A literature review of relevant luminescence spectra for silicon solar cell materials has been performed. Three multi crystalline silicon samples in particular has been the focus of attention, one electronic grade sample R6, and two solar grade samples ES1, and MH2, where MH2 has added chromium. A list of relevant luminescence spectra has been compiled, and can be found in the appendix.The samples was measured using low temperature micro photoluminescence. They where cooled down by liquid helium in a cryostat, and excited using a laser. Photoluminescence was captured by a camera mounted on a spectrometer. Noise components was measured and removed, but are subject to changes in between measurements, causing some unwanted artifacts to appear in the end result.Luminescence due to P and B doping atoms are identified in ES1, and MH2 as expected, and a weak boron bound exciton line is also present in the clean sample R6. R6 also show signs of having a carbon-carbon complex impurity forming at grain boundaries. Lines attributed to chromium boron pairs where not observed in MH2, presumably due to the lack of such pairs. ES1 exhibits a luminescence attributed to a higher quality material, than both MH2, and R6. Expected behavior is for R6 to have such traits, but this is not the case. The reason for ES1 to show this enhanced luminescence is not known. Lines attributed to dislocations are observed in all the samples, but consist of less intense peaks than expected.Local heating is a severe problem using micro photoluminescence. Bound excitons, impurity lines, and dislocation related lines, all loose intensity at higher temperatures. The intrinsic TO line also have a substantial broadening with respect to energies, suggesting that local temperatures are as much as 70K higher than the sample holder temperature, when exciting with 128 mW using a 2 µm spot diameter.

Over the recent years semiconductor nanowires have gained much attention for their potential to either improve existing technology or create novel devices. This potential has been realized in devices such as semiconductor nanowire lasers[2-3] and nanowire single-photon detectors[4]. With nanowire technology it could be possible to create single-photon nanowire lasers that emit photons in the near infrared region. Such devices should prove very interesting for telecommunications and quantum cryptography.The purpose of this master thesis was the study of the optical properties of GaAs nanowires with GaAsSb inserts. For this reason, both nanowires with and without an AlGaAs coating to increase the nanowire Quantum Efficiency (QE) have been subjected to low temperature PL spectroscopy. In an attempt to determine the physical origin of the different optical properties of different nanowires, µ-PL spectroscopy, Scanning Transmission Electron Microscopy (STEM) and Transmission Electron Microscopy (TEM) was carried out on the same nanowires of a sample with AlGaAs shell nanowires. Through these measurements, it was found that STEM at 30 kV did not change the optical properties of the nanowire, but 200 kV TEM had a detrimental effect on nanowire PL. Through the structurally and optically correlated examination, it was found that stacking faults near the insert was not the origin of the power dependent behavior of the insert emission, and in combination with PL measurements of both zincblende (ZB) and wurtzite (WZ) GaAs nanowires the electronic band structure of the nanowire inserts was determined to very likely be type-II. Also, a theoretical explanation of the origin of the observed insert emission behavior was presented, and polarization dependent PL measurements were presented and discussed.

One of the leading causes of death in the western world today is heart diseases, and atherosclerotic plaque that ruptures in the coronary arteries is believed to be one of the main causes of heart attacks.The Capacitive Micromachined Transducer has good acoustic matching with fluids, and is considered a good candidate for improving intravascular ultrasound diagnostics.Further evaluation and characterization of a CMUT operating in immersion has been the objective of this thesis, and it is a continuation of the work started in the project Characterization of Capacitive Ultrasound Transducers. The same CMUT have been studied in both, but a backing layer was added to it for the testing done during the work on this thesis.Pulse-echo measurements with the CMUT immersed in rapeseed oil have been performed, and there has also been conducted measurements to find the attenuation of the oil. The results from the attenuation measurements have then been employed to simplify the analysis of the pulse-echo measurements.Any definitive characteristics for the CMUT was not found during these tests due to disturbances in the frequency responses. This is suspected to be because of line resistances and parasitic capacitances in the system. This suspicion is supported by the findings from studying the impedance response of the system.The backing layer added to the CMUT have proved to be very effective in dampening the ringing effect on the pulses emitted by the CMUT. There have also been signs of unexpected alteration of the CMUTs frequency characteristics. One possible source of this is that the process of adding the backing layer have resulted in that the layer exerts force on the CMUT, and by this changing the tension of the membranes.

