Electrical Properties of Defects in 4H-SiC Investigated by Photo-Induced-Currents Measurements

In this paper we have studied the connection between crystal quality and electrical transport in 4H-SiC by simultaneous micro-photoluminescence (μPL) and photocurrent (PC) measurements. We have used a focused HeCd laser at 325 nm (i.e. above bandgap) to measure with a spatial resolution of few microns both the μPL spectra and the I-V characteristics in 4H-SiC/Ni Schottky diodes. We found that the PC signal acquired along a defect can give information on its spatial distribution in depth. The minority carrier lifetime has been also estimated and its dependence on the emission wavelength has been determined for several stacking faults.

Correlations between Crystal Quality and Electrical Properties by Means of Simultaneous Photoluminescence and Photocurrent Analysis

In this paper we have studied the connection between crystal quality and electrical transport in 4H-SiC by simultaneous micro-photoluminescence (μPL) and micro-photocurrent (μPC) measurements. We have used a focused HeCd laser at 325nm (i.e. above bandgap) to measure with a spatial resolution of few microns both the μPL spectra and the I-V characteristics in 4H-SiC/NiSi Schottky diodes. We found that extended defects exhibiting a photoluminescence peak located at 2.9eV (i.e single Shockley or bar shaped stacking faults) can produce an increase of the measured PC whereas other defects, such as the (4,4) stacking fault, can be considered as ‘killer defects’, strongly reducing the photocurrent.

Preparation and Photoluminescence of Fe-Doped In2O3 Nanowires

Fe-doped In2O3nanowires were synthesized on an Si substrate with the deposited Au layer by a CVD method and characterized by XRD, SEM, TEM , the PL measurement was performed using HeCd laser excitation at 325 nm. Fe-doped In2O3nanowires preferentially grow along the [10 direction The PL spectra of the Fe-doped In2O3nanowires show an ultraviolet (UV) emission and a blue emission. The property of PL of the Fe-doped In2O3nanowires are discussed.

Photoreflectance of AlGaN/GaN Heterostructure Measured by Using Mercury Lamp as Pump Beam

Photoreflectance (PR) spectra of a GaN thin film and an AlGaN/GaN heterostructure were measured by using a HeCd laser or a mercury lamp as a pump beam. The wavelengths (λ) of the HeCd laser and the mercury lamp are 325 nm and 253.7 nm, respectively. The energy of the HeCd laser is lower than band-gap energy of AlxGa1-xN (x > 0.2), so electron-hole pairs cannot be generated in the AlGaN layer. Hence, the PR of the AlGaN was measured by using Argon ion laser (λ =300 nm) or quadrupled Nd:YAG (λ =266 nm) rather than HeCd laser in the previous works. In this work, the mercury lamp was used as the pump beam. Although the mercury lamp is a diffused source, it is not a hindrance to the PR measurements. The signal to noise ratio is improved by using defocused pump and probe beams in the PR measurement.

Defects in Irradiated ZnO Thin Films Studied by Photoluminescence and Photoconductivity

Pulsed-laser-deposited ZnO thin films were exposed to a 1.5 MeV helium ion beam to study the changes in radiative and non-radiative recombination. We first measured photoluminescence (PL) spectra at 4.2 K excited with the 325 nm line of a HeCd laser. The as-deposited films showed a donor-bound exciton peak at 3.3567 eV attributed to Zn interstitials. After irradiation the donor-bound-exciton dominated PL spectra shifted to acceptor-bound behaviour with a signal at 3.3519 eV, tentatively attributed to Li or Na acceptors. In contrast to the approximately 30 % decrease of the PL signal near the band edge, we observed a strong concomitant enhancement of the green/orange PL band, located between 2.1 eV and 2.8 eV, by a factor of over 4. Candidates for those transitions are Li impurities and/or O vacancies. For comparison, the steady-state photocurrent decreased strongly in the irradiated region, which can also be attributed to increased non-radiative recombination through oxygen-related defects.

LUMINESCENT PROPERTIES OF SOL-GEL DEPOSITED Eu:TiO2 THIN FILMS

In this work we show the results on tile growth and optical characterization of TiO 2 thin films doped with Eu atoms. Eu:TiO2 films were grown at room temperature with different Eu concentrations by sol-gel on Si Corning glass substrates. A different crystalline structure is developed for the films deposited on Corning glass than those deposited on Si as observed from x-ray diffraction experiments. Room and low temperature photoluminescence (PL) was measured by using two different lines (325 and 442 nm) of a HeCd laser. A strong PL signal associated to the 5 D 0→7 F 2 transition from Eu +3 was observed. A better emission was obtained from those films deposited on Si substrates, Finally, the evolution of the PL signal is studied when the samples are annealed at different temperatures in O 2 atmosphere.