Transistors, Quantum Wells, and Superlattices

Before the invention of the transistor in 1947 at Bell Laboratories by John Bardeen, Walter H. Brattain, and William B. Shockley, vacuum tubes were the workhorse of electronics. Vacuum tubes were bulky and fragile, required high voltage ( 45 V) and a heater current to operate, and had lifetimes comparable to electric light bulbs. It is certainly no exaggeration to say that the transistor made possible modem solid-state electronics. Transistors serve much the same fimction as the old vacuum tubes but are much smaller, mgged, operate on low voltages, and have virtually infinite lifetimes. 

Once the purification and processing technology required to make transistors was developed, a virtual explosion of new concepts became possible resulting in a vast array of new electronic and photonic devices, a few of which will be described in this chapter. 

---

Nanocomposites in the form of superlattice structures have been fabricated with metallic, " semiconductor,and ceramic materials " " for semiconductor-based devices. " The material is abruptly modulated with respect to composition and/or structure. Semiconductor superlattice devices are usually multiple quantum structures, in which nanometer-scale layers of a lower band gap material such as GaAs are sandwiched between layers of a larger band gap material such as GaAlAs. " Quantum effects such as enhanced carrier mobility (two-dimensional electron gas) and bound states in the optical absorption spectrum, and nonlinear optical effects, such as intensity-dependent refractive indices, have been observed in nanomodulated semiconductor multiple quantum wells. " Examples of devices based on these structures include fast optical switches, high electron mobility transistors, and quantum well lasers. " Room-temperature electrochemical... 

---