Formation of TiN/TiSi2/p+-Si/n-Si by rapid thermal annealing (RTA) silicon implanted with boron through titanium

A low temperature method of fabricating conductive (3.5 Ω/ sq.) p⁺/n junction diodes possessing excellentI-Vcharacteristics with reverse-bias leakage less than -3 nA.cm^-2at -5 V is described. Single crystal n-type 〈100〉 Si is implanted with 60 keV¹¹B+through 0.028-µm thick sputtered Ti film. Rapid thermal annealing (RTA) in an N2ambient simultaneously forms a 0.36-µm deep p⁺/n junction and a 0.063-µm thick bilayer of TiN and TiSi2with a resistivity of 22 µΩ.cm. The electrical properties of these diodes are not degraded by annealing for 30 min at 500°C, suggesting that the outer layer of TiN is an effective diffusion barrier between TiSi2and Al.     

Two-dimensional analysis for CuxS-CdS solar cells with nonuniform skin region

Due to rapid diffusion of externally applied copper along the disordered region of the grain boundaries, the skin region of the CuxS-CdS solar cell consists of alternate layers of thick and thin regions of p-CuxS. A two-dimensional idealized analysis leading to the short-circuit current, open-circuit voltage, conversion efficiency and spectral response of the cell is presented. For a typical cell, the variations of these parameters with grain size and width of the disordered regions are shown. It was pointed out that for such a cell, there is an optimum crystallite size for maximum conversion efficiency of the cell. The spectral response characteristics shows a relative improvement in the low-frequency side with increase in density of the CdS crystallites. This is probably due to the vertical junctions formed at the disordered regions.     

The design and fabrication of thin-film CdS/Cu2S cells of 9.15-percent conversion efficiency

Thin-film polycrystalline CdS/Cu2S cells with energy conversion efficiencies in sunlight of up to 9.15 percent and areas of ∼1 cm²have been developed. The improvement over previously achieved efficiencies is due to the development of techniques to separately measure and minimize fill factor losses. Specific design and fabrication changes based on a detailed quantitative analysis of the cell operation, were introduced to correct series resistance, shunt conductance and field effect losses. Further increases in efficiency can be expected from the development of a planar junction thin-film CdS/Cu2S cell.     

Theoretical analysis of Cu2S—CdS solar cells with rough interfaces

It has been found experimentally that the junction interface of a Cu2S-CdS solar cell shows a rough structure. The Cu2S can form deep dips between the grains of the CdS layer. By using an idealized geometry for such a Cu2S layer, the minority-carrier concentration and hence the characteristics of such a solar cell will be determined. The numerical method will be based on an integral equation technique.     

The photoresponse of CdS/CuInSe2thin-film heterojunction solar cells

The effect of light bias on the spectral current response and spectral capacitance characteristics of CdS/CuInSe2thin-film heterojunction solar cells has been investigated. Monochromatic light bias has been used to identify specific wavelength regions responsible for the spectral behavior seen under white light bias. Variations with light or voltage bias are consistent with the effect of the field on interface recombination in both high and low CdS resistivity devices. Devices with high CdS resistivity show spectrally dependent enhancement and quenching effects very similar to those reported for CdS/Cu2S devices in which the space charge region was primarily in the CdS. It is concluded that in high CdS resistivity devices the junction behavior is controlled by the photoconductive CdS as has been established in CdS/Cu2S cells. Low CdS resistivity CdS/CuInSe2devices show none of these effects.     

Formation of shallow p+-n junctions using boron-nitride solid diffusion source

Shallow p⁺-n junctions on the order of 0.1-µm deep have been fabricated using boron-nitride (BN) solid diffusion sources. The process combines the hydrogen-injection method and rapid thermal processing (RTP). Sheet resistivities, in ranges from 50 to 130 Ω/sq with junction depths from 0.1 to 0.19 µm, are possible in this technique. Diode characteristics of 0.11-µm junctions show low reverse leakage current, of the order of 10 nA/cm², indicating the possibility of this method to form PMOS source-drain contacts.     

