Quantum Dot Transistor Could Provide Platform for Super-Compact Counters

SÃO CARLOS, Brazil — A transistor based on quantum dots has been developed. The device, which contains micrometric and nanometric parts, can see light, count and store information within its own structure, removing the need for a complementary memory unit.

Researchers produced the transistor by coating a crystal substrate with thin film. On this microscopic substrate, nanoscopic droplets of indium arsenide act as quantum dots, confining electrons in quantized states. Memory functionality is derived from the dynamics of electrical charging and discharging of the quantum dots, creating current patterns with periodicities that are modulated by the voltage applied to the transistor’s gates or to the light absorbed by the quantum dots.

“The key feature of our device is its intrinsic memory stored as an electric charge inside the quantum dots,” said professor Victor Lopez Richard, Federal University of São Carlos (UFSCar). “The challenge is to control the dynamics of these charges so that the transistor can manifest different states. Its functionality consists of the ability to count, memorize and perform the simple arithmetic operations normally done by calculators, but using incomparably less space, time and power.”

According to Richard, the transistor is not likely to be used in quantum computing because this would require other quantum effects. However, it could lead to the development of a platform for use in equipment such as counters or calculators, with memory intrinsically linked to the transistor itself and all functions available in the same system at the nanometric scale, with no need for a separate space for storage.

“Moreover, you could say the transistor can see light because quantum dots are sensitive to photons, and just like electric voltage, the dynamics of the charging and discharging of quantum dots can be controlled via the absorption of photons, simulating synaptic responses and some functions of neurons,” Richard said.

Further research will be necessary before the transistor can be used as a technological resource. For now, it works only at extremely low temperatures — approximately 4 kelvin, the temperature of liquid helium.

“Our goal is to make it functional at higher temperatures and even at room temperature. To do that, we’ll have to find a way to separate the electronic spaces of the system sufficiently to prevent them from being affected by temperature. We need more refined control of synthesis and material growth techniques in order to fine-tune the charging and discharging channels. And the states stored in the quantum dots have to be quantized,” Richard said.

“In this article, we show that transistors based on quantum dots can perform complex operations directly in memory,”  he said. “This can lead to the development of new kinds of device and computer circuits in which memory units are combined with logical processing units, economizing space, time and power consumption.”

The transistor was developed by researchers at UFSCar Würzburg University and the University of South Carolina.

The research was published in Nano Letters (doi: 10.1021/acs.nanolett.6b04911).

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