A strong anisotropy of electron spin decoherence is observed in GaAs/(AlGa)As quantum wells grown on (110) oriented substrate. The spin lifetime of spins perpendicular to the growth direction is about one order of magnitude shorter compared to spins along (110). The spin lifetimes of both spin orientations decrease monotonically above a temperature of 80 and 120 K, respectively. The decrease is very surprising for spins along (110) direction and cannot be explained by the usual Dyakonov Perel dephasing mechanism. A novel spin dephasing mechanism is put forward that is based on scattering of electrons between different quantum well subbands.The electron spin in semiconductors has recently become a focus of intense research in the context of spinelectronics or spintronics. This new kind of electronics aims to utilize spin for devices with unprecedented properties [1,2,3]. A prime condition for the development of potential applications is the understanding of spin decoherence, i.e. the loss of spin memory, in semiconductor structures [4]. The main reason for spin decoherence at room temperature is the intrinsic spin splitting of the conduction band, which occurs in all binary semiconductors. The spin splitting, which acts as an effective magnetic field, depends on the electron's momentum and is the basis for the Dyakonov-Perel (DP) spin relaxation mechanism [5,6]. Semiconductor heterostructures are in this context of particular interest since spin splitting in conduction and valence band can be controlled via dimensionality and orientation of crystal axes [7]. Ohno et al. observed very long electron spin decoherence times at room temperature in GaAs quantum wells (QWs) grown on (110) oriented substrates that exceeded the coherence times in usual (100) grown QWs by more than one order of magnitude [8,9]. However, slow spin dephasing in (110) QWs had been demonstrated only for electron spins oriented along the crystal growth direction. The dynamics of in-plane spin was left unexplored.Starting point for the theoretical description of the spin dynamics in (110) QWs is the Dresselhaus-Hamilton for binary semiconductorswhere i = x, y, z are the principal crystal axes with i + 3 → i, Γ is the spin-orbit coefficient for the bulk semiconductor, and σ i are the Pauli spin matrices [10]. Comparing eq.(1) with the spin Hamilton for a free electron in a magnetic field (H = 1 2 i µ B σ i B i ) one easily recognizes that random scattering of electrons leads to an effective k dependent random magnetic field with components in x, y, and z direction. This random magnetic field destroys the average spin orientation of an ensemble of electrons by rotating individual spins in different directions. The DP effect increases in bulk semiconductors with temperature due to occupation of higher k-states with larger spin splittings despite a motional narrowing effect at higher temperatures (spin lifetime τ s is inversely proportional to momentum scattering time τ * p ). In (110) QWs, however, the spin splitting (effective magnetic field)

We experimentally demonstrate the reduction of the laser threshold of a commercial GaAs∕(AlGa)As vertical-cavity surface-emitting laser (VCSEL) by optical injection of spin-polarized electrons at room temperature. Calculations with a rate-equation model reproduce the measured reduction of 2.5% for injected electrons with 50% spin polarization. The model predicts an improved threshold reduction of 50% in otherwise identical VCSELs grown on a (110) substrate due to the enhanced spin lifetime in such structures.

Very high precision measurements of the electron Landé g factor in GaAs are presented using spin-quantum beat spectroscopy at low excitation densities and temperatures ranging from 2.6 to 300 K. In colligation with available data for the temperature-dependent effective mass temperature dependence of the interband matrix element within a common five-level k · p theory can model both parameters consistently. A strong decrease in the interband matrix element with increasing temperature consistently closes a long lasting gap between experiment and theory and substantially improves the modeling of both parameters. DOI: 10.1103/PhysRevB.79.193307 PACS number͑s͒: 78.55.Cr, 71.18.ϩy, 78.20.Ci, 78.47.Cd The semiempirical k · p theory is a universal tool to calculate the band structure in semiconductors and semiconductor heterostructures and is regularly employed in such different fields as the physics of semiconductor laser design, the quantum Hall effect and spintronics. The part of the theory describing magnetic field related phenomena has been extensively improved since its introduction by Kane 1 and Luttinger and Kohn 2 in the mid fifties. Nowadays, five and more band k · p models are state of the art and many lowtemperature experiments have confirmed the incredible accuracy of k · p calculations. [3][4][5][6][7][8] All these experiments support the validity of k · p theory whereas a single but central experiment, which measures the temperature dependence of the electron Landé g factor in GaAs, shows a strong discrepancy between experiment and k · p theory. 9In this Brief Report we present extremely high precision, temperature-dependent measurements of the electron Landé g factor and show that by introducing a temperaturedependent interband matrix element yields a consistent explanation for the temperature dependence of the electron Landé g factor and the effective mass within common k · p theory, while keeping full temperature dependence on the very well-known interband critical points. The k · p theory is a perturbation theory calculating the electronic band structure by expansion around a single point in the Brillouin zone. In direct semiconductors such as GaAs, the high symmetry ⌫ point is the natural expansion point. The only input parameters are in this case the measured band gaps at k = 0 and the interband matrix elements ͑P , PЈ , PЉ ,...͒. The change in the band-gap energies with the lattice temperature are very well known for GaAs and the only remaining relevant parameter which does not possess a direct experimental access is the interband matrix element P or the related Kane energy E P = ͑2m 0 / ប 2 ͒P 2 , respectively. 1 The temperature dependence of P has been assumed to be marginal since P is inversely proportional to the interatomic distance a ͑Ref. 10͒ and the well-known change in a with temperature T due to anharmonic lattice potential is small. According to the relation E P ϰ 1 / a 2 between 0 and 300 K E P should change about −0.4% or less.11,12 However, this procedure only considers the static...

No abstract

No abstract