Comparison of AlxGa1-xN films grown on sapphire by MBE underN-rich and Ga-rich conditions

Al{sub x}Ga{sub 1-x}N layers grown under N-rich and Ga-rich conditions were investigated using transmission electron microscopy (TEM) and photoluminescence (PL). Despite a high density of threading dislocations ({approx}10{sup 10} cm{sup -2}) these layers had high PL quantum efficiencies. Both, TEM and PL studies showed significant differences between layers grown under N- and Ga-rich conditions. The results indicate that edge dislocations do contribute to nonradiative recombination in Al{sub x}Ga{sub 1-x}N layers

Photoluminescence from structural defects in GaN

We studied optical manifestation of structural defects in unintentionally doped GaN. A series of sharp peaks (labeled as Yi with i=1,2,y,11) was observed in the low-temperature photoluminescence spectrum in the photon energy range between 2.6 and 3.46 eV. We attribute the majority of these peaks to excitons bound to yet unidentified structural defects. A preliminary transmission electron microscopy study in one of the samples exhibiting strong Yi lines revealed numerous inclusions, presumably inversion domains, which may be responsible for at least some of the Yi lines

Comparison of AlxGa1-xN films grown on sapphire by MBE under N-rich and Ga-rich conditions

Al{sub x}Ga{sub 1-x}N layers grown under N-rich and Ga-rich conditions were investigated using transmission electron microscopy (TEM) and photoluminescence (PL). Despite a high density of threading dislocations ({approx}10{sup 10} cm{sup -2}) these layers had high PL quantum efficiencies. Both, TEM and PL studies showed significant differences between layers grown under N- and Ga-rich conditions. The results indicate that edge dislocations do contribute to nonradiative recombination in Al{sub x}Ga{sub 1-x}N layers

Recombination at surface states in GaN

We have studied radiative and nonradiative recombination at surface states in GaN, including as-grown samples and those treated with acids or bases. The surface states manifested themselves in two ways: (i) a reversible increase of the photoluminescence (PL) intensity after ultraviolet (UV) illumination in vacuum and (ii) appearance of new PL bands after treatment with acid or base and subsequent exposure to air. It has been established that the GaN surface physi-sorbs species from air (presumably oxygen) which induce surface states acting as nonradiative recombination centers. It has been found that nonradiative recombination of photogenerated carriers via surface states comprises more than 70% of the recombination in some GaN samples. Another type of the surface state, which participates in radiative recombination, has been found in GaN samples with Ga polarity after brief etching of the surface with hot acid or base and subsequent exposure to air. In such samples, a broad PL band emerges in the blue region of the spectrum at low temperatures. The blue band has been attributed to transitions of photogenerated electrons from donors in the near-surface depletion region to the surface states introduced by the above-mentioned procedure. The changes in the GaN surface caused by etching were examined by atomic force microscopy. In some samples the blue band appeared even when no evidence of the layer etching was found except for quite shallow etch pits formed at dislocation sites. The emerging blue band can be related to the surface states formed on the a-planes of etch pits

Loop-mediated isothermal amplification (LAMP) method for fast detection of Campylobacter spp in meat food products and environmental objects of a processing plant’s

There is constant necessity of developing the accurate and fast methods for detection of foodborne pathogens. Microorganisms of Campylobacter genus are one of the main causes of foodborne diseases worldwide. Fast identification of Campylobacter at all stages of the food life cycle is an efficient strategy to control foodborne campylobacteriosis. This article the authors evaluated a commercial loop-mediated isothermal amplification (LAMP) system with bioluminescence, called as the 3M™ Molecular Detection Analysis (MDA), which was used to find Campylobacter in food products with the help of a certain standard method, which is referred to as the reference method. The results of this study showed that the commercial LAMP based method is as efficient as the reference method, and features high specificity and minimum determinability (sensitivity). The LAMP based method has been shown to be a fast and reliable method for detection of Campylobacter spp. scarce presence (10 CFU/25 g) in meat, meat products, as well as carcass swabs and production facilities’ environment. The LAMP analysis required about 24-27 hours to achieve a result. However the LAMP based method will facilitate the detection of Campylobacter, as it provides much easier and faster detection of Cam pylobacter spp., including Campylobacter jejuni/Campylobacter coli, than standard microbiological methods. The LAMP based method is an efficient tool to prevent the spreading of Campylobacter spp. contamination in food products

Electrical, structural and optical characterization of free-standing GaN template grown by hydride vapor phase epitaxy

Electrical, structural, and optical properties of a free-standing 200 lm thick n-type GaN template grown by hydride vapor phase epitaxy have been investigated. Hall mobilities of 1100 and 6800 cm2/V s have been obtained at room temperature and 50 K, respectively. Quantitative analysis of acceptor concentration, donor concentration and donor activation energy has been conducted through simultaneous ®tting of the temperature dependent Hall mobility and carrier concentration data which led to a donor concentration of 2:10 1016 cmÿ3 and an acceptor concentration of 4:9 1015 cmÿ3. The resultant donor activation energy is 18 meV. The analysis indicates that the dominant scattering mechanism at low temperatures is by ionized impurities. The extended defect concentrations on Ga- and N-faces were about 5 105 cmÿ2 for the former and about 1 107 cmÿ2 for the latter, as revealed by a chemical etch. The full width at half maximum of the symmetric (0 0 0 2) X-ray di\u80raction peak was 6900 and 16000 for the Ga- and N-faces, respectively. That for the asymmetric (10±14) peak was 10300 and 14000 for Ga- and N-faces, respectively. The donor bound exciton linewidth as measured on the Ga- and N-face (after a chemical etch to remove the damage) is about 1 meV each at 10 K. Instead of the commonly observed yellow band, this sample displayed a green band, which is centered at about 2.45 eV

Scanning tunnelling luminescence studies of nitride semiconductor thin films under ambient conditions

We have investigated the properties of a commercial light-emitting diode (LED) structure containing an InGaN single quantum well (SQW) by scanning tunneling luminescence (STL). Data was acquired under ambient conditions, i.e., in air and at room temperature, using our unique STL microscope with a novel light collection geometry. Scanning tunneling microscopy (STM) images revealed the presence of hexagonal pits in the structure, with STL images showing strong luminescence from these pits. The variation of STL intensity with bias voltage shows the STL threshold at --2.1 V is numerically similar to the peak position of the SQW luminescence band. A slight shoulder at --2.8V corresponds to the plateau of the delocalised absorption profile, observed in macroscopic measurements. The peak observed at --3.2 V is close to the observed GaN band edge emission