200 most important Astronomy topics - Sykalo Eugen 2023

The Quantum Tunneling

Quantum tunneling is a phenomenon that occurs when a particle passes through a potential energy barrier that it would not possess sufficient energy to surmount. This counterintuitive phenomenon is a result of the wave-like nature of particles, as described by quantum mechanics.

Understanding Quantum Tunneling

In classical mechanics, particles are thought of as having a definite position and momentum at any given time. However, in quantum mechanics, particles are described by wave functions that express the probability of finding the particle in a particular position and momentum state. These wave functions can extend beyond classically allowed regions, meaning that there is a finite probability that the particle will be found on the other side of an energy barrier.

This probability of tunneling depends on various factors, including the height and width of the barrier and the energy of the particle. Generally, the higher the barrier and the lower the energy of the particle, the lower the probability of tunneling.

Quantum tunneling has been studied extensively in the context of nuclear fusion, where it plays a crucial role in the fusion of atomic nuclei in stars. In this process, two positively charged atomic nuclei must be brought close enough together that they can overcome their electrostatic repulsion and fuse into a single, heavier nucleus. However, because of the Coulomb barrier, the energy required for this process is extremely high. Quantum tunneling provides a way for the nuclei to overcome this barrier and fuse at lower energies.

Another example of quantum tunneling is in the context of scanning tunneling microscopy (STM), a technique used to image surfaces at the atomic scale. In STM, a fine metal tip is brought very close to a surface, and a voltage is applied between the tip and the surface. Electrons can tunnel through the vacuum between the tip and the surface, allowing the STM to detect the surface topography with atomic resolution.

Applications of Quantum Tunneling

Quantum tunneling has numerous applications in various fields, from electronics to biology. One of the most notable applications is in the field of electronics, where it is used in the construction of tunnel diodes and flash memory devices.

A tunnel diode is a type of diode that operates on the principle of quantum tunneling. It consists of a p-n junction in which the doping level is extremely high, resulting in a very narrow depletion region. When a voltage is applied to the diode, electrons can tunnel through the depletion region, resulting in a large current flow. Tunnel diodes are used in various applications, including in oscillators, amplifiers, and detectors.

Flash memory is a type of non-volatile memory that uses quantum tunneling to program and erase memory cells. Flash memory cells consist of a floating gate transistor that stores charge. To program a cell, a high voltage is applied to the gate, causing electrons to tunnel through the oxide layer and onto the floating gate. To erase a cell, a high voltage is applied to the substrate, causing electrons to tunnel back off the floating gate. Flash memory is used in various applications, including in USB drives, digital cameras, and solid-state drives.

In biological systems, quantum tunneling is believed to play a role in various enzymatic reactions. For example, the enzyme cytochrome P450 uses quantum tunneling to transfer hydrogen atoms between different molecules, a process that is essential for the metabolism of drugs and toxins in the liver.

Another area where quantum tunneling has been applied is in the development of more efficient solar cells. In 2019, a team of researchers from the University of California, Berkeley, and the Lawrence Berkeley National Laboratory demonstrated a new type of solar cell that uses quantum tunneling to capture a wider spectrum of light, resulting in higher energy conversion efficiencies. The researchers achieved this by placing a thin layer of metal between the semiconductor and the metal contact, creating a tunneling junction that allows for more efficient charge carrier generation.

Recent Developments in Quantum Tunneling

Recent research has focused on using quantum tunneling to create more efficient solar cells. In 2019, a team of researchers from the University of California, Berkeley, and the Lawrence Berkeley National Laboratory demonstrated a new type of solar cell that uses quantum tunneling to capture a wider spectrum of light, resulting in higher energy conversion efficiencies.

The researchers achieved this by placing a thin layer of metal between the semiconductor and the metal contact, creating a tunneling junction that allows for more efficient charge carrier generation. The metal layer acts as a barrier that allows only electrons with a specific energy to pass through, effectively widening the range of light that can be absorbed by the solar cell.

Another recent development in quantum tunneling research is the discovery of a new type of tunneling, called "resonant tunneling," in which the particle tunnels through a series of energy barriers rather than a single barrier. This discovery has significant implications for the development of more efficient electronic devices.

Resonant tunneling has already been used in the development of quantum well infrared photodetectors (QWIPs), which are used to detect infrared radiation. QWIPs consist of multiple layers of semiconductor material, with each layer acting as a barrier to the flow of electrons. When a photon of infrared radiation is absorbed by the QWIP, it creates an electron-hole pair that can tunnel through the barriers and generate a current. By carefully controlling the thickness of the layers, researchers can tune the QWIP to detect specific wavelengths of infrared radiation.