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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Calculation of transient photocurrents in insulators with trapped space charge.

The transit times and pulse shapes of photoinjected carriers moving in the presence of trapped space charge are derived. Two distributions are considered: uniformly trapped space charge, and trapped space charge decreasing exponentially in position from the injecting electrode. The pulse shapes are in some cases similar to those arising from transient space-charge-limited currents. The results in the case of the exponentially trapped space charge may have application in analysis of pulses taken in the presence of space charge trapped in the excitation layer or on the surface of insulators.

Hermann, A. M.↗
NASA NTRS1976

Correlation of photocurrent-voltage curves with flat-band potential for stable photoelectrodes for the photoelectrolysis of water

Using the differential capacitance technique, the flat-band potential of n-type TiO2, SnO2, SrTiO3, KTaO3, and KTa(0.77)Nb(0.23)O3 electrodes has been determined as a function of pH in aqueous electrolytes. Plots of flat-band potential vs. pH are linear in all cases and have a slope of approximately 0.059 V/pH unit. The flat-band potential correlates nicely with the onset for photoanodic currents corresponding to O2 evolution at the n-type semiconductor and H2 at the dark Pt cathode. The ordering of flat-band potentials at a given pH is SrTiO3 of the order of KTaO3 of the order of KTa(0.77)Nb(0.23)O3 greater than TiO2 greater than SnO2 (SnO2 most positive vs a saturated calomel electrode).

Bolts, J. M.↗
NASA NTRS1979

A note on photocurrents in extrinsic semiconductors

The advent of the concept of holes and careful determination of mobilities have made it possible to realize that the potential difference between the contacts of an irradiated semiconductor in the absence of current flow is due to the difference in mobility of electrons and holes. In this paper, a preliminary analysis shows that charge neutrality and zero-current condition are compatible. This situation is clarified and it is found that the equation for the electric field E in the absence of current is not absolutely correct even under low-level injection conditions. In particular, it is shown that fairly large currents can be generated by suitable light sources, currents which are entirely due to the disparity between electron and hole mobilities.

Von Roos, O.↗
NASA NTRS1978

The decrease in effective photocurrents due to saddle points in electrostatic potentials near differentially charged spacecraft

The reported investigation had the objective to illustrate the presence of important multidimensional effects in spacecraft charging. Two-dimensional codes have been under development by Parker (1976). A description is presented of a calculation which was performed using the three-dimensional NASA Charging Analyzer Program (NASCAP). NASCAP was run to calculate the electrostatic potentials on the surface of, and in the space surrounding, a sunlit Teflon-coated sphere. Currents to the sunlit surfaces were determined on the basis of an approximate photosheath model for strong differential charging.

Mandell, M. J.↗
NASA NTRS1985

Photocurrent images of amorphous-silicon solar-cell modules

Results obtained in applying the unique characteristics of the solar cell laser scanner to investigate the defects and quality of amorphous silicon cells are presented. It is concluded that solar cell laser scanners can be effectively used to nondestructively test not only active defects but also the cell quality and integrity of electrical contacts.

Kim, Q.↗
NASA NTRS1990

Role of photocurrent in low-temperature photoemission studies of Schottky-barrier formation

Photoelectron spectroscopy is frequently used to study band bending in semiconductors due to charge stored in surface or interface states. This paper examines how such experimental results are modified by photovoltages generated within the band-bending region not only by ambient light sources, but by the incident X-rays themselves. Recent experiments which have suggested dopant-dependent and reversible temperature-dependent band bending in the initial stages of formation of the metal-GaAs(110) interface are used as an example. It is shown that the reported dependence derives from a photovoltaic effect.

Hecht, M. H.↗