A. Buczkowski

Recombination at clean and decorated misfit dislocations

The electrical activity of interfacial misfit dislocations in silicon has been examined using the electron beam induced current technique in a scanning electron microscope. Clean dislocations formed during high‐temperature Si(Ge) chemical vapor epitaxy were studied. These defects were subsequently decorated with known metallic impurities (Au and Ni) by diffusion at different temperatures from a backside evaporated layer. Differences in electrical activity are discussed in relation to the detection limits of electron beam induced current technique and energy levels anticipated for the clean or decorated dislocations.

Bulk and surface components of recombination lifetime based on a two‐laser microwave reflection technique

An algorithm for separating the bulk and surface components of recombination lifetime, tailored for contactless measurement techniques with laser excitation, is presented in the paper. In order to analyze the carrier decays and subtract the surface recombination term, two lasers operating at 910 and 830 nm are applied. A separation of carrier decay resulting from the different contribution of surface and bulk components due to difference in the light absorption is observed for such a case. This separation is a function of surface recombination velocity S. An experimental verification of the analysis is presented using microwave absorption/reflection measurements.

Separation of the bulk and surface components of recombination lifetime obtained with a single laser/microwave photoconductance technique

An algorithm for separating the bulk and surface components of recombination lifetime obtained via a contactless single laser excitation/microwave reflection decay measurement is presented. The surface recombination component of lifetime is determined by extrapolating the tail portion of the carrier decay curve to the carrier axis. Although the slope of this curve depends on both surface and bulk properties, it is shown that the y intercept depends only on the surface component of lifetime. A wide range of surface lifetimes, corresponding to surface recombination velocities from 102 to 105 cm/s, and bulk lifetimes from a few microseconds to several hundred microseconds can be measured. An experimental verification of the analysis is presented using microwave absorption/reflection measurements on silicon wafers representing a wide variety of bulk and surface lifetime components.

Electrical activity of dislocations: Prospects for practical utilization

The electrical activity of interfacial misfit dislocations in silicon has been examined using the electron beam induced current technique (EBIC) in a scanning electron microscope. “Clean” misfit dislocations, i.e. no EBIC contrast, formed during high-temperature Si(Ge) chemical vapor epitaxy were studied. These defects were subsequently decorated with known metallic impurities (Au and Ni) by diffusion at 400° C to 1130° C from a back-side evaporated layer. Qualitative analysis of the electrical activity in relation to the energy levels anticipated for the clean or decorated dislocations is presented. Of particular interest is the case of defect-induced conductivity type inversion which occurred both at the top surface and at the buried dislocated interfaces of the multilayer. The prospects for using dislocations in a beneficial manner as active elements in electronic devices are discussed.

Transient recovery of minority‐carrier lifetime in silicon after ultraviolet irradiation

A recovery process of minority‐carrier recombination lifetime after ultraviolet (UV) irradiation has been investigated with a laser‐microwave photoconductance technique for silicon wafers with native oxide. It is found that the effective lifetime which greatly increases after UV irradiation recovers to the initial value primarily with an exponential law characterized by a specific time constant called recovery time. The recovery time depends on experimental conditions where, for example, an accumulation effect of UV irradiation is observed. A mechanism of the effective lifetime recovery process is correlated mainly with the behavior of slow states associated with the silicon/native oxide interface.

Noncontact energy level analysis of metallic impurities in silicon crystals

Noncontact laser/microwave deep level transient spectroscopy (LM‐DLTS) based on the measurement of microwave reflection power as a function of temperature has been developed and applied to Czochralski silicon crystals intentionally contaminated with selected metals during crystal growth. The energy levels related to these metallic impurities in p‐type silicon have been obtained on bare silicon for the first time without any electrode contact or special sample preparation. The data agree in very satisfactory fashion with results obtained by conventional DLTS.

Photothermal rate-window spectrometry for noncontact bulk lifetime measurements in semiconductors

A new noncontact technique for the determination of excess carrier lifetimes in semiconductors is presented. The technique employs a square laser pulse (hν≥Eg) and measures the infrared photothermal radiometric response of the sample. By applying the photothermal rate‐window concept, the excess photoexcited carrier bulk lifetime was measured with optimal signal‐to‐noise (S/N) ratio and simple, unambiguous interpretation from the maximum position of the rate‐window signal. The technique has been applied to Au‐, Fe‐, and Cr‐doped Czochralski silicon crystals. The experimental results from boxcar and lock‐in rate‐window methods were found to agree very well. The results are further mostly in agreement with those from the noncontact laser/microwave detection method.

Formation of cylindrical n/p junction diodes by arsenic enhanced diffusion along interfacial misfit dislocations in p‐type epitaxial Si/Si(Ge)

Arsenic enhanced diffusion along individual misfit dislocations in Si/Si(Ge) heterostructures has been detected and imaged using scanning electron microscopy (SEM) and in the electron beam induced current (EBIC) mode. The formation of buried cylindrical, or conical, diodes surrounding misfit dislocations has been observed. The diffusion enhancement is not uniform for each dislocation. EBIC/SEM micrographs reveal a dark recombination contrast in the vicinity of the dislocation core and a white generation signal within the space‐charge region of the surrounding n/p diode. Based on an experimental isoconcentration etching profile and a simple model for enhanced diffusion, the dislocation diffusion coefficient for arsenic is estimated to be up to six orders of magnitude higher than that in the host crystal.

Photoconductance minority carrier lifetime vs. surface photovoltage diffusion length in silicon

Recombination lifetime and diffusion length measured with the photoconductance decay and surface photovoltage techniques are compared theoretically and experimentally, and reasons for possible discrepancies are discussed. Specific examples are given which show that, if full advantage of these noncontact and nondestructive procedures is to be taken, it is necessary that surface recombination be considered in the analysis of any experimental data. This is particularly true for samples where the diffusion length is greater than one-fourth of the wafer thickness, a condition for which it is essential that theoretical algorithms for separating the bulk and surface components of recombination be developed.

Noncontact characterization for grown‐in defects in Czochralski silicon wafers with a laser/microwave photoconductance method

Minority‐carrier recombination lifetime mapping has been performed with a noncontact laser/microwave photoconductance method for as‐polished wafers containing a ring‐shaped distribution of embryonic defects which form stacking faults during subsequent heat treatment. Using an algorithm for the separation of bulk and surface components of the recombination lifetime, four regions, which cannot be distinguished with other techniques such as x‐ray topography and preferential chemical etching, were clearly observed in the maps as those with different lifetimes. The result can be attributed to the inhomogeneous distribution of grown‐in defects, most likely intrinsic point defects and/or oxygen related defects. Moreover, the lifetime was correlated to the surface microroughness of the polished wafers.