When a electron is displaced in a semiconductor,the hole that's left behind is
When an electron is displaced in a semiconductor, the hole that is left behind is essentially the absence of an electron in the valence band. In other words, a hole is a region within the crystal lattice where an electron should exist but doesn't.
To understand this concept further, we need to first understand the energy levels in a semiconductor. In a semiconductor material, there are two main energy bands: the valence band (the lower energy band) and the conduction band (the higher energy band). The valence band is occupied by electrons, while the conduction band is empty or only partially occupied.
When an electron is excited by thermal energy or an external energy source, it can be promoted from the valence band to the conduction band, leaving behind a vacant spot in the valence band. This vacant spot is referred to as a hole. The movement of this hole is analogous to the movement of a positive charge.
Semiconductors are typically doped with impurity atoms to enhance their electrical conductivity. A commonly used dopant is pentavalent impurities (such as phosphorus or arsenic) that have five valence electrons. When these atoms are incorporated into the crystal lattice of a semiconductor, four of their valence electrons participate in covalent bonds, while the fifth valence electron remains loosely bound.
Now, when thermal energy is applied to this doped semiconductor, an electron from an impurity atom can break free from its covalent bond and move to the conduction band, leaving a vacant covalent bond behind. This vacancy acts as a positive charge and contributes to the formation of a hole.
In summary, when an electron is displaced in a semiconductor, the hole that is left behind represents the absence of an electron in the valence band, creating a region with a positive charge.