Characteristics of an all-implanted p+-n-n+solar cell

This work presents the main electrooptical parameters of a p⁺-n-n⁺single-crystalline silicon solar cell, whose front p⁺-n junction and the backside n-n⁺contact were fabricated through masked ion implantation of boron (¹¹B+) and phosphorus (³¹p+), respectively. The distinctive feature of the cells consists of the use of the front junction silicon dioxide mask as an AR layer in the finished devices.     

Negative resistance and filamentary currents in avalanching silicon p+-i-n+junctions

Space-charge effects in avalanching p⁺-i-n⁺diodes give rise to a current-controlled bulk negative resistance. It is shown that this negative resistance gives rise to an instability which tends to lead to the formation of current filaments. A steady state can be found in which the generation of carriers in the filament by impact ionization is balanced by radial diffusion of carriers. We present the results of approximate numerical calculations of filament current-density profiles and total filament current as a function of applied voltage. The total filament current is a decreasing function of the applied voltage; thus, the diode exhibits a quasistatic negative external resistance. It is suggested that this negative resistance may be used to interpret observed sub-transit-time oscillations of p⁺-i-n⁺structures.     

Avalanche multiplication noise characteristics in thin GaAs p+-i-n+ diodes

Avalanche noise measurements have been performed on a range of homojunction GaAs p⁺-i-n⁺ and n⁺-i-p ⁺ diodes with “i” region widths, ω from 2.61 to 0.05 μm. The results show that for ω⩽1 μm the dependence of excess noise factor F on multiplication does not follow the well-established continuous noise theory of McIntyre [1966]. Instead, a decreasing noise factor is observed as ω decreases for a constant multiplication. This reduction in F occurs for both electron and hole initiated multiplication in the thinner ω structures even though the ionization coefficient ratio is close to unity. The dead-space, the minimum distance a carrier must travel to gain the ionization threshold energy, becomes increasingly important in these thinner structures and largely accounts for the reduction in noise     

A study of the conversion efficiency limit of p+-i-n+silicon solar cells in concentrated sunlight

The conversion efficiency limit of p⁺-i-n⁺silicon solar cells in concentrated sunlight is explored with numerical simulations of an idealized p⁺-i-n⁺cell having field-induced junctions. Conversion efficiencies greater than 30 percent are calculated for this cell operating in sunlight concentrated 1000 times. The relative importance of bulk and surface recombination in limiting the cell conversion efficiency is illustrated for operation in 1 to 1000 suns. For surface recombination velocities below 100 cm/s, it is shown that bulk recombination losses limit the cell performance rather than recombination losses occurring in the p⁺or n⁺regions. The results show that Auger recombination in the bulk region will limit ultimately the cell conversion efficiency.     

Dielectric relaxation in Si—SiO2—Cr structures

The dielectric behavior of thermally grown SiO2was examined using Si-SiO2-Cr structures. The relaxation spectrum exhibits a time dependence indicative of diminishing charge-carrier concentration. The relaxation process is characterized by activation energies of 29-32 kcal/mole; this, together with the considerably higher loss measured in specimens contaminated with Na2CO3, suggests sodium as the carrier source.     

Low-frequency noise in Cr—SiO2—N-Si tunnel diodes

Low-frequency noise of Cr-SiO2-n-Si tunnel diodes with about 30-Å-thick oxides is investigated as function of bias, frequency, and temperature. Measurements of1/fnoise are explained by a theory employing the two step tunneling model of Sah. Electrons from the Si conduction band are trapped by states at the Si-SiO2interface and then tunnel into bound states of the oxide located close to the interface. The oxide states of density N00can be represented by a frequency dependent parallel admittance exhibiting frequency-dependent thermal noise that modulates the dc currentItunneling through the oxide barrier. This generates flicker noise at the device terminals proportional toI^{2}N_{00}and inversely proportional to frequencyfand tunneling areaA. The valueA = 5. 10-3A0, determined by fitting theoretical and experimental curves at low frequency, is only a small fraction of the gate area A0, since tunneling preferentially occurs through the thinnest parts of the oxide. The currentIalso exhibits full shot noise at high frequency and low current. Qualitative agreement between theoretical and measured noise is found over 9 decades. Measurements at low temperature show additional noise of generation-recombination centers at larger frequencies and currents.     

