A thin film photovoltaic solar cell having an opaque electrical contact which consists of a low-cost substrate, such as a metal alloy or a metallurgical grade crystalline silicon and a barrier layer which is optically reflective, a first semiconductor layer, a second semiconductor layer, a transparent electrical contact and an encapsulant.

A thin film photovoltaic solar cell and method of making the same

The origins of dislocations in GaP grown by liquid phase epitaxy (LPE) and their effects upon green electroluminescence (EL) efficiency have been investigated by chemical etch pitting and scanning electron microscopy. Under normal growth conditions, the dislocation etch pit density (ρD) and configuration in the epitaxial layers are controlled by, and are approximately the same as, that in the liquid encapsulated Czochralski substrate. All dislocations which are revealed by chemical etching in the p LPE layer cause a localized reduction in luminescence. The dislocations are shown to behave as regions of rapid (nonradiative) recombination. Typically, reductions of a factor of ∼2 in green EL efficiency occur when ρD for the LPE layers is in the ∼2–5×105 cm−2 range, corresponding to an average separation of about two to four diffusion lengths in this material. The experimental results are supported by a simple theoretical model for the effects of dislocations on EL efficiency. These considerations explain why...

Effect of dislocations on green electroluminescence efficiency in GaP grown by liquid phase epitaxy

High quality single crystal silicon-germanium-on-insulator has the potential to facilitate the next generation of photonic and electronic devices. Using a rapid melt growth technique we engineer tailored single crystal silicon-germanium-on-insulator structures with near constant composition over large areas. The proposed structures avoid the problem of laterally graded SiGe compositions, caused by preferential Si rich solid formation, encountered in straight SiGe wires by providing radiating elements distributed along the structures. This method enables the fabrication of multiple single crystal silicon-germanium-on-insulator layers of different compositions, on the same Si wafer, using only a single deposition process and a single anneal process, simply by modifying the structural design and/or the anneal temperature. This facilitates a host of device designs, within a relatively simple growth environment, as compared to the complexities of other methods, and also offers flexibility in device designs within that growth environment.

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Next Generation Device Grade Silicon-Germanium on Insulator

Group IV lasers are expected to revolutionize chip-to-chip optical communications in terms of cost, scalability, yield, and compatibility to the existing infrastructure of silicon industries for mass production. Here, we review the current state-of-the-art developments of silicon and germanium light sources towards monolithic integration. Quantum confinement of electrons and holes in nano-structures has been the primary route for light emission from silicon, and we can use advanced silicon technologies using top-down patterning processes to fabricate these nano-structures, including fin-type vertical multiple quantum wells. Moreover, the electromagnetic environment can also be manipulated in a photonic crystal nano-cavity to enhance the efficiency of light extraction and emission by the Purcell effect. Germanium is also widely investigated as an active material in Group IV photonics, and novel epitaxial growth technologies are being developed to make a high quality germanium layer on a silicon substrate. To develop a practical germanium laser, various technologies are employed for tensile-stress engineering and high electron doping to compensate the indirect valleys in the conduction band. These challenges are aiming to contribute towards the convergence of electronics and photonics on a silicon chip.

Group IV Light Sources to Enable the Convergence of Photonics and Electronics

The doping dependence of the bulk efficiency for both n‐ and p‐type GaP:N has been investigated experimentally and theoretically. Experimental data are presented for p‐type Zn,N‐doped, n‐type Te,N‐doped, and n‐type S,N‐doped GaP over a majority‐carrier range 5×1016−2×1018 cm−3. The efficiency data and photoluminescent decay time data on the same samples are compared to a simple equilibrium model for the recombination kinetics in nitrogen‐doped GaP. The model predicts that the efficiency should scale linearly with the minority‐carrier lifetime, majority‐carrier concentration, and the nitrogen concentration in the doping range considered. The comparison of the theoretical results with the experimental data shows that the bulk efficiency of p‐type material agrees quantitatively with the analytical prediction. For Te‐ and S‐doped material, which have widely different and varying minority‐carrier lifetimes, the bulk efficiency of n‐type material is shown to depend linearly upon the minority‐carrier lifetime ov...

Kinetics of recombination in nitrogen‐doped GaP

A single‐step liquid phase epitaxy process has been developed for the growth of efficient green light‐emitting diodes (LED's), in which all doping is accomplished from the vapor phase. The use of vapor‐phase doping increases the flexibility of the LPE process since junction formation and control of doping profiles is accomplished by regulating the composition and flow rates of the doping gases. This method has been applied to multislice growth on large area substrates (up to 38 mm in diameter). Thin melts and nearly complete utilization of the GaP initially dissolved in the melt minimize the gallium usage. Encapsulated LED's with efficiencies in the 0.10–0.15% range at 7 A/cm2 are obtained routinely. These efficiencies are comparable to the highest values reported to date for low current operation. Efficiencies as high as 0.2% have been obtained at 7 A/cm2 using this method. The short deposition time for this single‐step method, reproducibility, multislice capability, and minimum gallium consumption make this method economically attractive for the high level production of efficient green LED's.

D. D. Roccasecca

Papers

Vapor‐Doped Multislice LPE for Efficient GaP Green LED's

Vapor-doped multislice lpe for efficient gap green led′s