs(001) by MBE has been performed. Through transient measurements on reflection high energy electron diffraction (RHEED) specular beam, we obtain information about nucleation and evolution of the QDs in situ, in contrast to most previous reports that required growth interruption. Based on the observation, we have been able to distinguish processes that are dependent and independent of growth rate. In addition, the results reveal that surface migration of In/As atoms and their incorporation into QDs, with the aid of the wetting layer, can be observed. We also provide a quantitative discussion on these processes.
INTRODUCTION Self-assembled (SA) quantum dots (QDs) have been widely studied due to the relative easiness in their preparation to realize QDs which are expected to be applied to various future optoelectronic devices [1,2]. SA QDs can be prepared by solely depositing materials that have different bandgaps and lattice constants to the with respect to the substrate by epitaxial crystal growth techniques without any other fabrication processes. InAs QDs on GaAs(001) grown by molecular beam epitaxy (MBE) or metal-organic chemical vapor deposition (MOCVD) have been their typical examples, and their optoelectronic properties have been extensively investigated [3-6]. While SA QDs have proven to be useful for fundamental studies on the electronic properties of QDs, it is essential that their size and spatial distribution are controlled for practical device application. A number of attempts have been reported on the control of size, density, or spatial distribution, and the progress has been remarkable [7-12]. However, since SA QDs are formed through random processes, it has so far not been possible to achieve prefect size and distribution uniformity without processing the substrate prior to crystal growth. A number of studies have been performed to understand the fundamental mechanisms of SA QD formation that would provide us with information to achieve such goal. Here, real-time observation of SA InAs QD growth on GaAs(001) by MBE has been performed. In contrast to most previous reports that employed growth interruption for the observation of surfaces during growth, by following the time transient of RHEED specular beam in detail, we obtain information about nucleation and evolution of the QDs, and have been able to distinguish processes that are dependent and independent of growth rate. In addition, the results reveal that surface migration of In/As atoms and their incorporation into QDs, with the aid of the wetting layer, can be observed.
EXPERIMENTAL A solid source III-V MBE (modified Eiko EW-100) was used in the present study. The machine was equipped with Ga, In, and Al K-cell
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