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InxGa(1−x)N/GaN multiquantum-well light-emitting diodes (LEDs) having periodic thickness variations (TVs) in InxGa(1−x)N active layers exhibit substantially higher optical efficiency than LEDs with uniform InxGa(1−x)N layers. In these nanostructured LEDs, the thickness variation of the active layers is found to be more important than the In composition fluctuation in quantum confinement of excitons (carriers). Detailed scanning transmission electron microscopy-atomic number Z contrast analysis, where image contrast is proportional to Z2 (Z being the atomic number), was carried out to investigate the variation in thickness as well as the spatial distribution of In. In the nanostructured LEDs, there are short-range thickness variations (SR-TVs) (3–4 nm) and long-range thickness variations (LR-TVs) (50–100 nm) in InxGa(1−x)N layers. It is envisaged that LR-TV is key to quantum confinement of the carriers and enhancement of the optical efficiency. We propose that the LR-TV is caused by two-dimensional strain ...

Transparent heat-mirror films, which transmit solar radiation but reflect ir thermal radiation, have potentially important applications in solar/thermal/electric conversion, solar heating, solar photovoltaic conversion, and window insulation. We have used rf sputtering to prepare two types of films: TiO(2)/Ag/TiO(2) and Sn-doped In(2)O(3). To characterize the properties of heat-mirror films for solar-energy collection, we define the parameters alpha(eff), the effective solar absorptivity, and epsilon(eff), the effective ir emissivity. For our Sn-doped In(2)O(3) films, alpha(eff)/epsilon(eff) is comparable to the values of alpha/epsilon reported for the leading selective absorbers. Even higher values of alpha(eff)/epsilon(eff) are obtained for the TiO(2)/Ag/TiO(2) films.

High efficiency solar cells have many practical uses. Concepts for obtaining high-efficiency solar cells using III-V compounds have achieved record efficiencies and are expected to improve even further. Single-junction cells will eventually reach 30% at AM 1.5 at one sun, and two-cell tandem structures will reach 40%. Thin-film III-V cells have now reached efficiencies close to double the efficiencies of thin-film cells using other materials. Inexpensive production techniques are now within reach. The future of III-V cells for both space and terrestrial applications is very bright.

Recent efforts to improve space solar cell efficiency have involved development of various types of multijunction tandem solar cells. This paper reviews the limits to the efficiency of present-day designs and the most recent results from many active investigations involving silicon, germanium, CuInSe2 and III–V materials.

The successful monolithic interconnection of four thin-film single-crystal GaAs cells, demonstrating one of the key advantages of thin-film cells made by the cleavage of lateral epitaxy for transfer (CLEFT) process, is reported. Monolithically series-interconnected 16 cm/sup 2/ thin-film four-cell strings exhibiting a V/sub oc/ of 4.04 V and a total-area submodule efficiency of 21.0% under AM 1.5 global illumination at 26 degrees C was successfully fabricated. An eight-cell string which had a V/sub oc/ of 7.96 V, an AM 1.5 efficiency of 21.2%, and a total submodule area of 2 cm/sup 2/ was produced. Details of the cell fabrication process and the cell performance are presented. >

We have found that InxGa(1-x)N/GaN multi-quantum-well (MQW) light emitting diodes (LEDs) having periodic thickness variation (TV) in InxGa(1-x)N active layers exhibit substantially higher optical efficiency than LEDs with uniform InxGa(1-x)N layers. In these nano-structured LEDs, the thickness variation of the active layers is shown to be more important than In composition fluctuation in quantum confinement of excitons (carriers). Detailed STEM-Z contrast analysis, where image contrast is proportional to Z2(atomic number)2, was carried out to investigate the thickness variation as well as the spatial distribution of In. In the nanostructured LEDs, there are short-range (SR-TV, 3 to 4 nm) and long-range thickness variations (LR-TV, 50 to 100 nm) in InxGa(1-x)N layers. It is envisaged that LR-TV is the key to quantum confinement of the carriers and enhancing the optical efficiency. We propose that the LR-TV thickness variation is caused by two-dimensional strain in the InxGa(1-x)N layer below its critical thickness. The SR-TV may be caused by In composition fluctuation. The observations on thickness variation are in good agreement with model calculations based upon strain effects.