Low avalanche noise characteristics in thin InP p+-i-n+ diodes with electron initiated multiplication

We have performed electron initiated avalanche noise measurements on a range of homojunction InP p⁺-i-n⁺ diodes with “i” region widths, w ranging from 2.40 to 0.24 μm. In contrast to McIntyre's noise model a significant reduction in the excess noise factor is observed with decreasing w at a constant multiplication in spite of α, the electron ionization coefficient being less than β, the hole ionization coefficient. In the w=0.24 μm structure an effective β/α ratio of approximately 0.4 is deduced from the excess noise factor even when electrons initiate multiplication, suggesting that hole initiated multiplication is not always necessary for the lowest avalanche noise in InP-based avalanche photodiodes     

Impedance measurement of the illuminated metal—SiO2—Si diodes

Impedance measurement of light-illuminated MIS diodes was made. It becomes clear from the results that in the inversion region conductance of the MIS structure is more sensitive to illumination than its capacitance and that negative photoconductivity appears at low frequency, which is explained by the theory of Grosvalet et al.     

Dielectric loss and current—Voltage measurements in sodium-contaminated Si—SiO2—Cr structures

A detailed study of the small-signal ac response of ntentionally sodium-contaminated Si-SiO2-Cr structures has been made with mobile ion concentrations of 10¹⁰-10¹²ions/cm², in the frequency range of 0.05-100 Hz, between temperatures of 300 and 450°C. The time dependence of the observed relaxation phenomena, attributed to the existence of deep traps near the SiO2-Cr interface, is slow enough to consider the measured relaxation spectra as quasi static. The dc bias dependence of the relaxation mechanism, manifested by a loss maximum around 0.6 V and by a monotonic decrease of the absorption frequency with increasing bias, is ascribed to shallow traps located at the SiO2-Cr interface. The trapping as well as the long range migration of Na⁺ions in SiO2has been carefully studied by I-V and C-V measurements carried out on both contaminated and on ultraclean samples. The long-range motion of the ions leads to the thickness dependence of the relaxation time. However, since the ac response is determined in the two halves of the measuring cycle alternately by the migration of ions in the bulk of the SiO2and by their emission from the shallow traps, the relaxation time is also dependent on the effect of the traps. Consequently, the observed bias-dependent activation energies, ranging from 0.91 to 1.21 eV, may also be interpreted as intermediate values, arising from the conduction of Na⁺ions in SiO2films with an activation energy of less than 0.91 eV, and from the release of ions from the traps having activation energies equal to or greater than 1.21 eV.     

A Monte Carlo investigation of multiplication noise in thin p+-i-n+ GaAs avalanche photodiodes

A Monte Carlo (MC) model has been used to estimate the excess noise factor in thin p⁺-i-n⁺ GaAs avalanche photodiodes (APD's). Multiplication initiated both by pure electron and hole injection is studied for different lengths of multiplication region and for a range of electric fields. In each ease a reduction in excess noise factor is observed as the multiplication length decreases, in good agreement with recent experimental measurements. This low noise behavior results from the higher operating electric field needed in short devices, which causes the probability distribution function for both electron and hole ionization path lengths to change from the conventionally assumed exponential shape and to exhibit a strong dead space effect. In turn this reduces the probability of higher order ionization events and narrows the probability distribution for multiplication. In addition, our simulations suggest that fur a given overall multiplication, electron initiated multiplication in short devices has inherently reduced noise, despite the higher feedback from hole ionization, compared to long devices     

Forward current—Voltage and switching characteristics of p+-n-n+(epitaxial) diodes

The forward-biased current-voltage and forward-to-reverse biased switching characteristics of p⁺-n-n⁺epitaxial diodes are investigated. The manner in which the n-n⁺junction affects the flow of injected minority carriers in the epitaxial region is characterized by a leakage parameter a. Experimentally, for diodes with epitaxial film widths much less than a diffusion length, a "box" profile accurately describes the injected minority carriers in the n region. The current is found to increase with increased epitaxial width at a fixed bias. A general switching expression for epitaxial diodes is presented and the validity of the expression is shown experimentally. The experimental values of a, determined independently from the current-voltage and switching characteristics, are in good agreement and show that the leakage of the high-low junction is dominated by the recombination of minority carriers in the n-n⁺space-charge region.     

Switching in Nb—Nb2O6—Nb devices with doped Nb2O5amorphous films

Switching properties of Nb-Nb2O5-Nb devices with doped Nb2O5amorphous films were studied as a function of applied voltage and temperature. A continuous recording of the switching process made possible the determination of switching parameters as a function of small voltage increments. Using this technique, it is found that switching occurs within 2.5 mV with a delay time > 1 ms. A switching device of this type can support an input power of ∼1 W.     

