High-low Junction Research Articles

Modelling of high-injection effects in bipolar devices

An analytical model for minority carrier transport and recombination in quasi-neutral regions at arbitrary injection levels is presented. The proposed approach retains a general dependence of the transport parameters on the doping concentration, and can thus be applied to arbitrary doping profiles. It also includes heavy doping effects and injection-dependent recombination mechanisms. Simple closed-form analytical expressions are derived for the minority-carrier currents in bipolar transistors, and for the effective recombination velocity of high-low junctions.

Influence of built-in potential on the effective surface recombination velocity for a heavily doped high-low junction

An analytical expression for the built-in potential in a heavily doped high-low (p +−p) junction has been derived. The magnitude of built-in potential at different values of dopant density is estimated numerically. Band gap narrowing, carrier degeneracy, dopant density-dependent dielectric constant and also effects of carrier lifetime across the junction are considered in the analysis. The variation of surface recombination velocity with dopant density has been shown graphically through numerical analysis, where the variation of built-in potentials is incorporated.

A simple general analytical solution for the quantum efficiency of front-surface-field solar cells

The optimisation of a FSF solar cell or a BSF thin film solar cell necessitates an understanding of the characteristics of an illuminated high-low junction. However, except for minority carrier reflection, the photocurrent collection property of the light-generated carriers in the high region by a high-low junction has rarely been treated previously. It is the purpose of this paper to present a simple solution for the contribution of the light-generated current from the high region. The model shows that a high-low junction may be very efficient in light-generated current collection, and this property is primarily responsible for the increase of the short wavelength quantum efficiency using a FSF. The effects of the FSF layer doping concentration and its thickness on the quantum efficiency are discussed by using the computed results; the optimisation of the FSF is then made. The calculations take into account the high doping effects of degeneracy and bandgap narrowing.

Low-temperature characteristics of well-type guard rings in epitaxial CMOS

Characterization and simulation of minority-carrier well-type guard rings in epitaxial substrate at 77 K were performed and compared with those at RT. The escape probability in a narrow guard-ring structure under the same amount of minority carrier injection increases by about one order of magnitude when temperature decreases to 77 K. This degradation in the guard-ring efficiency can be attributed to the enhanced drift mechanism in the conductivity-modulated layer between the well bottom junction and the epitaxial high/low junction at 77 K. In contrast, this mechanism enhances the width dependence of the escape probability at 77 K. The higher minority-carrier recombination velocity of the epitaxial high-low junction contributes to the stronger width dependence secondarily. When the epitaxial layer thickness becomes thinner, the simulation also demonstrates a stronger width dependence of the escape current as well as a reduction in its magnitude. A lightly-doped epitaxial layer on a heavily-doped substrate exhibits even more importance in the guard ring efficiency for low temperature operation, and its thickness should be kept as thin as possible.

High-temperature characteristics of epitaxial high-low junction n +−n−p + silicon diodes

The electrical characteristics of epitaxial high-low junction n +−n−p + silicon diodes were investigated in the temperature range 27–310°C. The forward current conduction mechanism was predominantly diffusion, as indicated by the near-unity diode quality factors. Conductivity modulation in the lightly doped n epitaxial region improves the forward current conduction at high current levels. The reverse current increases exponentially with increasing temperature. The weak voltage dependence of the reverse current indicates that the predominant conduction mechanism is diffusion, as predicted by the ideal Shockley equation. The improvement in reverse current characteristics of the n +−n−p + diode over that of the n +−p + diffused diode is due to (a) the high quality of the epitaxial n-p+ junction as a result of the pre-epitaxy surface treatment, and (b) the n-side of the np junction of the n +−P + diode being more heavily doped than the lightly doped n epitaxial layer of the n +−n−p + diode.

New formulation of the collector current and current gain relations for design purposes of power transistor switches

New, compact analytical formulas for the collector current and current gain of bipolar power transistors are derived for operation in quasisaturation and saturation regions. The derivation is based on a regional approach taking into consideration current gain dependency on collector minority carrier lifetime and effective surface recombination velocity at the low-high (n-n+) junction. The paper represents an attempt to apply the theory of low-high junction (LHJ) to a bipolar power transistor operated in the saturation region. The current-voltage characteristics predicted by the proposed formulation are compared with the experimental results available in the literature to demonstrate the validity and usefulness of the new formulation. The new set of equations can be used as the basis of the design framework for the evaluation of optimal parameters of bipolar power transistor switches.

