摘要:

A new class of cascade high‐efficiency photovoltaics designed for space‐based applications is proposed. The design improves upper subcell performance and avoids electrical and optical losses associated with an intercell ohmic contact. Multijunction upper subcells reduce bulk recombination of photogenerated minority carriers by decreasing the average collection distance, yielding improved spectral response and radiation tolerance. A three‐terminal design is employed which circumvents the need for a monolithic intercell contact and, thus, the losses associated with such a contact. Problems related to array interconnection of three‐terminal devices may be solved by creating a two‐terminal cell from complementary pairs (n‐p‐nandp‐n‐p) of three‐terminal cells. Simulations of lattice‐matched AlGaAs‐GaAs and lattice‐mismatched AlGaAs‐InGaAs cascade cells show that one‐sun AM0 efficiencies in excess of 26% and 28%, respectively, are possible.

ISSN:0021-8979    

DOI:10.1063/1.341142

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The short‐circuit current decay technique has been used in the literature to determine the minority‐carrier lifetime in the base of solar cells. The dependence of the short‐circuit current decay on the wavelength of the excitation light is reported in detail. Both the theoretical expressions and experimental results are presented. The experimental results agree reasonably well with the theory.

ISSN:0021-8979    

DOI:10.1063/1.340084

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A computer simulation model of amorphous silicon solar cells using a Scharfetter and Gummel solution of Poisson’s equation and Taylor and Simmons occupancy statistics for the dangling bond gap states (Dstates), has been developed. With a suitable choice of parameters, the numerical results for solar cell collection efficiency and dark and illuminatedI‐Vcharacteristics agree well with experimental values. The model has been used specifically to study the influence of interface states at the TCO‐p(transparent conductive oxide),p‐i,i‐n, andn‐metal interfaces and to explain the beneficial role of a graded‐band‐gap layer at thep‐iinterface.

ISSN:0021-8979    

DOI:10.1063/1.340085

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The Leibnitz rule of integral calculus yields a useful expression for the quasistatic capacitance versus voltage characteristic of ap/njunction space‐charge layer that holds for all doping profiles and for forward as well as for reverse applied voltages. This capacitance is the sum of two components. One accounts for the incremental mobile charge within the volume of the layer. The other accounts for the incremental mobile charge at its edges.This expression enables novel analytical characterizations and interpretations of numerical solutions.

ISSN:0021-8979    

DOI:10.1063/1.340086

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A Ag‐Se/Ge‐Se inorganic resist is applied in x‐ray lithography using synchrotron radiation (SR). Usable sensitivity of 0.3–3 times that of a polymethylmethacrylate (PMMA) resist and high contrast (&ggr;∼3.5) are obtained through SR exposures. By utilizing the fringes of masked SR flux caused by Fresnel diffraction, 500‐A˚‐wide fine lines are formed by using x rays of 2–10 A˚ in wavelength. It is determined that a high‐density resist, such as a Ag‐Se/Ge‐Se inorganic resist, is favorable for forming micropatterns using x rays because of the short ranges of the electrons generated by the x rays in the resist.

ISSN:0021-8979    

DOI:10.1063/1.340087

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Superconducting transition and critical current of a Y‐Ba‐Cu‐oxide compound prepared by ceramic technique have been studied for the samples which have the same nominal composition and sintering conditions, while systematically varying the calcining temperature from 850 to 1000 °C. It was observed that the shape of the superconducting transition in resistivity measurement markedly depends on the calcining temperature. All samples showed metallic behavior in normal state and samples which have lower resistivity showed higher critical current density. The resistivity just above onset temperature decreased with increasing the calcining temperature up to 950 °C, but above 975 °C the opposite behavior was observed. This behavior was discussed in connection with x‐ray diffraction patterns of the samples.

ISSN:0021-8979    

DOI:10.1063/1.340088

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Atomic force microscopy (AFM) is a new technology currently being developed. Stylus profilometry (SP) was developed earlier. A procedure is reported here which combines features of both SP and AFM. In this approach a stylus scans a sample surface and responds to contact forces. Force values are maintained within the elastic range of the sample, and high resolution is achieved by means of a sensitive tunnel gap feedback circuit control. Initial tests of performance have been conducted over a range of applied loads with tungsten styluses on phlogopite mica samples to image lamellar steps with subnanometer resolution.

ISSN:0021-8979    

DOI:10.1063/1.340089

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

We have measured the thermal conductivity &kgr; of a single crystal of barium fluoride from room temperature down to 20 K. This material is used as a substrate for growth of PbTe and other semiconductor materials with applications as electronic devices. The room temperature value of &kgr; is 0.07 W cm−1 K−1, and the thermal conductivity increases as temperature is lowered. At 20 K, the onset of a peak is observed, with a maximum value of approximately 13 W cm−1K−1. The results are compared with existing data in the literature, and a fit to the data assuming Umklapp scattering of phonons is performed.

ISSN:0021-8979    

DOI:10.1063/1.340090

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A cross‐sectional transmisson electron microscope (XTEM) study of intrinsic solid‐phase epitaxial (SPE) growth in self‐ion‐implanted (001) Si has been carried out. The activation energy of the self‐ion‐implanted silicon was measured to be 2.6±0.2 eV. The value is remarkably close to those obtained in the two most recent studies by other techniques. The pre‐exponential factor is lower than that reported by Lietoilaetal. [J. Appl. Phys.53, 4399 (1982)] annealed under similar conditions. The variation in proximity to the surface and difference in the distribution of the microstructural defects in the two studies are suggested to be possible causes for the discrepancy. The advantages of utilizing the XTEM technique to study epitaxial growth of self‐ion‐implanted amorphous thin films are demonstrated. The accuracy in the XTEM measurement of the SPE regrowth rate in Si+‐implanted (001) Si is discussed.

ISSN:0021-8979    

DOI:10.1063/1.340091

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Photoluminescence linewidth systematics for the case of semiconductor quantum well structures with a graded interface composition profile are studied within a model which attributes the linewidth to alloy disorder and alloy composition fluctuation effects. Results are presented for two specific types of gradations derived from consideration of typical experimental situations, and comparison is made with the available experimental data.

ISSN:0021-8979    

DOI:10.1063/1.340092

出版商:AIP    

年代:1988

数据来源: AIP