Room-temperature optical and spin polarization up to 35% is reported in InAs/GaAs quantum dots in zero magnetic field under optical spin injection using continuous-wave optical orientation spectroscopy. The observed strong spin polarization is suggested to be facilitated by a shortened trion lifetime, which constrains electron spin relaxation. Our finding provides experimental demonstration of the highly anticipated capability of semiconductor quantum dots as highly polarized spin/light sources and efficient spin detectors, with efficiency greater than 35% in the studied quantum dots.

Effect of postgrowth hydrogen treatment on defects and their role in carrier recombination in GaNP alloys is examined by photoluminescence (PL) and optically detected magnetic resonance. We present direct experimental evidence for effective activation of several defects by low-energy subthreshold hydrogen treatment (andlt;= 100 eV H ions). Among them, two defect complexes are identified to contain a Ga interstitial. Possible mechanisms for the H-induced defect activation and creation are discussed. Carrier recombination via these defects is shown to efficiently compete with the near band-edge PL, explaining the observed degraded optical quality of the alloys after the H treatment.

Recently discovered effect of spin-filtering and spin amplification in GaNAs enables us to reliably obtain detailed information on the degree of spin loss during optical spin injection across a semiconductor heterointerface at room temperature. Spin polarization of electrons injected from GaAs into GaNAs is found to be less than half of what is generated in GaNAs by optical orientation. We show that the observed reduced spin injection efficiency is not only due to spin relaxation in GaAs, but more importantly due to spin loss across the interface due to structural inversion asymmetry and probably also interfacial point defects.

Spintronics explores the spin degree of freedom of the electron to sense, store, process and transfer information in addition to the electron charge. Semiconductor spintronics promises to combine new spin enabling functionality with the present-day microelectronics and optoelectronics. It also opens the door to new generation of devices, and to the merging of electronics, photonics and magnetics. The success of spintronics relies on our ability to create and control spins. Among many obstacles, generation of electron spin polarization and coherence at room temperature is one of the most important as well as the most challenging issues, which has attracted intense research efforts during recent years. Significant progresses have been made both theoretically and experimentally, while many issues remain unresolved.

This book provides an in-depth review of the rapidly developing field of spintronic semiconductors. It covers a broad range of topics, including growth and basic physical properties of diluted magnetic semiconductors based on II-VI, III-V and IV semiconductors, recent developments in theory and experimental techniques and potential device applications; its aim is to provide postgraduate students, researchers and engineers a comprehensive overview of our present knowledge and future perspectives of spintronic semiconductors.

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Generating, manipulating and detecting electron spin polarization and coherence at room temperature is at the heart of future spintronics and spin-based quantum information technology. Spin filtering, which is a key issue for spintronic applications, has been demonstrated by using ferromagnetic metals, diluted magnetic semiconductors, quantum point contacts, quantum dots, carbon nanotubes, multiferroics and so on. This filtering effect was so far restricted to a limited efficiency and primarily at low temperatures or under a magnetic field. Here, we provide direct and unambiguous experimental proof that an electron-spin-polarized defect, such as a Ga_i self-interstitial in dilute nitride GaNAs, can effectively deplete conduction electrons with an opposite spin orientation and can thus turn the non-magnetic semiconductor into an efficient spin filter operating at room temperature and zero magnetic field. This work shows the potential of such defect-engineered, switchable spin filters as an attractive alternative to generate, amplify and detect electron spin polarization at room temperature without a magnetic material or external magnetic fields.

Oxygen and zinc vacancies are unambiguously shown to be formed in as-grown ZnO bulk crystals grown from melt without being subjected to irradiation, from electron paramagnetic resonance (EPR) and optically detected magnetic resonance (ODMR) studies. Concentrations of the defects in their paramagnetic charge states and are estimated to be ~2 × 10¹⁴ cm⁻³ and ~10¹⁵ cm⁻³, respectively. The defect is concluded to act as a deep acceptor and to exhibit large Jahn–Teller distortion by 0.8 eV. The energy level of the defect corresponding to the (2–/–) transition is E_v + 1.0 eV. The isolated Zn vacancy is found to be an important recombination centre and is concluded to be responsible for the red luminescence centred at around 1.6 eV. On the other hand, the oxygen vacancy seems to be less important in carrier recombination as it could be detected only in EPR but not in ODMR measurements. Neither isolated nor centres participate in the so-called 'green' emission. It is also shown that whereas the concentrations of both defects can be reduced by post-growth annealing, the Zn vacancy exhibits higher thermal stability. The important role of residual contaminants such as Li in the annealing process is underlined.

Optical spin injection is studied in novel laterally-arranged self-assembled InAs/GaAs quantum dot structures, by using optical orientation measurements in combination with tunable laser spectroscopy. It is shown that spins of uncorrelated free carriers are better conserved during the spin injection than the spins of correlated electrons and holes in an exciton. This is attributed to efficient spin relaxation promoted by the electron–hole exchange interaction of the excitons. Our finding suggests that separate carrier injection, such as that employed in electrical spin injection devices, can be advantageous for spin conserving injection. It is also found that the spin injection efficiency decreases for free carriers with high momentum, due to the acceleration of spin relaxation processes.