Spectroscopy Of Quantum Wells Research Articles

Single-Photon Detection System for Quantum Optics Applications

We describe the design and characterization of a fiber-coupled double-channel single-photon detection system based on superconducting single-photon detectors (SSPD), and its application for quantum optics experiments on semiconductor nanostructures. When operated at 2-K temperature, the system shows 10% quantum efficiency at 1.3-¿m wavelength with dark count rate below 10 counts per second and timing resolution <100 ps. The short recovery time and absence of afterpulsing leads to counting frequencies as high as 40 MHz. Moreover, the low dark count rate allows operation in continuous mode (without gating). These characteristics are very attractive-as compared to InGaAs avalanche photodiodes-for quantum optics experiments at telecommunication wavelengths. We demonstrate the use of the system in time-correlated fluorescence spectroscopy of quantum wells and in the measurement of the intensity correlation function of light emitted by semiconductor quantum dots at 1300 nm.

Imaging spectroscopy of quantum wells with interfacial fluctuations: A theoretical description

We present a theoretical approach for the simulation of scanning local optical spectroscopy in disordered quantum wells (QWs). After a single realization of the disorder potential, we calculate spectra on a mesh of points on the QW plane, thus obtaining a three-dimensional matrix of data from which we construct two-dimensional spectroscopic images of excitons laterally localized at interface fluctuations. Our simulations are in close agreement with the experimental findings, and contribute to the interpretation of spatially resolved spectra in QWs.

Porter-Thomas Distribution of Oscillator Strengths of Quantum Well Excitons

Within the inhomogeneously broadened ground-state exciton line, the distribution of oscillator strengths is studied. We present theoretical and numerical evidence for a transition from a centered distribution in the low-energy tail (optimum fluctuation regime) to a broad, approximately exponential distribution in the high-energy side (Porter-Thomas distribution). This can be understood as going from Lifshitz tail states to Anderson-localized states, which we analyze in momentum space. Near-field optical spectroscopy of quantum wells is identified as an almost ideal system for collecting large data samples on wavefunction statistics in random systems.

Surface photovoltage spectroscopy of quantum wells and superlattices

Surface photovoltage spectroscopy (SPS) has been employed to monitor optical transitions in quantum well and superlattice structures at room temperature. Excellent agreement is found between theoretical predictions of heavy hole and electron energy level positions and the observed transitions. The results show that using this technique, the complete band diagram of the quantum structure may be constructed. SPS emerges as a powerful tool capable of monitoring optical transitions above the lowest one in a simple to interpret, contactless, and nondestructive way.

Probing terahertz dynamics in semiconductor nanostructures with the UCSB free-electron lasers

The UCSB free-electron lasers provide kilowatts of continuously tunable radiation from 120 GHz to 4.8 THz. They have the most impact on terahertz science and technology that require a tunable, high power source to explore non-linear dynamics or that sacrifice incident power to recover the linear response of systems with very small cross-section. We describe three experiments that demonstrate the utility of these lasers in experiments on the terahertz dynamics of semiconductor nanostructures: (i) terahertz dynamics of resonant tunneling diodes, (ii) saturation spectroscopy of quantum wells and (iii) photon-assisted tunneling in superlattices.