Contactless Evaluation of the Surface Recombination Property of Silicon with an Ion-Implanted Layer

AbstractThe surface properties of silicon are investigated by the noncontact laser (λ=774nm)/microwave method. The effective surface recombination velocity (Seff) at an n+n high-low junction interface is estimated by fitting the experimental decay curve for excess carriers with the theoretical decay curve. The results show that Seg decreases as the dopant concentration increases and that Seff at the n+n high-low junction formed with a dose of 1×l015 ions/cm2 has values lower than 1 cm/s. And it is shown that Scff is inversely proportional to the potential barrier height of the n+n high-low junction. Similar results are obtained using an N2 laser (λ=337.1nm) instead of a laser diode (λ=774nm, 904nm) as a carrier excitation pulse source.

A high-low emitter bipolar power transistor

Bipolar power transistors with a high-low emitter profile were fabricated and their electrical characteristics were investigated. The maximum do current gain of these high-low emitter transistors is in the range of 600 to 700 at a collector current of 600 :mA to 700 mA. This is attributed to the minority carrier reflection of the high-low emitter junction and enhanced material properties of the epitaxial base and lightly-doped emitter. The low base current activation energy (0.9 eV) is attributed to n + emitter band-gap shrinkage and minority carrier reflection of the high-low emitter junction. These transistors also have a smaller percentage increase in maximum do current gain with increasing temperature than do conventional bipolar power transistors.

An uncooled FIR detector using the avalanche injection effect

An uncooled FIR detector using an avalanche injection effect is proposed for improvement of the minimum detectable power, and experimental results at a wavelength of 10.6μm are given. The detectors are formed in a p-type semiconductor and do not have a p-n junction but a high-low junction. The highly doped region acts as an absorber of FIR incident power and also an emitter of hot carriers excited by the FIR power. A responsivity of 500 V/W and NEP of 5.5 ∗ l0 −9 W was obtained. These values are attractive for practical applications of FIR sensors and are better than those for the usual room temperature operated CMT detectors.

Analytical model of the effective recombination velocity of diffused p− p+ ( n− n+) high-low junctions at arbitrary injection level

This paper proposes an analytical model of the minority carrier transport across p− p + ( n− n +) high-low junctions, which is used to study the physical factors affecting the injection dependence of the effective recombination velocity (ERV) of such structures. In particular analytical expressions, valid at any injection level, of the recombination factors of the space charge region and of the quasi-neutral region of the junction are presented. The model is based on an original extension of the continuity equation written in terms of the minority-effective majority carrier product, which allows to describe the simultaneous occurrence of heavy doping and high injection effects. Comparison of this model with experiments and computer simulations indicates that the injection dependence of ERV starts to saturate as the injection level reaches the onset doping value of the heavy doping effects. The above model is shown to explain ERV measurements carried out on n− n + junctions of different thickness and for a wide range of injection levels.

Contactless Characterization of the Surface Property of the Si+-Implanted GaAs

ABSTRACTThe surface recombination of GaAs which has a high carrier concentration layer (HCCL) formed by Si+ implantation has been investigated using the reflectance microwave probe (RMP) method. The RMP method enables us to evaluate the surface property of GaAs contactlessly and easily. The experimental results of the samples which were implanted with doses ranging from 1.0×1011 to 3.9×1012cm-2 at an energy of lOOke V indicate that the effective surface recombination velocity decreases with dosage because of HCCL formed after the annealing. On the other hand, the results of the samples which were implanted with a dose of 3.9 × 1012cm-2 at energies ranging from 30 to 180keV indicate that the effective surface recombination velocity increases with energy for energies larger than 50keV. We understood the reason by comparing with the numerical calculation results of an effective surface recombination velocity at a high-low junction interface.

An H-L junction room temperature long-wavelength IR detector using the avalanche effect

A room temperature long-wavelength 10.6 mu m avalanche-type detector using laser-induced hot carriers is proposed for improvement of the minimum detectable power. The detectors are made by constructing high-low (H-L) junctions on p-type Ge. The L region is a substrate layer and the H region is a layer which absorbs 10.6 mu m radiation, and its also acts as a hot carrier emitter. This junction is referred to as the L-H junction. A responsivity of 41 V W-1 was obtained at wavelength 10.6 mu m under avalanche voltage conditions. This is comparable with the responsivity of CMT detectors operated at room temperature.

A novel PHL-emitter bipolar transistor—Fabrication and characterization

The polysilicon high-low-emitter (PHL-emitter) bipolar transistors have been fabricated and characterized. It is shown that the fabricated PHL-emitter bipolar transistors exhibit higher maximum current gain with lower activation energy, higher emitter-base breakdown, and better hot-carrier reliability than those of the fabricated conventional bipolar transistor. However, a little degradation in cutoff frequency for the fabricated PHL-emitter bipolar transistors due to the presence of the high-low emitter junction has also been observed. The effects of the n − implant dose on the electrical characteristics of the fabricated PHL-emitter bipolar transistors have been examined and discussed.

