What Is a Quantum Dot?

I'm sure most of you have heard a few things about quantum dots in science news, however most of these never seem to present what a quantum dot really is. Quantum dots are usually constructed out of semiconductors and routinely studied in electronic devices such as transistors, light emitting diodes or laser diodes. It should be noted that researchers in this field mostly believe that the quantum dots will contribute to the creation of the next generation of computers once stable qubits are being developed.

Quantum dot semiconductors have the properties of confining their excitons in all three spatial dimensions, meaning that they are restricted between bulk semiconductors and individual molecules. Alternatively, traditional semiconductors with unconfined excitons are characterized by an electron-hole pair with a bond called the Borh exciton radius. However, this system is unstable resulting in a change in semiconductor properties if constraint between the two isn't broken.

Quantum dots have multiple methods of fabrication, starting with the synthesizing of colloidal semiconductor nanocrystal dissolved in solutions through a traditional chemical process. Colloidal semiconductors can be fabricated out of semiconductors, such as cadmium selenide, indium arsenide or even indium phosphide. Within the diameter of 10 to 50 atoms, the volume of solution can contain from 100 to 100,000 atoms, representing a quantum dot.

Thus, in a sphere with a diameter ranging from 2 to 10 nanometers, a colloidal semicondutor may contain up to three million quantum dots. Individual quantum dots are being assembled into highly-ordered array structures through electrochemical processes.

Once fabricated, quantum dots can be used in a broad range of practical applications, however the most immediate and wide applications of such electronic devices are in optical elements, in the demonstration of single electron transistors and in the creation of qubits. Biological analysis and the improvement of photovoltaic devices are only two of the other multiple applications of quantum dots.



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