Much of our understanding of electron transport in solids is based on the semiclassical picture that views electrons as particles obeying Newtonian mechanics. Quantum effects such as energy quantization, tunneling and optical transitions in solids cannot be understood within this conceptual framework. Quantum effects are present in devices with dimensions smaller than 100 nanometers. With advances in preparation techniques of ultrathin heterolayers is posible create abrupt potencial variations like quantum barriers and wells, along the direction perpendicular to the layer plane. If the caracteristic width of wells is comparable to the wavelenght of the electrons, a series of quantum states will be formed in the wells. The control and modulation of transitions between these electronic states allow the creation of all kinds of optoelectronic devices