Tunneling currents in the copper sulfide/cadmium sulfide heterojunction

The parameters controlling the photovoltaic properties of the Cu2S/CdS heterojunction have been investigated. It is found that the behavior of the short-circuit current and the open-circuit voltage are describable in terms of a deep, donor-like level in the CdS region adjacent to the metallurgical interface. When tunneling from this level into the Cu2S is the mechanism controlling the current flow, theJ_{SC}-V_{OC}characteristics of the device are described by the equationJ_{SC} = J_{00} exp (a_{i}(E_{I} - Phi_{T}_{0})) {exp (a_{i}q V_{OC})-1}where JSCis the short-circuit current, J00is the current preexponential factor,Phi _{T}_{0}is the zero-bias barrier height in the CdS, EIis the ionization energy of the deep donor, VOCis the open-circuit voltage, and aiis a tunneling factor dependent on the net positive charge density in the CdS near the interface. The relative probability of tunneling from this level to the Cu2S is derived, as is the probability of tunneling from the level to the CdS conduction band. The photocapacitance effects observed in this junction are attributed to the joint action of this level and an acceptor state due to copper in the CdS. Combining the results from the tunneling calculation, theJ_{SC}-V_{OC}data, and the quenching spectra of the photocapacitance, the ionization energy of the donor level is determined to be 0.45 eV and the density of these levels exceeds 10¹⁹cm^-3near the interface. The donor level acts as a recombination center, reducing JSC, and as a tunneling center, reducing VOC. Since these levels exist in junctions produced by the dipping method or by the dry method, they set fundamental limits to the efficiency of devices fabricated using these methods.     

Double heterojunction AlxGa1-xAs/GaAs bipolar transistors (DHBJT's) by MBE with a current gain of 1650

Double heterojunction AlGaAs/GaAs bipolar junction transistors (DHBJT's) grown by molecular beam epitaxy (MBE) were fabricated and tested. Devices with 0.2-µm and 0.1-µm base thicknesses exhibited common emitter current gains of up to 325 and 1650, respectively, in a wide range of collector currents. To obtain such high current gains, growth conditions had to be optimized and controlled. These high current gains, compared with the previous best value of 120 obtained in a MBE-grown transistor, make the HBJT's very promising for low-power high-speed logic application.     

High-efficiency millimeter-wave GaAs/GaAlAs power HEMT's

The power, gain, and efficiency of 0.5-µm gate-length, 75- and 50-µm gate-width multiple heterojunction high electron mobility transistors (HEMT's) have been evaluated from 10 to 60 GHz. At 10 GHz, with a source-to-drain voltage as low as 2.4 V, the device delivers a power density of 0.37 W/mm with 13.4-dB gain and 60.8-percent efficiency. At 60 GHz, a 50-µm device gave 0.4 W/mm with 3.6-dB gain and 14-percent efficiency. The power density and efficiency of these 0.5- µm gate-length HEMT's above 40 GHz are the best reported for a three-terminal device. Fundamental frequency oscillations up to 104 GHz were observed when a device was bonded as a free-running oscillator.     

Ga0.4In0.6As/Al0.55In0.45As pseudomorphic modulation-doped field-effect transistors

High-performance pseudomorphic Ga0.4In0.6As/ Al0.55In0.45As modulation-doped field-effect transistors (MODFET's) grown by MBE on InP have been fabricated and characterized. DC transconductances as high as 271, 227, and 197 mS/mm were obtained at 300K for 1.6-µm and 2.9-µm gate-length enhancement-mode and 2-µm depletion-mode devices, respectively. An average electron velocity as high as 2.36 × 10⁷cm/s has been inferred for the 1.6-µm devices, which is higher than previously reported values for 1-µm gate-length Ga0.47In0.53As/Al0.48In0.52As MODFET's. The higher bandgap Al0.55In0.45As pseudomorphic barrier also offers the advantages of a larger conduction-band discontinuity and a higher Schottky barrier height.     

