Optical Suppression of Defect-Related Photoluminescence in GeSn

We report on studies of sub-bandgap defect related photoluminescence (DRL) signals originating from radiative recombination through traps in the bandgap of cooled mono-like silicon wafers. Spectrally resolved photoluminescence (SPL) and multivariate curve resolution (MCR) have been used in combination, to study the behaviour of sub-bandgap photoluminescence (PL) emissions in wafers cut from different heights in a pilot-scale mono-like silicon ingot. No DRL signals were found in the main mono-like body. Strong defect related sub-bandgap emissions correlating with heavily dislocated areas, are found directly above some of the seed junctions. The DRL signal exhibits a correlation with the number of axis with small angle misalignment in the junctions of the seeds. The signal conventionally labelled D1 (0.80 eV) decreases with ingot height. A mechanism relating this signal to oxygen is proposed. The signals D3 (0.94 eV) and D4 (1.00 eV) are found to co-occur, supporting previous studies, and similarly to the D2 (0.87 eV) signal, their strength is found to increase with ingot height. As the content of the transition metal impurities in the ingot is supposed to increase with height, this supports a reported link between the D3 and D4 signals with Fe, as well as a link between D2 and other impurities. An emission previously found in multicrystalline material and labelled D07 (0.70 eV), is found to solely exist as the only DRL signal recorded by us in parasitic crystals, growing into the main mono-like ingot from the crucible walls. This contradicts the common notion that the D1–D4 signals are strongly related to, and always follow dislocations. Total photoluminescence spectrum (right) and distribution (left) of the PL signal with centre energy 0.70 eV emanating from the parasitic crystals growing into the bulk mono-like Si crystal from the crucible walls.

Defect related photoluminescence in Si wires

Role of silver doping on the defects related photoluminescence and antibacterial behaviour of zinc oxide nanoparticles

The Ni1−xAlxO (x = 0.05) nanocrystalline synthesized by chemical route using sol gel method calcined at 600 °C. Scanning electron microscopy (SEM) has been carried out to study the morphology for our sample. In addition, UV-visible spectroscopy has been carried out to determine the optical band-gap energy (3.92 eV) via Tauc model with associated Urbach (EU) energy (1.78 eV) that confirms the increased disorder with Al (x=0.05) incorporation into NiO lattice. The deconvoluted PL spectrum using Gaussian function of sample exhibits violet and green emission when NiO is doped with Al (x=0.05) which are indicative of Ni interstitial (Nii) and oxygen vacancy (Vo), respectively.

Band gap tuning of Ga2O3–Al2O3 ceramics

Structural and optical studies of gamma irradiated N-doped 4H-SiC

Zinc oxide (ZnO) has been attractive for optoelectronics application due to its wide band gap (E <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</inf> =3.37 eV) and large exciton binding energy (~60 meV) characteristics. However, p-type doping of ZnO is still controversial and problematic. Therefore, there is considerable interest in fabrication of n-ZnO/p-GaN heterojunction LEDs. In this work, we fabricated the LEDs consisting of n-ZnO nanorod arrays on p-GaN substrate. ZnO nanorod arrays were fabricated by a hydrothermal method. Hydrothermal methods have the advantage that they are simple, inexpensive and environmentally friendly. However, nanorods fabricated by hydrothermal methods typically have large numbers of defects due to the low growth temperature (90 °C). The defect related photoluminescence (PL) is significantly affected by annealing, and under suitable conditions it can be entirely eliminated. As- grown nanorods exhibit UV emission and large yellow defect emission which is likely due to the presence of OH groups. The PL spectra can be significantly improved by annealing the nanorods at 200 °C under Ar flow. Therefore we investigated the influence of argon annealing of ZnO nanorods on the performance of ZnO/GaN LEDs, as well as the influence of annealing environments. Devices with ZnO rod length ~ 250 nm were fabricated and the results obtained are discussed.

