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Results for “heterojunctions”

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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Heat treatment effects in Cu2S-CdS heterojunction photovoltaic cells

The optical and electronic properties of single crystal Cu2S-CdS photovoltaic cells were investigated. In these cells trapped charge near the interface which is manifested by a persistent increase in junction capacitance (the photocapacitance) plays a significant role in determining the carrier transport properties. It was found that the severe degradation in short-circuit current observed in heat-treated cells can be separated into two components: (1) a relatively small thermal component occurring on heat-treatment in the dark, and (2) a much larger degradation caused by exposure to light at room temperature. By a short additional heat-treatment above approximately 100 C the cell can be completely restored to its condition before the optically caused degradation with no effect on the depletion layer width.

Fahrenbruch, A. L.↗
NASA NTRS1975

Internal optical losses in very thin CW heterojunction laser diodes

Theoretical calculations are presented showing the relationship between the internal laser absorption and structural parameters appropriate for CW room-temperature lasers. These diodes have submicron-thick recombination regions, and very small spacings between the heat sink and the recombination region to minimize the thermal resistance. The optical loss is shown to be strongly dependent on the degree of radiation confinement to the active region. In particular, absorption in the surface GaAs layer providing the ohmic contact becomes very significant when the intermediate (AlGa)As layer is reduced below about 1 micron. It is further shown that excessive penetration into the GaAs regions gives rise to anomalies in the far-field radiation profiles in the direction perpendicular to the junction plane.

Butler, J. K.↗
NASA NTRS1975

Glass-Si heterojunction solar cells

Experimental studies and models for In2O3/Si and SnO2/N-Si solar cells are considered for their suitability in terrestrial applications. The silicon is the active material, and the glass serves as the window to solar radiation, an antireflection coating of the Si, and a low resistance contact. Results show that amorphous windows or layers suppress photocurrent. The interfacial SiO2 layer suppresses photocurrent and increases series resistance. Suppression increases with illumination.

Anderson, R. L.↗
NASA NTRS1977

A theoretical study of heterojunction and graded band gap type solar cells

A computer program was designed for the analysis of variable composition solar cells and applied to several proposed solar cell structures using appropriate semiconductor materials. The program simulates solar cells made of a ternary alloy of two binary semiconductors with an arbitrary composition profile, and an abrupt or Gaussian doping profile of polarity n-on-p or p-on-n with arbitrary doping levels. Once the device structure is specified, the program numerically solves a complete set of differential equations and calculates electrostatic potential, quasi-Fermi levels, carrier concentrations and current densities, total current density and efficiency as functions of terminal voltage and position within the cell. These results are then recorded by computer in tabulated or plotted form for interpretation by the user.

Sutherland, J. E.↗
NASA NTRS1977

The influence of stripe width on the threshold current of double-heterojunction lasers

Experimental measurements of the threshold current of oxide-isolated stripe laser as a function of stripe width and p-layer resistivity are presented. A calculation of the influence of carrier outdiffusion has been made, including the effect of current leakage beyond the stripe edges. The calculated threshold increase is in substantial agreement with experiment for stripe widths down to about 10 microns. The data also yield an effective diffusion length of about 7 microns for the lasers studied. Deviations between experimental and calculated thresholds occurring at stripe widths of 4-6 microns are represented by an empirical curve which is compared with previously published calculations of threshold gain.

Ladany, I.↗
NASA NTRS1976

Computer analysis of heterojunction and graded bandgap solar cells

The development and application of a graded bandgap solar cell computer analysis program is discussed. The basic device equations as used in the computer analysis are discussed and the techniques used to model material parameter variations are described. Finally, the results of the computer analysis of several Al(x)Ga(1-x)As and GaAs(1-x)P(x) solar cell structures are presented along with a discussion of the effects of interface states and various composition profiles on maximum solar cell efficiency.

Sutherland, J. E.↗
NASA NTRS1979

Material growth and characterization directed toward improving III-V heterojunction solar cells

In addition to the existing materials growth laboratory, the photolithographic facility and the device testing facility were completed. The majority of equipment for data acquisition, solar cell testing, materials growth and device characterization were received and are being put into operation. In the research part of the program, GaAs and GaA1As layers were grown reproducibly on GaAs substrates. These grown layers were characterized as to surface morphology, thickness and thickness uniformity. The liquid phase epitaxial growth process was used to fabricate p-n junctions in Ga(1-x)A1(x)As. Sequential deposition of two alloy layers was accomplished and detailed analysis of the effect of substrate quality and dopant on the GaA1As layer quality is presented. Finally, solar cell structures were formed by growing a thin p-GaA1As layer upon an epitaxial n-GaA1As layer. The energy gap corresponding to the long wavelength cutoff of the spectral response characteristic was 1.51-1.63 eV. Theoretical calculations of the spectral response were matched to the measured response.

Stefanakos, E. K.↗
NASA NTRS1983

Microcrystalline silicon growth for heterojunction solar cells

A total of sixteen runs of e-beam vacuum deposition of p type microcrystalline Si (m-Si) films were attempted on n type or p-n junction single crystalline Si (C-Si) substrates. The m-Si film thickness varied from .15 to .7 um and metal contacts were deposited after plasma hydrogenation. The p-m-Si on n-c-Si structure had a Voc of up to 490 m V while no Voc improvements were observed in the p-m-Si on p-n C-Si structure against p-n controls. Both CFF and Jsc were lower than control. Possible problem areas were interfaced between m-Si and C-si and the back contacts due to lack of sintering for fear of dehydrogenation.

Iles, P. A.↗