The controlling influence of the Cu2S optical absorption coefficient on the short-circuit currents of Cu2S/CdS solar cells

Cu2S is a p-type defect semiconductor and is the main optical absorber-current generator in the Cu2S/CdS solar cell. This cell undergoes large reversible changes in its short-circuit current depending upon the ambient to which it is exposed. While a large number of mechanisms have been proposed for this effect, we find that it can be accounted for solely on the basis of changes in the absorption coefficient of the Cu2S, as controlled by the position of the Fermi level in the degenerate material. We have calculated the relation between the absorption coefficient and sheet resistance for degenerate Cu2S, and compared the results to existing experimental data on material prepared in the same way as solar cells. We find good agreement between the experimental data and our calculations if Cu2S is acting as a direct-gap semiconductor. Based upon the magnitude of the experimental changes in absorption coefficient with sheet resistance we have calculated the expected change in short-circuit current that would be produced in a typical Cu2S/CdS solar cell. The changes in short-circuit current calculated are on the order of 20-40 percent for ρ/d changing by an order of magaitude. These results are in agreement with the results on actual cells.     

Junction-current-confinement planar light-emitting diodes and optical coupling into large-core diameter fibers using lenses

High-radiance AlGaAs-GaAs double-heterostructure light-emitting diodes utilizing junction current confinement are described. Diode resistance and junction ideality factor are investigated as a function of emission diameters from 10 to 75 µm. Near-field intensity profiles indicate tight current confinement over the full range of emission diameters. Rise-time measurements are consistent with a simple carrier lifetime model for >25-µm emission diameters. An effective radiative-recombination constant, B = 1.5(±0.5) × 10-¹⁰cm³/s is deduced from the rise-time data and model. Peak wavelength and spectral width data are discussed in terms of junction current density and temperature. With decreasing emission diameter, the optical coupling efficiencies into 100- and 200-µm core diam high-numerical-aperture fibers increased from 10 to 25 percent and 25 to 50 percent, respectivley, using spherical glass lenses.     

Mo- and Ti-silicided low-resistance shallow junctions formed using the ion implantation through metal technique

Mo-and Ti-silicided junctions were formed using the ITM technique, which consists of ion implantation through metal (ITM) to induce metal-Si interface mixing and subsequent thermal annealing. Double ion implantation, using nondopant ions (Si or Ar) implantation for the metal-Si interface mixing and dopant ion (As or B) implantation for doping, has resulted in ultrashallow ( ≤ 0.1-µm) p⁺-n or n⁺-p junctions with ∼30-Ω sheet resistance for Mo-silicided junctions and ∼5.5-Ω sheet resistance for Ti-silicided junctions. The leakage current levels for the Mo-silicided n⁺-p junctions (0.1-µm junction depth) and the Mo-silicided p⁺-n junction (0.16-µm junction depth) are comparable to that for unsilicided n⁺-p junction with greater junction depth ( ∼0.25 µm).     

Design analysis of the thin-film CdS—Cu2S solar cell

A detailed model of the CdS-Cu2S solar cell was used to analyze design limits of cell configurations based on present laboratory technology. The parameters controlling the short-circuit current, open-circuit voltage, and fill factor are treated. The limits for each of these factors is obtained. The results indicate that the attainable conversion efficiency of the CdS-Cu2S solar cell extrapolating from the present processing technology is roughly 10 percent, as compared to a theoretical efficiency of 16 percent, if no losses occurred. A similar analysis for a cell using Cd1-xZnxS in place of CdS yields an attainable efficiency of 15 percent and a theoretical efficiency of over 26 percent. The model identifies those processing parameters which must be improved in order to optimize cell efficiency. Once technology is improved, the processing parameters will be reassessed with an aim towards increasing the maximum attainable efficiency.     

Modeling physical limitations on junction scaling for CMOS

Accurate calculations of diffusion and ion-implantation processes in silicon require the utilization of complex steady-state physical models that include the effects of both vacancies and self-interstitials. A new one-dimensional computer program, PROSIM II, has been developed for use in experimental junction formation studies that impact on advanced MOS technologies. PROSIM II has been used to study the scaling limits of counter-doped junctions for CMOS using both conventional furnace annealing and rapid thermal annealing processes. It is found that double implants of boron and arsenic can be used to produce a minimum 3000-Å-deep junction and still satisfy sheet resistance requirements for a 1-µm process.     