Characterize silicon wafers used in solar cell production with a NIR-LCI interferometer. The interferometer is further developed and measurements on silicon samples are carried out.

In this project, the growth parameters of Pulsed Laser Deposition are optimized in order to obtain a high quality interface between two complex oxides, LaAlO3 and SrTiO3. The prepared samples are compared by their sheet resistance, and the influence by the various growth parameters are investigated.The main finding is that reducing the laser fluence significantly lowers the sheetresistance. The lowest obtained sheet resistance was 81.2kohm. This value wasobtained with a laser fluence of 0.7 J/cm^2 and the results indicate that morecan be gained by going even lower. In previous work, a strong anisotropy of the sheet resistance has been observed. The anisotropy is further studied in this project and compared with the step-and-terrace topography at the interface. Atomic Force Microscopy is used to obtain the step directions and terrace widths, and these values are compared with resistance measurements. No correlation is found between these data. The results suggests that the anisotropy is due to other factors than the steps-and-terraces.

In the work with this master thesis, electron beam lithography (EBL) and other cleanroom methods was used to develop a reproducible process for making ohmic contactsto nanowires (NWs), with the aim of investigating different dopants’ influence ontheir physical properties. After optimizing the EBL process, good alignment of thecontact patterns to the NWs was achieved by doing a thorough alignment procedure.A detailed write field alignment close to the sample position prior to the 3-point alignment, along with consistent use of alignment positions, was found the be especially important to reduce misalignment.For surface treatment it is shown how a diluted HCl solution is used to removenative oxide on the NW surface, and how a solution of citric acid and hydrogen peroxidecan be used to effectively etch the AlGaAs shell of core-shell nanowires, thoughselective etching of AlGaAs on GaAs is difficult. Further, an ammonium sulphidesolution is used to passivate the surface prior to metal deposition.Metalization was done using an electron beam evaporator, however optimal thinfilms could not be achieved due to the presence of strain. This is believed to originate in the evaporation of electron beam resist (ER) during metal deposition due to high local heating of the samples. While this was remedied by, among other, depositing thinner films at high deposition rates, it could not be fully avoided. Nevertheless, satisfactory lift-off was still achieved in most cases.IV characterization of the different samples was done using a probing station. Thesamples generally display asymmetric and non-linear characteristics, indicating thatohmic contacts have not been achieved. Annealing tests was also done on a numberof samples, and while this generally resulted in more linear IV curves, the currentwas also reduced in most cases.

Intermediate band solar cells (IBSC) is a proposed new type of solar cell device that has an intermediate energy band in the band gap. One possible implementation of IBSCs is by using arrays of nano-sized semiconductor particles known as quantum dots (QDs). InAs QDs can be grown on GaAs by using molecular beam epitaxy (MBE). As a part of this growth process, an InAs wetting layer (WL) is formed on which the InAs QDs grow. One possible method of determining the WL thickness is by using x-ray diffraction (XRD), which is a non-destructive analysis technique used to extract information about the structure and composition of crystalline thin films.An InAs/GaAs bilayer sample grown by MBE was investigated. This sample was grown without rotation, meaning the thicknesses of the deposited layers are expected to exhibit a gradient across the sample. Based on the geometry of the MBE machine, the variation in deposited thicknesses across the sample was estimated to be ±3.4% for InAs and ±4.2% for GaAs. XRD rocking curve measurements were performed around the 004 reflection in thirteen different locations on this sample. LEPTOS software was used to simulate XRD curves, and these simulations were fitted to the XRD measurements by varying the thicknesses of the simulated InAs and GaAs layers. It was found that the GaAs thicknesses across the sample varied as expected, while the variation in InAs thicknesses was much larger than expected. It was also found that the measured thicknesses of the InAs layer were significantly thinner than the nominal value. This is a strong indication that there are QDs on the sample, and that only the WL of the QDs contributes to the x-ray curve.LEPTOS was also used to simulate several cases of alloying of an InAs/GaAs bilayer. It was found that if the entire InAs layer is segregated into an InAs/GaAs alloy, this causes the diffraction peaks to weaken as the InAs/GaAs interfaces become less abrupt. It was also found that intermixing causes a significant change in the XRD curve because the amount of GaAs in the InAs/GaAs bilayer structure increases.

