Abstract:We report on the design, fabrication, and measurement of ultrathin film a-Si:H solar cells with nanostructured plasmonic back contacts, which demonstrate enhanced short circuit current densities compared to cells having flat or randomly textured back contacts. The primary photocurrent enhancement occurs in the spectral range from 550 nm to 800 nm. We use angle-resolved photocurrent spectroscopy to confirm that the enhanced absorption is due to coupling to guided modes supported by the cell. Full-field electromagnetic simulation of the absorption in the active a-Si:H layer agrees well with the experimental results. Furthermore, the nanopatterns were fabricated via an inexpensive, scalable, and precise nanopatterning method. These results should guide design of optimized, non-random nanostructured back reflectors for thin film solar cells.

There is currently worldwide interest in developing silicon-based active optical components in order to leverage the infrastructure of silicon microelectronics technology for the fabrication of optoelectronic devices. Light emission in bulk silicon-based devices is constrained in wavelength to infrared emission, and in efficiency by the indirect bandgap of silicon. One promising strategy for overcoming these challenges is to make use of quantum-confined excitonic emission in silicon nanocrystals. A critical challenge for silicon nanocrystal devices based on nanocrystals embedded in silicon dioxide has been the development of a method for efficient electrical carrier injection. We report here a scheme for electrically pumping dense silicon nanocrystal arrays by a field-effect electroluminescence mechanism. In this excitation process, electrons and holes are both injected from the same semiconductor channel across a tunnelling barrier in a sequential programming process, in contrast to simultaneous carrier injection in conventional pn-junction light-emitting-diode structures. Light emission is strongly correlated with the injection of a second carrier into a nanocrystal that has been previously programmed with a charge of the opposite sign.

The use of nonionizing energy loss (NIEL) in predicting the effect of gamma, electron and proton irradiations on Si, GaAs and InP devices is discussed. The NIEL for electrons and protons has been calculated from the displacement threshold to 200 MeV. Convoluting the electron NIEL with the "slowed down" Compton secondary electron spectrum gives an effective NIEL for C o a gammas, enabling gamma-induced displacement damage to be correlated with particle results. The fluences of 1 MeV electrons equivalent to irradiation with 1 Mrad(Si) for Si. GaAs and InP are given. Analytic proton NIEL calculations and results derived from the Monte Carlo code TRIM agree exactly so long as straggling is not significant. The NIEL calculations are compared with experimental proton and electron damage coefficients using solar cells as examples. A linear relationship is found between the NIEL and proton damage coefficients for Si, GaAs and InP devices. For electrons, there appears to be a linear dependence for n-Si and n-GaAs, but for p-Si there is a quadratic relationship which decreases the damage coefficient at 1 MeV by a factor of-10 below the value for n-Si. The present results greatly extend the range of environments for which damage calculations based on NIEL can be applied. The NIEL results are presented in tabular form for ease of calculation. * The threshold energies used were 21 and 12.9 eV for Si; 10 eV for Ga and As; 6.7 eV for In and 8.7 eV for P.

The method for predicting solar cell degradation in space radiation environments developed recently at the US Naval Research Laboratory (NRL) is compared in detail with the earlier method developed at the US Jet Propulsion Laboratory (JPL). Although both methods are similar, the key difference is that in the NRL approach, the energy dependence of the damage coef®cients is determined from a calculation of the nonionizing energy loss (NIEL) and requires relatively few experimental measurements, whereas in the JPL method the damage coef®cients have to be determined using an extensive set of experimental measurements. The end result of the NRL approach is a determination of a single characteristic degradation curve for a cell technology, which is measured against displacement damage dose rather than¯uence. The end-of-life (EOL) cell performance for a particular mission can be read from the characteristic curve once the displacement damage dose for the mission has been determined. In the JPL method, the end result is a determination of the equivalent 1 MeV electron¯uence, which would cause the same level of degradation as the actual space environment. The two approaches give similar results for GaAs/ Ge solar cells, for which a large database exists. Because the NRL method requires far less experimental data than the JPL method, it is more readily applied to emerging cell technologies for which extensive radiation measurements are not available. The NRL approach is being incorporated into a code named SAVANT by researchers at NASA Glenn Research Center. The predictions of SAVANT are shown to agree closely with actual space data for GaAs/Ge and CuInSe 2 cells¯own on the Equator-S mission.

After decades of process scaling driven by Moore's law, the silicon microelectronics world is now defined by length scales that are many times smaller than the dimensions of typical micro-optical components. This size mismatch poses an important challenge for those working to integrate photonics with complementary metal oxide semiconductor (CMOS) electronics technology. One promising solution is to fabricate optical systems at metal/dielectric interfaces, where electromagnetic modes called surface plasmon polaritons (SPPs) offer unique opportunities to confine and control light at length scales below 100 nm (refs 1, 2). Research groups working in the rapidly developing field of plasmonics have now demonstrated many passive components that suggest the potential of SPPs for applications in sensing and optical communication. Recently, active plasmonic devices based on III-V materials and organic materials have been reported. An electrical source of SPPs was recently demonstrated using organic semiconductors by Koller and colleagues. Here we show that a silicon-based electrical source for SPPs can be fabricated using established low-temperature microtechnology processes that are compatible with back-end CMOS technology.