Intersubband photoconductivity of self-assembled InAs quantum dots embedded in InP

In this article, we present the results from photoconductivity measurements in the infrared spectral region (3-10 mum) on ensembles of self-assembled InAs quantum dots embedded in a matrix of InP. In the spectral distribution of the photocurrent, peaks are observed which we interpret in terms of transitions from the dots' ground- and first-excited states to the conduction band of the dots/matrix. Furthermore, we have calculated the expected photoresponse and found it to be in qualitative agreement with our experimental data

Optical properties of a silver-related defect in silicon

Doping crystalline silicon with silver results in a photoluminescence center with multiplet zero-phonon structure near 778.9 meV. We show that the published assignments of the vibronic sidebands are wrong, with severe implications for the relative transition probabilities of the luminescence transitions from the excited states. At low temperature, most of the luminescence intensity derives from the phonon sideband associated with a forbidden zero-phonon line through the phonon-assisted coupling of two of the excited states of the center. The effective mass of the vibration is determined from isotope effects to be close to the mass of one Ag atom. Uniaxial stress and magnetic perturbations establish that the current assignment of the electronic structure of the center is incorrect and that it is best described by a new variant on the "pseudodonor" model. An electron orbits in an effective T-d environment, with an orbital triplet as its lowest-energy state, giving a j=3/2 electron state. A tightly bound hole has its orbital angular momentum quenched by the C-3v symmetry of the center, leaving only spin angular momentum (s=1/2). These particles couple to give J=2,1,0 states. Using this model, the temperature dependence of both the total luminescence intensity and measured radiative decay time can be understood. These data allow an estimate to be made of the thermally induced transition rate of the electron from the effective-mass excited states into the conduction band

Stable hydrogen pair trapped at carbon impurities in silicon

Local mode spectroscopy and ab initio modeling are used to investigate two trigonal defects found in carbon rich Si into which H had been in-diffused. Isotopic shifts with D and 13C are reported along with the effect of uniaxial stress. Ab-initio modeling studies suggest that the two defects are two forms of the CH2* complex where one of the two hydrogen atoms lies at an anti-bonding site attached to C or Si respectively. The two structures are nearly degenerate and possesess vibrational modes in good agreement with those observed experimentally. The defects are energetically favorable in comparison with separated Cs and H2 in Si and may represent aggregation sites for hydrogen.Validerad; 2003; 20070223 (kani)</p