Injection-level effects in irradiated, lithium- containing solar cells.
Injection level effects on minority carrier lifetimes in lithium-doped devices and solar cells irradiated by electrons and reactor neutrons
Brucker, G. J.↗
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The properties of nickel in silicon.
Active Ni centers properties in Si with emphasis on increasing and reducing minority carrier lifetime in silicon integrated circuits, discussing energy levels
Ghandhi, S. K.↗
Radiation kinetics in electronic materials Semiannual report
Degradation and recovery of minority carriers in solar cells including lithium
Sosin, A.↗
Light microprobe investigation of Cu2S-CdS heterojunctions
Minority carrier diffusion lengths on sides of copper sulfide-cadmium sulfide heterojunctions measured by light microprobes
Bube, R. H.↗
Radiation effects in bulk lithium- and aluminum-doped silicon
Co-60 gamma radiation and isochronal annealing temperature effects on minority carrier lifetime of Al and Li doped bulk silicon
Bass, R. F.↗
Some major results of the Fourth Annual Conference on Effects of Lithium Doping on Silicon Solar Cells
Lithium doped silicon solar cells having dimensions as large as 12 sq cm are now possible, due to significantly improved boron-diffusion techniques. A large increase was observed in the short circuit current measured in tungsten light for cells that were fabricated using the improved diffusion techniques as compared with previous cells, indicating a preservation of minority carrier diffusion length in the base region of the former cells. Sintering of the contacts of lithium doped cells fabricated from Lopex silicon resulted in large increases in maximum power, mostly due to an open circuit voltage improvement, over non-sintered cells. Efficiencies as high as 12.8% were observed, with the average efficiency being about 11.9%.
Berman, P. A.↗
Radiation damage annealing kinetics
Various spectral response studies are reported that assess lithium doping effects on the recovery process of electron damaged silicon solar cells. Measurements of both the minority carrier lifetimes and the energy level spectrum of the defects are used to predict lifetime damage constants and carrier removal rates relevant to the operation of the solar lithium-doped cell and its annealing kinetics.
Dresselhaus, M. S.↗
The influence of degeneracy on the emitter efficiency of a bipolar transistor
An expression for the emitter efficiency is derived taking the degeneracy of the emitter into account. It is found that, even if there is no recombination of minority carriers in the emitter, degeneracy reduces the emitter efficiency. In addition this first order theory explains experimental results on temperature dependence of current gain and predicts an optimum emitter design for a fixed type of emitter profile.
Deman, H. J. J.↗
GaAs vapor-grown bipolar transistors.
Discussion of an approach for the fabrication of high-temperature GaAs transistors which is centered on the preparation of n-p-n three-layered structures entirely by a vapor-phase growth technique, as described by Tietjen and Amick (1966). The low growth temperature of approximately 750 C is thought to reduce contamination during crystal growth and to contribute to the reasonably high minority-carrier lifetimes obtained for the vapor-grown p-n junctions. The fact that impurity concentrations and layer thicknesses can be precisely controlled for epitaxial layers as thin as 1 micrometer is an important feature of this growth technique.
Nuese, C. J.↗
On the wide-range bias dependence of transistor d.c. and small-signal current gain factors.
Critical reappraisal of the bias dependence of the dc and small-signal ac current gain factors of planar bipolar transistors over a wide range of currents. This is based on a straightforward consideration of the three basic components of the dc base current arising due to emitter-to-base injected minority carrier transport, base-to-emitter carrier injection, and emitter-base surface depletion layer recombination effects. Experimental results on representative n-p-n and p-n-p silicon devices are given which support most of the analytical findings.
Schmidt, P.↗
Fundamental properties of semiconductor materials, and material performance in detectors
Procedures for determining fundamental properties of semiconductor materials, their performance as radiation detectors, and their service life as such detectors are given. Relationships were established between the minority carrier lifetime in the bulk of the material and the charge collection efficiency of the detector.
Casper, K. J.↗
Effects of nuclear radiation on a high-reliability silicon power diode. 4: Analysis of reverse bias characteristics
The effects of nuclear radiation on the reverse bias electrical characteristics of one hundred silicon power diodes were investigated. On a percentage basis, the changes in reverse currents were large but, due to very low initial values, this electrical characteristic was not the limiting factor in use of these diodes. These changes were interpreted in terms of decreasing minority carrier lifetimes as related to generation-recombination currents. The magnitudes of reverse voltage breakdown were unaffected by irradiation.
