ABSTRACT
Crucial to the operation of all these devices are the fundamental processes of spin injection
into the semiconductor, the spin-diffusion length within the semiconductor, and spin-dependent detection.
There have been several attempts to fabricate spin transistors that exploit the spin-dependent scattering of charge carriers to yield a device with high current gain and high magnetic sensitivity. The first such attempt was Johnson’s all-metal threeterminal device,
which added a third terminal to the middle paramagnetic layer of a giant magnetoresistive (GMR) multilayer. The electrical characteristics of this purely ohmic device are magnetically tuneable, but, due to its all-metal construction, its operation yields only small voltage output changes and no power gain. Subsequent versions of the spin transistor have attempted to integrate semiconductors with spin electronics to generate novel functionality. There are two major variants. In the first, the metallic components retain their spin selectivity while the semiconductor is used only to control the distribution of applied potentials across the device. Most versions
fall into this category, including the Monsma hot electron spin-valve transistor.
