Complex sentence: Quantum heterostructure is a heterostructure in a substrate (usually a semiconductor material), with size restricting the movements of the charge carriers and forcing them into a quantum confinement, leading to formation of a set of discrete energy levels at which the carriers can exist.
Split into simpler sentences: Quantum heterostructure is a heterostructure in a substrate (usually a semiconductor material), where size restricts the movements of the charge carriers forcing them into a quantum confinement. This leads to the formation of a set of discrete energy levels at which the carriers can exist.