This letter reports the attainment of a monolithically integrated light‐emitting diode array on a silicon integrated circuit. The emitters are first formed epitaxially on a lattice‐matched substrate and are subsequently transferred to the silicon. Interconnections are made using thin‐film techniques between the 128 separately addressable light‐emitting diodes and the driver circuit. This work demonstrates attainment of a high level of optoelectronic/logic integration.

Graded‐index separate‐confinement heterostructure single‐quantum‐well GaAs/AlGaAs diode lasers exhibiting continuous (cw) operation at room temperature have been grown on a Si substrate by organometallic vapor‐phase epitaxy, without the use of molecular‐beam epitaxy. To improve the quality of the laser structure, a defect‐filtering layer was incorporated between this structure and a GaAs buffer layer about 1.5 μm thick grown on the substrate. Of four types of defect‐filtering layers investigated, the most effective was one grown with thermal cycling, which made it possible to obtain pulsed threshold current densities as low as 350 A/cm2 for broad‐stripe lasers with a cavity length of 500 μm. Ridge‐waveguide lasers with this type of defect‐filtering layer have exhibited cw threshold currents as low as 25 mA and a differential quantum efficiency of 55%.

High efficiency solar cells have many practical applications. Concepts for obtaining high-efficiency solar cell modules are well understood. Single junction III–V cells composed of either gallium arsenide or indium phosphide have achieved high efficiencies. In particular, gallium arsenide cells have now reached 25.7% one-sun efficiency. To achieve over 30% one-sun efficiency, multi-bandgap structures may be needed with III-V cells playing a major role. A detailed description of multi-bandgap solar cells is given.

Computer analysis of amorphous solar cells indicates that a substantial increase in conversion efficiency can be achieved by using two-cell tandem structures instead of single-junction cells. A further increase in efficiency is calculated for three-cell tandem structures, but this increase is probably too small to justify their added complexity. Practical air mass 1 efficiencies of 16% – 17% at 1 sun can be expected for optimal two-cell structures, compared with 12% – 13% expected for single-junction cells. In optimal two-cell structures the top cell has a band gap of 1.85 eV, which is easily attainable with hydrogenated amorphous silicon films; the bottom cell has a band gap of 1.35 eV, which may be achieved with an alloy system such as hydrogenated amorphous Si 1−x Ge x or hydrogenated amorphous Si 1−x Sn x . Either two-terminal or four-terminal configurations can be used for two-cell tandem structures. The four-terminal configuration has the advantage of requiring less accurate control of film deposition parameters, since the efficiency depends less critically on the band gaps of the two component cells.

Well‐aligned grains of dimensions up to 2–3×100 μm have been obtained by laser crystallization of amorphous Ge films on fused‐silica substrates. A theoretical model has been developed for the dynamics of the crystallization process, a solid‐phase transformation that is greatly accelerated by liberation of the latent heat of transformation, resulting in either periodic or runaway motion of the crystallization front. We believe that scanning of amorphous films with an energy beam of large aspect ratio may be developed into an effective process for preparing large‐grained or even single‐crystal sheets of Ge and other semiconductors, including Si and GaAs.

The In and Sn 3d3/2 and 3d5/2 ESCA peaks and the oxygen 1s peak of Sn‐doped In2O3 films were compared with those for In2O3 films and In2O3, SnO, SnO2, and Sn3O4 powders. Comparison of as‐grown with sanded surfaces revealed Sn‐rich surface layers in.those films having good optical and transport properties. These experimental fins are interpreted with a schematic energy‐band model and the assumption that film darkening in Sn‐doped In2O3 films is caused by the formation and growth of an Sn3O4‐like second phase in the bulk. Suppression of these phase could be accomplished by higher substrate temperatures, which permit equilibrium conditions to be attained. Sn‐rich phases to migrate to the films surface, and the tine disproportionates to Sn2+ and Sn4+ ions.

