Kc Heasman

Characteristics of rare-earth element erbium implanted in silicon

Rare‐earth element erbium implanted into silicon was studied by photoluminescence and Rutherford backscattering analysis. Two sets of luminescent bands related to the weakly crystal field split spin‐orbit levels 4I13/2→4I15/2 of Er 3+ (4f 11) at different lattice sites having different symmetries were observed.

Influence of the barriers on the temperature dependence of threshold current in GaAs/AlGaAs quantum well lasers

Using window devices, light emission has been observed from the barrier regions of lasers with 25-A-wide quantum wells. From measurements of threshold current as a function of temperature on devices grown by molecular-beam epitaxy using different Al cells for the barriers, the strong influence of nonradiative barrier recombination processes on the threshold current has been demonstrated. Further measurements of threshold current as a function of hydrostatic pressure show that recombination from the L and X conduction-band minima makes an important contribution to the current. The calculations show how the temperature dependence of threshold depend on factors such as cavity length and the number of quantum wells. >

Lattice locations of erbium implants in silicon

Abstract The lattice locations of erbium implanted in silicon were studied by backscattering angular scanning in combination with photoluminescence measurements. The results show that the positions of erbium implants depend on annealing conditions and have tetrahedral and/or orthorhombic symmetries in different cases.

Calculations of the threshold current and temperature sensitivity of A (GaIn)As strained quantum well laser operating at 1.55 μm

Abstract In order to illustrate the benefits to lasers of reducing the effective mass for holes, we consider 40A wide strained Ga0.33In0.67As wells in Ga0.71In0.29As. This system meets the experimentally determined criteria for good quality growth and the top of the valence band is shown to be light-hole-like (m∗ = 0.087) over more than 2kT at room temperature. The band-gap corresponds to 1.55 μm operations but it is shown that the standard loss mechanisms of Auger recombination and intervalence band absorption are greatly reduced compared to the bulk. A threshold current density of Jth = 165 A cm−2 and a To of 104K can be achieved in a separate confinement laser with 4 wells. Increasing the number of wells increases both Jth and To. Analytical expressions are derived for the optimum threshold current density and number of wells in such structures.

The achievement of 20% efficiency in a CZ silicon solar cell under concentration

The laser grooved, buried grid solar cell made in a production facility with silicon CZ wafers had previously demonstrated efficiencies of over 18% at 19/spl times/ concentration. Recent work has succeeded in reducing the cell series resistance and efficiencies of 20.1% (38 cm/sup 2/) at 10 Suns and 19.8% at 20 Suns have been achieved. Efficiency in the best solar cell has been maintained to over 18% at 40/spl times/.<<ETX>>

Concepts for the manufacture of silicon solar cell modules for use in concentrating systems up to 5/spl times/

The use of low-level concentration up to 5/spl times/ offers the possibility of reduced system cost for larger photovoltaic (PV) systems with more efficient use of silicon. Modifications of standard one-Sun laser grooved buried grid (LGBG) cells are described together with the development of cell and interconnection and packaging arrangements to give low cell operating temperatures and low series resistance under concentration. Field tests on a cost effective PV receiver design are given.

Investigation of thin aluminium films on the rear of monocrystalline silicon solar cells for back surface field formation

The trend to thinner crystalline silicon wafers in the production of silicon solar cells instigates a re-evaluation of the back surface field (BSF) formation. Aluminium layers, whose thickness is typically over 10 /spl mu/m, are commonly used for BSF formation. Such thick films, however, cause severe warping on thin solar cells (<250 /spl mu/m). This study investigates the use of thin Al films of between 0.1 and 2.0 /spl mu/m and focuses on the aluminium/rear surface structure after sintering in a mixed nitrogen and oxygen gas atmosphere at temperatures between 820/spl deg/C and 995/spl deg/C. It is shown that the rear surface morphology has a strong influence on the reaction of Al with Si. Secondary electron and focused ion beam microscopy reveal that thin Al layers form Al islands on smooth surfaces but the Al agglomerates at the apex of pyramids when the surface is textured. In both cases the Al dissolves the Si rear surface inhomogeneously. The structural results are correlated with electrical measurements of laser grooved buried contact solar cells. The correlation shows increasing short circuit current with increasing Al film thickness. The results are used to explain deviations of the standard theory of the Al:BSF formation when using thin Al films.

Solar cells design for low and medium concentrating photovoltaic systems

The solar cell is the key element of any CPV system, and its design plays an important role in enhancing the performance of the entire system. Special types of cells are required in the CPV systems capable of operating at high concentrations and elevated temperatures. These Concentrator solar cells differ significantly from the usual solar cells in the method of manufacture, the overall cell design and their performance. Systematic design and manufacture of the cell ensures better performance in a given CPV system. A number of factors come into play while designing the solar cell for a specific system these include concentration, cell material properties, expected operating temperature, shape, bus bar configuration and finger spacing. Most of these variables are decided on based on some rules of thumb and PC1D calculations. However, there is scope for design improvement and cell optimization by performing a detailed analysis based on the illumination profile incident on the cell. Recent studies demonstrat...

First results on the apollon project multi-approach for high efficiency integrated and intelligent concentrating PV modules (systems)

Next generation concentrating photovoltaic technologies could have a large-scale impact on world electricity production once they will become economically attractive and grid parity will be reached. To proceed towards this important goal, a new large integrated project, APOLLON, has started in July 2008, within the frame of the 7th European Framework program, having the main objective of substantial decrease the Concentrating Photovoltaic (CPV) technology cost to a target value of 2 Euro/W. This ambitious objective is targeted to be reached after five years of research and technological activities in which, both ¿point focus¿ and ¿dense array¿ CPV technologies will be implemented by facing all the technology-critical issues related to each component of the CPV systems. With this contribution we report the principal results obtained during the first year of the project regarding Multi-Junction (MJ) solar cells, concentrator optics, assembling, tracking and testing.

Prospects for high efficiency silicon solar cells in thin Czochralski wafers using industrial processes

Lower PV systems cost can be achieved if less silicon material is used in modules and if higher solar cell efficiencies can be achieved cost effectively. In this study the efficiency limits of mass production high efficiency laser grooved buried grid solar cells have been modelled for thinner and thinner wafers. PC1D modelling has been coupled with a 3D ray tracing simulation RAYN to predict cells performance. Given suitable surface passivation, light trapping and minority carrier lifetime, solar cell efficiency can actually increase with decreasing wafer thickness. Cells were made by the RP-PERC process, using thinned industrial grade Czochralski silicon wafers. Cells (4cm/sup 2/) of over 20% efficiency were fabricated in wafers with a final thickness of 115 /spl mu/m. Standard production LGBG cells had poor BSFs but on process optimisation nearly 17% efficiency were made in 140 /spl mu/m micron wafers on an industrial production line.