What Is a Quantum Well?

A quantum well refers to a potential well on a microscopic scale comparable to the De Broglie wavelength of an electron. The concept of quantum wells was proposed early in the development of quantum mechanics. ^[1]

Quantum well

Quantum well

The quantum confinement effect creates discrete energy levels in the quantum well. In a double-barrier quantum well structure, resonant tunneling can occur only when the energy of the emitter electrons is equal to the energy level in the quantum well and the lateral momentum is conserved. Further increasing the electric field makes the discrete level of the quantum well lower than the band edge of the emitter, the tunneling current decreases sharply, and the negative differential resistance phenomenon appears. This is the basic principle of the resonant tunnel diode (RTD). The I - V characteristic curve of RTD peak-to-valley current ratio has been applied to high-frequency oscillators and high-speed logic circuits. ^[1]
Excitons in quantum wells also move quasi-two-dimensionally. Due to the quantum confinement effect, the binding energy of the two-dimensional exciton in the quantum well is close to 4 times the binding energy of the exciton of the semiconductor material, making it possible to observe strong absorption peaks or strong fluorescence peaks caused by exciton effects at room temperature. This characteristic, coupled with the two-dimensional characteristics of the density of states in the quantum well, and various control measures of the band engineering, can reduce the threshold current of the quantum well laser, the adjustable emission wavelength, the differential gain, and the characteristic temperature. Semiconductor quantum wells have also been widely used in other optoelectronic devices. ^[1]