Research approaches to obtain solar cell modules with 1 sun efficiencies of 20-30 percent at air mass 1 are now well understood. Such high efficiency modules should become available in the near future. It can be expected that these modules will be extensively used in terrestrial power generation, space power generation, and consumer electronics. To achieve practical module efficiencies significantly above 30 percent, it will be necessary to employ concepts other than spectral splitting, such as spectral compression and broad band detection. A major breakthrough in these areas is not anticipated at this time.

Spatially resolved (∼1 μm) Raman scattering measurements of the Si optical phonon spectrum have been used to map the stress in silicon‐on‐sapphire device structures. Devices defined by an isolated island etch technique exhibit a stress relaxation extending about 1.5 μm from the edges of a 6‐μm‐wide Si stripe. Devices defined by a local oxidation of the Si exhibit a more uniform stress profile.

By using a simple analytical model for GaAs solar cells with the nu+/p/p+ shallow‐homojunction structure, we have obtained good between compter calculations and experimental data for the external quantum efficiency and AM1 conversion efficiency of thin‐film GaAs cells with different values of + layer thickness grown on Ge substrates. The calculations yield values for material properties of the GaAs layers composing the cells and also permit the optimization of cell design parameters. In addition, the agreement between calculation and experiment demonstrates that the Ge substrates play a passive role. Thus we have succeeded in fabricating efficient thin‐film GaAs solar cells on non‐GaAs substrates.

Examen des principales imperfections topographiques et discussion de leur variation avec les profils thermiques presents durant le processus de recristallisation. Observation de vides formes dans les films cristallises par contamination lors de la preparation de la pastille

A simple formulation has been derived for the temperature dependence of cell parameters for any solar cell material. Detailed calculations have been performed for high-quality monocrystalline GaAs, Si and Ge cells. Preliminary experimental data for GaAs and Si cells are close to the calculated values. In general, the higher the energy gap of a material, the small is the temperature dependence of its solar cell parameters.

We have recently reported the fabrication of single‐crystal GaAs shallow‐homojunction solar cells that have conversion efficiencies of about 20% at AM1 (17% at AM0). These cells employ an n+/p/p+ structure, prepared by chemical vapor deposition on either GaAs or Ge substrates. We have now demonstrated the superior resistance of such cells to 1‐MeV electron radiation, which produces effects approximating those due to space radiation. The experiments were done on four cells at fluences up to 1016 e/cm2. One of the cells was found to have both higher initial and final maximum power per unit area than any space cells previously reported.

We have recently developed a zone-melting recrystallization technique for preparing large-area, high-quality Si films on SiO 2 . The key feature of this technique is the use of two graphite strip heaters, one of which is movable. The substrates used are bulk fused silica, sapphire, or single-crystal Si wafers that have been overcoated with SiO 2 . Films recrystallized without seeding contain widely-spaced grain boundaries and many sub-boundaries within each grain. Grain boundaries can be eliminated by either multiple-seeding or single-seeding methods. Extensive electrical measurements have been made on films recrystallized without seeding on SiO 2 -coated Si wafers. Sub-boundaries are found to have no significant effect on n-channel MOSFETs, which have characteristics comparable to those of such devices facricated directly on single-crystal Si wafers. High-yield transistor arrays and CMOS circuits have been made in films on 2 inch diameter wafers. Some remaining materials issues, such as film uniformity and wafer flatness, must still be addressed. We believe that most of these issues can be resolved, so that zone-melting recrystallization should become an effective technique for producing high-quality silicon-on-insulator wafers for commercial IC processing.

