In this report we present an ab initio electronic-structure calculations of hydrogenated germanium cages Ge n H n TM (TM = Cu and Zn, n = 12 to 24) using density functional theory with polarized basis set (SDD) nanoclusters. In the first step of the calculation, geometrical optimizations of the nanoclusters have been done. In the next step only the ground state optimized geometries are used to calculate the binding energy (BE), HOMO-LUMO gap and embedding energy (EE) of the clusters. Based on these values a comparative study on different doping and also with respect to the pure cages are done. It is found that though the doping with Cu can be taken favorable in the cages, but Zn is not.

We report on the energetic locations of the defects created by oxygen in nanocrystalline Si and the relationship between defects and minority carrier lifetime. The energy of the defects was determined using capacitance-frequency measurements, and the minority carrier lifetime was determined using reverse recovery measurements. We show that oxygen increases deep defect densities, with the defect densities being measured between 0.35 eV and 0.55 eV below the conduction band. It is found that oxygen-induced defects can be reduced and lifetime increased by compensating with B. The minority carrier lifetime is found to be inversely proportional to defect density and the capturecross section of holes is estimated to be $4 Â 10 À17 cm 2 . V C 2013 AIP Publishing LLC.It is well known that increasing oxygen content in nanocrystalline Si:H (nano Si) leads to increasing defect density 1-3 and a loss of device performance, 2 with significant losses in quantum efficiency, current, voltage, and fill factor as oxygen content increases. 2 There is also some evidence that doping density in the materials increases as the oxygen content increases. 2 Oxygen is an ever-present impurity because most films and devices are grown using plasmaassisted chemical vapor deposition (PECVD) techniques and the plasma also decomposes oxygen molecules into O, which then readily gets into the Si lattice. In crystalline Si, O is known to introduce energy states at $0.38 and 0.55 eV below the conduction band. 4 There has been some debate about whether oxygen in nano Si is in the amorphous matrix which surrounds nano Si, or within the grain itself. To resolve this issue, it is necessary to find out the energetic location of O centers in this material. In this paper, we report on such a measurement. We also measure minority carrier (hole) lifetime in nano Si samples and show that the lifetime is inversely related to the total defect density. From the relationship between lifetime and defect density, we can estimate the capture cross-section of O induced centers. We also show that compensation with B leads to passivation of O induced defects in this material.The samples were p þ -n-n þ devices, deposited on planar stainless steel foil, using PECVD from a mixture of silane and hydrogen. 5-7 To avoid cross-contamination, the middle n-layer was deposited in a reactor which was not contaminated with either P or B. Typical growth temperatures were $250 C, and growth pressure $100 mT. 5 The crystallinity of the material was measured using Raman spectroscopy 8 and was kept approximately constant independent of thickness by using a graded hydrogen dilution profile. 9 The ratio of crystalline to amorphous phase was approximately 1:1. The oxygen content of the samples was varied by introducing ppm levels of oxygen from an 108 ppm oxygen diluted in helium mixture and controlling the flow rate of this mixture.Care was taken to maintain the same crystallinity in the devices when the flow of He was varied to introduce different levels of oxygen.The energetic location...

We report on the measurement of defect densities and minority carrier lifetimes in nanocrystalline Si samples contaminated with controlled amounts of oxygen. Two different measurement techniques, a capacitance-frequency (CF) and high temperature capacitancevoltage techniques were used. CF measurement is found to yield noisy defect profiles that could lead to inconclusive results. In this paper, we show an innovative technique to remove the noise and obtain clean data using wavelet transforms. This helps us discover that oxygen is creating both shallow and deep/midgap defect states in lieu with crystalline silicon. Minority carrier lifetime measured using reverse recovery techniques shows excellent inverse correlation between deep defects and minority carrier lifetimes through which hole capture cross section can be evaluated.

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