Magnus Karlsteen

Broadening of submonolayer CdSe sheets in CdSe/ZnSe superlattices studied by x-ray diffraction

We present x-ray diffraction studies of a CdSe distribution profile along the growth direction in CdSe/ZnSe submonolayer superlattices (SLs) grown by molecular beam epitaxy. The performed theoretical simulations show that the shape of both (004)- and (002)-reflection rocking curves is very sensitive to the vertical CdSe distribution around the intended deposition yplanes. In particular, broadening of the CdSe submonolayer insertions results in a decrease in SL (±1) and (±2) satellite intensities. Comparison of the simulations and experimental data allows us to conclude that CdSe sheets in the as-grown SL samples are asymmetrically broaden up to 5 monolayers.

Thermoexcited and photoexcited carrier transports in a GaAs/AlGaAs quantum well infrared photodetector

A study of the carrier transport performance of our quantum well infrared photodetector (QWIP) is carried out in this work. AlGaAs/GaAs QWIP devices were fabricated and characterized. Carrier transport between adjacent quantum wells are modeled by both the tunneling and thermoexcitation effects. The strengths of the two transport effects are quite small (tunneling is small due to thick barrier and thermoexcitation is small due to the low device working temperature). However the thermoexcitation effect dominates in our QWIP devices and the thermally activated carriers transport across the optical active multiple quantum well (MQW) region in the three-dimensional drift-diffusion manner. At zero bias the energy band structure of our sample is almost at a condition of flat band. Due to the thick multiple quantum well region and the high doping levels in the contacts, the external bias largely applies linearly across the MQW region. Current increases with increasing bias and it becomes saturated when the drift...

Hexagonal InN/sapphire heterostructures: interplay of interface and layer properties

Abstract Formation of an AlInN interface transition layer in plasma-assisted molecular beam epitaxy (PA MBE) of InN/Al 2 O 3 (0001) structure has been found by high-resolution X-ray diffraction (XRD), transmission electron microscopy (TEM), secondary ion mass-spectroscopy (SIMS) and optical transmission techniques. Having a thickness of below 100 nm, an Al content of ∼0.3 and rather sharp interfaces, the interlayer improves the quality of the main InN film, allowing its high-temperature growth without In droplet formation. XRD Θ -rocking curves width of 350 arc sec, Hall mobility of 600 cm 2 /V s (300 K) at electron concentration of around 10 20 cm −3 have been achieved for the best InN epilayer. Employed initial growth stage affects significantly the quality of both the AlInN interface layer and the InN layer.

Copper allergy from dental copper amalgam

A 65-year-old female was investigated due to a gradually increasing greenish colour change of her plastic dental splint, which she used to prevent teeth grinding when sleeping. Furthermore, she had noted a greenish/bluish colour change on the back of her black gloves, which she used to wipe her tears away while walking outdoors. The investigation revealed that the patient had a contact allergy to copper, which is very rare. She had, however, had no occupational exposure to copper. The contact allergy may be caused by long-term exposure of the oral mucosa to copper from copper-rich amalgam fillings, which were frequently used in childhood dentistry up to the 1960s in Sweden. The deposition of a copper-containing coating on the dental splint may be caused by a raised copper intake from drinking water, increasing the copper excretion in saliva, in combination with release of copper due to electrochemical corrosion of dental amalgam. The greenish colour change of the surface of the splint is probably caused by deposition of a mixture of copper compounds, e.g. copper carbonates. Analysis by the X-ray diffraction technique indicates that the dominant component is copper oxide (Cu2O and CuO). The corresponding greenish/bluish discoloration observed on the back of the patients gloves may be caused by increased copper excretion in tears.

Fine structures of photoresponse spectra in quantum well infrared photodetector

We study the fine structures in the photoresponse spectra of GaAs/AlGaAs quantum well infrared photodetectors and the influences from γ irradiation (1-16 Mrad), rapid time annealing (800, 850 and 900 °C for 30 s) and ion implantation (450 keV 0.7×, 1.0× and 5.0×1015 cm−2). With the theoretical analysis a ±-monolayer change has been concluded in the well width of the as-grown GaAs quantum wells in our photodetector. The γ irradiation decreases the carrier lifetime (the relaxation energy Γ increases with the irradiation dose α in the manner of Γ∝α1.5), while the rapid thermal annealing and ion-implantation processes enhance the Al diffusion across the GaAs/AlGaAs heterointerfaces the relaxation energy increases at the same time.

