Kenta Arai

Indium Reevaporation during Molecular Beam Epitaxial Growth of InGaAs Layers on GaAs Substrates.

We have studied the In reevaporation behavior during InGaAs growth by molecular beam epitaxy (MBE) on GaAs substrates along with lattice-matched InGaAs on InP substrates for comparison. A proposed rate-equation model for surface processes has proved that the In surface segregation effects due to the In-Ga replacement on the activation energy of In desorption are negligible. The growth temperature was changed from 540°C to 680°C. The growth rates RInGaAs for InGaAs and RGaAs for GaAs were determined by measuring the intensity oscillation of reflection high-energy electron diffraction (RHEED) beam. The activation energy of In reevaporation decreases with the strain in InGaAs/GaAs. The In incorporation fraction decreases with the strain in InGaAs. The In incorporation fractions of unstrained InGaAs/InP systems are larger than those of strained InGaAs/GaAs systems. The compressive stress in InGaAs shows stronger influence on decreasing In incorporation as compared to tensile stress.

Self-assembled formation of ZnCdSe quantum dots on atomically smooth ZnSe surfaces on GaAs(001) by molecular beam epitaxy

Abstract We investigate growth conditions to obtain atomically flat ZnSe film surfaces on GaAs(001) without forming ZnSe-related dot structures. It is found that high temperature growth is favorable for the growth of ZnSe with a smooth surface. In order to prevent degradation of interface properties at high substrate temperature, two-step growth of ZnSe layers is employed, where a low-temperature growth step is followed by high temperature growth. The two-step process enables one to grow ZnSe with atomically flat surface without ZnSe-related dots structures. The formation of self-assembled ZnCdSe quantum dots (QDs) is achieved on such atomically surfaces. Typical QD size is: base diameter of 21±3 nm and height of 8±2 nm. Even at a total deposition of ZnCdSe of 3.5 monolayer (ML), the QD density is as low as ∼2.4 μm −2 . It is found that these QDs are formed on a ZnCdSe wetting layer whose thickness is at least 3 ML.

Self-organized formation processes of CdSe quantum dots studied by reflection high-energy electron diffraction

Initial stages of the growth of CdSe layers on ZnSe and formation processes of CdSe quantum dots (QDs) are studied by in situ reflection high-energy electron diffraction (RHEED). The growth process of the CdSe layer at the initial stage is divided into five stages: (1) stable two-dimensional (2D) growth, (2) metastable 2D growth, (3) metastable growth just before the onset of QD formation, (4) QD formation, and (5) coalescence of QDs. There is a critical growth stage at which the formation of QDs is initiated. It is demonstrated by the RHEED investigation that the formation of the QD is associated with the release of strain energy. Because the strain energy stored in the dislocation-free 2D layer cannot be fully released as long as the surface is flat, in order to decrease the strain energy, the development of the islands occurs, competing with smaller increase of the surface energy.

Photoluminescence and cathodoluminescence studies of ZnSe quantum structures embedded in ZnS

Abstract Ultrathin ZnSe quantum structures embedded in ZnS are investigated in a wide range of atomic layer epitaxy (ALE) growth conditions. The optical properties of the grown ZnSe/ZnS quantum structures are studied by photoluminescence (PL), photoluminescence excitation (PLE), and cathodoluminescence (CL) spectroscopy. A sharp PL emission is observed at around 3.05 eV, which reveals exciton localization tentatively associated with quasi-0D ZnSe quantum dots (QDs) formed on a wetting layer of 1 monolayer (ML) ZnSe.

Optical Properties of Manganese-Doped ZnSe/ZnS Quantum Dots Grown by Molecular Beam Epitaxy

Optical properties of Mn-doped ZnSe/ZnS quantum dots (QDs) have been investigated by both steady-state and time-resolved photoluminescence (PL) measurements. Strong photoluminescence associated with Mn intra-d shell transitions has been observed for QDs with a longitudinal thickness of just few monolayers (MLs). The PL decay involves two processes with different lifetimes of which the faster one has a lifetime of about 5 µs which is almost independent of the well thickness, while the other process has a lifetime varying from 40 to 80 µs when the well width decreases from 6 to 0.25 ML. The experimental results are interpreted by the use of rate equations which suggests that the enhanced Mn emission might be due to the relatively enhanced energy transfer from the QDs to the Mn atoms.