Room‐Temperature Electron Spin Amplifier Based on Ga(In)NAs Alloys

Abstract

Efficient generation, maintaining, manipulation and detection of electron spin polarization and coherence at room-temperature (RT) in semiconductors is a prerequisite for the success of future semiconductor spintronics and quantum information technologies. [1][2][3][4][5] Potential spintronic devices are expected to be based on fundamental building blocks such as spin filters (or spin injectors or spin aligners), spin amplifiers and spin detectors. During the past decade spin filters and spin detectors have been a main focal point of intense research efforts in the field of semiconductor spintronics that have led to many innovative approaches and encouraging developments. [1][2][3][4][5] In sharp contrast, experimental developments in spin amplifiers have so far been extremely limited. This is despite of the facts that many theoretical proposals for a wide variety of model spin amplifiers have been suggested during the past decade, ranging from spin amplifiers using spin injection pillar [6,7] or a dual-drain nonlocal lateral spin valve [8] or non-magnetic semiconductors, [9] unipolar spin transistors, [10] Submitted to 2 magnetic dipolar transistors, [11,12] spin gain transistors, [13] and optically controlled spin transistors. [14] As most of the proposed models require the involvement of a spin-functional diluted magnetic semiconductors (DMS), a lack of true DMS that can provide spin-polarized carriers at RT has so far prevented experimental realization of these proposed spin amplifiers.To our knowledge, the highest temperature at which a spin amplifier has so far been experimentally demonstrated to function is 150 K using a dual-drain nonlocal lateral spin valve based on an ferromagnetic metal-semiconductor hybrid structure. [8] Here we propose and demonstrate a new concept of a defect-enabled spin amplifier based on a non-magnetic semiconductor (Figure 1a). We shall show that a large spin gain (up to 2700 %) can be obtained at RT by employing Ga(In)NAs. This spin amplification functionality is facilitated by the spin-dependent recombination processes via defects, [15][16][17] which was also recently explored for spin filtering. [15,18] Spin amplification in the proposed spin amplifier is self-triggered by incoming conduction electrons with a finite spin polarization regardless of how weak and which direction the spin polarization is. Therefore, the sign of the spin polarization of the outgoing electrons from such a spin amplifier exactly follows that of the incoming electrons. Such spin amplification is generally efficient because even very weak spin polarization of incoming conduction electrons can dynamically polarize the spins of the defect electrons to a much greater degree, thanks to a much longer spin lifetime of the defect electrons commonly known in semiconductors. The spin-polarized defects can then in turn selectively capture and deplete conduction electrons with an opposite spin orientation (i.e. minority spin) governed by the Pauli exclusion principle, leading to greatly enhanced spin polarizat...

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

“…Though the Overhauser field cannot be determined at RT simultaneously by optical polarization and ODMR, due to the instrumental limitation for the latter as described in the Methods section, this conclusion is supported by the following experimental findings. Firstly, the Ga i defects have been identified as the source of the defect-engineered spin-filtering/amplification effect that has led to strong spin polarization of conduction-band electrons 25,32 . From Hanle experiments, conduction-band electron spin polarization at RT is nearly entirely governed by the spin polarization of the electron localized at the defect 32,33 .…”

“…Firstly, the Ga i defects have been identified as the source of the defect-engineered spin-filtering/amplification effect that has led to strong spin polarization of conduction-band electrons 25,32 . From Hanle experiments, conduction-band electron spin polarization at RT is nearly entirely governed by the spin polarization of the electron localized at the defect 32,33 . It is, therefore, natural to expect that even a slight alternation in the spin polarization of the defect electron by the nuclear field induced by the DNP of the Ga i defect can result in a sizeable change in conduction-band electron spin polarization.…”

Origin of radiative recombination and manifestations of localization effects in GaAs/GaNAs core/shell nanowires

“…11,12 Moreover, strong spin-dependent recombination in these materials mediated by defects allows achieving a record-high electron spin polarization of up to 43% at room temperature (RT), which makes the Ga(In)NAs alloys an ideal materials system for innovative spin filters, spin detectors, amplifiers, and nuclear spin hyperpolarizers operational at RT. [13][14][15][16] Most recently, it was shown that GaNAs can be grown not only in planar but also in NW architecture, i.e., as a shell layer in GaAs/GaNAs core/shell structures. 17,18 This raises the prospect of combining advantages of this materials system with those offered by the one-dimensional (1D) NW architecture.…”

Effect of hyperfine-induced spin mixing on the defect-enabled spin blockade and spin filtering in GaNAs

“…Examples include its vital role in the spin blockade in semiconductor double quantum dots (QDs) due to the mixing of singlet/triplet states, 10,11 in the magnetoresistance effect observed in organic semiconductors, 15 in spin decoherence/relaxation in InAs QDs, 16 in hyperpolarization of local nuclear spins in semiconductors, 17 and in controlling electron spin coherence time of the P donor site in Si 6 and the nitrogen-vacancy center in diamond in the vicinity of 13 C nuclei spin bath. 7 In this work, we attempt to examine the role of HFI in the room-temperature (RT) defect-engineered spin-filtering effect, which has recently been demonstrated to be able to generate >40% spin polarization (P e ) of free electrons [18][19][20][21][22][23][24][25][26][27][28] and to amplify fast-modulating spin signals up to 2700% at RT 29 in Ga(In)NAs alloys. Since the key to the success of the defect-engineered spin-filtering is generation and maintaining of strong spin polarization of the electron localized at the spin-filtering defects, namely, Ga 2+ i interstitials, 18,[22][23][24][25] it is natural to ask whether HFI-induced spin mixing at such defects with a nonzero nuclear spin (I = 3/2 for its core Ga atom) will significantly affect the spin-filtering effect.…”