A laser augmented reaction: SF6+ SiH4→S*2+ SiF4+ HF + H2· retention of isotopic selectivity during detonation

A single unfocused pulse of a free running CO2laser, area ∼ 8 cm², initiates an explosive reaction between SF6and SiH4. This occurs at a minimum energy of 4 J [full width at half maximum (FWHM)sim 1.5 /mus] of which about one half is absorbed in an 8 cm long cell; total pressure 12 torr; 0.65 <p(SiH4)/p(SF6) < 1.8. The spectral and temporal distributions of the emitted chemiluminescence depend sensitively on the fuel to oxidizer ratio, and on the pulse energy; we investigated the range 4 → 20 J. The principal emission is due to S2(B^{3}Sigma-_{u} rightarrow X^{3}Sigma-_{g}). Transitionsupsilon' (0-4) rightarrow upsilon" (2-15)were recorded. In the³Sigma-_{u}state, vibrational temperatures range from 3000-13000 K. The luminosity peaks sharply at (SiH4)/(SF6) = 1.0 ± 0.05. On each side of the maximum of the emission versus composition curve [at (SiH4)/(SF6) ≈ 0.95 and 1.22, for a 12 J pulse] the residual SF6(0.2-0.5 percent of initial amount) is enriched in³⁴SF6; the observed fractionation factors at these two compositions are 8 ± 2. The separation between the two sharply peaked optimum compositions appears to increase with increasing pulse energy. Preliminary results with other fuels suggest that the concurrent absorption of CO2laser radiation by the fuel, as well as a highly exothermic reaction, are pre-requisite for fine tuning of composition, injected power, and total pressure for optimum isotope fractionation.     

Corner currents in rectangular diffused p+-n-n+diodes

The low-level injection dc characteristics of rectangular p⁺-n-n⁺diodes are discussed, and the vertical, lateral, and corner current components are analyzed and measured. It is shown that the corner current can be a significant fraction of the total current and a simple analytic expression is given.     

Very-shallow low-resistivity p+-n junctions for CMOS technology

Shallow p-n junctions 110 nm deep have been fabricated using rapid thermal diffusion from a spin-on oxide source. Surface concentrations greater than 3 × 10²⁰cm^-3are possible, with sheet resistivities less than 100 Ω/sq and a maximum reverse-bias leakage at 5 V of 3 nA.cm^-2. Results from 150-nm junctions are also given and are compared with BF2ion implantation.     

Oxynitride gate dielectrics for p+-polysilicon gate MOSdevices

Different oxynitride gate dielectrics (NH₃-nitrided, reoxidized NH₃-nitrided, N₂-annealed NH₃-nitrided, and N₂O grown oxides) are investigated for use in p⁺-polysilicon gate MOS devices. The comparison is based on flatband voltage shift as well as decrease in inversion capacitance. Results show that NH₃-nitrided and N ₂-annealed NH₃-nitrided oxides best suppress the boron penetration and, consequently, these two undesirable effects. These findings are explained on the basis of the distribution of nitrogen in various oxynitride dielectrics     

A method for the characterization of p+-n-n+diodes using DC measurements

An experimental technique using only dc terminal measurements with a special set of masks is presented for characterizing device properties of single diffused p⁺-n-n⁺diodes. The vertical and lateral current components are separately obtained. The carrier lifetimes in the epitaxial layer and the p⁺diffusion, and the recombination velocity at the oxide-silicon p⁺interface are experimentally determined. Examples are given and possible sources of errors are discussed.     

MBE grown n+-i-δ(p+)-i-n+GaAs V-groove barrier transistor

The three-terminal n⁺-i-δ(p⁺)-i-n⁺V-groove barrier transistor (VBT) has been successfully fabricated by molecular beam epitaxy (MBE). The base terminal is connected to the δ(p⁺), the thin p⁺layer, by depositing aluminum on the etched V-groove. The demonstrated device possesses high potential of ultra-high-frequency (f_{r} > 30-GHz), high-power, and low-noise capability due to carriers transporting by thermionic emission and being controlled by the base-emitter bias.     

Evaluation of the profile constants of p+-n-n+hyperabrupt junctions

A method for evaluating the profile constants of a p⁺-n-n⁺hyperabrupt junction is given. The method is useful in the design and characterization of hyperabrupt tuning varactors.     

Device simulation of submicrometer gate p+-i-p+ diamond transistors

Two-dimensional device simulation of submicrometer gate diamond p ⁺-i-p⁺ transistors with a SiO₂ gate insulator was investigated using the MEDICI device simulation program. A large modulation of the source-to-drain current was obtained in the accumulation mode. The computed diamond device characteristics were equivalent or better than the simulation results of 6H-SiC MESFET's. It was concluded that the problems in diamond MESFET associated with the deep acceptor levels due to boron doping can be overcome in the p⁺ -i-p⁺ diamond FET's because of the hole injection and the space charge limited current