Leakage current study of a high-low junction with variation of injection level

Leakage current study of a high-low junction with variation of injection level

Minority carrier accumulation at high-low junctions

The semiconductor transport equations have been solved for lifetime semiconductors under the assumption of quasineutrality which is calculated to be valid up to relatively high current densities. The effective diffusion length of minority carriers is shown to be (strongly) current dependent. Of the four nonequilibrium processes, minority carrier accumulation is treated analytically in greater detail, showing current dependent resistance decreases which are confirmed by both numerical solutions of the transport equations and experiments.

Physical models for predicting the performance of Si/Si, AlGaAs/GaAs, and Si/SiGe solar cells

Abstract Analytical and physical models for homojunction and heterojunction solar cells are developed, and the performances of solar cells made by the Si/Si homojunction and made by the increasingly important and popular AlGaAs/GaAs and Si/SiGe heterojunctions compared. The models developed, which include relevant device physics such as the effective surface recombination velocity at the high-low junction and band discontinuities associated with heterojunctions, correctly explain the solar cell characteristics experimentally observed. Our calculations suggest that the highest efficiencies attainable for AlGaAs/GaAs, Si/Si, and Si/SiGe cells, with optimized doping concentrations but without surface passivation and geometry optimization, are 21.25%, 17.8% and 13.5%, respectively, under 1 AM1.5 sun condition. For concentrator cell applications, the efficiencies improve to about 24.5%, 22.2%, and 22.0% for AlGaAs/GaAs, Si/Si, and Si/SiGe cells, respectively, under 100 AM1.5 suns. While the AlGaAs/GaAs cell possesses the highest efficiency among the three cells, the Si/Si and Si/SiGe cells can achieve a satisfactory conversion efficiency at high sun concentration (22% at 100 suns), making them attractive for concentrator cell applications because their processing is the same as or is compatible with existing silicon technology. Model predictions for two Si/Si and one AlGaAs/GaAs cells compare favorably with data reported in the literature.

High-performance 0.10- mu m CMOS devices operating at room temperature

The authors have fabricated 0.10- mu m gate-length CMOS devices that operate with high speed at room temperature. Electron-beam lithography was used to define 0.10- mu m polysilicon gate patterns. Surface-channel type p- and n-channel MOSFETs were fabricated using an LDD structure combined with a self-aligned TiSi/sub 2/ process. Channel doping was optimized so as to suppress punchthrough as well as to realize high transconductance and low drain junction capacitance. The fabricated 0.10- mu m CMOS devices have exhibited high transconductance as well as a well-suppressed band-to-band tunneling current, although the short-channel effect occurred somewhat. The operation of a 0.10- mu m gate-length CMOS ring oscillator has been demonstrated. The operation speed was 27.7 ps/gate for 2.5 V at room temperature, which is the fastest CMOS switching ever reported.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Modelling of a Forward-Biased High-Low Junction

A model is presented to investigate the variation of majority carrier density as a function of position for a forward-biased high—low junction. The model is developed in order to obtain a new approximate analytical solution of Poisson's equation for such a junction with a sufficiently large doping difference between the two sides. A comparison of the present work with that of previous work is made through graphical analysis. Es wird ein Modell entwickelt, um die Änderung der Majoritätsladungsträgerdichte mit der Position an einem vorwärtsgespannten Stufenübergang zu untersuchen. Es wird eine neue analytische Näherungslösung der Poissongleichung für einen solchen Übergangs mit hinreichend großer Differenz zwischen den Dotierungen auf beiden Seiten des Übergangs erhalten. Ein Vergleich der Ergebnisse mit früheren Daten wird graphisch durchgeführt.

The use of generalised models to explain the behaviour of ohmic contacts to n-type GaAs

The use of two generalised carrier transport models to account for the N D −1 dependence of the specific contact resistance (ρ c) of metal-semiconductor Ohmic contacts to n-type GaAs is proposed. Both models include the effects of thermionic emission and diffusion across the high-low barrier junction a priori. Calculations of ρ c , and comparison with experimental data, show conclusively that thermionic emission is the dominant transport mechanism across the barrier. It is stressed that these models do not rely on prior choices of either of the transport processes. These conclusions are arrived at a posteriori.

Current-voltage characteristics of bipolar transistors including quasi-saturation, finite collector lifetime, and high-low junction effects

Abstract A physics-based and compact model is developed to predict the bipolar transistor DC characteristics covering all saturation, quasi-saturation, and active operations. The present model differs from the existing models in that the present model employs a regional approach rather than the charge-control approach used previously and that the present model requires only the physical parameters, such as device make-up, whereas the previous models often require parameters extracted from measurements. Device physics relevant to the base-collector junction, like current-induced base widening and conductivity modulation and electron-hole recombination in the quasi-neutral collector layer, are accounted for in the analysis. We show that the current-voltage characteristics predicted by the present model compare favourably with that obtained from measurements and simulations reported in the literature.