A novel technique for direct measurements of contact resistance between interlaced conductive yarns in a plain weave

Contact resistance between interlaced conductive yarns will under certain circumstances constitute a problem for sensor applications and electrical routing in interactive textile structures. This type of resistance could alter the effective area of the sensor and introduce hot-spots in the routing. This paper presents a technique for measuring contact resistances on fabric samples. The samples used are unit cells of plain weave, that is, two conductive (silver-coated) yarns in the warp direction and two in the weft direction. The numerical values for the contact resistance are of the order of Rc ≈ 0.3 Ω. A resistor network made of through-hole film resistors with known values is used for evaluation of the method. The results show that the technique provides values typically within ±1% error compared with the known resistor values. Thus, the method can be used in order to calculate the contact resistances of a woven conductive textile.

Characterization of strain relaxation in low-defect-density thin single and step-graded germanium buffer layers by high-resolution two-dimensional x-ray diffraction mapping

Double-crystal x-ray diffraction rocking curves and two-dimensional reciprocal space mapping (2D-RSM) are utilized to characterize the degree of strain relaxation, lattice parameters and assessment of defect propagation in two growth approaches to yield relaxed germanium buffer layers on silicon substrates. Two schemes are investigated: direct epitaxy of a single relaxed buffer layer (SE-RBL) and step-graded multiple relaxed buffer layers (GM-RBLs). The characteristics of these two growth schemes offer prospects of a much thinner grown layer compared with previously reported approaches. Two-dimensional reciprocal space mapping shows that an SE-RBL with a thickness of less than 0.35??m has a superior quality over the GM-RBLs. A high relaxation factor (R = 0.986?0.002) is obtained from the asymmetric (113) 2D-RSM of the SE-RBL with 100% Ge content. Further, the ratios of full width at half maximum of the layer to substrate FWHM (L/S) of nearly unity for both ? and ?/2? scan directions imply a very high-quality crystalline relaxed buffer layer is realized. The 2D-RSM of the material deposited using the GM-RBL scheme, the first of its kind regarding the total grown thickness (approximately 6??m), also show a mosaic final Ge buffer layer with an indication of reduction of dislocation density.

Spatial distribution of Cd in CdSe/ZnSe superlattices studied by X-ray diffraction

Abstract Double and triple X-ray diffractomery was used for a structural characterization of the short-period superlattices (SLs) CdSe/ZnSe with submonolayer sheets of CdSe. The multilayer structures containing SLs were grown by molecular beam epitaxy (MBE) on (001) GaAs substrates. The period of SLs was in range (30–60 A), the nominal thickness of CdSe sheets varied from 0.2 to 1.2 monolayer. The parameters of SLs have been determined. Broadening of CdSe sheets in direction normal to interface has been revealed. Full width at half maximum (FWHM) of this broadening is equal to about 4.5 monolayers and does not depend on the period and content of Cd in SLs.

Thermal depth profiling of materials for defect detection using hot disk technique

A novel application of the hot disk transient plane source technique is described. The new application yields the thermal conductivity of materials as a function of the thermal penetration depth which opens up opportunities in nondestructive testing of inhomogeneous materials. The system uses the hot disk sensor placed on the material surface to create a time varying temperature field. The thermal conductivity is then deduced from temperature evolution of the sensor, whereas the probing depth (the distance the heat front advanced away from the source) is related to the product of measurement time and thermal diffusivity. The presence of inhomogeneity in the structure is manifested in thermal conductivity versus probing depth plot. Such a plot for homogeneous materials provides fairly constant value. The deviation from the homogeneous curve caused by defects in the structure is used for inhomogeneity detection. The size and location of the defect in the structure determines the sensitivity and possibility of detection. In addition, a complementary finite element numerical simulation through COMSOL Multiphysics is employed to solve the heat transfer equation. Temperature field profile of a model material is obtained from these simulations. The average rise in temperature of the heat source is calculated and used to demonstrate the effect of the presence of inhomogeneity in the system.

Plasma-assisted MBE growth of GaN and InGaN on different substrates

We investigate structural and optical properties of GaN and InGaN on sapphire and neodymium gallate substrates, deposited by MBE using a novel RF and conventional ECR nitrogen activators. The GaN/NdGaO 3 layer demonstrates higher luminescence efficiency compared with GaN/Al 2 O 3 . Dislocation density in GaN/NdGaO 3 , estimated using X-ray diffraction measurements, is much less than that in the layers on sapphire substrate (the dominant vertical screw dislocation density is 10 4 or less). The layers demonstrate a direct correlation between the dislocation density and incorporation of oxygen and other contaminations determined by secondary ion mass spectroscopy measurements, with the lowest impurity concentration located in the GaN/NdGaO 3 epilayers. All the layers grown by the novel nitrogen source exhibit negligible yellow photoluminescence band independently of the substrate type.