Electron spin dynamics in GaAsN and InGaAsN structures

Abstract

We report on optical orientation experiments in undoped GaAsN epilayers and InGaAsN quantum wells (QW), showing that a strong electron spin polarisation can persist at room temperature. We demonstrate that the spin dynamics in these dilute nitride structures is governed by a spin-dependent recombination process of free conduction electrons on deep paramagnetic centres.

Room-temperature defect-engineered spin filter based on a non-magnetic semiconductor

“…Spin polarization of the electrons at Ga i 2+ was provided by optical orientation 15 using circularly polarized light (σ ± ) via spin-dependent recombination (SDR) [16][17][18][19][20][21] , as described in the "Methods" section . The spin-filtering effect induced by the spin-polarized defects drives the spins of the conduction and localized electrons at Ga i 2+ towards complete alignment when no further electron capture and recombination can occur via the defects as shown in Fig.1b.…”

“…on the number of photo-generated free carriers). Representative results obtained at RT and B=0 are shown in Fig.3, and were analyzed by the following coupled nonlinear rate equations 19,21 : Here G ± is the photo-generation rate of free carriers and n ± (N ± ) the density of conduction electrons (the density of the defects occupied by a single electron), where the "±" signs refer to the electron spin orientations S z =±1/2. N ↑↓ corresponds to the concentration of the defects having two spin-paired electrons, and N c the total defect concentration.…”

“…In the analysis we use τ d =10 ns, τ sc =1.5 ns and τ s =150 ps. 19,21 Here we assume that τ d is governed by the radiative time of the BB PL transition. The analysis is not sensitive to τ d as long as it is much longer than the electron capture & recombination time via the spin-filtering defects, i.e.…”

“…After the subsequent recombination between one of two localized electrons and an unpolarized free hole (due to much faster spin relaxation), a half number of the Ga i 2+ are left with a localized electron with its spin orientation parallel to that of the conduction electrons. Such a continuous SDR process [16][17][18][19][20][21] will dynamically polarize the spin of the first localized electrons at the Ga i 2+ towards that of conduction electrons.…”

Efficient room-temperature nuclear spin hyperpolarization of a defect atom in a semiconductor

“…Our approach exploits the recently discovered defect-engineered spin-filtering effect 25 , which has been demonstrated to be capable of generating strong spin polarization of conduction-band electrons in a semiconductor at RT. Strong conduction-band electron spin polarization of 440% can be obtained at RT in Ga(In)NAs by spin-filtering through Ga i interstitial defects [25][26][27][28][29] . By taking advantage of the spin-filtering effect and going beyond merely generating conduction-band electron spin polarization that was the focal point of the previous studies [25][26][27][28][29] , we shall show in this work that strong and efficient nuclear spin polarization of the core Ga atom of the Ga i defects can be achieved at RT by optical orientation.…”