High Doping Effects Research Articles

A Comparison of the Diffusivity of As and Ge in Si at high Donor Concentrations

AbstractThe effect of high background doping (8×1019 - 5×1020 cm-3 ) on the diffusion of Ge and As in Si has been studied. A strong enhancement is found for As for donor concentrations higher than ~2×1020 cm-3 , but not for Ge. These experimental findings are discussed within the percolation model.

高圧力下のＩＩＩ‐Ｖ族化合物半導体の電気特性と光学特性

The high electric field properties of InP have been studied as a function of pressure to 55kbar. The measured threshold field for transferred electron instability showed an initial increase with pressure, and after passing through a maximum at 30-33kbar it decreased gradually. Monte Carlo calculations based on a stronger Γ-L scattering assumption seemed to agree better with the experimental data. The experimental results also indicated that a change from the two- to the three-level operation occurred near 30-33kbar.Photoluminescence (PL) and optical absorption measurements on the heavily doped GaAs have been made as a function of pressure to 60kbar at 77K. With increasing pressure the spectrum shifted towards the higher energy side. The pressure dependence of the emission peak across the direct gap showed a noticeable change in slope at about 30kbar. For pressures above 35kbar the PL intensity suddenly decreased. The pressure dependence of the absorption edge in the heavily doped samples was quite different from that in the undoped or moderately doped samples. The observed behavior can be explained in terms of the effect of high doping on the inversion of the Γ and X conduction bands at high pressure.

Effect of high doping on the photoluminescence edge of GaAs and InP

A theoretical method for calculating the variation of optical transition energy Eg,opt in semiconductors with heavy n doping is presented. The calculations based on the Moss–Burstein shift and band-gap shrinkage take into account both exchange and Coulomb interactions, the latter being calculated for nonparabolic bands. A comparison with the experimental values of Eg,opt for heavily n-doped GaAs and InP shows good agreement over wide ranges of temperature and doping and can satisfactorily explain photoluminescent emission at energies up to 1.65 eV in GaAs (1.8 °K) and 1.91 eV in InP (300 °K).

The physical behaviour of an n+p silicon solar cell in concentrated sunlight

The performance of a simple n + p silicon solar cell at various illumination levels is analysed by a modified form of the Gummel and De Mari numerical algorithms. Effects of high doping, such as bandgap narrowing together with the correction to density of states are included. The effective recombination life time of the charge carriers due to both Shockley-Read-Hall recombination via traps and Auger recombination is taken into account. The base acceptor doping concentration is 10 16 cm −3. The light concentration is varied from 1 to 200 AM1. The physical mechanisms of the device at various levels of illumination are discussed by determining the cell parameters, namely, saturation current density, short circuit current density, ideality factor and fill factor. The ideality factor which is close to 1 at low illumination suggests that the cell is controlled by diffusion-recombination processes. The high value of the ideality factor, which is very much greater than 1 but less than 2, at high-illumination is attributed to high-injection effect. The efficiency reaches a maximum around 100 AM1 and starts falling beyond that. This fall is due to the high-injection and the voltage drop in the base layer. The fill factor starts falling at high-illumination.

An analytical model for high-low-emitter (HLE) solar cells in concentrated sunlight

A current-voltage characteristic is derived for the high-low emitter (HLE) solar cell in concentrated sunlight. For high-level injection, the ambipolar approach is used to yield the complete information of the low emitter concentration region, including the ohmic drop, the Dember voltage, the minority carrier current density, the minority-carrier distribution and the electric field distribution. High doping effects including Auger recombination and bandgap narrowing are considered. The dependences of short-circuit current, open-circuit voltage, fill factor and conversion efficiency on the variations of the geometrical dimensions and material parameters are discussed in detail for silicon single crystal materials. It is shown that the maximum conversion efficiency of 22% at 100 suns AMO can be obtained for silicon high-low emitter solar cell.

Updating the limit efficiency of silicon solar cells

Since the 1970 evaluation of the "limit efficiency" and design goals for the silicon solar, cell, performed under file auspices of the National Academy of Sciences, some performance limiting phenomina, such as Auger recombination and bandgap narrowing in heavily doped material, have been recognized, some improvements in material parameters, such as minority-carrier lifetimes and surface-recombination velocities, attained, and some remedial designs, such as surface texturizing, increasing the internal optical reflectance at the back surface of the cell, and applying "BSF" structures, evolved. A re-evaluation of the "limit efficiency"' under consideration of the new circumstances has, therefore, been carried out, following the previous approach of analyzing an idealized device structure by use of presently realistic-appearing material parameters, to obtain a conversion efficiency value which represents an upper limit to that technologically achievable in the near future. Removing the idealizations, "design goals" are established which lie near 90 percent of the limit efficiency. The new computations have shown that there exists a second design approach to obtaining high open-circuit and maximum power point voltages, after the first one, relying on high impurity concentration in both the front and the base regions of the cell, has been found limited by the "heavy doping effects." This second approach involves the "narrow-region" design for both the front and base regions of the solar cell, and relies heavily on low effective surface-recombination velocities front and back, as well as a textured front surface and an optical internally reflecting back surface. Using this design, the undesirable effects of high doping can be completely avoided, and the limit efficiency of the solar cell maintained at its earlier value near 25 percent. With the minority-carrier lifetime/impurity concentration model chosen as "realistic," the optimum cell design requires a thin cell, in the 50- to 150-µm range.

High injection in a two-dimensional transistor

A generally accepted theory for bipolar transistors operated at high current densities has not yet been established. Controversy exists as to whether high current Performance is affected primarily by vertical or lateral phenomena. This paper solves the high injection problem by means of a two-dimensional numerical algorithm. The results of some calculations pertaining to a particular example show that base push-out is clearly the dominating mechanism. Emitter crowding caused by lateral majority-carrier current flow in the active base is moderated by base conductivity modulation; it is, however, not negligible. The major limitation of the present work results from the fact that high doping effects are not considered. Thus accurate h <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">FE</inf> predictions cannot be given.