Counting of deep-level traps using a charge-coupled device

Quantization in dark current generation has been observed for the first time through the use of a virtual-phase charge-coupled device. Two sites for bulk silicon dark current have been identified with capture cross sections of 1.8 × 10^-15cm²and 5.4 × 10^-16cm², and concentrations of 1.3 × 10⁹cm^-3and 1.5 × 10⁸cm^-3, respectively.     

RF Sputtered gold-amorphous silicon Schottky-barrier diodes

Gold Schottky-barrier diodes formed on reactively sputtered amorphous silicon thin films have been investigated. Device forwardI-Vcharacteristics are well modeled as a Schottky diode in series with a temperature activated series resistor. At 300K, the forward current indicates a diode correction factor of 1.4 and a saturation current of 5.8 × 10^-10A/cm². The metal-semiconductor barrier height is 0.93 eV. Capacitance versus frequency measurements indicate a depletion region thickness of 3000 Å. In the depletion region, the mobility-lifetime products are estimated to be of the order of 5 × 10^-11cm²/V which is substantially less than the value of 10^-7cm²/V in the quasi-neutral region, It is suggested that deep gap states are responsible for this difference. Carrier recombination in the depletion region limits the photovoltaic performance.     

Ultrasmall superconducting tunnel junctions

Extremely small-area superconducting Josephson junctions have been fabricated using a newly developed electron-beam lithography technique. The junctions are composed of Pb-In base electrodes and Pb counter electrodes. Areas of the junctions range from 1 to 3 × 10^-10cm². The estimated capacitance is ∼10^-15F. Junctions have been produced with resistances of ∼100 Ω which have ∼20-percent hysteresis in the critical current at a temperature of 4 K.     

Integral heat-sink IMPATT diodes fabricated using p+etch stop

The problems in batch fabrication of integral heat-sink IMPATT diodes are greatly simplified through a newly developed preferential etching technique. Devices fabricated utilizing the new technique have thermal resistance (θjc) values of 17-20°C/W for an active area of 2 × 10^-4cm².     

Fast determination of the effective channel length and the gate Oxide thickness in polycrystalline Silicon MOSFET's

MOSFET's with variable channel lengths have been fabricated in both mono- and fine-grained polycrystalline silicon. We present a new method based upon a simple CV technique, to measure the effective channel length and gate oxide thickness. The channel-length reduction of the poly-Si MOSFET's was about 7.8 µm from which an effective lateral diffusion coefficient at 1000°C of phosphorus of 5 × 10^-13cm²/s was calculated. The electron mobility was in the range of 10-20 cm²/V.s and the threshold voltage was about 17 V. The MOSFET's in mono-Si have been used as a reference. The results of measurements on these devices are in agreement with literature.     

Some reactive effects in forward biased junctions

The small-signal equivalent parallel capacity of forward-biased semiconductor junctions is strongly dependent on the current. At very low currents (less than 10 µa for a junction area of 1 mm²) the capacity appears to be chiefly due to space charge effects. For currents up to approximately 100 µa, the capacity complies with Shockley's predicted low-level theory. For larger currents, however, there is a definite deviation from the low-level diffusion predominance and capacity reaches a maximum after which it decreases through zero and then goes to large inductive values. The latter phenomena is explained, qualitatively, by considering an inductance in series with the diffusion capacity. The capacity increases linearly with current but the inductance (due to conductivity modulation) increases faster. The result is that a change from an equivalent RC circuit to an equivalent RL circuit is made at high enough currents (5 ma is a typical value for the 1 mm²junction area). Measurements were made on abrupt silicon junction diodes with junction areas of about 7 × 10^-4, 10^-2, 10^-1cm²and on the emitter junction (about 5 × 10^-5cm²) of a diffused base silicon transistor.     

A method of determining impurity diffusion coefficients and surface concentrations of drift transistors

In order to control the electrical parameters of drift transistors, it was found necessary to control the impurity concentration gradient in the base. An extension of the space charge widening theory provides a method of calculating this gradient, the surface concentration, and the diffusion coefficient. By this method, the diffusion coefficient of arsenic into germanium at 725°C was found to be 3.1 × 10^-12cm²/second and the initial surface concentration was of the order of 10²⁰atoms/cm³. Universal graphs for design calculations and rapid reference are presented.     

On oxide—nitride interface traps by thermal oxidation of thin nitride in metal-oxide-nitride-oxide-semiconductor memory structures

Charging properties of metal-oxide(top-oxide)-nitride-oxide (tunnel-oxide)-semiconductor (MONOS) memory structures characterized by very low program voltage have been investigated and analyzed. By comparing the experimental observations with theoretical calculations, the capture cross section of the electron traps generated at the top oxide-nitride interface by thermal oxidation of the thin nitride primarily effecting the memory action of the MONOS devices is estimated to be about 6 × 10^-14cm².     

A SiC backward diode

SiC backward diodes which operate between 77°K and 1000°K have been developed. Figures of merit (γ√R) of 19 300, 3960, and 15 at 12.5 MHz, 50 MHz and 8.8 GHz, respectively, have been measured with detector area on the order of 10^-5cm². These results are compatible with a prior analysis which predicted an upper frequency limit of between 0.1 and 1.0 GHz for SiC backward diodes.     

