Book: Resonant Tunneling Diode Photonics: Devices and Applications

Authors:

Charlie Ironside,Department of Physics and Astronomy, Curtin University, Bentley, Western Australia

Bruno Romeira,Department of Nanophotonics, Ultrafast Bio- and Nanophotonics group,

INL – International Iberian Nanotechnology Laboratory, Av. Mestre José Veiga s/n,

4715-330 Braga, Portugal

Jose´ Figueiredo,Department of Physics of the Faculty of Sciences at University of Lisbon, Campo Grande,

1740-016 Lisboa, Portugal

Morgan

Check out :-https://iopscience.iop.org/book/978-1-64327-744-8

Quantum Effects Building the Future of Electronics

Introduction: Beyond Moore’s Law

For decades, the relentless march of technology has been powered by a simple principle known as Moore’s Law: the number of transistors on a chip doubles roughly every two years, making our computers faster and more powerful. But that march is slowing. As components shrink to near-atomic scales, the bizarre rules of quantum mechanics begin to interfere, making further progress with traditional designs incredibly difficult. As the demand for “beyond Moore’s law technologies” becomes urgent, a new approach is emerging.

Instead of fighting the strange effects of quantum mechanics, scientists are now learning to harness them. They are building a new generation of devices that operate on principles that seem to defy common sense. A prime example of this new paradigm is the Resonant Tunnelling Diode (RTD), a semiconductor device whose incredible speed and functionality are derived directly from the counter-intuitive nature of the quantum realm. By embracing these bizarre effects, we are not just pushing the limits of electronics—we are rewriting the rules entirely.

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1. To Help Electrons Flow, Add Another Wall

The first quantum trick sounds like a paradox: to make it easier for an electron to pass through an energy barrier, you should add a second one right behind it. In classical physics, this is like trying to run through two walls instead of one—it should be harder, not easier. But in the quantum world, particles like electrons also behave like waves. In a single-barrier setup, the probability of an electron “tunnelling” through is vanishingly small across almost all energy levels. But by adding the second barrier, a sharp, narrow “transmission peak” emerges, where the probability of tunnelling for an electron with the perfect resonant energy shoots up dramatically—in some cases approaching 100%.

This happens because the two parallel barriers create a tiny space—a quantum well—between them. Think of it like a guitar string. A string of a specific length will only resonate powerfully at a specific frequency (a musical note). The quantum well acts like that fixed length, and only electrons with the corresponding “frequency”—the correct energy—can resonate and pass through. All others are simply turned away. This highly selective resonance is the core principle of the Resonant Tunnelling Diode.

This leads to the somewhat counter-intuitive conclusion that adding an energy barrier increases the probability of transmission through the structure at energies below the height of the barrier.

This effect is a foundational quantum trick. It doesn’t just allow electrons to pass through “impassable” walls; it allows engineers to precisely control electron flow at the quantum level, enabling the powerful behaviors that follow.

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2. Get More by Pushing Less: The Power of “Negative Resistance”

In every electronic device you own, the relationship between voltage and current is simple: push with more voltage, and you get more current. The Resonant Tunnelling Diode, however, has a region in its operation where it does the exact opposite. This property is known as Negative Differential Conductance (NDC), where increasing the voltage across the device paradoxically causes the current flowing through it to decrease. This is not just a curiosity; it means that in this operational range, the device defies the normal rules of resistance. Instead of consuming energy, it actively generates RF power, making it a nanoscale engine for ultra-high-frequency signals.

This strange electrical behavior is the key to the RTD’s extraordinary performance. In this NDC region, the device isn’t absorbing power like a typical resistor; it is actually generating power, giving it “electrical gain.” This ability to amplify signals at incredibly high speeds is a direct result of the quantum tunnelling mechanism.

The impact of this property is profound. By harnessing negative resistance, RTDs can act as the fastest electronic oscillators ever built at room temperature. Electronic oscillators based on this principle have been demonstrated to operate at frequencies up to an incredible 1.93 THz. To put that in perspective, 1.93 THz is nearly 1,000 times faster than the gigahertz clock speeds of today’s top-tier computer processors.

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3. It Thinks, Therefore It Is: Building an Artificial Neuron

The complex, highly nonlinear behavior of the RTD bears a striking resemblance to a fundamental biological process: the firing of a neuron. As far back as the 1960s, scientists used a similar device, the Esaki tunnel diode, to create an electronic circuit that could simulate a nerve axon. Today, this concept has evolved into a key strategy for building “neuromorphic” or brain-like computing systems.

Modern RTD-based devices, which can be integrated with tiny lasers or photodetectors, can produce sharp “spikes” and “bursts” of signals that mimic the action potentials of biological neurons. This behavior is called “excitability” and is characterized by an “all-or-none response.” An input signal below a certain threshold produces a tiny, negligible effect. But an input that crosses that threshold triggers a large, standardized output pulse, exactly like a neuron firing. This capability is the foundation for neuromorphic photonic computing, which aims to process information with the efficiency and style of the human brain.

This ability to build a device that fires like a neuron is a direct consequence of engineering at a very specific physical size. As Nobel laureate Alain Aspect explained, this is the realm of the mesoscopic:

‘between the scale of a single atom and the macroscopic world, one finds the mesoscopic scale, where it is the object itself, and not only the material of which it is made, that needs to be described by quantum mechanics’

— Alain Aspect

The RTD is not just made of quantum materials; at the mesoscopic scale, the device itself is a quantum object, and its bizarre, neuron-like behavior is the result.

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Conclusion: The Quantum Leap Forward

The future of high-speed electronics is being built on principles that defy our everyday intuition. By adding a second barrier to help electrons flow (resonant tunnelling), pushing with more voltage to get less current (negative resistance), and building devices that fire like brain cells (excitability), scientists are moving beyond the limits of classical physics.

This represents a fundamental paradigm shift. For half a century, we treated quantum weirdness as a bug to be squashed. Now, we’re deploying it as the ultimate feature, building an entirely new class of electronics that thinks, oscillates, and computes in ways classical physics deemed impossible.