Recombination lifetime in oxygen-precipitated silicon

The recombination lifetime degrades when interstitial oxygen precipitates in Czochralski-grown silicon. We have observed a more severe degradation in p-type than in n-type material. Based on recombination lifetime, deep-level transient spectroscopy, Fourier-transform infra-red transmission, and transmission electron microscopy measurements, we attribute the degradation mainly to interface states at the precipitate-silicon interface acting as recombination centers. Positive charge in the oxygen precipitates (OP's), causing an electron-attractive space-charge region (scr) around the precipitate in p-Si and a hole-repulsive accumulation layer in n-Si, is proposed to explain the lifetime differences between n-type and p-type silicon.     

Recombination lifetime profiling in very thin Si epitaxial layersused for bipolar VLSI

A recently proposed measurement technique (P. Spirito and G. Cocorullo, IEEE Trans. Electron Devices, vol.ED-32, no.9, p.1708-13, 1985) to evaluate the recombination lifetime along epitaxial layers is used to characterize the quality of very thin Si epitaxial layers used for bipolar technology. The experimental results show the ability of the technique to give accurate and detailed information on the quality of epilayers that could be useful in monitoring and improving the growth process. The experimental results show that the lifetime values in thin epilayers are not correlated with doping profiles in the same layers; moreover, they are only slightly dependent on different processes used to make the test devices     

Recombination centers in silicon transistor emitter-base junctions

Analysis of the temperature dependence of silicon transistor emitter-base junction forward characteristics has yielded information about the recombination centers that give rise to the "non-ideal" component of the base current. The recombination centers are either slightly above midgap with electron capture cross-section much larger than hole capture cross-section, or slightly below midgap with hole capture cross-section much larger than electron capture cross-section.     

Microsecond carrier lifetime measurements in silicon via quasi‐steady‐state photoluminescence

Modulated quasi‐steady‐state photoluminescence is used in photovoltaics in order to measure the injection‐dependent effective minority carrier lifetime of silicon wafers. In spite of the very advantageous properties of this measurement technique, its wide dissemination in photovoltaics has been hampered so far because of a relatively poor sensitivity limit in terms of carrier lifetime. A systematic analysis of the sensitivity‐limiting mechanisms led to a substantial upgrade of sensitivity, tackling the range of effective lifetimes of 1 µs. This paper discusses the requirements to reach this level of sensitivity. Most prominently, the dependence of a silicon photodiode's response time with respect to the wavelength of the detected light is addressed. As an alternative, InGaAs photodiodes are implemented. The sensitivity of this method with respect to carrier lifetime is evaluated. Copyright © 2011 John Wiley & Sons, Ltd.     

Optical silicon lifetime measurements in heavily doped diffused regions

Monochromatic visible light at various wavelengths was used to generate photocurrent in a silicon n+-p diffused diode. A numerical model which includes electric field, heavy doping band gap reduction and doping level mobility dependence was used with fitting techniques to determine the carrier lifetime in the n+-region at each wavelength.     

Metal-to-metal antifuses with very thin silicon dioxide films

Antifuse samples with very thin insulating oxide were fabricated using a technique of two-step PECVD oxide deposition. Dielectric strength as high as 13 MV/cm was obtained for our samples. Defect density and uniformity have been improved in this way. The on-state resistance of the programmed antifuses shows a stronger dependence on the oxide thickness when it was programmed at the lower current than when it was programmed at the higher current     

An improved test structure for recombination lifetime profilemeasurements in very thick silicon wafers

A new test structure for recombination lifetime profile measurements has been designed and applied, for the first time, to the characterization of very thick bulk silicon wafers. The capability of the new test device to reject parasitic effects, affecting the reliability of the measure in bulk wafers, is shown by means of two-dimensional (2-D) simulations and experimental results. The proposed device has permitted the characterization of two P-type silicon bulk samples. For the first time a clear experimental evidence that the dopant acts as a recombination center has been found in this kind of material     

A new cell structure for very thin high-efficiency silicon solarcells

The cell has a corrugated structure, which is formed by aligned V grooves on both the front and back surfaces. The substrate thickness is reduced to 50 μm while retaining high mechanical strength. This permits ease of handling during the fabrication process and subsequent procedures. This thin substrate promises a very high open-circuit voltage, and the structure is also beneficial to high optical performance. The surface reflectance is reduced in the same manner as that of V-grooved cells, but the optical path is lengthened by a minimum of four times the substrate thickness. Performance of experimental cells is also discussed     

Recombination lifetime in a semiconductor laser diode

The effect of minority carrier lifetime on the impedance of the laser within a diffusion or a drift length from the junction is analyzed. Lifetime shorting due to stimulated recombination (which is a function of the injection current) is considered and the effect of cavity size on the ability to modulate the laser at high frequencies is pointed out.     

