Notizen: Previous perturbed angular correlation (PAC) spectroscopy measurements on the donor indium in CdTe and its alloys have revealed several defect complexes. One defect characterized by two sets of quadrupole interaction parameters, νQ=83 MHz, η=0.08 and νQ=92 MHz, η=0.08, was observed in Hg0.8Cd0.2Te (x=0.2 MCT) and attributed to the substitutional indium–metal vacancy complex InM2+3+VM2+. A defect characterized by νQ=61±1 MHz and asymmetry parameter η between 0 and 0.19 was seen in CdTe and widely attributed to the same complex. Both of these assignments were based mainly on an observed relationship between complex formation and the loss of metal ions. In this article we present PAC measurements on 111In-doped x=0.45 MCT (Hg0.55Cd0.45Te). These measurements reveal defects having quadrupole interactions very similar to those seen previously in CdTe and in x=0.2 MCT. Two unique defect fractions f1 and f2, characterized by νQ1=60±3 MHz, η1≈0–0.2, and νQ2=87±4 MHz, η2≈0–0.15, were seen in x=0.45 MCT, in some cases simultaneously. The observation of both of these interactions in the same material—if they correspond to the defects seen in CdTe and x=0.21 MCT—precludes the possibility that they both correspond to precisely the same defect. We also observed a change in the relative fractions of these two defects with time at room temperature; the fraction f2 vanished over a period of a day, while f1 and f0 (the fraction of indium atoms in sites having cubic or higher symmetry) increased. While we cannot rule out the possibility of a slow electronic transition, at present we favor a model in which one of the interactions (probably the one near 60 MHz) corresponds to a complex in which indium is paired to a fast-diffusing monovalent metal ion like Ag+, Cu+, or Li+. © 1995 American Institute of Physics.

Notizen: We report the fabrication, chemical, optical, and photoluminescence characterization of amorphous silicon-rich oxynitride (SiOxNy:H) thin films by plasma-enhanced chemical-vapor deposition. The film compositions were followed by changes in the refractive index. X-ray photoelectron and Fourier transform infrared spectroscopy indicate that the chemical composition is dominated by silicon suboxide bonding with N present as a significant impurity. A broad tunable photoluminescence (PL) emission is visible at room temperature with a quantum efficiency of 0.011% at peak energies to 3.15 eV. The radiative lifetimes are less than 10 ns, and there is nearly no temperature dependence of the PL intensity down to 80 K. Ex situ annealing at temperatures above 850 °C results in an increase in PL efficiency by nearly three orders of magnitude, and the PL intensity is independent of the annealing ambient. The PL results are remarkably similar to literature results in oxidized porous silicon and oxidized nanocrystalline Si thin films, and suggest that the radiative center is due to the defect structure in the silicon suboxide moiety. © 1995 American Institute of Physics.

Notizen: We report electroluminescence (EL) from 50 nm silicon oxynitride films on p-type crystalline silicon substrates in a Au/silicon oxynitride/Si structure. The EL intensity has a peak below 2.45 eV, and is consistent with radiative recombination of injected carriers. The EL is present only in annealed samples, and the emission is similar to the photoluminescence from the same samples. The current–voltage behavior is indicative of space charge-limited current. No polarity or field dependence of the EL peak energy is observed. This phenomenon is attributed to the relaxation of carriers down the band tails before recombination. © 1999 American Institute of Physics.

Notizen: We have studied the photoluminescence (PL) mechanism of photo- and electroluminescent amorphous silicon oxynitride films grown by plasma enhanced chemical vapor deposition. The composition of the films was determined by Rutherford backscattering spectrometry and monitored by the index of refraction with single-wavelength ellipsometry. Two sets of samples were grown, each with different reactant gas residence times in the deposition chamber. For samples grown with a residence time of about 5 s, the energy of the PL peak for 2.54 eV excitation is 2.3 eV for stoichiometric films and redshifts with increasing silicon content to 1.7 eV for the most silicon-rich films. The energy of the PL peak for 3.8 eV excitation is 2.8 eV for stoichiometric films and 2.1 eV for the most silicon-rich films. For stoichiometric films, the PL intensity is independent of temperature between 80 and 300 K using 2.54 eV excitation, but the PL intensity decreases by a factor of two over the same temperature range for 3.8 eV excitation. The authors interpret these aspects of the PL as consistent with tail-state recombination. Other results imply the PL is due to a specific luminescence center related to Si–Si or Si–H bonding. A 450 °C anneal reduces the paramagnetic defect density in the films, as detected by electron paramagnetic resonance, by an order of magnitude, but does not increase the PL intensity, while a 950 °C anneal increases both the defect density and the PL intensity. In addition, films in a second set of samples, grown with a residence time of 1.8 s, display very different PL behavior than samples in the first set with the same composition. Samples near stoichiometry in the second set have a PL peak at 2.06 eV and are 20 times less intense than stoichiometric samples in the first set. Optical absorption measurements indicate both types of samples contain Si–Si bonds, with the second set containing many more Si–Si bonds than the first. Fourier-transform infrared measurements indicate the presence of a Si–H bond that is stable at temperatures of 950 °C in the first set, but not in the second set. Thus, the study as a whole suggests a complete picture of luminescence in our silicon oxynitride films must incorporate elements of both tail-state and luminescence center models. The relation of the results to other PL studies in silicon alloys and porous silicon is discussed. © 1999 American Institute of Physics.