We investigated experimentally and theoretically the valence-band structure of wurtzite InP nanowires. The wurtzite phase, which usually is not stable for III-V phosphide compounds, has been observed in InP nanowires. We present results on the electronic properties of these nanowires using the photoluminescence excitation technique. Spectra from an ensemble of nanowires show three clear absorption edges separated by 44 meV and 143 meV, respectively. The band edges are attributed to excitonic absorptions involving three distinct valence-bands labeled: A, B, and C. Theoretical results based on "ab initio" calculation gives corresponding valence-band energy separations of 50 meV and 200 meV, respectively, which are in good agreement with the experimental results.

We report polarized Raman scattering and resonant Raman scattering studies on single InAs nanowires. Polarized Raman experiments show that the highest scattering intensity is obtained when both the incident and analyzed light polarizations are perpendicular to the nanowire axis. InAs wurtzite optical modes are observed. The obtained wurtzite modes are consistent with the selection rules and also with the results of calculations using an extended rigid-ion model. Additional resonant Raman scattering experiments reveal a redshifted E 1 transition for InAs nanowires compared to the bulk zinc-blende InAs transition due to the dominance of the wurtzite phase in the nanowires. Ab initio calculations of the electronic band structure for wurtzite and zinc-blende InAs phases corroborate the observed values for the E 1 transitions.

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We found out that the polar pattern for the zinc-blende InAs LO mode displayed in Fig. 2(b) of our original paper represents the backscattering Raman intensities from a (112) top surface and not as stated in the original manuscript from a (110) top surface. In the latter the LO mode is forbidden for all configurations. In addition, varying the rotation angle θ with respect to the [112] direction (see Fig. 1 in the original paper) leads to changes in the polar patterns for the LO mode in case of perpendicular analysis, as illustrated in Fig. 1. For the parallel analyzer this mode is always forbidden. For completeness, the analytical expressions for the Raman intensities for both TO and LO modes as a function of the rotational angle θ and the polarization angle φ used to obtain the polar plots are given asThese results do not affect the interpretation of the experiments on the wurtzite nanowires. In the case of the reference zinc-blende (110) InAs substrate, the appearance of the forbidden LO mode is attributed to the fact that the laser excitation energy (2.41 eV) is close to the E 1 transition of InAs bulk (2.57 eV), breaking the selection rules.We would like to thank M. R. Correia for pointing out these discrepancies. LO, ⊥

We report experimental evidence of excitonic spin-splitting, in addition to the conventional Zeeman effect, produced by a combination of the Rashba spin-orbit interaction, Stark shift and charge screening. The electric-field-induced modulation of the spin-splitting are studied during the charging and discharging processes of p-type GaAs/AlAs double barrier resonant tunneling diodes (RTD) under applied bias and magnetic field. The abrupt changes in the photoluminescence, with the applied bias, provide information of the charge accumulation effects on the device.The effect of the spin-orbit (SO) interaction in quasitwo-dimensional (Q2D) systems has attracted renewed attention in recent years. The topic has been on the focus of many optical and transport investigations of spin-related phenomena in nanoscopic systems [1,2,3], a subject of great fundamental and technological interest [4,5,6,7]. In this letter, we address experimental evidence of electric field coupling to the spin degree of freedom of carriers in RTD; here in particular, the prevailing influence can be attributed to the SO and Stark effects on the hole electronic structure. These interactions are relevant to the study of the internal electric fields and the charge accumulation in the structure. The simultaneous investigation of optical and transport properties at high magnetic and electric parallel fields, has permitted a thorough characterization of the main processes involved in the system response. The novelty of this result consists of the optical detection of electric field modulation of the effective spin-splitting beyond the Zeeman effect and its unambiguous correlation to the transport mechanisms which is responsible for the charge buildup in the states of the RTD.This study is carried out on a symmetric p − i − p GaAs/AlAs RTD, that has been previously used to characterize hole space charge buildup and resonant effects in a magnetic field [8]. The structure is in the form of a 400µm diameter mesa with a metallic AuGe annular top contact to allow optical access. The diode was mounted in a superconducting magnet and the emission spectra were recorded using a double spectrometer coupled to a CCD system with polarizer facilities to select left (right) σ +(−) configurations. When light from an Ar + laser is focused close to the surface, minority electrons are created [8]. As the bias approaches a resonant condition, the carrier density inside the QW increases and then decreases, resulting in the negative differential resistance (NDR) region when the resonance is traversed. The photo-generated electrons tunneling into the QW layer can recombine with the injected holes or tunnel out of the well layer. These processes are represented schematically in the Fig. 1 (a).The I − V characteristics, shown in Fig. 1 (b), displays a series of peaks associated with the injected holes (I dark ) from the hole accumulation layer formed in the outside interface of the diode (see Fig. 1 (a)). Under illumination, an increase of current is observed (I light ) due to ...

We present variational calculations of the binding energy for positively and negatively charged excitons ͑trions͒ in idealized GaAs/Al 0.3 Ga 0.7 As quantum wells with parabolic electrons and holes energy dispersions. The configuration interaction method is used with a physically meaningful single-particle basis set. We have shown that the inclusion of more than one electron quantum-well solution in the basis is important to obtain accurate values for the binding energies. The effects of longitudinal electric-field and quantum-well confinement on the charged excitons bound states are studied in the absence of magnetic field and the conditions for the trion ionization are discussed.

We present a model that takes into account the interface-defects contribution to the binding energy of charged excitons ͑trions͒. We use Gaussian defect potentials and one-particle Gaussian basis set. All the Hamiltonian defect terms are analytically calculated for the s-like trial wave functions. The dependence of the binding energy and of the trion size on the quantum-well width and on the defect size are investigated using a variational method for GaAs/Al 0.3 Ga 0.7 As quantum wells. We show that even in the case of strictly structural defects the trion is more strongly affected than the exciton.

Most of III-V semiconductors which acquires the zincblende phase as bulk materials, adopt the metastable wurtzite phase when grown in form of nanowires. These are new semiconductors, with new optical properties, in particular a different electronic band gap when compared with that grown in the zincblende phase. The electronic gap of wurtzite InAs at the Γ−point of the Brillouin zone (E 0 gap) have been recently measured, E 0 = 0.46 eV at low temperature. The electronic gap at the A−point of the Brillouin zone (the equivalent to the L−point in the zincblende structure, E 1 ) has also been recently obtained based on a resonant Raman scattering experiment. In this work, we calculate the band structure of InAs in the zincblende and wurtzite phases, using the full potential linearized augmented plane wave method, including spin-orbit interaction. The electronic band gap has been improved through the modified Becke-Johnson exchange-correlation potential. Both the E 0 and E 1 gap agrees very well with the experiment. From the calculations, a crystal field splitting of 0.122 eV and a spin-orbit splitting of 0.312 eV (the experimental value in zincblende InAs is 0.4 eV) has been obtained. Finally, we calculate the dielectric function of InAs in both the zincblende and wurtzite phases and a comparative discussion is given.