This is longest established in III–V semiconductors, from the GaAs/AlGaAs superlattice through quantum wells (QWs) and modulation doping to quantum wires and quantum dots . Such low-dimensional structures form the basis of the QW lasers and p-HEMTs produced in huge volumes by MBE for optoelectronic and microwave applications. The combination of precise growth control and in situ analysis makes MBE the preeminent technology used to meet such demands.