P. Emanuelsson

Defects in porous silicon investigated by optically detected and by electron paramagnetic resonance techniques

The defect properties of as‐etched and annealed porous silicon are studied by electron paramagnetic resonance (EPR) and optically detected magnetic resonance (ODMR). The paramagnetic defect observed is closely related to the Pb0 center at the Si/SiO2 interface. In EPR a minimum defect density of 1016 cm−3 is observed for the as‐etched silicon, which reaches a maximum of 8×1018 cm−3 for samples annealed at about 400 °C. In the ODMR experiments, the same dangling bond center is observed on the 1.5 eV luminescence band enhancing the luminescence—but with increased sensitivity and as a decrease of the emission intensity in the infrared emission band at 1 eV of porous silicon.

Photoluminescence and optically detected magnetic resonance investigations on porous silicon

In porous silicon beside the visible red emission a luminescence band in the near-infrared spectral region of 0.8eV to 1.2eV can be observed at low temperatures. The exact energetical position of both emission bands can be changed by the preparation conditions of the material. The optically detected magnetic resonance experiments reveal that the spin resonance of Pb0-centres and a center with a g=2.013 signature strongly enhance the radiative decay via the infrared band. This gives evidence that these defects are directly responsible for this emission.

Microwave detection of Shubnikov–de Haas oscillations in In0.53Ga0.47As/InP single quantum wells

Shubnikov–de Haas oscillations in 150 A single quantum wells of In0.53Ga0.47As/InP are detected without contacts, using a conventional electron paramagnetic resonance (EPR) spectrometer. The two‐dimensional properties of the signal are verified and the carrier concentration is deduced from the period of the oscillations. The effective mass m* = 0.041mo obtained from the temperature dependence of the amplitude of the oscillations confirms that the signal originates from the In0.53Ga0.47As quantum well.

DAMAGE INDUCED BY PLASMA ETCHING : ON THE CORRELATION OF RESULTS FROM PHOTOLUMINESCENCE AND TRANSPORT CHARACTERIZATION TECHNIQUES

Plasma dry etching, used for the fabrication of low‐dimensional structures, is known to create defects in the material which affect both the optical and the transport properties of the sample. We compare the results obtained from three different methods of characterizing the damage induced by electron cyclotron resonance metalorganic reactive ion etching to the two‐dimensional electron gas (2DEG) in GaAs/AlGaAs heterostructures: photoluminescence, transport measurements, and electron paramagnetic resonance. Etching impairs the quality of luminescence and decreases the single‐particle relaxation time, while the concentration of a surface related paramagnetic defect (probably dangling bonds) is increased. However, detailed experiments show no correlation between the density of defects and transport or luminescence properties, nor between transport and luminescence properties. In particular, hydrogen passivation, which improves the luminescence properties after etching, leads to deteriorated transport proper...

Carrier-modulated, microwave-detected Shubnikov-de Haas oscillations in two-dimensional systems

It was recently shown that Shubnikov–de Haas (SdH) oscillations observed in conventional resistance measurements can be dramatically enhanced by light‐induced carrier modulation [S. E. Schacham, E. J. Haugland, and S. A. Alterovitz, Appl. Phys. Lett. 61, 551 (1992)]. Here we report on a similar observation in the case of contact‐free, microwave‐detected SdH oscillations. In the original version of this nondestructive technique [P. Omling, B. Meyer, and P. Emanuelsson, Appl. Phys. Lett. 58, 931 (1991)], magnetic‐field modulation was applied in order to enhance the sensitivity. If, instead, the carrier concentration is modulated by illumination, we show that a similar enhancement in the sensitivity of the signal is obtained. We demonstrate that very simple microwave equipment can be used for the measurements, and that the accessible magnetic‐field region can be extended, allowing for contact‐free transport investigations in the high magnetic‐field region.

EPR identification of a trigonal FeIn defect in silicon

Abstract A new electron paramagnetic resonance signal is observed in silicon which has been co-doped with indium and iron. The spectrum shows trigonal symmetry, and the involvement of one Fe and one In atom is proven from the observed hyperfine interactions. The defect is identified as an InS-Fei pair oriented along a [111] axis.

Identification of the iron-boron line spectrum in silicon

A new line spectrum at about 860 meV has been observed in silicon co-doped with iron and boron. The isochronal annealing behaviour of this line spectrum and the FeB centre was studied by transmission spectroscopy and electron paramagnetic resonance (EPR), respectively. The good agreement between the two measurements strongly suggests that the line spectrum originates from excitations at the trigonal FeB pair complex, well known from previous EPR studies. The positions of the FeB donor and acceptor levels were estimated to be at Ev+110 meV and Ec-275 meV respectively, in close agreement with previously reported values for the FeB pair. Furthermore, the energy difference between the ground and first excited states of this centre was determined to be 1.09 meV, which compares favourably with the 0.75 meV EPR value previously obtained.

Identification of hole transitions at the neutral interstitial manganese center in silicon

The observation of a sharp line transmission spectrum in Mn‐doped silicon is reported. Isochronal annealing behavior of both the line spectrum and the interstitial Mn center as determined by electron paramagnetic resonance is shown to be in excellent agreement. The temperature dependence of the spectrum is explained by the population of a local phonon mode in the initial state of the transitions. The spectrum is tentatively assigned to bound‐to‐bound hole transitions at the neutral interstitial Mn center.

Identification of the neutral charge state of platinum in silicon

Abstract A comparison of optical cross sections of platinum in silicon obtained from Fourier photoconductivity and photoelectron paramagnetic resonance (photo-EPR) measurements shows that the detailed structure in the high-resolution Fourier spectra is caused by the neutral Pt0 defect. The hole ionization of Pt0 to the Pt- defect observed in EPR.

Quality of Bulk CdTe Substrates and its Relation to Intrinsic Defects

Both the cadmium vacancy (V cd ) and the tellurium vacancy (V Te ) in CdTe are identified by means of electron paramagnetic resonance (EPR). The V cd is a double acceptor and the EPR spectrum is observed in its single negative charge state. The symmetry is found to be trigonal, which can be explained in a model in which the hole occupies a dangling bond t 2 orbital and the orbital degeneracy is removed by a static Jahn-Teller distortion. The hyperfine interaction shows that the hole is localised on one of the four Te neighbours. The EPR spectrum of V Te + reveals cubic (unperturbed) symmetry and the hyperfine structure shows that the unpaired electron is equally spread over the four Cd neighbours Photo-EPR measurements locate the 0/+ state of V Te at Ev + 0.2 eV and the 2-/- acceptor level of V Cd to be situated less than 0.47 eV above the valence band.