Recombination in hydrogenated amorphous silicon

Investigations of transient photoconductivity in a-Si: H lead to the conclusion that tunnel recombination of localized excess carriers may predominate in the temperature range from liquid-helium temperatures up to temperatures at which the material was synthesized. Fiz. Tekh. Poluprovodn. 32, 923–930 (August 1998)     

Recombination in highly injected silicon

Recent advances in solar cells designed to operate under high-level injection conditions have produced devices that are approaching some of the limits imposed by the fundamental band-to-band Auger recombination in Silicon. A device has been optimized to study this recombination by using the fabrication technology developed for point-contact solar cells. Using both steady-state and transient measurements, the recombination rates in high-resistivity Si in the injected carrier density range of 10¹⁵to 2 × 10¹⁷carriers / cm³were investigated. The coefficient of the recombination, which depends on the carrier density cubed, is found to be 1.66 × 10^-30cm⁶/s ± 15 percent. This result is four times higher than the ambipolar Auger coefficient commonly used in the modeling of devices that operate in this injected carrier density range and lowers the expected limit efficiencies for silicon solar cells.     

Easy-to-use surface passivation technique for bulk carrier lifetime measurements on silicon wafers

A novel, easily applicable surface passivation technique is presented, which, in combination with contactless photocoductance decay (PCD) measurements, allows a quick estimation of the bulk carrier lifetime of crystalline silicon wafers. The proposed passivation technique requires neither a chemical pre-cleaning of the silicon wafer nor expensive instrumentation. On both surfaces of the wafer a thin varnish film is deposited using a spinner. Subsequently, both surfaces of the coated silicon wafer are charged by means of a corona chamber. Using microwave-detected PCD measurements, we experimentally demonstrate that this novel surface passivation scheme provides differential surface recombination velocities in the 30–70 cm s⁻¹ range on p-as well as n-type silicon wafers. © 1998 John Wiley & Sons, Ltd.     

Recombination and trapping in multicrystalline silicon

Minority carrier recombination and trapping frequently coexist in multicrystalline silicon (mc-Si), with the latter effect obscuring both transient and steady-state measurements of the photoconductance. In this paper, the injection dependence of the measured lifetime is studied to gain insight into these physical mechanisms. A theoretical model for minority carrier trapping is shown to explain the anomalous dependence of the apparent lifetime with injection level and allow the evaluation of the density of trapping centers. The main causes for volume recombination in mc-Si, impurities and crystallographic defects, are separately investigated by means of cross-contamination and gettering experiments. Metallic impurities produce a dependence of the bulk minority carrier lifetime with injection level that follows the Shockley-Read-Hall recombination theory. Modeling of this dependence gives information on the fundamental electron and hole lifetimes, with the former typically being considerably smaller than the latter, in p-type silicon, Phosphorus gettering is used to remove most of the impurities and reveal the crystallographic limits on the lifetime, which can reach 600 μs for 1.5 Ωcm mc-Si. Measurements of the lifetime at very high injection levels show evidence of the Auger recombination mechanism in mc-Si. Finally, the surface recombination velocity of the interface between mc-Si and thermally grown SiO₂ is measured and found to be as low as 70 cm/s for 1.5 Ωcm material after a forming gas anneal and 40 cm/s after an anneal. These high bulk lifetimes and excellent surface passivation prove that mc-Si can have an electronic quality similar to that of single-crystalline silicon     

Recombination of self-trapped excitons in silicon nanocrystals grown in silicon oxide

The kinetics of photoluminescence (PL) and steady-state PL from silicon nanocrystals formed in the SiO₂ matrix by silicon ion implantation were studied experimentally for the first time in the temperature range from liquid-helium to room temperature. A dramatic increase in the photoluminescence decay time, accompanied by PL intensity quenching, is observed below 70 K. The results obtained indicate that the silicon nanocrystal PL arises from radiative recombination of excitons self-trapped at the silicon nanocrystal-SiO₂ interface.     