Experiments on high-perveance electron guns with a subfocusing electrode

High-perveance electron guns with a subfocusing electrode were designed analytically, produced, and tested. The experiments are carried out to evaluate the design method. Perveance of guns are 1.7 to 1.3 × 10^-6A/V^3/2, convergence angles being 30°. The results confirmed that it was possible to design electron guns of perveance up to 3.0 × 10^-6A/V^3/2.     

A new method of growing GaP crystals for light-emitting diodes

A method named synthesis, solute diffusion (SSD) has been developed for growing compound semiconductor crystals, GaP in particular, for light-emitting diode (LED) use. The grown crystal is cylindrically shaped and is composed of fairly large-size grains. Growth rate is limited by the diffusion process of phosphorus in the gallium melt. The diffusion coefficient was obtained from the growth rate and found to be 8×10^-5cm²s^-1at 1100°C with an activation energy of 0.65 eV. Donor impurities, tellurium or sulfur, can be reproducibly incorporated from 3×10¹⁷to 4×10¹⁸cm^-3, with segregation coefficients at 1150°C, 0.038 and 1.0, respectively. The quality of the grown crystals was observed to be exceptionally good, and the saucer-type pits were hardly observable in the crystal on modified AB etching. Highly efficient red-light-emitting junctions were reproducibly grown by only one single-layer-single-liquid-epitaxy process, in which zinc was doped from the vapor phase. A double-layer-single-epitaxy process, which we call "liquid epitaxial grown-in junction" process, was also developed and it produced highly efficient green LED's. The LED's grown on the SSD wafers have efficiencies up to 7.4 percent for red and 0.15 percent for green.     

A polysilicon—Silicon n-p junction

Phosphorus-doped polycrystalline silicon is grown in an epitaxial reactor by the reduction of a hydrogen-diluted silane-phosphine mixture passing over a substrate heated to 800°C. The influence of the phosphine-silane ratio on growth rate, electrical resistivity, active donor concentration, and Hall mobility is examined. It is found that phosphine inhibits growth rate at 800°C to a lesser degree than it does at lower growth temperatures. Growth rate progressively drops to 0.6 of the undoped value as the phosphine-silane ratio is increased to 10^-1. Resistivity drops from 1 to 10^-3Ω. cm as active phosphorus concentration varies between 10¹⁸and 4 × 10²⁰cm^-3, while Hall mobility rises from 4 to 30 cm²/ V.s. Diodes are formed between the grown polysilicon layers and the single-crystal p-type silicon substrates. They are found to have recombination currents critically dependent on the phosphine/ silane ratio during growth of the polysilicon. As this ratio increases above 10^-5, recombination decreases, while mobility in the polysilicon increases. These results support the "dopant segregation" theory of conduction in polysilicon. For ratios of 10^-3to 10^-2the diodes obtained showed a recombination factor approaching those of diffused diodes and are useful devices, for example, as the emitter-base junction of a shallow-base high-frequency, bipolar transistor.     

A 64K SRAM with high immunity from heavy ion induced latch-up

A 64-kbit SRAM with high latch-up immunity has been developed with the application of a well-source structure combined with an epi-substrate. Heavy-ion beam exposure tests reveal that the device has high immunity from cosmic-ray induced latch-up, and the soft-error cross section is about 8.6 × 10^-7cm²/(bit particle) for 73-MeV Ar ions.     

Properties of ion-implanted junctions in mercury—cadmium—telluride

The formation of n-p junctions by ion-implantation in Hg0.71Cd0.29Te is shown to be a result of implantation damage. n-p photodiodes have been made by implantation of Ar, B, Al, and P in a p-type substrate with acceptor concentration of 4 × 10¹⁶cm^-3. The implanted n-type layer is characterized by sheet electron concentration of 10¹⁴to 10¹⁵cm^-2and electron mobility higher than 10³cm². V^-1. s^-1, for ion doses in the range 10¹³-5 × 10¹⁴cm^-2. The photodiodes have a spectral cutoff of 5.2 µm, quantum efficiency higher than 80 percent, and differential resistance by area product above 2000 Ω . cm²at 77 K. The temperature dependence of the differential resistance is discussed. The junction capacitance dependence on reverse voltage fits a linearly graded junction model. Reverse current characteristics at 77 K have been investigated using gate-controlled diodes. The results suggest that reverse breakdown is dominated by interband tunneling in field-induced junctions at the surface, for both polarities of surface potential.     

Source—Drain contact resistance in CMOS with self-aligned TiSi2

The contact resistance between TiSi2and n⁺-p⁺source-drain in CMOS is studied for a variety of junction profiles and silicide thicknesses. It is shown that the measured contact resistance is consistent with the transmission-line model for electrically long contacts. The contact contribution to the total device series resistance can be significant if excessive silicon is consumed during silicide formation. Contact resistivities of 3 × 10^-7and 1 × 10^-6Ω . cm²can be obtained for 0.15-0.20-µm-deep arsenic and boron junctions, respectively, if the interface doping concentration is kept at 1 × 10²⁰/cm³. Furthermore, low-temperature measurements show that the contact resistivity is nearly constant from 300 to 77 K, as would be expected from a tunneling-dominated current transport at the TiSi2-n⁺and TiSi2-P⁺interfaces.     

