Optical modulators. The quantum well intersubband kind

Perfecting thin film growth techniques have made possible today's search for new, ultrafast optoelectronic devices. The techniques include: molecular beam epitaxy (MBE), organometallic chemical vapor deposition (OMCVD) and atomic layer epitaxy (ALE). By using these methods, scientists and engineers can grow multilayered semiconductor structures of different materials, with extremely high purity, sharp interfaces, and narrow doping profiles. The thickness of each layer has as its lower limit only one atomic layer. By superposing successive materials of different bandgaps, we can create quantum well structures in which electrons or holes are confined to potential wells in the conduction or valence bands. This quantization has allowed for the observation of quantum effects impossible to observe in the bulk materials. One effect is the electron or hole subband-to-subband transition within a conduction or a valence band in a quantum well. This is best known as the inter-subband transition. Before to this concept is examined, the author reviews the optical modulator, its pros and cons, and how quantum wells are used to realize a modulator.<
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