A Self-Organized Molecular Beam Epitaxial Growth of the InSb/AlGaSb Quantum Dots on High-Index GaAs Substrates
- PDF / 2,346,165 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 31 Downloads / 180 Views
of (GaSb) 2o/(AlSb) 20, a 1 gim GaSb, and a 15 nm A1O. 5Gao. 5Sb were grown at 550 'C. Subsequently, the growth was interrupted until the substrate had cooled down to 400 'C. On top of the Al 0.5Ga 0.5Sb whose lattice constant is about 6 % smaller than that of InSb, we grew InSb QDs at a rate of 0.03 ML/s. For samples to measure PL spectra, a 50 nm Alo.5Gao.5Sb cap layer was grown on the InSb QDs. The whole growth process was in-situ monitored by reflection high-energy electron diffraction (RHEED). The surface morphology of the film was ex-situ characterized in air by atomic force microscopy (AFM) at room temperature. The PL from the samples was measured at 17 K using the excitation of the 514.5 nm line of a 50 mW Ar ion laser. 3.
GROWTH ON (100) SUBSTRATES
Growth on just (100) GaAs substrates is discussed in this section. During the A10.5Ga 0 .5Sb growth, we observed a RHEED pattern of streaked (1x3) indicating an Sbstabilized surface. The succeeding growth interruption made the reconstruction much sharper due to the flattening of the surface in an atomic scale. During the InSb growth, this streaked (1x3) reconstruction continued up to 2.5 ML and then gradually changed to a faint chevronlike pattern. In Fig.2, we show an in-situ measured response of the specular spot intensity in the RHEED pattern. The electron beam was introduced in the [010] direction. After 2.5 cycles of oscillations, the RHEED intensity started a rapid and monotonous decrease, which indicates the change of growth mode from two-dimensional (2D) to 3D at 2.5 ML. These experimental data suggest that the coherent growth to Alo.5 Ga0 .5Sb is limited within the initial 2.5 ML of the InSb. The 2D/3D transition, however, depended on the growth condition as is observed generally in other material systems, and the chevronlike pattern also developed after closing the cell shatter even though the InSb growth was interrupted at less than 2.5 ML. This change can be understood by a formation of 3D islands to relax the excess strain in the 2D InSb film via surface transport. Because such accommodation was not observed for films less than 1.4 ML, we can conclude that the critical thickness under thermal equilibrium was about 1.4 ML for the nucleation of 3D islands on the 2D wetting layer.
~2.5ML
.•
,
In On 0
30
60
90 Time (sec)
120
150
180
Fig.2 In-situ measured [010] RHEED patterns and corresponding change of the specular spot intensity. In agreement with the RHEED experiment, an AFM observation revealed no 3D islands characteristic of S-K mode growth on samples with 1.4 ML InSb. At 1.6 ML, square-cone7 shaled islands, QDs, developed clearly although their areal density was relatively low, ~lx10 cm". The QD density increased with InSb thickness and reached to -lxl0 8 cm 2 at around 2 ML, and then saturated to -2x108 cm"2 at around 6 ML. In this saturation region, from 2 to 6 ML, the increase in the total volume of the QDs roughly corresponded to the total amount of the InSb deposited. More than 6 ML, however, the QD density gradually decreased wi
Data Loading...
