Laser-induced infrared photocarrier radiometry ͑PCR͒ is introduced theoretically and experimentally through deep subsurface scanning imaging and signal frequency dependencies from Si wafers. A roomtemperature InGaAs detector (0.8-1.8 m) with integrated amplification electronics is used instead of the liquid-nitrogen-cooled HgCdTe photodetector (2-12 m) of conventional photothermal radiometry. PCR measures purely electronic carrier-wave ͑CW͒ recombination. The InGaAs detector completely obliterates the thermal-infrared emission band (8-12 m), unlike the known photothermal signal types, which invariably contain combinations of carrier-wave and thermal-wave infrared emissions due to the concurrent lattice absorption of the incident beam and nonradiative heating. The PCR theory is presented as infrared depth integrals of CW density profiles. Experimental aspects of this methodology are given, including the determination of photocarrier transport parameters through modulation frequency scans, as well as CW scanning imaging. The PCR coordinate scans at the front surface of 500Ϫm-thick Si wafers with slight back-surface mechanical defects can easily ''see'' and create clear images of the defects at modulation frequencies up to 100 kHz, at laser-beam optical penetration depth ϳ1 m below the surface ͑at 514 nm͒. The physics of the contrast mechanism for the nonthermal nature of the PCR signal is described: it involves self-reabsorption of CWrecombination-generated IR photons emitted by the photoexcited carrier-wave distribution depth profile throughout the wafer bulk. The distribution is modified by enhanced recombination at localized or extended defects, even as remote as the back surface of the material. The high-frequency, deep-defect PCR images thus obtained prove that very-near-surface ͑where optoelectronic device fabrication takes place͒ photocarrier generation can be detrimentally affected not only by local electronic defects as is commonly assumed, but also by defects in remote wafer regions much deeper than the extent of the electronically active thin surface layer.

A recently introduced infrared photocarrier radiometry technique has been used to determine the temperature dependence of carrier mobility in Si wafers. In addition, its potential to determine simultaneously the carrier lifetime, diffusion coefficient, and surface recombination velocity is reported. This noncontact, nonintrusive, and all-optical technique relies on the detection of infrared radiation from harmonically excited free carriers (pure electronic diffusion-wave detection). Using a multiparameter fitting to a complete theory, the results showed that the lifetime increases with temperature, the diffusion coefficient decreases [D(T)∼T−1.5], and the temperature dependence of carrier mobility is μ(T)=(1.06±0.07)×109×T−2.49±0.01 cm2/V s.

The determination of the electronic transport properties of ion-implanted silicon wafers with the photocarrier radiometry ͑PCR͒ technique by fitting frequency scan data to a single layer model via a multiparameter fitting procedure is presented. A three-layer model is used to simulate the inhomogeneous structure of the ion-implanted wafers. The effects of the structural, electronic, and optical properties of the implanted layer, which are affected significantly by ion implantation, on the frequency behavior of the PCR signal of implanted wafers are discussed. Data simulated with the three-layer model are fitted to a single-layer model to extract the electronic transport properties of implanted wafers. The fitted carrier lifetime and diffusion coefficient are found to be close to that of the substrate layer which is assumed to remain intact after the ion implantation process. When self-normalized relative amplitude is used in the multiparameter fitting, the fitted surface recombination velocity is determined primarily by the level of electronic damage and is approximately independent of the level of optical damage. Experiments with boron implanted wafers were performed and the experimental results were in agreement with the simulations. These results show that the PCR technique is capable of measuring the bulk transport properties of ion-implanted silicon wafers.

Simulations are performed to investigate the accuracy of the simultaneous determination of the electronic transport properties (the carrier lifetime, the carrier diffusion coefficient, and the front and rear surface recombination velocities) of silicon wafers by means of the photocarrier radiometry (PCR) technique through fitting frequency-scan data to a rigorous model via a multi-parameter fitting process. The uncertainties of the fitted parameter values are analyzed by calculating the dependence of the square variance including both amplitude and phase variances on the electronic transport properties. Simulation results show that the ability of the PCR to accurately determine carrier lifetimes gradually decreases for lifetimes longer than roughly 100 microseconds. In case the carrier diffusion coefficient is previously known, the carrier lifetime and front surface recombination velocity can be determined with uncertainties approximately ±20% or less. Experiments with an ion-implanted silicon wafer were performed and the carrier lifetime and front surface recombination velocity were determined with estimated uncertainties approximately ±30% and ±15%, respectively.

Articles you may be interested inThree-layer photocarrier radiometry model of ion-implanted silicon wafers J. Appl. Phys. 95, 7832 (2004); 10.1063/1.1748862Carrier-density-wave transport property depth profilometry using spectroscopic photothermal radiometry of silicon wafers II: Experimental and computational aspects A theoretical model for the photothermal radiometric ͑PTR͒ signal from an indirect band-gap semiconductor excited by a laser of arbitrary wavelength is presented. The model has been used to investigate the spectral dependence of the sensitivity of the PTR signal to variations in the electronic transport parameters of the sample. Simulations show slight variations of the sensitivity to carrier lifetime and carrier diffusivity with excitation wavelength due to changes in the strength of the thermal contribution to the signal that are a result of changes in the difference between the photon energy and the band gap. The sensitivity of the PTR signal to changes in the front surface recombination velocity is shown to have a strong dependence on the excitation wavelength with the sensitivity decreasing as the absorption depth of the excitation source increases, allowing spectroscopic carrier-density-wave depth profilometric measurements.