Photocarrier Radiometry Research Articles

Radiation intensity dependence of CdSe photothermal and photocarrier radiometry response evidenced by step-sine modulation method

The radiation intensity dependence of photothermal (PT) and photocarrier (PC) signals from n-type CdSe single crystals was investigated by modulated infrared radiometry (MIRR) in the mid-IR range (5–11.3 μm) with superbandgap photoexcitation. The influence of dc temperature increase of the sample was avoided by a new step-sine modulation method that combines the advantages of transient and periodical modulation. With increasing laser intensity I, the amplitude of the PC component shows a sub-linear dependence (|SPC| ∝ I0.5), while the PT one has the expected linear dependence (|SPT| ∝ I). As a result, the transition frequency ft between the two components is shifted to higher frequencies, which is explained in the frame of a simple model. The origin of the observed effects is the decrease of the effective photocarrier lifetime τ ∝ I−0.5 over three laser intensity decades. In contrast, previous studies on nonlinear PC response in semiconductors performed in the near-IR range (0.7–1.8 μm) have found supra-linear |SPC| dependence with exponent between 1 and 2. This difference is attributed to the fact that the near-IR radiometric signal features characteristics of a photoluminescence (PL) signal that are different from those of the mid-IR PC signal, as shown in our previous study [J. Appl. Phys. 119, 125108 (2016)] on the same CdSe samples.

Evolution of surface recombination property of silicon wafers during laser irradiation by differential photocarrier radiometry

Understanding the surface recombination property of semiconductor materials is beneficial for improving the performance of optoelectronic devices. In this paper, differential photocarrier radiometry (PCR) is carried out to investigate the evolution of the surface recombination velocities of silicon wafers induced by laser irradiation. The PCR signal and the surface recombination velocities were found to be strongly dependent on the quality of the wafer surface and the duration of laser irradiation. The native oxide surface was more susceptible to laser irradiation than the Al2O3 passivated surface due to more surface defects being annealed. A surface-defect annealing model was used to explain the transient behavior of the PCR signal and the surface recombination velocity.

Photothermal radiometry methods in materials science and applied chemical research

In this Review, the main techniques of the photothermal radiometry family with their varieties (modulated and pulsed photothermal radiometry and infrared photocarrier radiometry) and related methods (infrared thermography) are considered from the viewpoints of their specific features and application in chemical research and related disciplines. The basics of the methods and their technical implementation are briefly described. The focus of the paper is to examine the possibilities of photothermal radiometry methods—as techniques combining molecular spectroscopy and thermal characterization—physical and analytical chemistry, materials sciences, and biomedical research. The Review discusses the techniques of photothermal radiometry that find their applications in the various fields of the materials science like investigation of the thermal and structural properties of materials, defectoscopy, and dynamics of thermal processes. It also discusses the techniques that are used in the applied chemical research, in the evaluation of the optical properties at molecular or substance levels and the assessment of various substances including biomaterials. The outlooks of the further development in this area are briefly discussed.

Evaluation of the performance degradation of silicon solar cell irradiated by low-level (

Radiation damage induced by energetic particles such as protons and electrons beams could cause permanent deterioration of electrical characteristics of the semiconductor material, which is one of the primary reasons for failures of the space solar cells. This paper discusses the degradations of carrier lifetime and diffusion length of c-Si solar cell with low-level energy (<1 MeV) electron and proton irradiations using Photocarrier Radiometry (PCR) methodology. A theoretical one-dimensional two-layer PCR model was used to evaluate these two parameters of the c-Si solar cells. Monte Carlo Simulations (MCS) were employed to analyze the radiation damage of c-Si solar cell induced by electron and proton irradiations at different energies. Experimental investigations on PCR signals of c-Si solar cells irradiated by electron and proton beams were presented. The results show that the carrier lifetime and diffusion length are dramatically reduced due to the radiation damage induced by the low-level energy electron and proton irradiation.

Surface recombination property of silicon wafers determined accurately by self-normalized photocarrier radiometry

Surface recombination has a great impact on the performance of solar cells and photodetectors, and thus is necessary to be accurately determined. In this paper, a self-normalized photocarrier radiometry (PCR) with mean square variance graph is employed to improve the determination accuracy of the surface recombination velocities of silicon wafers and to reduce the influence of initial values on multi-parameter estimations. In this method data obtained from both the illuminated front surface and the illuminated rear surface are employed. The uncertainties of the estimated carrier recombination parameters, especially for the surface recombination velocities are improved significantly. Moreover, the influence of instrumental frequency response (IFR) on the multi-parameter estimation is totally eliminated. Theoretical simulations and experiments are performed to confirm the theoretical predictions. The estimated average uncertainties of the front and back surface recombination velocities for the sample used are approximately ± 7.60% and ± 5.71% by the proposed method, which are much improved than ± 13.65% and >±50% by the conventional method.