By using the CLEFT process, epitaxial GaAs films can be grown on a reusable GaAs single‐crystal substrate and transferred to amorphous substrates. An essential step in forming the epitaxial films is lateral growth seeded from openings in a mask on the single‐crystal substrate. The lateral growth process has been studied as a function of growth conditions and crystal orientation, and optimized to give continuous films with specular surfaces. Very few defects are found in the films by cathodoluminescence and transmission electron microscopy. As an initial demonstration of film quality, solar cells having efficiencies as high as 17% at AM1 and an area of (1)/(2) cm2 have been fabricated. The CLEFT process is advantageous for device applications because amorphous or polycrystalline substrates can be much less expensive than single‐crystal substrates, and also because they can have electrical and optical properties leading to improved device performance.

Thin-film solar cells have received a great deal of attention for use in terrestrial flat-plate systems. The large-area capability and effective use of solar absorbing materials gives these cells significant advantages over thin-film cells for low-cost systems. Our approach has been to use a separable film technology, the CLEFT process, to produce thin-film GaAs with state-of-the-art heterostructures capable of very high efficiencies. We have fabricated 4-cm 2 thin-film GaAs cells with conversion efficiencies as high as 21.5% one sun AM1.5 global. These results and our effort to increase cell area and reduce cell costs are discussed.

We have used Auger−electron spectroscopy and ion−beam etching to study the room−temperature oxidation of sputtered and electron−beam−evaporated Ge films. Both amorphous and polycrystalline films were examined, as well as single−crystal Ge. Electron−escape−depth effects were removed by a deconvolution procedure in order to obtain the O distribution function. Large differences of O distribution were found between sputtered and e−beam amorphous films. Sputtered amorphous films oxidize in the same manner as single−crystal Ge, with the O confined to the first 5−10 A of the surface. In e−beam amorphous films, the depth of O penetration is more than 200 A, although the heavily oxidized region is still only 10−12 A thick. Polycrystalline films have heavily oxidized layers 6−9 A thick, with some O present to a depth of 100−200 A.

Heteroepitaxial films of Ge1−xSix alloys have been obtained by transient heating of Ge‐coated Si single‐crystal substrates with a graphite strip heater. Structural characterization shows the films to be of good epitaxial quality. As the maximum temperature during heating is increased, the Ge content and the microtwin density of the films decrease.

Computer analysis has been used to determine the conversion efficiency of polycrystalline CdS- and Cd0.8Zn0.2S-based solar cells. For CdS-based cells the maximum calculated air mass 1, 1 sun efficiencies at 27 °C are 16% for single-junction cells, 21% for two-cell tandem structures and 24% for three-cell tandem structures. For Cd0.8Zn0.2S-based devices the corresponding efficiencies are 19%, 26% and 29%–30%. The improvements obtained in the three-cell structures appear to be too small to justify their added complexity. Somewhat higher efficiencies are calculated for two-cell tandem structures with a single-crystal Ga1−xAlxAs or GaAS1−xPx top cell and A CdS- or Cd0.8Zn0.2S-based bottom cell. However, unless the fabrication cost of the polycrystalline bottom cell is sufficiently low, such structures may not be economical.

Computer analysis has been used to determine the conversion efficiency of amorphous-on-crystalline and crystalline-on-amorphous two-cell tandem structures as a function of the energy gaps of the component cells. Four-terminal (separately connected) structures have higher efficiencies than two-terminal (series-connected) structures and are less sensitive to variations in energy gap, operating temperature and air mass. The optimal amorphous/crystalline tandem structures show only a modest increase in efficiency over their component crystalline cells. Unless the production costs of the tandem structures are low, this increase may not be sufficient to justify their adoption.

An rf sputtering process was used without postdeposition annealing to prepare Sn-doped In/sub 2/O/sub 3/ films with low electrical resistivity (down to 2 x 10/sup -4/ ohm-cm), high visible transmission, and high infrared reflectivity (up to 93 percent at 10 ..mu..m) for applications as transparent conductors and heat mirrors. Substrate heating is accomplished entirely by the electron bombardment intrinsic to rf sputtering, rather than by using an auxiliary resistance heater. The film properties improve with increasing substrate temperature up to 650/sup 0/C, the maximum employed, and are relatively independent of other sputtering parameters. The electrical and optical properties of the films do not depend significantly on the crystallographic orientation, degree of texture, or substrate material.

