eV PL Band Research Articles

Magneto-optical study under pulsed high magnetic fields of [formula omitted]- FeSi2 single crystals grown by a chemical vapor transport method

We measured the photoluminescence (PL), the optical absorption and the magneto-optical absorption of β- FeSi2 single crystals which were fabricated by a chemical vapor transport method. The characteristic 0.8 eV-PL bands of β- FeSi2 thin films were not observed in our single crystals. However, we found new two PL lines (0.717 and 0.737 eV) and new two absorption peaks (0.858 and 0.909 eV) at low temperatures. All the samples which were measured in this study were classified into two groups according to the absorption peak energies. The two types of samples showed different absorption energies, but the magnetic field dependencies of the energy shifts are quite the same. Furthermore, the evaluated effective g factor is about 4 for both types of samples.

Role of ballistic transport in photoluminescence excitation of Si nanocrystals

Photoluminescence of Si NCs with the size (10–300nm) bigger than the exciton Bohr radius in the bulk Si crystals (4.8nm) has been considered. Photoluminescence in such NC systems is analyzed from the point of view of new concept based on the effect of hot carrier ballistic transport in excitation of suboxide defect-related photoluminescence at the Si/SiOx interface. The dependence of the 1.70eV PL band integrated intensity on Si NC sizes was numerically calculated on the base of the hot carrier ballistic PL model. The well correlation between calculated and experimental results has been obtained for Si NCs with the size from the 30–150nm range.

Effects of B and N implantation on optical absorption and photoluminescence and comparison to the effects of implanting Si, Ge, O, and Ar in silica

Silica samples were implanted at multiple energies with B and N ions, which resulted in a constant concentration implanted layer ∼600 nm thick starting ∼100 nm below the sample surface. The energies to produce the constant concentration layer ranged from 35 to 320 keV and the concentrations were 0.03–2.1 at.% for B and 0.024–2.5% for N. The optical absorption of the suite of samples was measured from 2.8 to 6.5 eV. No bands were detected at energies <2.8 eV. Bands which have been identified in the literature as intrinsic to SiO 2 were fitted to the data with only one free parameter, the amplitudes of the maxima of the bands. This fit was within ±2% from 2.8 to 5.4 eV. To fit the data from 5.4 to 6.6 eV we assumed that there was a single band with an energy >6.5 eV. The nonlinear fitting program calculated a band at 6.76 ± 0.06 eV with a width at half maximum amplitude of 0.81 ± 0.08 eV, for all concentrations of B and a band at 6.65 ± 0.06 eV with a full width at half maximum of 0.67 ± 0.08 eV for the N implanted samples to achieve a fit to ±2% from 5.4 to 6.5 eV. In the range of energies from 2.0 to 6.5 eV no bands attributable to either B or N were required to fit the observed optical absorption. Excitation of the samples with 5 eV photons produced a photoluminescence [PL] band at 4.43 ± 0.02 eV with a full width at half maximum amplitude [FWHM] of 0.53 ± 0.02 eV. When measured at 4.43 eV the photoluminescence excitation [PLE] band had a maximum at 5.00 ± 0.02 eV with a FWHM of 0.40 ± 0.02 eV. Bands with approximately the same energies and FWHMs were observed in the N samples as observed in the B samples. The correlation of the amplitudes of these PL bands with the amplitudes of the absorption bands at 5.01 and 5.17 eV is less than one. Based on a comparison of the absorption amplitudes deduced from the linear and nonlinear fitting procedure, and PL and PLE amplitudes in the B, Si, N, O, and Ar samples, an absorption band at 5.00 ± 0.02 eV producing the PL at 4.43 ± 0.02 eV is due to a Si related defect state. In the Ge case PL bands were observed at 4.38 ± 0.02 and 3.23 ± 0.02 eV with PLE bands at 4.98 ± 0.2 and 5.18 ± 0.02 eV, respectively. An absorption band at 5.17 eV is the source of the 3.23 eV PL band and is, therefore Ge related. The fitted absorption spectra in the Ge case required another absorption band at 5.54 ± 0.07 eV as well as a band at 6.87 ± 0.04 eV to fit the spectra in the Ge case for all concentrations, to within the ±2%. PL bands at other energies were not detected in the PL spectra of any of the samples when excited with energies in the 4.5–6.4 eV range.

Optical characterization of crystalline silicon embedded in a‐Si matrix

The photoluminescence of pure amorphous Si films and films with embedded Si quantum dots and large nano-crystallites is correlated with XRD and AFM measurements. Several PL bands in the IR spectral range with maxima at 0.90, 0.98, 1.18 and 1.39 eV have been revealed in studied samples. The 0.90–0.98 eV PL bands are attributed to band tail luminescence in Si nano-crystallites. Concurrently, the 1.18 and 1.39 eV PL bands are assigned to radiative transitions between quantum confined levels within Si quantum dots embedded into a-Si matrix. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Optical investigation of Si nano-crystals in amorphous silicon matrix

Paper presents the comparative investigation of photoluminescence and Raman scattering spectra of pure amorphous silicon films and amorphous silicon films with different size Si nanocrystallites. Several PL bands in the IR spectral range with maxima at 0.90, 0.98, 1.14 and 1.36eV have been revealed in studied samples. The 0.90–0.98eV PL bands are attributed to the band tail luminescence in Si nano crystallites with the size of 15–20 nm. Concurrently, the 1.18 and 1.36eV PL bands are connected, apparently, with radiative transition between quantum confined levels within Si QDs (size of 5–6nm) embedded into a-Si matrix.

