Optoelectronic structures for semiconductor spintronics and quantum computation

A multitude of optical techniques were employed to study optoelectronic structures for semiconductor based spintronics and quantum computation. Optical polarization spectroscopy is utilized to demonstrate electrical injection of spin-polarized carriers into a semiconductor, a vital step in developing spin-based electronics. A fourteen-fold anisotropy in the injection efficiency is observed when comparing polarized injection parallel or perpendicular to the charge transport in a vertically-biased spin-polarized light emitting diode. Electroluminescence (EL) is collected from a quantum well (QW) placed a distance d (20–420nm) below a ferromagnetic semiconductor allowing spin polarized transport through GaAs at 5K < T < 60K. Additionally, an exponential increase in the polarization (0.5–7%) is measured as d decreases for collection parallel to the growth direction, while the in-plane polarization from the perpendicular direction remains unchanged.; As an alternative to injecting spin electrically, optical injection of spinpolarized carriers by circularly polarized excitation could be utilized. To this end, a pump-probe photoluminescence (PL) technique with ultrafast time resolution (∼150fs) is employed to monitor the coupling between quantum dots (QD)s and a high Q (∼7000) microcavity, an initial step in implementing optical control of individual electron spins for performing quantum computation. By measuring the lifetimes from QDs resonant and non-resonant with the cavity, we observe both a six-fold enhancement and a 0.77 times reduction of the spontaneous emission rate at T = 5K. In addition, this technique reveals the onset of coherent coupling at the lasing threshold through qualitative changes in the dynamic behavior and a tripling of the resonant QD emission rate is observed.; As optoelectronic structures approach smaller dimensions, near-field scanning optical microscopy (NSOM) may be utilized to correlate microstructure with light emission with ∼100 nm spatial resolution for T = 5–300K. The efficient optical properties of GaN despite its large dislocation density (−1010/cm2) provide an ideal system to characterize NSOM. Correlations are found between the PL and sub-micron defects in SQW and MQW samples. Additionally, lasers are investigated by imaging the EL at the onset of lasing along their facet. Broad spectral emission from a strain-compensating layer reveals inefficient lasing through absorption and reemission of the lasing mode.