An optical transmission technique has been used to measure the propagation velocity of the crystallization front during scanned laser crystallization of amorphous Ge films on fused‐silica substrates. The measurements confirm our theoretical model for the solid‐phase amorphous‐to‐crystalline transformation. According to this model, the periodic structural features of the crystallized films are formed because the crystallization front moves in a series of periodic jumps between rest positions, with the velocity of the front during each jump much higher than the laser scanning velocity. The measured values of the crystallization‐front velocity range from 140 to 260 cm/sec, compared with the laser scanning velocity of only 0.5 cm/sec.

A CMOS test circuit chip containing six arrays of 360 to 533 parallel transistors, two 31-stage ring oscillators, and two inverter chains has been designed for evaluating SOI wafers prepared by using the graphite strip-heater technique for zone-melting recrystallization of poly-Si films on SiO 2 -coated Si substrates. One 2-in-diameter wafer has been evaluated in detail by testing all the circuits on each of 98 chips fabricated in the recrystallized film. These measurements reveal a good yield of functional circuits, and most of the failures can be explained by obvious metallization defects. The operating characteristics of each type of circuit are quite uniform from chip to chip. For the ring oscillators, which have a 5 µm gate length and fan in and out of one, at a supply voltage of 5 V the switching delay time is about 2 n s per stage and the power-delay product is 0.2-0.3 pJ per stage.

Two theoretical descriptions have been developed for the phase boundary dynamics during crystallization of amorphous films by scanning with the slit image of a cw laser or of any cw energy beam. The first reduces the problem to the solution of a one-dimensional integral equation, which allows a choice of initial conditions. Depending on the background temperature, numerical solutions yield either periodic or runaway motion of the amorphous-crystalline (a-c) boundary, as observed in experiments on scanned laser crystallization of thin films of a-Ge on fused-silica substrates. The calculations give a semi-quantitative fit to the experimental results for the spatial periodicity observed in the crystallized films as a function of background temperature. Profiles of film temperature as a function of distance from the laser image at successive times have been computed for both the periodic and runaway cases. The model qualitatively explains many of the effects observed during scanned cw laser crystallization, including periodic fluctuations in light emission. The second theoretical description is a more exact two-dimensional treatment, applicable only to cases of steady-state motion of the a-c boundary, which rigorously handles heat flow into the substrate. This treatment has been used to calculate the boundary velocity during steady-state runaway.

Heteroepitaxial Ge films have been obtained by solid‐phase crystallization of amorphous Ge deposited on single crystal Si substrates. The Si substrates were chemically cleaned by conventional procedures without any attempt to achieve atomically clean surfaces. Epitaxial crystallization of the amorphous Ge films were accomplished by furnace annealing at temperatures of 500°–900°C. The as‐crystallized Ge films contain dislocations and twins whose densities decrease with increasing annealing temperature. Significant reduction in twin density has been achieved by using an ion implantation and reannealing treatment. Epitaxial layers of good crystal quality have been grown by chemical vapor deposition on heteroepitaxial Ge films subjected to this treatment.

Selective-black absorbers have high solar absorptivity and low infrared emissivity. We have prepared excellent selective-black absorbers by using r.f. sputtering to deposit MgO-Au and Cr2O3-Cr cermet films, which are highly absorbing in the solar spectrum and highly transparent in the infrared, on metal substrates. Both types of films are found to consist of individual crystallites less than 200 A in size. Absorbers with solar adsorptivity of over 0.9 and infrared emissivity of less than 0.1 have been prepared by depositing films of 75 vol.% MgO-25 vol.% Au on molybdenum-coated stainless steel. These absorbers are stable in air up to 400°C. Absorbers with similar optical properties have been obtained by depositing films of 71 vol.% Cr2O3-29 vol.% Cr on nickel-coated stainless steel, provided that these films are covered with a Cr2O3 antireflection coating. These absorbers are stable in air up to 300°C. Computer calculations indicate that even better selective properties can be obtained by using Cr2O3-Cr films with a graded composition profile rather than a discrete Cr2O3 coating.