In this article, the thermal neutron irradiation (NI) effects on the structural properties of n-4H–SiC and electrical properties of Al/n-4H–SiC Schottky contacts have been reported. The noticeable modifications observed in the irradiated samples were studied by using different techniques. The X-ray diffraction studies revealed a decrease in the lattice parameter of the irradiated samples due to isotopic modifications and irradiation-induced defects in the material. As a result, the energy bandgap, Urbach energy, longitudinal optical phonon‒plasmon coupling mode, free carrier concentration, defect related photoluminescence and nitrogen bound exciton photoluminescence bands were prominently affected in the irradiated samples. The current–voltage characteristics of neutron irradiated Al/n-4H–SiC Schottky contacts were also strikingly affected in terms of zero-bias offset as well as decrease in the forward current. These modifications along with the increase in the Schottky junction parameters (such as ideality factor, Schottky barrier height and series resistance) were attributed to neutron-induced isotopic effects and decrease in the free carrier concentration due to induced defect states.

Radial distribution of some defect-related optical absorption and PL bands in silica glasses

Photoluminescence and electrical characterization of SiGe/Si heterostructures grown by rapid thermal chemical vapour deposition

Enhancement of the UV photoluminescence emission of sol–gel synthesized tin oxide nanoparticles is achieved by a combination of thermal annealing and Co doping. The UV as well as the defect-related visible photoluminescence are correlated to the structural characteristics and surface Sn(OH)2 content. The nanoparticle structure, size, crystallinity, and Sn(OH)2 content are monitored by a combination of X-ray diffraction, transmission electron microscopy, and Raman spectroscopy. In the undoped powders, a suitable annealing leads to a significant UV luminescence at around 365 nm. After doping with Co and annealing, the UV emission is further enhanced. The improvement in the UV emission intensity following annealing and Co doping of SnO2 is demonstrated to be due to a reduction in the hydroxyl content. The defect-related broad visible photoluminescence (∼400–650 nm) can be deconvoluted into three bands at around 440 nm (blue), 510 nm (green), and 600 nm (orange). The green emission is related to Sn(OH)2 determined by Raman spectroscopy. The blue and orange emissions are attributed to oxygen vacancies.

The photoluminescence (PL) of InAlAs grown on InP has been studied in a wide range of temperatures and excitation intensities. A novel emission ascribed to the presence of defects has been found by about 120–180 meV below the near band edge (NBE) line. The novel wide PL band is observed in the spectra only in a limited range of temperatures of 50–160 K, and is seen neither at liquid helium nor at room temperatures. The analysis of the PL behaviour with sample temperature and excitation power together with non-stationary PL kinetics allows us to conclude that both the NBE PL and the novel PL band are controlled by transitions via states of band tails formed due to alloy disorder in these films. The NBE PL is caused by recombination of carriers in the band tails, while deep levels related to defects and located in the same regions as the deepest band tail states are supposedly involved in the defect-related PL transitions. We demonstrate that no defect-related PL is found in the spectra if quasi-stoichiometric growth conditions were used during film growth, which resulted in a PL efficiency by about 1–2 orders of magnitude greater than that of samples grown under more common As-rich conditions.

In this study, ZnO nanorods (NRs) are grown on the ZnO seed layer incorporating carbon nanotubes (CNTs). Field emission scanning electron microscope (FESEM) and transmission electron microscope (TEM) images show that CNTs are well distributed in the seed layer. X-ray photoelectron spectra (XPS) reveal the enhancement of oxygen defect-related chemical bindings and photoluminescence (PL) spectra show the increase of defect-related PL intensity. The enhanced oxygen defects for ZnO NRs on CNT-incorporated seed layer improve the electron concentration and the conductivity after light/gas sensing; as a result, the light/gas dual-sensing behaviors for CNT-incorporated ZnO NRs sensor are boosted. Owing to steady response, simple fabrication, and compact size, light/gas dual-sensing chips with ZnO NRs on CNT-incorporated seed layer are promising for ultraviolet (UV) light and gas detection.

Optical properties of high-quality ZnO thin films grown by a sputtering method

Optical and electrical evaluations of SiGe layers on insulator fabricated using Ge condensation by dry oxidation