Characteristics of a 1.2-µm CMOS technology fabricated on an RF-heated zone-melting recrystallized SOI

0.7-5-µm CMOSFET's were fabricated on SOI which was recrystallized using an RF-heated zone-melting recrystallization (RFZMR) method. The leakage currents of n-channel MOSFET's having gate lengths between 5- and 0.7-µm range between 10^-14and 10^-12A/µm and show no dependence on channel length. Those of the p-channel MOSFET's were 10^-14-10^-12A/µm when the gate lengths were longer than 1.2 µm, and increased when the gate lengths were shorter than 1.0 µm. The propagation delay time of the CMOSFET inverter was 0.13 ns per stage at a supply voltage of 3.5 V.     

n+-p-p+structure InP solar cells grown by organometallic vapor-phase epitaxy

The fabrication of n⁺-p-p⁺InP solar cells by OMVPE has been studied. A conversion efficiency (active area) as high as 20 percent under AM1.5 illumination has been obtained. It is experimentally verified that the n⁺-p-p⁺InP solar cell has a higher resistance to radiation degradation than the n⁺-p InP solar cell. Diode characteristics and photovoltaic performances such as saturation current density, diode-ideality factor, and open-circuit voltage for the n⁺-p-p⁺cells are found to drastically deteriorate when junction depth decreases to ≤ 0.15 µm. An electron concentration dependence of a hole diffusion length in n-InP is estimated from the measurement of photoluminescence spectra. For the improvement of photovoltaic performances, a series of systematic examinations has been made on the relationship between collection efficiency and hole diffusion length from photogenerated carrier distribution analysis.     

Increases in energy conversion efficiency for thin-film polycrystalline CdS/Cu2S photovoltaic cells

Thin-film polycrystalline CdS/Cu2S photovoltaic solar cells with terrestrial energy conversion efficiencies in sunlight up to 7.8 percent have been developed. The major improvements are due to the increased optical transmission and electrical contact properties of the current collection system.     

InAsSb/InAsSbP double-heterostructure lasers emitting at 3–4 µm: Part I

Previous publications concerned with the development and investigation of InAsSb/InAsSbP double heterostructure lasers emitting at 3–4 μm fabricated by liquid phase epitaxy are reviewed. In pulsed mode, the maximum operating temperature of the lasers is 203 K, the characteristic temperature is 35 K, and differential quantum efficiency is 20±5% at 77K. Mesa-stripe lasers with a 10-to 30-μm stripe width and a 200-to 500-μm cavity length can operate in CW mode up to 110 K. The total optical output power of more than 10 mW at λ=3.6 μm is obtained at T=82 K in CW mode. The output power per mode does not exceed 2 mW/facet. A single-mode lasing is achieved in the temperature range of 12–90 K. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 34, No. 11, 2000, pp. 1396–1403. Original Russian Text Copyright ? 2000 by Danilova, Imenkov, Sherstnev, Yakovlev.     

A study of far-field patterns from high performance 1.3-µm InGaAsP-InP edge-emitting LED's

Liquid-phase epitaxy InGaAsP-InP 1.3-µm edge-emitting LED's are fabricated with a very simple Schottky-delineated stripe structure. With a stripe 50 µm wide and 200-250 µm long, typical characteristics of these devices include 170 µW of optical power coupled into a 60-µm core 0.2-NA graded index fiber, 600-Å spectral halfwidths, 2-5-ns risetimes. Unlike GaAs-GaAlAs edge-emitting LED's, best results of coupling efficiency are obtained with InGaAsP-InP LED's whose active layer thickness is in the range 0.12-0.15 µm, due to asymmetry in the far-field patterns. Our study of these far-field patterns shows that this asymmetry is governed by the quality of the active layer material located near the InGaAsP-nInP hetero-interface.