Bulk Carrier Recombination Research Articles

Bulk carrier lifetime measurement by the microwave reflectance photoconductivity decay method with external surface electric field

We attempted to measure the bulk carrier recombination lifetime of Si wafers by the microwave reflectance photoconductivity decay (PCD) method. Voltage was applied between an external electrode and a Si wafer to suppress surface recombination. Before the measurement, the surface state density was reduced by a chemical treatment using NH4OH–H2O2–H2O and diluted HF solutions. Carrier lifetime as long as 1 ms was measured by the present method for a wafer with a bare surface. Comparison with results for oxidized wafers show that the present method can suppress surface recombination more effectively than thermal oxidation, which has been often used for surface passivation in PCD measurements.

Electrical characterization of shallow cobalt-silicided junctions

The impact of the thickness of the cobalt-silicide layer on the electrical diode characteristics will be reported, with particular emphasis on the current-voltage (I-V characteristics, the surface and bulk carrier recombination lifetime and the low-frequency noise. It is shown that for thicker silicides the generation-recombination of holes in the top n+-layer is enhanced, giving rise to a higher diffusion current, an increase in the noise and a larger surface recombination velocity. It is believed that these parameters are closely linked, as the underlying physical phenomenon is the minority carrier recombination. In addition, it is shown by transmission electron microscopy that the silicide-silicon interface roughness is increased for larger cobalt thickness, which may explain some of the observations.

Evaluation of Oxygen‐Related Carrier Recombination Centers in High‐Purity Czochralski‐Grown Si Crystals by the Bulk Lifetime Measurements

Present day high‐purity Czochralski(CZ)‐grown Si crystals are characterized by the bulk carrier recombination life‐time measurements. The bulk lifetime of the p‐type as‐grown Si with resistivity ∼10 Ω‐cm is found to be as high as 500 μs for a CZ‐Si crystal with and as high as ∼1 ms or even higher for a low‐oxygen CZ‐Si crystal with. The as‐grown bulk lifetime is revealed to depend not only on resistivity under the framework of the Shockley‐Read‐Hall (SRH) relation, but also on the oxygen concentration. The dominant recombination center of the as‐grown crystal is found to be an SRH‐type deep‐level center which is considered to be an oxygen‐related defect complex. The complex is quenched easily by a heat‐treatment at a temperature as low as 650°C. Effective density of a recombination center, existing after the 650°C heat‐treatment in the p‐type crystal, correlates well with the amount of oxygen precipitation generated by a subsequent two‐step heat process . Thus the dominant recombination center after the 650°C heat‐treatment is considered to be closely related to the oxygen precipitation nuclei toward the subsequent precipitation formation heat process.

An in-depth analysis of the 'Elymat' technique for characterizing metallic microcontamination in silicon: Experimental validation for iron contamination in p-type wafers

Application of the on-line Elymat technique for measuring bulk carrier recombination lifetime is numerically analysed using a complete three-dimensional carrier transport simulation including the Dember electric field, the characteristics of the laser beam, the transport parameters of the wafer and Shockley-Read-Hall recombination kinetics. We found a strong dependency of the measured lifetime on the shape and power of the laser beam as well as on the deep energy level of the impurity in the gap, owing to nonlinear effects not described by the classical model. Our numerical simulations show that the use of a small laser beam permitting the approximation of point-like excitation gives the most reliable results. The comparison between our numerical simulations and experimental results for iron-contaminated p-type samples with a resistivity between 1 and 18 Omega cm shows that the donor level of Fe-B pairs at Ec-0.3 eV and not the classical acceptor level at Ev+0.1 eV is the predominant site of recombination of Fe-B pairs in p-type silicon in the above doping range. First results for the electron and hole capture cross sections for this defect will be given. Based on these results, the sensitivity of the technique is shown to be less than 1011cm-3 in the case of Fe-B pairs corresponding to less than 10 PPT (parts per trillion).

Influence of nonequilibrium charge carrier recombination on the signal shape and magnitude in the photodeflection spectroscopy method under pulse excitation

A theory of signal shaping is proposed for semiconductor investigation by the method of photodeflection spectroscopy with pulse excitation that would take account of the influence of charge carrier recombination on the temperature distribution in the specimen. Quantitative computations are performed for silicon that demonstrate the change in PDS signal amplitude and shape when taking account of bulk carrier recombination. It is shown that taking account of the influence of bulk recombination discloses the possibility of obtaining additional quantitative information about the charge carrier lifetime in the specimen.

Carrier‐Driven Photochemical Dry Etching of Indirect III‐V Compound Semiconductors

The carrier‐driven photochemical dry etching of both direct‐ and indirect‐gap semiconductors depends strongly on the depth of generation of free carriers and the recombination behavior of those carriers. While excitation across the lowest energy gap, , of a direct semiconductor produces many near‐surface carriers to drive etching, too few carriers may be generated near the surface by excitation across of an indirect semiconductor for etching to occur. However, excitation across the direct gap of an indirect semiconductor produces sufficient near‐surface carriers for rapid etching. Enhanced bulk carrier recombination in very heavily doped materials can suppress etching in both direct and indirect semiconductors.

Effect of Temperature on the Operation of a Photoelectrochemical Device: Studies on the n ‐ GaAs / Room Temperature Molten Salt Electrolyte Interface

The effect of temperature on the photovoltaic performance of a photo‐electrochemical (PEC) system was evaluated by measurements on a model system comprising the pyridinium chloride (BPC)|carbon cell containing the ferrocene/ferricenium ion couple. Changes in the solar cell parameters for this system with temperature were monitored for the range from ambient to 85°C. The short‐circuit current densities showed a systematic increase over the temperature range while the open‐circuit voltage and fill‐factor (FF) showed a linear decrease at the rate of 3.6 mV/°C and 0.001/°C, respectively. The energy conversion efficiency (η) of the device showed a maximum at an intermediate temperature (∼50°C) beyond which the decline in and FFoutweighed the beneficial effect of temperature on , leading to a rapid fall‐off in η at temperatures above ∼60°C. The linear decrease of with increasing temperature was seen to be directly related to the increased dark current density at elevated temperatures. Analysis of the dark currentvs. voltage data by Schottky diode theory revealed the expected exponential dependence of the reverse saturation current density on temperature for the model PEC system. Measurement of the semiconductor flatband potential for the interface at varying temperatures revealed a further origin for the increase in dark currents with temperature. The shift in to positive potentials with increasing temperature reduced the effective activation energy (or barrier height) for electron injection from the electrolyte into the semiconductor in the dark. These results are discussed in terms of two mechanisms: (i) direct charge transfer between the semiconductor and the occupied redox levels in the electrolyte and (ii) electron injection into the semiconductor mediated by trap levels in the energy bandgap of the semiconductor. Finally, the effect of temperature on the Schottky diode parameters of the , cell is discussed in terms of enhanced surface and bulk carrier recombination effects at elevated temperatures. These lead to the observed deterioration in the fill‐factor because of the increased series resistance associated with recombination‐generation current flow paths.