Theory of electrical spin-detection at a ferromagnet/semiconductor interface

Abstract

We present a theoretical model that describes electrical spin-detection at a ferromagnet/semiconductor interface. We show that the sensitivity of the spin detector has strong bias dependence which, in the general case, is dramatically different from that of the tunneling current spin polarization. We show that this bias dependence originates from two distinct physical mechanisms: 1) the bias dependence of tunneling current spin polarization, which is of microscopic origin and depends on the specific properties of the interface, and 2) the macroscopic electron spin transport properties in the semiconductor. Numerical results show that the magnitude of the voltage signal can be tuned over a wide range from the second effect which suggests a universal method for enhancing electrical spin-detection sensitivity in ferromagnet/semiconductor tunnel contacts. Using first-principles calculations we examine the particular case of a Fe/GaAs Schottky tunnel barrier and find very good agreement with experiment. We also predict the bias dependence of the voltage signal for a Fe/MgO/GaAs tunnel structure spin detector.

Giant enhancement of spin detection sensitivity in (Ga,Mn)As/GaAs Esaki diodes

“…A further increase of the voltage rapidly decreases the signal. For reverse bias the signal rapidly drops to zero before changing its sign at V 3T = −0.1 V. The behavior at low positive and low negative bias resembles well NL experiments on the Fe/GaAs system with a biased detector, interpreted in terms of bias dependence of the detector sensitivity [18,19]. The sensitivity is defined as a change in a voltage drop V across the biased FM-SC interface as a result of spin accumulation μ s generated in the SC.…”

“…Such a comparison is essentially needed in order to unambiguously establish a correlation between the 3T signal and the actual spin accumulation in the channel. What also has been overlooked in the recent discussion is the detection sensitivity of spin detecting contacts [18,19]. It was shown theoretically by Chantis and Smith [18] and observed experimentally by Crooker et al [19] that a current-biased spin detector has its sensitivity dramatically changed compared to a nonbiased case.…”

“…What also has been overlooked in the recent discussion is the detection sensitivity of spin detecting contacts [18,19]. It was shown theoretically by Chantis and Smith [18] and observed experimentally by Crooker et al [19] that a current-biased spin detector has its sensitivity dramatically changed compared to a nonbiased case. This makes charge transport through the detecting contact, in particular in the presence of any nonlinearity, a very important factor.…”

“…[18]. This means that the spin detection sensitivity is amplified by the ratio of the differential resistance and the interface resistance, a measure of nonlinearity of the I-V curve.…”

“…[19]. As a result of nonlinearity in the region (ii) the detection sensitivity is further enhanced [18], reaching a factor of 36. As the nonlinear contribution to the enhancement reaches the factor of 8 at the maximum (see the top panel in Fig.…”