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. Quantum heterostructures have sharper density of states than structures of more conventional sizes. Quantum heterostructures are important for fabrication of short-wavelength light-emitting diodes and diode lasers, and for other optoelectronic applications, e.g. high-efficiency photovoltaic cells.