Been, J. F.↗
Photoemission from cesium-oxide-activated InGaAsP.
Zinc-doped InGaAsP quaternary III-V material of the proper composition range shows superior photoemission properties to either InGaAs or InAsP ternary material. The minority-carrier diffusion length in the quaternary material is at least as long as that in InAsP and much longer than observed in InGaAs. The barrier height at the InGaAsP-Cs2O interface is lowered by cooling, giving increased electron escape probability and new highs in quantum efficiency over a wide wavelength range. For example, a 1.06-micron quantum efficiency of 7.5%/incident photon was observed at -90 C.
James, L. W.↗
CdS-metal contact at higher current densities.
An investigation is conducted concerning the mechanisms by which a steady flow of current proceeds through the contact when an external voltage is applied. The main characteristics of current mechanisms are examined, giving attention to photoemission from the cathode, thermionic emission, minority-carrier extraction, and the tunneling of electrons. A high-field domain analysis is conducted together with experimental studies. Particular attention is given to the range in which tunneling predominates.
Stirn, R. J.↗
Design, fabrication and characteristics of new types of back surface field cells
Several new types of back surface field (BSF) cells were designed and fabricated. These include boron and phosphorus diffused BSF cells, single crystal epitaxially grown BSF cells and chemically vapor deposited (CVD) polycrystalline BSF cells. Boron diffusion yielded 10 ohm-cm BSF cells with 0.6 volt open-circuit voltages and collection efficiencies equal to those previously reported for aluminum alloying. The epitaxially grown cells also exhibited high open-circuit voltages and collection efficiencies and may be more radiation damage resistant. The polycrystalline cells had very high internal series resistance. No direct relationship was found to exist between collection efficiency and open-circuit voltage, V sub oc in BSF cells. Results indicate that the V sub oc effect is not caused simply by the mechanism of blocking of minority carriers.
Mandelkorn, J.↗
Low-high junction theory applied to solar cells
Recent use of alloying techniques for rear contact formation has yielded a new kind of silicon solar cell, the back surface field (BSF) cell, with abnormally high open circuit voltage and improved radiation resistance. Several analytical models for open circuit voltage based on the reverse saturation current are formulated to explain these observations. The zero SRV case of the conventional cell model, the drift field model, and the low-high junction (LHJ) model can predict the experimental trends. The LHJ model applies the theory of the low-high junction and is considered to reflect a more realistic view of cell fabrication. This model can predict the experimental trends observed for BSF cells. Detailed descriptions and derivations for the models are included. The correspondences between them are discussed. This modeling suggests that the meaning of minority carrier diffusion length measured in BSF cells be reexamined.
Godlewski, M. P.↗
Development and performance of IR detectors in the 1.5 to 2.4 micrometer region that operate at 240 K
High performance 1.5 to 2.4 micrometers (Hg,Cd)Te photodetectors for operating at 240 K or above are discussed. The detailed characterization of the detector with respect to detector temperature and background flux led to a development of an empirical model for minority carrier trapping. The concept of detective time constant is presented and successfully demonstrated by the four detectors delivered on this contract. An alternative approach is presented with the use of photovoltaic (Hg,Cd)Te detectors.
Chiang, A. F.↗
Methods of improving the efficiency of photovoltaic cells
Work on aluminum-alloyed silicon grating cells is continued. Optimization of the geometry (grating line width and spacing) confirms the analysis of such cells. A 1 sq cm grating cell was fabricated and its i-V characteristic was measured under an AMO solar simulator. It is found that the efficiency of this cell would be about 7.9%, if it were covered by the usual antireflection coating. The surface of the cell is not covered by a diffused junction. The response is blue shifted; the current is somewhat higher than that produced by a commercial Si cell. However, the open circuit voltage is low, and attempts to optimize the open circuit voltage of the aluminum-alloy junctions are described. A preliminary X-ray topographic examination of GaAs specimens of the type commonly used to make solar cells is studied. The X-ray study shows that the wafers are filled with regions having strain gradients, possibly caused by precipitates. It is possible that a correlation exists between the presence of low mechanical perfection and minority carrier diffusion lengths of GaAs crystals.
Loferski, J. J.↗