The transport properties of zone-melting-recrystallized Si films on SiO 2 -coated Si substrates have been studied by the fabrication and characterization of thin-film resistors and n-channel MOSFET's. Subgrain boundaries, which are the predominant crystal defects in the films, have a relatively low trapping state density (7-8 × 1011cm-2) and low resistance. N-channel MOSFET's fabricated in the films exhibit high surface electron mobilities (∼ 640 cm2/V-s) for electron transport either parallel or perpendicular to the subgrain boundaries.

Spectrally selective coatings have potentially important applications in solar-thermal-electric conversion, solar photovoltaic conversion, solar heating and window insulation. These coatings can be divided into two classes: transparent heat mirrors transmit solar radiation and reflect thermal radiation; selective absorbers absorb solar radiation and have a low IR emissivity. We prepared by r.f. sputtering cermet absorbers (MgO-Au and Cr 2 O 3 -Cr) and transparent heat mirror films (TiO 2 /Ag/TiO 2 , tin-doped In 2 O 3 and tin-doped In 2 O 3 microgrids) that have excellent wavelength-selective properties. We also recently succeeded in preparing excellent tin-doped In 2 O 3 films on Mylar by ion beam sputtering. The tin-doped In 2 O 3 films also have good electrical conductivities, making them excellent transparent conductors.

Heteroepitaxial Ge films have been obtained by solid‐phase crystallization of amorphous Ge deposited on single‐crystal 〈100〉Si substrates. The substrates were chemically cleaned by conventional procedures without any attempt to achieve atomically clean surfaces. The as‐crystallized Ge films contain dislocations and twins. Reduction in twin density has been achieved by using an ion implantation and reannealing treatment. Epitaxial GaAs layers of good crystal quality have been grown by chemical vapor deposition on heteroepitaxial Ge films subjected to this treatment.

The transition temperatures (Tt) and heats of crystallization (ΔH) of a‐Ge, a‐Si, and a‐Ge1−xSix films deposited by rf sputtering have been measured by differential scanning calorimetry (DSC). Both Tt and ΔH (per gram) increase linearly with x in the alloy system. Overlapping exothermic multiple peaks are observed in the DSC traces of a‐Ge and a‐Si samples prepared at high deposition rates, suggesting that multiple amorphous configurations may coexist in these materials.

Finely grained films of three cermets‐MgO/Au, MgO/Ag, and MgO/Ni‐have been grown by rf sputtering from composite targets. Electron‐microscopic studies show that MgO/Au and MgO/Ag films consist of small crystallites (usually

Very large differential-sputtering effects in fine-grained (particle size < 50 A) MgO/Au cermet films have been observed by Auger electron spectroscopy. Under Ar-ion bombardment, the surface Au content was found to decrease exponentially with time by up to a factor of 20. A theoretical model for differential sputtering of granular systems is presented that gives good agreement with the experimental data. The differential sputtering produces a MgO-rich surface layer and therefore results in excellent secondary-electron-emission properties for low-energy incident electrons.

By using a new method, which we have named the LESS technique (lateral epitaxy by seeded solidification), single‐crystal Si films have been grown over insulating layers on single‐crystal Si substrates. An amorphous or polycrystalline Si film is deposited on the insulating layer, in which narrow stripes have been opened to expose the substrate. By using two carbon strip heaters, one of which is movable, the Si film is melted and frozen in such a manner that solidification begins within the stripe openings, where it is seeded by the substrate. The resulting single‐crystal regions in turn seed lateral single‐crystal growth over the adjacent insulating layer. Continuous single‐crystal Si films have been obtained over SiO2 layers with openings spaced 50 or 500 mm apart, and single‐crystal growth extending as far as 4 mm over Si3N4 has been observed.