A high gain silicon photodetector

High gain silicon photodetectors were designed and fabricated using a sandwich structure of gold compensated n-type material. Steady-state photoconductive current gains as high as 26 were measured, while transient peak gains of 50 were attained. The measured response time varied from 10^-6to 2×10^-7sec, depending inversely upon the incident light intensity. The electron lifetimes were calculated using the existing capture cross-section data of the gold recombination centers. These results are in good agreement with the estimated electron lifetime based upon the measured photoconductive current gain and the calculated transit time values. The detectivity of some of the devices was typically D^*(λp, 900, 1) =9.5×10⁹cm (c/s)^1/2/watt and the noise equivalent power NEP = 1.6×10^-11watts/(c/s)^1/2.     

Electron microprobe analysis of impurity heterogeneities in thermally grown silicon oxide

The electron probe X-ray microanalyzer is a powerful tool for studying impurity distribution and motion in thin films. This analytical instrument is capable of detecting metallic impurities present in areas as small as 1 × 10^-6mm²and in concentrations of greater than 1 × 10¹⁹atoms/cm³. The analysis requires no sample preparation and is essentially a nondestructive test. This instrument was used to examine unoxidized and oxidized silicon surfaces and a finished microcircuit. With the electron microprobe, aluminum-bearing regions approximately one microns in diameter were detected on the bare surface of mechanically polished silicon slices. These aluminum-rich regions are believed to be alumina abrasive used in polishing. If these regions are not removed by chemical etching they will generate oxide defects during oxidation. These defects were found to contain Al (1 × 10²¹atoms/cm³and Na (1 × 10²⁰atoms/cm³). Other oxide defects, i.e., pinholes, generated during oxidation varied in size from 0.5 to 5.0 microns and were found to contain Na (1×10²¹atoms/cm³) and K (5×10²¹atoms/cm³). Mg and Ca (1 × 10²⁰atoms/cm³) were occasionally observed in these defects. After oxidation, all these impurities could be removed with a hot hydrochloric acid and deionized water rinse; surprisingly, this treatment reduced the silicon surface charge in the MOS structure (X_{0} cong 1500Å) by approximately 1.4 × 10¹¹charges/cm². The surface charge could be further reduced by heating the oxidized wafer at 900°C in a silicon nitride tube.     

Water vapor penetration rate into enclosures with known air leak rates

The rate at which water vapor penetrates a faulty seal in a "hermetically sealed" device has been examined both experimentally and theoretically in this study. The experimental data were generated by studying the rate of moisture ingress into two types of packages; a TO-5 can and a ¼ × ¼ in ceramic flatpack. The TO-5 packages were fitted with capillary tubes of varying diameters with known air leak rates and represented the gross leak range (down to 10^-5atm . cm³/s) while the ¼ × ¼ in ceramic flatpacks were used to study the fine leak range (10^-6to 10^-8atm . cm³/s). Both type packages were fitted with miniature moisture sensors (surface conductivity type) and calibrated at known relative humidities prior to sealing. The finished test packages were then exposed to constant high-humidity conditions and monitored for moisture content as a function of time. A theoretical analysis was performed by using conventional leak rate equations to convert air leak rates, at standard test conditions, to water vapor leak rates at partial pressure differentials seen typically at room ambient conditions. These data compared favorably with the experimental results in the range tested and suggests that present hermeticity specifications are too lenient for long-term reliability requirements.     

Responsivity of ion-implanted p-n junction in a GaAs electroabsorption avalanche detector

The performance characteristics of an ion-implanted p-n junction electroabsorption avalanche detector (EAD) are reported. Wtih avalanche-assisted multiplication, the optical gain reaches value of over 500 and the devices achieved a peak responsibility of 200 A/W at a wavelength of 0.88 µm. Owing to the combination of the Franz-Keldysh effect with avalanche multiplication, a narrowband, i.e., self-filtering, response of 50 nm full-width half-magnitude was demonstrated. With a 50-Ω load the pulse response of this large-area EAD, i.e., 1.6 × 10^-2cm², is about 5-10 ns and is RC time constant limited.     

Characteristics of a Raman laser excited by an ordinary ruby laser

The stimulated Raman effect of benzene has been observed using an ordinary (nongiant) ruby laser. The build-up of oscillation at the v2, 2v2, 3v2and 4v2Stokes lines and also at the first v1Stokes line have been observed. The threshold exciting power for laser action in the v2Stokes line has been measured to be 9.5 kW. A rate equation for the Raman laser has been given, and the total scattering cross section for the v2Raman line of benzene has been determined as σ = 0.46×10^-28cm². The estimation based on the results of this investigation indicates that it is possible to construct a Raman laser of benzene using an Ar gas laser.