Recombination saturation effects in silicon solar cells

Significant interest has recently been shown in the use of dark and illuminated current-voltage (I-V) measurements for the characterization of high-efficiency silicon solar cells. Similar nonideal behavior, in the form of “humps” in dark I-V curves, has been observed by various research groups but apparently different interpretations of this effect given. In this paper we present detailed computer simulations of solar cells with defects (producing recombination centers within the bandgap) at a number of specific positions in the devices. It is found that a distinct shoulder (or “hump”) occurs in the I-V characteristics when the recombination centers exhibit unequal electron and hole capture rates. Furthermore, it is shown that these shoulders are a result of the saturation of (Shockley-Read-Hall) recombination via the defect levels, which dominates behavior at low forward bias. As the bias voltage is increased, recombination in the defected region increases again, beyond the saturation level. The simulations show conclusively that the shoulders in the measured dark I-V curves of high-efficiency silicon solar cells produced at the University of New South Wales arise from the rear Si-SiO₂ interface     

Recombination activity of interfaces in multicrystalline silicon

Semiconductors - The electrical activity of grain boundaries in multicrystalline silicon grown from metallurgical silicon by the Bridgman method is investigated by the method of electron-beam...     

On the determination of the emitter saturation current density from lifetime measurements of silicon devices

Contactless photoconductance measurements are commonly used to extract the emitter saturation current density (J_oe) for crystalline silicon samples containing an emitter on the surface. We review the physics behind the analysis of J_oe and compare the commonly used approximations with more generalised solutions using two‐dimensional device simulations. We quantify errors present in such approximations for different test conditions involving varying illumination conditions and surface properties in samples with the same emitter on both sides. The simulated J_oe obtained from the dark hole current from the emitter into the bulk is nearly the same as the simulated J_oe determined by photoconductance measurements of the rear diffusion. The simulated J_oe at the front emitter is equivalent to that at the rear emitter only when the sample is subject to a nearly constant and flat generation profile. For illumination conditions including visible light, the simulated J_oe at the front emitter is smaller than the simulated J_oe at the rear emitter. Both J_oe at the rear emitter and from the dark hole current in the emitter remain nearly constant over a wide range of base doping densities. The approximations used for the determination of J_oe from photoconductance measurements make J_oe dependent on the excess minority carrier density. Lifetime measurements demonstrate that, even in high‐quality silicon, J_oe should be determined from the analytical solution as a function of excess minority carrier density including Shockley‐Read‐Hall recombination. Copyright © 2012 John Wiley & Sons, Ltd.     

Minority-carrier lifetime measurements on silicon solar cells using Iscand Voctransient decay

Measurements of the transient decay of short-circuit current and open-circuit voltage of solar cells provide sufficient information, in principle, to determine both the effective back-surface recombination velocity S and the base minority-carrier lifetime τ. The practical use of the method is illustrated by an example, and the technique is applied to a variety of cells. Analysis of the effect of different cell thickness on the measurement is included. Finally, some limitations, both fundamental and experimental, are discussed.     

Recombination level selection criteria for lifetime reduction in integrated circuits

In the past, lifetime control in integrated circuits has been done on an empirical basis. This paper introduces selection criteria for recombination centers which are to be used for reducing minority carrier lifetime in integrated circuits. It is shown that the recombination level should have a large lifetime ratio (τ_SC/τ_LL) in order to obtain minority carrier lifetime reduction with minimal increase in the leakage current, and should possess large capture cross section values in order to minimize compensation effects. Using these criteria, preferred locations for the recombination center have been defined for both p and n type silicon, and the trade-off between reduction of lifetime and increase in leakage current has been shown to degrade with increase in resistivity and ambient temperature. These criteria have also allowed a quantitative comparison between various lifetime control techniques for the first time, and platinum doping has been identified as the most favorable lifetime control process at the present time.