A report describes an experimental study of the sizes and concentrations of capped (buried) and surface In0.6Ga0.4As/GaAs quantum dots that were grown by metal-organic vapor deposition under the same conditions except for the inclusion or exclusion of capping. [InxGa1-xAs/GaAs quantum dots are lens-shaped islands (typically a few nanometers thick and tens of nanometers in diameter) of InxGa1-xAs grown on a GaAs substrate. As used here, "capping" signifies the growth of a layer of GaAs over the InxGa1-xAs islands.] In the experiments, the sizes of the capped In0.6Ga0.4As/GaAs islands were measured by transmission electron microscopy (TEM).

This work was done by Rosa Leon of Caltech for NASA's Jet Propulsion Laboratory. To obtain a copy of the report, "Adatom condensation and Quantum Dot sizes in InGaAs/GaAs (001)," access the Technical Support Package (TSP) free on-line at www.nasatech.com/tsp  under the Physical Sciences category.

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Sizes of Surface and Capped InxGa1-x/GaAs Quantum Dots

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NASA Tech Briefs Magazine

This article first appeared in the November, 2001 issue of NASA Tech Briefs Magazine (Vol. 25 No. 11).

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Overview

The document presents a technical report on an experimental study conducted by Rosa Leon at NASA's Jet Propulsion Laboratory, focusing on the sizes and concentrations of InₓGa₁₋ₓAs/GaAs quantum dots. These quantum dots are lens-shaped islands, typically a few nanometers thick and tens of nanometers in diameter, grown on a GaAs substrate using metal-organic vapor deposition. The study specifically compares capped and uncapped (surface) quantum dots, where "capping" refers to the growth of a GaAs layer over the InₓGa₁₋ₓAs islands.

The research employs transmission electron microscopy (TEM) and atomic-force microscopy to measure the sizes of both capped and surface quantum dots. The findings indicate that for a given island concentration, the surface islands are significantly larger than the buried (capped) islands. This size difference is observed to decrease with increasing concentration of the quantum dots. The report attributes this phenomenon to a hypothesized subprocess occurring during the cooldown phase to room temperature after the growth of the islands. In this subprocess, the quantum dots act as sinks or seeds for the condensation of Ga and As adatoms from the surrounding material, influencing their final size.

The document emphasizes the implications of these findings for the understanding of quantum dot growth and the potential applications in nanotechnology. The research is part of a broader effort to explore the properties of semiconductor materials, which are crucial for various technological advancements, including optoelectronics and quantum computing.

Additionally, the report includes a disclaimer stating that the information is provided under the sponsorship of NASA and does not imply any endorsement of specific commercial products or manufacturers. The work was carried out under contract with NASA, highlighting the collaboration between the Jet Propulsion Laboratory and the agency.

Overall, this study contributes valuable insights into the behavior of quantum dots, particularly in how their size and concentration can be manipulated through growth conditions, which is essential for future applications in advanced materials and devices.