Sávhatárok

Sávhatárok, or band edges, is a term used in physics and engineering to describe the boundary energies or frequencies that delimit a band. The concept appears in several contexts, most prominently in solid‑state physics and in the management of electromagnetic spectra.

In solid‑state physics, electrons in a crystalline solid occupy continuous energy bands separated by gaps. The upper boundary of the valence band (the valence-band maximum, E_v) and the lower boundary of the conduction band (the conduction-band minimum, E_c) are the band edges. The energy difference between these edges is the band gap, E_g = E_c − E_v, a key parameter that governs a material’s optical and electronic properties. Band-edge positions determine absorption and emission thresholds, carrier dynamics, and the response to temperature, strain, and doping. In semiconductors, there are direct and indirect band gaps, which describe whether the band edges occur at the same momentum value and influence light emission efficiency.

In communications and signal processing, a band refers to a continuous range of frequencies, and the band edges are the lower and upper frequency limits of that range. The bandwidth is the difference between these edges. Band edges are central to spectrum allocation, regulation, finite guard bands between adjacent bands, and the design of filters and receivers.

Techniques to determine band edges include photoemission spectroscopy (ARPES), optical absorption and photoluminescence measurements, ellipsometry, and various theoretical band-structure calculations. Variations in edges due to temperature, strain, or doping are important for material design and device performance.