Abstract :
This paper traces the research and development steps that led to selectively doped heterostructure transistors and integrated circuits. The transistor is the fastest switching transistor known, whereas integrated circuits built with the device outperform all other circuits of equivalent function. The work began with studies of GaAs optical spectroscopy at low temperatures using (Al, Ga)As-GaAs-(Al, Ga)As heterostructures to obtain micrometer-thick GaAs layers for absorption measurements. To prepare thinner layers, a multilayer (Al, Ga)As/GaAs structure containing 10 or 20 GaAs layers interleaved with (Al, Ga)As support layers were grown. With ∼200-Å-thick GaAs layers, the absorption spectrum at 2 K showed quantization of electron motion. Doping experiments resulted in the concept of doping the wider band-gap (Al, Ga)As to supply carriers to the undoped narrower bandgap GaAs. The removal of impurities from the GaAs layer results in higher carrier mobility due to greatly reduced impurity scattering. This technique, called modulation doping, resulted in a new generation of higher speed devices and circuits. The basic device is known as a selectively doped heterostructure transistor or SDHT.