Correlation between the 1.5 eV photoluminescence band and peroxy linkage in silica glass

In order to understand the origin of the 1.5 eV PL band in silica glass, we studied the correlation between the 1.5 eV PL band and the peroxy linkage (POL: O 3Si–O–O–SiO 3) or the molecular chlorine models (possible origins of the 3.8 eV absorption band) by laser irradiation at low temperatures (∼20 K). On the basis of our results, we conclude that the origin of the 1.5 eV PL band is not molecular chlorine but POL.

Point defects in Cl and Na doped CdTe monograin powders

Monograin CdTe powders were grown by recrystallization in isothermal ampoules in the presence of CdCl2 and CdCl2–NaCl liquid phases. The conductivity of n-type CdTe samples quenched from 750°C was high for low sodium concentrations and decreased abruptly by seven orders of magnitude with a simultaneous appearing of photosensitivity at sodium concentrations of CNa=1018 cm−3. A high n-type conductivity is possibly based on the ionization of the chlorine induced donor defects: ClTex→ClTe°+e′. A low conductivity at high Na levels may be connected with the compensation of these donors by acceptors: NaCdx+ClTe°+e′→NaCd′ClTe°. The same complex defect can serve as one of the radiative recombination centers of the 1.4 eV PL band. The 1.4 eV PL band intensity increased with increasing CNa, reached a maximum in the vicinity of CNa=1018 cm−3 and then decreased abruptly. The latter can be caused by NaCd′Nai° or by (NaCd′Nai°)2, serving as s-center of non-radiative recombination.

Radiative and nonradiative recombination centers in Cl and Na doped CdTe monograin powders

The wide 1.4 eV photoluminescence band, photoconductivity and dark conductivity of CdTe monograin powders were studied as a function of Na concentration. The donor-acceptor complex NaCdClTe is proposed as the radiative recombination center responsible for the 1.44 eV PL band as well as for the photoconductivity. The high n-conductivity of CdTe monograins with low Na concentration is determined by the ionization of shallow ClTe donor defects. The sharp decrease of the conductivity (107 times) in vicinity of equal concentrations of Na and Cl is due to the high level of compensation ClTe• + e′ + NaCdx → Na′CdClTe•.

Characterization of Ion Implanted GaN

ABSTRACTLow temperature photoluminescence is used to study the levels introduced by low-dose implantation of Mg, C, and Be into GaN, together with Ne, Al, P, or Ar co-implantation species. None of the co-implants successfully creates shallow C or Be acceptors. The yellow (2.2 eV) PL band is strongly introduced by both C and Be implants, but not by Ar, Al, P, or Mg. We propose that it involves Ga vacancies stabilized by complexing with C and Be interstitial (or CGa) donors, which explains why C and Be are absent as substitutional acceptors. We observe excitons bound to isoelectronic PN in P-implanted GaN. They are absent in P+Mg implanted GaN, in which we observe new donor-to-acceptor pair peaks due to two deeper donor levels. We assign these levels to PGa antisite double donors, which are stable in p-type material

Correlation between 1.5 eV photoluminescence-band and 3.8 eV absorption band in silica glass

The 3.8 eV absorption band constitutes a characteristic feature of silica glass with excess oxygen. Since 1.5 eV PL band is formed in the presence of a 3.8 eV absorption band, we studied features of the PL near 1.5 eV to further understand the origin of 3.8 eV absorption band. The 1.5 eV PL band was found to have unique characteristics such as: (1) being the highest intensity PL band observed for an oxygen surplus sample with a 3.8 eV absorption band present, (2) having a long lifetime of several ms and (3) having a PL spectrum with hyperfine structure. We also studied the relationship between 1.5 eV PL band and 3.8 eV absorption band. Two types of inter-related behaviors were observed in the intensity of 1.5 eV PL band and the amplitude of 3.8 eV absorption band. Using a thermal heat treatment experiment, we found a linear correlation between 1.5 eV PL band and 3.8 eV absorption band. Also, by comparing the effect of irradiation time on 3.8 eV absorption and 1.5 eV PL bands at 20 K, we found that an increase in the irradiation time caused a decrease in the amplitude of both 3.8 and 1.5 eV bands. Similarities were also observed in the spatial distribution of the two bands. The results obtained suggest that 3.8 eV absorption band plays a role in the formation of 1.5 eV PL band.

