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The concentrating photovoltaic system represents one of the most promising solar technologies because it allows a more efficient energy conversion. When a CPV system is designed, the main parameter which has to be considered is the concentration factor that affects both the system energy performances and its configuration. An experimental characterization of a CPV system previously realized at the University of Salerno, is presented in this paper considering several aspects related to the optical configuration, the concentration factor and the solar cell used. In particular, the parameters of an Indium Gallium Phosphide/Gallium Arsenide/Germanium triple-junction solar cell are investigated as function of the concentration factor determined by means of an experimental procedure that uses different optical configurations. The maximum concentration factor reached by the CPV system is 310 suns. The cell parameters dependence on the concentration is reported together with an electroluminescence analysis of the Indium Gallium Phosphide/Gallium Arsenide/Germanium cell. A monitoring of the electrical power provided by the system during its working is also presented corresponding to different direct irradiance values. A mean power of 2.95 W with an average efficiency of 32.8% is obtained referring to a mean irradiance of 930 W/m 2 ; lower values are obtained when the irradiance is highly fluctuating. The concentrating photovoltaic system electric energy output is estimated considering different concentration levels; the maximal obtained value is 23.5 W h on a sunny day at 310×. Finally, the temperature of the triple-junction solar cell is evaluated for different months in order to evaluate the potential annual thermal energy production of the concentrating photovoltaic system.

The effect of the electrical field on the conductivity of linear low-density polyethylene/carbon nanotubes/ (LLDPE/CNT) composites during temperature cycling has been investigated. Under applied voltage a positive resistivity temperature coefficient was observed during heating already at low (2–3 wt%) CNT content, followed by a large negative temperature coefficient during cooling whose value depends on the applied voltage. The resistivity values after thermal cycling were markedly lower, while they slightly increased in the absence of an electrical field. The effects of thermal cycling on structural and physical properties of the composites have been evaluated by X-ray diffraction and differential scanning calorimetry.

Human Body Model ESD tests on two commercially available different types of wavelength division multiplexing bidirectional optoelectronic modules, intended for data transmission over multimode optical fibers at 820 and 1320 nm wavelengths, have been performed. These bidirectional modules incorporated pin diode receivers and light emitting diode in a single package. In particular, the 820 nm light emitting diodes had rather high damage threshold pulse amplitudes of about +10,000 V under forward bias and −5000 V under reverse bias conditions, and no active layer degradation has been observed. In-situ measurements of the optical transients emitted during forward bias ESD pulses enabled a damage pulse threshold detection of a LED without the need of further optoelectronic characterization. The receiver photodiodes, however, were very sensitive to reverse bias ESD pulses. The InGaAs photodiodes degraded during ESD pulses with amplitudes as low as −150 V and in the case of the Silicon photodiodes as low as −175 V.

An overview over typical defects and reliability aspects regarding the operation of InGaAs InP avalanche photodiodes for the use in fiber-optic communication systems is given. Measurements regarding the performance and stability of different types of top illuminated InGaAs InP Separate Absorption Grading Multiplication avalanche photodiodes have been compared with special emphasis on the homogeneity of the photoresponse. High resolution scanning optical microscopy measurements at different wavelengths allowed to identify specific technological problems. Guard ring misalignment resulting in increased responsivity of the junction perimeter have been found on devices from one manufacturer. The responsivity images of the active area of some of the investigated photodiodes showed sharp peaks due to microplasma formation. The impact of these microplasmas on dark current and photocurrent of the devices has been investigated in detail. A step-stress test performed at successively increasing temperatures resulted in the catastrophic failure of the tested devices from one family. An analysis of the dark current-voltage characteristics before and after degradation leads to the conclusion that a modification of the semiconductor-insulator interface properties caused a dramatic increase in the surface leakage currents.

In this work we describe the influence of the growth parameters on the optical and crystallographic properties of InGaAs/InP short period superlattices (SPSLs). The optimized growth conditions applied for multiquantum wells are no longer appropriate when the period thickness is below 85 A and quasi-continuous growth interruption times are required. The assessment of new growth conditions enabled the realization of SPSL structures with ultimate period of 31 A presenting good optical and structural properties. The electron wave-function coherence length of seven SPSLs was evaluated. Application of these devices enabled the realization of Wannier-Stark modulators operating at 1545 nm with extinction ratio of 22 dB at 2.5 V reverse bias. The electron wave-function was evaluated, for the first time in the InGaAs/InP system, to be at last seven SPSL periods using both transmittance and photocurrent methods. The on state attenuation determined using Wood's method is below 2 dB in the range between 1540 and 1555 nm. SPSL structures are therefore well suited for the realization of guided wave electro-optic modulators based on the Wannier-Stark effect.

Multilayers of a-Si:N/a-SiN:H and a-Si:H/a-SiC:H were investigated by contactless transient photoconductivity measurements. A faster decay of the photoconductivity was observed in the a-Si:H/a-SiC:H multilayer whereas the a-Si:H/a-SiN:H multilayer was characterized by a slower decay relative to a pure a-Si:H film. These effects are ascribed to defects associated with interface states. The electron mobility in the thin a-Si:H layers of the multilayers does not appear to be appreciably different from that in pure a-Si:H films.

Hydrogen profiles for layered a-Si:H structures are presented. Substantial accumulation of hydrogen at the p-i interface is found. Additional incorporation of hydrogen in p-layers is also observed for intermediate boron doping levels compared to intrinsic layers. Hydrogen profiles in single pin and in pinpin amorphous silicon structures enable determination of individual layer thickness.

The optoelectronic properties of a-Si:H films grown at different substrate temperatures between 30°C and 250°C were evaluated in-situ by contactless Time Resolved Microwave Conductivity (TRMC) measurements. The transient photoconductivity induced by 532nm laser pulses during the growth of multilayer systems composed of a-Si:H layers deposited at different temperatures made a direct comparison of these films possible. The maximum height of the TRMC signal was observed to decrease strongly with decreasing deposition temperature. Additionally, the annealing of layers deposited at low temperatures was studied by TRMC, stationary photoconductivity, IR and ESR measurements. Whereas a considerable increase of the photoconductivity and the TRMC signal and a decrease in the spin density was observed during annealing at 250°C, the IR transmission spectra remained unchanged.