P-type GaAs semiconducting nanowires (NWs) with NW/electrode contacts have been examined by fabricating single NW devices to investigate their electrical properties. Both NWs grown with Au-assisted and Ga-assisted vapor-liquid-solid (VLS) method have been examined, with great emphasis on Ga-assisted NWs because these show superior contact properties. The NWs were grown using molecular beam epitaxy (MBE) and electrical contacts were fabricated using electron beam litography, electron beam evaporation for metallization and annealing to enhance ohmic behaviour of the contacts. Two different types of contacts were tested. One was metal contacts where various combinations of metal layers were tested, including such metallizations as Pt/Ti/Pt/Au and Pd/Zn/Pd/Au. The second electrode type was graphene which is expected to show very interesting electric and optoelectronic properties.It is shown in this thesis that ohmic contact with linear I-V characteristics has been achieved by two different methods. The first being annealing of the NW contact after contact fabrication. The second is by increasing doping concentration during NW growth. It is also shown that Pt/Ti/Pt/Au metallization is the layer configuration that exhibits the best ohmic contact and the most consistency in electrical measurements. 4-probe measurements were also carried out to measure the intrinsic resistivity of the NW, which makes it possible to estimate its doping concentration and carrier mobility.NW/graphene contact was also tried.Mechanical exfoliation of kish graphite was performed to make high-quality graphene, which was selctively placed to make NW contact. However it is found that heating of the EBL-resist during e-beam evaporation caused the graphene to wrinkle and dissolve. CVD-grown graphene on Cu-foil was also tested. Inspection after the graphene transfer proved that the graphene that was used was incontinous and flaky making it difficult to obtain proper contacts to NWs. In addition the NWs connected to graphene probably suffered from over-etching due to multiple etching steps. Since a lot of efforts was put into obtaining a suitable measure of making NW/graphene contacts only preliminary measurements were conducted, so these results has yet to be verified.

A macro-photoluminescence study of self-catalyzed nanowires, using a specializedsetup for this purpose, has been performed. Several samples were even comparedto single nanowire micro-photoluminescence measurements, on the samesamples, done by other students in the nanowire group at NTNU. The macrophotoluminescence measurements were done by changing parameters such as temperature and excitation power. A 532 nm laser was used to excite the wires and thephotoluminescence was measured by a CCD detector attached to a spectroscope.Using macro-photoluminescence measurements in a qualitative comparison withmeasurements done on single nanowires by micro-photoluminescence spectroscopycan give the researcher a decent understanding of the quality of the sample and itscontributions to photoluminescence. Measurements done in this thesis show probablecontributions from most types of transitions expected in zinc-blende nanowires,consisting of such defects as dense zinc-blende/wurtzite heterostructures, highlytwinned regions, but also from nanowires of higher purity.As nanowires move closer to the realization of e.g. nanowire based solar cells,such macro-photoluminescence measurements will become increasingly importantin deciding the overall quality of the grown structures.

In this thesis, single zincblende GaAs nanowires grown by molecular beam epitaxy using the self-catalyzed approach were studied with m-photoluminescence spectroscopy in order to assess the optical quality of self-catalyzed GaAs nanowires grown for the first time at NTNU and to compare the optical properties of self-catalyzed GaAs nanowires with Au-assisted GaAs nanowires and bulk GaAs references. The low temperature and temperaturedependence measurements revealed type II recombinations between zincblende and wurtzite segments occurring at the nanowire tips, however it was established that radiative recombination does not take place in the zincblende GaAs nanowire core. As the thesis progressed, valuable feedback was given to the growers in order to optimize nanowire growth conditions. The thesis builds upon data from earlier work within this project andprovides a foundation for future work on self-catalyzed GaAs nanowire devices at NTNU.