Photoluminescence Properties of Z-Bands in CdTe

We have studied the photoluminescence band shape of the 1.36 eV (Z-band) and the 1.32 eV (Z′- band) PL bands in high purity low-temperature-grown n-type bulk polycrystalline CdTe as a function of the excitation power and temperature. Both bands have a nonsymmetrical shape with a gradual decrease on the high-energy side but the variation of the shape with temperature and excitation power is different for Z- and Z′-bands. Both bands have the same temperature quenching activation energy ET = 35 meV. On the basis of our investigations we assign the 1.32 eV emission to a free-to-bound recombination near dislocations and the 1.36 eV emission to a DA emission near the same dislocation. Both bands are related to a shallow acceptor EA = 35 meV (probably Li or Na), whose concentration in the bulk is quite low. The Z-band is also related to a deep donor (ED ≥ 200 meV), probably of intrinsic origin.

Colour-switching effect of photoluminescent silicon after spark-processing in oxygen

We report on a new colour-switching effect of photoluminescing spark-processed silicon which was prepared in pure oxygen. Whereas as-prepared specimens display an orange PL peaking at 655 nm (1.89 eV), the PL changes to a more intense blue emission centred at 475 nm (2.61 eV) when the sample is subjected to a lower pressure. The same blue PL band is observed after heat treatments up to . Moreover, at annealing temperatures above a third radiative transition emerges in the infrared and eventually dominates the spectrum. A model is suggested that links ozone molecules, generated during spark-processing and incorporated into the sp-matrix, to the orange PL band. The results of heat treatments and temperature-dependent PL measurements allow for the relationship of the 2.61 eV band to oxygen deficiency centres, created by out-driven ozone molecules. The IR band is discussed in the light of luminescing properties of porous silicon and silicon oxides. The experiments demonstrate that the UV/blue (3.25 eV) and green (2.36 eV) PL bands for Si spark-processed in air cannot be related to radiative transitions in silicon oxides.

Photoluminescence from deep acceptor-deep donor complexes in CdTe

The deep donor-deep acceptor defect model is proposed for the 0.7 and 1.1 eV PL bands in CdTe. It is shown that the interstitial defects with different symmetry are involved in these DA pairs.

Effect of the vacuum annealing on p-type CdTe

The photoluminescence spectra and formation of the complex defects in the Cl doped CdTe p-type layers are investigated. It is supposed that at low Cl concentration complex defects TeiClTe and VCdClTe are responsible for the low p-type resistivity in CdTe. At higher Cl concentration formed neutral complexes Tei2ClTe and VCd2ClTe increased the p-type resistivity. At high Cl concentration excess ClTe caused a high resistivity and photoconductivity of CdTe. It is proposed that Tei and complex defects with Tei caused the 1.4eV PL band quenching and the 1.0eV PL band formation. The unstable 1.25eV PL band is supposed to be due to VCd-VTe pair. Acceptor impurities in initial material as Cu and its complexes can increase the p-type resistivity value in CdTe: Cl.

Spatial distributions of impurities and defects in Te- and Si-doped GaAs grown in a reduced gravity environment

The spatial distributions of impurities and structural defects of Te- and Si-doped GaAs grown in space have been investigated using capacitance-voltage ( C-V) method and scanning photoluminescence (SPL) and cathodoluminescence image (CLI) techniques. The deep center profile and free carrier concentration profile both along the crystal growth direction and across the wafer are measured and discussed in terms of the impurity segregation and the reaction between shallow donors and Ga and As vacancies during the space crystal growth. Dislocation density and its features throughout the space grown crystals are reported. Fine impurity striations in parallel with the space crystal surface are observed and are believed to be related to the well-known Marangoni convection resulting from surface tension gradients. A tentative structural model for the identification of the 1.0 eV PL band is postulated on the basis of the new experimental data presented in this paper.

The Role of Oxygen in p-Type InP

AbstractWe have studied the influence of oxygen on the optical properties of Be implanted InP. Be implanted p-type InP without oxygen shows a strong deep photoluminescence (PL) band at 0.82 eV following anneal. As the oxygen concentration increases, the 0.82 eV PL-band disappears. We attribute the disappearance of this PL-band to the formation of oxygen complexes with the implantation induced defects. In epitaxial grown, nominally undoped InP a new PL-line is observed at ~1.2 eV. The paramagnetic state of the phosphorus on indium P^ antisite is observed by optically detected magnetic resonance (ODMR) as a modulation of the photoluminescence in all Be implanted samples without oxygen. The antisite resonance is detected as a reduction of the 0.82 eV PL-band and the 1.2 eV PL-band. The observation of the Fe3+ resonance by ODMR spectroscopy is reported for the first time.

Photoluminescence bands related to localized Mn2+ transitions in diluted magnetic semiconductors

Photoluminescence excitation measurements have been carried out on the diluted magnetic semiconductors Cd1−xMnxTe and Cd1−xMnxSe. The temperature dependence of the known 2.0 eV and 1.2 eV PL bands is discussed in terms of a configuration coordinate model involving Mn2+ intra-ion transitions. Two broad band emissions in Cd1−xMnxSe, at 2.13 eV and 1.35 eV, are reported which appear to be the analogies to the PL bands seen in Cd1−xMnxTe.