Nikhil Rangaraju

A Spin-Diode Logic Family

While most modern computing technologies utilize Si complementary metal-oxide-semiconductor (CMOS) transistors and the accompanying CMOS logic family, alternative devices and logic families exhibit significant performance advantages. Though heretofore impractical, diode logic allows for the execution of logic circuits that are faster, smaller, and dissipate less power than conventional architectures. In this paper, magnetoresistive semiconductor heterojunctions are used to produce the first complete logic family based solely on diodes. We utilize the diode magnetoresistance states to create a binary logic family based on high and low currents in which a full range of logic functions is executed. The diode is used as a switch by manipulating its magnetoresistance with current-carrying wires that generate magnetic fields. Using this device structure, we present basis logic elements and complex circuits consisting of as few as 10% of the devices required in their conventional CMOS counterparts. This diode logic family is therefore an intriguing potential replacement for CMOS technology as Si scaling reaches its inherent limits.

Spin-dependent magnetotransport in a p-InMnSb/n-InSb magnetic semiconductor heterojunction

The spin-dependent transport properties in p-InMnSb/n-InSb magnetic semiconductor heterojunctions are presented. A positive junction giant magnetoresistance is observed from 75 to 298 K. The magnetoresistance is attributed to conduction via two spin channels resulting from p-d exchange interaction. The magnetoconductance of the heterojunction and its magnetic field dependence are well-described by a two-band model where the bands are spin-polarized. At 75 K and zero field, the spin polarization in the alloy is 90% and decreases to 48% at 298 K. The large spin polarization indicates that InMnSb should be suitable for spin-based transistors that operate at room temperature.

InMnAs magnetoresistive spin-diode logic

Electronic computing relies on systematically controlling the flow of electrons to perform logical functions. Various technologies and logic families are used in modern computing, each with its own tradeoffs. In particular, diode logic allows for the execution of logic with many fewer devices than complementary metal-oxide-semiconductor (CMOS) architectures, which implies the potential to be faster, cheaper, and dissipate less power. It has heretofore been impossible to fully utilize diode logic, however, as standard diodes lack the capability of performing signal inversion. Here we create a binary logic family based on high and low current states in which the InMnAs magnetoresistive semiconductor heterojunction diodes implement the first complete logic family based solely on diodes. The diodes are used as switches by manipulating the magnetoresistance with control currents that generate magnetic fields through the junction. With this device structure, we present basis logic elements and complex circuits consisting of as few as 10% of the devices required in their conventional CMOS counterparts. These circuits are evaluated based on InMnAs experimental data, and design techniques are discussed. As Si scaling reaches its inherent limits, this spin-diode logic family is an intriguing potential replacement for CMOS technology due to its material characteristics and compact circuits.

Magnetocapacitance effect in InMnAs∕InAs p-n heterojunctions

The magnetocapacitance characteristics of an epitaxial p-n heterojunction between magnetic InMnAs and InAs are investigated. A large positive magnetocapacitance is observed at room temperature, which increases with reverse bias. For high reverse bias, the magnetocapacitance is linearly dependent on magnetic field. From capacitance-voltage measurements, the junction built-in voltage was determined and was observed to increase with magnetic field. The magnetocapacitance measurements support a model for a magnetic semiconductor heterojunction where spin-split polarized valence and conduction bands form due to the giant Zeeman effect.

Charge Transport in Magnetic Semiconductor p-n Heterojunctions

Previously, the p-n-p bipolar magnetic junction transistor was demonstrated using a magnetic semiconductor InMnAs as the collector. A current gain βdc as high as 20 of the transistor is observed at 300 K. A negative magnetoamplification of -150% is obtained when the applied magnetic field is 8 T. In order to assess the gain mechanism for such transistors, we measured the minority carrier lifetime in a p-n InMnAs/InAs heterojunction diode. A minority carrier lifetime of 320 ns was obtained at room temperature. For the p-n-p MJT, a decrease in the emitter injection efficiency with the magnetic field is observed for the various base currents, which is attributed to the positive magnetoresistance of the p-type InMnAs. The emitter injection efficiency decreases with the magnetic field leading to the observed negative magnetic amplification.