Final answer:
In physics, k space is a mathematical representation of the momentum space of particles where different momentum values are plotted along the axes. The filling of k space is determined by the geometry of the lattice in the material being studied. The Fermi level determines which energy bands are filled or empty in semiconductors.
Step-by-step explanation:
In physics, the phenomenon being referred to is the filling of k space. In condensed matter physics, k space is a mathematical representation of the momentum space of particles. It can be thought of as a 3D space where different momentum values are plotted along the axes.
The filling of k space is determined by the geometry of the lattice in the material being studied. In a simple example, when considering the energy levels of an electron in a one-dimensional lattice, the Brillouin zone represents the first unit cell of the lattice in k space. As energy levels are filled, they fill up the different lines or bands in k space.
For example, in semiconductors, the Fermi level determines which energy bands are filled or empty. The Fermi level corresponds to a specific total energy and hence momentum in k space. Energy bands below the Fermi level are filled with electrons, while those above the Fermi level are empty.