Solar cells with conversion efficiencies of 12% (AM1) have been fabricated from single-crystal GaAs epilayers grown by CVD on Ge-coated Si substrates. The cells utilize an n+/p/p+shallow-homo junction GaAs structure on a thin (

Conversion efficiencies up to 15% (AM1) have been obtained for antireflection‐coated InP homojunction solar cells, the highest efficiency values reported for InP cells of any type. The cells were fabricated on n+ p p+ structures formed by liquid phase epitaxy on single‐crystal InP substrates. The cell photovoltaic characteristics are not very sensitive to n+‐layer thickness, indicating that the surface recombination velocity is not as high as in homojunction GaAs solar cells. The performance of various antireflection coatings has been investigated.

High‐quality films of Sn‐doped In2O3 (ITO) have been prepared by ion‐beam sputtering at deposition temperatures below 100 °C. As in the case of rf‐sputtered films, the electrical and optical properties of these films depend strongly on the O2 partial pressure during deposition. As‐deposited films with low electrical resistivity (∼5.5×10−4 Ω cm), high visible transmission (≳80%), and high infrared reflectivity at 10 μm (∼84%) have been obtained at O2 pressures of (2–3) ×10−5 Torr by deposition on both glass and Mylar substrates.

Single‐crystal GaAs layers have been obtained by means of lateral epitaxial overgrowth seeded within stripe openings in a SiO2 mask over GaAs layers grown on Ge‐coated Si substrates. Transmission electron microscope and scanning cathodoluminescence studies indicate that the laterally overgrown GaAs layers have a dislocation density of less than 104 cm−2, compared to 107–108 cm−2 for the GaAs layers grown directly on the Ge/Si substrates. Initial experiments indicate that the electrical properties of the laterally overgrown layers are comparable to those of conventional GaAs epilayers grown on single‐crystal GaAs substrates.

Solar cells with conversion efficiencies as high as 17% at AM1 have been fabricated from single-crystal 10-µm-thick GaAs films prepared by the CLEFT process. These cells are the first devices to employ CLEFT films. In making a cell, a GaAs film with an n+/p/p+shallow-homojunction structure is grown by vapor-phase epitaxy on a specially masked single-crystal GaAs substrate, then transferred to a glass substrate that serves as the cell cover glass. The GaAs substrate can be reused repeatedly for preparing additional CLEFT films.

We have investigated the effects of irradiation with 1.5 MeV electrons on the electrical characteristics of n-channel MOSFET's fabricated in zone-melting-recrystallized Si films on SiO 2 -coated Si substrates. With a -15 V bias applied to the Si substrate during irradiation and device operation, the subthreshold leakage current remains below 0.2 pA/µm (channel width) for ionizing doses up to 106rad(Si). The negative substrate bias also reduces the shift of threshold voltage to less than 0.3 V for devices with 50 nm-thick gate oxide.

Excellent selective black absorbers for solar radiation, with solar absorptivity of over 0.9 and infrared emissivity of less than 0.1, have been obtained by using rf sputtering to coat metal substrates with a Cr2O3/Cr cermet film, then with a Cr2O3 antireflection coating. By determining the optical constants of Cr2O3/Cr films over the composition range up to 35 vol% Cr, it was found that films containing 29 vol% Cr are nearly optimum for this application. The optical and chemical properties of absorbers made with such films are quite similar to those obtained with electroplated Cr‐black coatings. This similarity suggests that the electroplated coatings are actually Cr2O3/Cr cermets comparable in composition and microstructure to the sputtered films.

Solid‐phase recrystallization of Si films prepared by chemical vapor deposition on fused silica substrates has been accomplished by transient heating on a graphite strip heater. This process increases the grain size from ∼50 nm to ∼1 μm. Thin‐film transistors fabricated in the recrystallized films exhibit surface electron mobilities of 15–20 cm2/V s and on:off current ratios in excess of 105 for a voltage swing of 10 V.