Heterostructure unipolar spin transistors

TL;DR

This paper explores heterostructure unipolar spin transistors, demonstrating how varying spin splittings in different regions can enhance performance by reducing unwanted currents and accelerating carriers.

Contribution

It introduces heterostructure design principles for unipolar spin transistors, showing how material choices and graded spin splittings improve device efficiency.

Findings

Using a collector with larger spin splitting improves performance.

Graded spin splitting in the base creates an effective drift field.

Material selection impacts current flow and device efficiency.

Abstract

We extend the analogy between charge-based bipolar semiconductor electronics and spin-based unipolar electronics by considering unipolar spin transistors with different equilibrium spin splittings in the emitter, base, and collector. The current of base majority spin electrons to the collector limits the performance of ``homojunction'' unipolar spin transistors, in which the emitter, base, and collector all are made from the same magnetic material. This current is very similar in origin to the current of base majority carriers to the emitter in homojunction bipolar junction transistors. The current in bipolar junction transistors can be reduced or nearly eliminated through the use of a wide band gap emitter. We find that the choice of a collector material with a larger equilibrium spin splitting than the base will similarly improve the device performance of a unipolar spin transistor. We also find that a graded variation in the base spin splitting introduces an effective drift field that accelerates minority carriers through the base towards the collector.