Explanation 1: Mechanism of a single-electron transistor
Conductor islands (dots) of approximately 10 nanometers in diameter are placed between the source and drain electrodes across a tunnel barrier. When an electron flows into a dot, the potential of the dot increases and the entry of other electrons is hindered by the Coulomb blockade phenomenon. Voltage applied to the gate electrodes controls the electrons in the dots and determines the on/off status of the current. In an AND/NAND logic circuit using four single-electron transistors or an AND/XOR one-bit adder using three, the circuit architecture is changed from the conventional logic gate to a binary decision graph suitable for single-electrons.
Explanation 2: Organometallic vapor phase selective epitaxy
This is a type of thin-film crystal growth method for compound semiconductors, in which gaseous organometallic and hydrogen compounds are used as sources. When these sources are sent onto a heated substrate crystal using hydrogen as a carrier gas, the thermally decomposed source gas grows in a thin-film form. In this study, a circuit diagram of 150 nanometers in width was drawn using electron lithography and etching (used for conventional semiconductor processing) and a GaAs (gallium arsenide) crystal was grown on it. The crystal can be grown to form a mountain shape by controlling the direction of its development through adjustment of temperature and other conditions, and the ridge part of the mountain has a width as small as several tens of nanometers. Evaporating a metal to serve as a conductor on this structure produces a single-electron transistor (Fig. 1).