We report the first well-resolved band-edge luminescence from excitons confined in fully strained SiGe quantum wells grown on Si. At liquid-He temperatures the photoluminescence is due to shallow bound excitons, and in addition to a no-phonon line, phonon-assisted transitions involving TA phonons and Si-Si, Si-Ge, and Ge-Ge TO phonons are observed. At higher temperatures the spectra are dominated by free-exciton luminescence. Quantum-confinement effects shift the observed free-exciton edge above the bulk strained band-gap energy, and also influence the relative intensities of the three TO-phonon replicas.

We report a new photoluminescence process in epitaxial Sil-,GeX layers grown on Si by rapid thermal chemical vapor deposition which we attribute to the recombination of excitons localized at random alloy fluctuations. This luminescence is characterized by saturation at very low excitation densities (N 100 PW cm-*), very long decay times (> 1 ms), and high quantum efficiency at low excitation. We have directly measured an external photoluminescence quantum efficiency of 11.5 *2%.

Coherent Si1−xGex alloys and multilayers synthesized by molecular beam epitaxy (MBE) on Si(100) substrates have been characterized by low-temperature photoluminescence (PL) spectroscopy and transmission electron microscopy (TEM). Phonon-resolved transitions originating from excitons bound to shallow impurities were observed in addition to a broad band of intense luminescence. The broad PL band was predominant when the alloy layer thickness was greater than 40–100 Å, depending on x and the strain energy density. The strength of the broad PL band was correlated with the areal density (up to ∼109 cm−2) of strain perturbations (local lattice dilation ∼15 Å in diameter) observed in plan-view TEM. Thinner alloy layers exhibited phonon-resolved PL spectra, similar to bulk material, but shifted in energy due to strain and hole quantum confinement. Photoluminescence excitation spectroscopy, external quantum efficiency, time-resolved PL decay, together with the power and temperature dependence of luminescence intensity, have been used to characterize Si1−xGex/Si heterostructures exhibiting both types of PL spectra. The role of MBE growth parameters in determining optical properties was investigated by changing the quantum well thickness and growth temperature. The transition from phonon-resolved, near-band-gap luminescence in thin layers to the broad PL band typical of thick layers is discussed in terms of a strain energy balance model which predicts a ‘‘transition thickness’’ which decreases with increase in x.

We report the first observation of photoluminescence from electron-hole plasmas in Si/S&,sGe&Si quantum wells. While at liquid helium temperature, luminescence due to shallow bound excitons is observed. At 77 K electron-hole plasma (EHP) luminescence dominates the spectra over a wide range of pump powers. Convolution of the occupied electron and hole densities of states gives an excellent fit to the photoluminescence line shape. A bandgap reduction of up to 15 meV at high carrier densities is observed for wide quantum wells, but no such shift is detected for narrow quantum wells.

A voltagetunable multicolor triplecoupled InGaAs/GaAs/AlGaAs quantumwell infrared photodetector for 8-12 μm detection Appl.A systematic study of stacked quantum well infrared photodetectors is undertaken to improve the understanding of the voltage-tunable multi-color spectral response. The multi-color capability is achieved by sequentially growing conventional one color detectors, separated by conducting layers. The behavior of the stacked devices is proven to correspond to the individual detectors simply acting in series with each other. The dc resistance, photocurrent and dynamic resistance characteristics of the individual detectors are examined and correlated with the voltage-tuning in the stack.

We report the first room-temperature 1.3 ,um electroluminescence from strained Sir-,Ge,/Si quantum wells. The electroluminescence is due to band-edge carrier recombination, and its intensity increases linearly with the forward current up to 1700 A/cm'. The internal quantum efficiency is estimated to have a lower limit of 2 x 10m4. As the temperature is increased from 77 to 300 K, luminescence from the silicon increases relative to that from the Sit-,GeX wells. A minimum band offset is required to have effective room-temperature luminescence from the Sr,-XGeX quantum wells.

We report the tist detailed study of quantum confinement shifts of band-edge photoluminescence energies in Si/strained Si, _ ,Ge,/Si single quantum wells. A quantum confinement energy of up to 45 meV has been observed for quantum wells as small as 33 A in width. The experimental results are in good agreement with a calculation of the hole confinement energies. The hole energy levels in quantum wells were obtained by numerically solving effective-mass equations with proper matching boundary conditions at interfaces using a 6 X 6 Luttinger-Kohn Hamiltonian. Both strain and spin-orbit interactions were included in the calculation.

In this study, we introduce a thin nickel interlayer to enhance the phase separation and silicon nanocrystal (Si-NC) growth in Si-rich silica films. Through TEM analysis, it is observed that the Si-NC density in the sample with a Ni interlayer is 2.6 times higher than that of the sample without Ni after high temperature annealing. The photoluminescence (PL) spectrum of the sample with a Ni interlayer is 2-5 times stronger than the one without Ni according to different silicon excess. By analysing the samples after rapid thermal annealing (RTA) with Fourier transform infrared absorption (FTIR), we find that nickel can induce phase separation in Si-rich silica films during annealing. Thermodynamic and kinetic analysis indicates a reduction of 31.4 kJ mol −1 in the Si-NC nucleation activation free energy by adding the nickel interlayer, which subsequently results in higher Si-NC density.