The increase in the world’s demand for energy, and the fact that at one point we will run out of oil and gas which are two major contributers of the world supply of energy toady, are two reasons for why new and reliable energy sources are needed. The solar industry is one of the fastest growing industires, but the price of energy delivered by solar cells is still too high compared to other alternatives. More research is therefore needed in order to drive the price of solar energy down.In this report seven silicon nitride films with different stoichiometry are deposited on silicon substrate by the plasma enhanced chemical vapor de- position (PECVD) method. The deposition conditions are selected in order to enhance the formation of silicon nanoclusters. Silicon nanostructures have interesting properties due quantum effects observed at these dimensions. The most interesting of these properties is the ability to tune the silicon nanos- tructures to absrob ligth at different wavelengths. High energy light cannot be utilized in silicon solar cells. With the application of silicon nanostruc- tures, this light can be absorbed and down-converted to usable light which is then transmitted into the solar cell. This would increase the efficiency of the soalr cell, which results in cheaper energy. Two ensembles of as-deposited and annealed (annealed at 1050◦ C) samples were characterized with dif- ferent techniques in order to find the thickness, composition, light emitting sources and optical constants of the films. The techniques used were ellipsom- etry, photo-luminescence (PL) and transmission electron microscopy (TEM).The results obtained shows that all films are porous (indicated by the low index of refraction). One of the effects of annealing is an increase in the refractive index for all samples, which is an indication that the films have become more compact as a result of the annealing process. PL is obtained for samples with a high flow of ammonia, while samples of a low flow have little or no PL. The annealing process increase the PL observed for samples with a high ammonia flow, while a reduction is observed for the samples with a low flow. TEM images reveals that only one sample has any nanostructures present, so the observed PL is likely related to defect states.

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.