Accurate characterization of surface recombination velocities of silicon wafers with differential nonlinear photocarrier radiometry

The surface recombination velocity (SRV), which reflects the fundamental characteristics of surface defects of semiconductor wafers, is an important parameter in evaluating the quality of surface passivation and electrical performance of surface devices. In conventional photocarrier radiometry (PCR) used for characterizing the electronic transport properties of electronically thick silicon wafers, the rear SRV usually cannot be determined directly due to the relatively low sensitivity of PCR signal to the rear SRV. On the other hand, the determination of front SRV is also very sensitive to the experimental measurement error, especially the measurement error of instrumental frequency response, which is not always easy to be accurately measured in the experiment. In this paper, the front and rear SRVs of silicon wafers are extracted simultaneously with high accuracy by a differential PCR via multi-parameter fitting of the experimental frequency dependences of amplitude ratio and phase difference of PCR signals obtained from the regular measurements and measurements with wafers being flipped respectively to a corresponding differential nonlinear PCR model. The comparison between the front and rear SRVs determined by the conventional and differential PCRs indicates that the differential PCR is highly accurate for the simultaneous determination of the front and rear SRVs of silicon wafers.

Differential nonlinear photocarrier radiometry for characterizing ultra-low energy boron implantation in silicon

The measuring of the depth profile and electrical activity of implantation impurity in the top nanometer range of silicon encounters various difficulties and limitations, though it is known to be critical in fabrication of silicon complementary metal–oxide–semiconductor (CMOS) devices. In the present work, SRIM program and photocarrier radiometry (PCR) are employed to monitor the boron implantation in industrial-grade silicon in an ultra-low implantation energy range from 0.5 keV to 5 keV. The differential PCR technique, which is improved by greatly shortening the measurement time through the simplification of reference sample, is used to investigate the effects of implantation energy on the frequency behavior of the PCR signal for ultra-shallow junction. The transport parameters and thickness of shallow junction, extracted via multi-parameter fitting the dependence of differential PCR signal on modulation frequency to the corresponding theoretical model, well explain the energy dependence of PCR signal and further quantitatively characterize the recovery degree of structure damage induced by ion implantation and the electrical activation degree of impurities. The monitoring of nm-level thickness and electronic properties exhibits high sensitivity and apparent monotonicity over the industrially relevant implantation energy range. The depth profiles of implantation boron in silicon with the typical electrical damage threshold (Y ED) of 5.3 × 1015 cm−3 are evaluated by the SRIM program, and the determined thickness values are consistent well with those extracted by the differential PCR. It is demonstrated that the SRIM and the PCR are both effective tools to characterize ultra-low energy ion implantation in silicon.

Quantitative Imaging of Defect Distributions in CdZnTe Wafers Using Combined Deep-Level Photothermal Spectroscopy, Photocarrier Radiometry, and Lock-In Carrierography

Quantitative Imaging of Defect Distributions in CdZnTe Wafers Using Combined Deep-Level Photothermal Spectroscopy, Photocarrier Radiometry, and Lock-In Carrierography

Fully nonlinear photocarrier radiometry / modulated photoluminescence dynamics in semiconductors: Theory and applications to quantitative deconvolution of multiplexed photocarrier density wave interference and recombination processes

Semiconductor characterization techniques based on modulated photoluminescence (PL) combine the general advantages of PL metrology with the superior quality benefits of modulated signal generation and lock-in detection. The exciting field of camera-based PL imaging has recently emerged and is proving to be very promising for in-line spatially resolved and globally integrated monitoring of dynamic electronic properties of semiconductor materials and devices during various fabrication and manufacturing stages. Yet, the multiple nonlinearities involved in dynamic PL and their behavior under modulated excitation have neither been adequately addressed theoretically nor quantitatively analyzed, resulting in either misleading interpretations of experimental data or leading to the popular compromise of using the physically ambiguous concept — effective lifetime — as the target measurement parameter, which lumps all the excess carrier de-excitation events together and creates persistent confusion in the comparison among different lifetime measurement techniques. By taking three dominant nonlinearities into account that contribute to dynamic PL responses in Si, the present investigation provides a fully nonlinear frequency-domain model of carrier recombination dynamics under harmonically modulated excitation, based on which six intrinsic electronic parameters of a Si wafer can be resolved and measured simultaneously, i.e. the doping density, the two Shockley-Read-Hall time constants, the radiative recombination coefficient, and the two Auger recombination coefficients. The combined theoretical and experimental technique represents a time demultiplexing methodology which allows the deconvolution of temporally superposed excess carrier de-excitation processes which might otherwise remain unresolved — hidden in superposition — as is typically the case with conventional effective lifetime metrologies. This all-optical and non-contacting electronic quality control approach links substrate property optimization and key device-fabrication processing steps to optimized device performance through elucidating the relationship between the global behavior of the system/device/material and the specific controlling/limiting dynamic (opto)electronic process(es) behind it.

An optoelectronic notch (‘dip’) phenomenon in the heterodyne photocarrier radiometry frequency response of Si wafers: a route to quantitative trap-state dynamic processes in semiconductors

An anomaly was observed in the heterodyne photocarrier radiometry (HePCR) frequency response of Si wafers in the form of a signal amplitude depression (‘dip’) accompanied by a 180° phase transition. This phenomenon resembles an electronic notch filter and was investigated experimentally and theoretically by invoking free-carrier-density-wave (CDW) kinetics in generic semiconductor systems. Both homodyne PCR and HePCR signals were obtained from n- and p-type wafers of different resistivities. Dynamic nonlinear rate-equation models with two bandgap carrier traps were introduced and analytical zeroth and first-order CDW solutions were obtained in the frequency domain. The experimental frequency responses of the HePCR optoelectronic notch phenomenon were found to be in very good agreement with the theory. Characteristic CDW recombination and trap capture and emission characteristic times were obtained and studied as functions of the illuminating laser intensity. The present newly observed HePCR notch phenomenon has revealed a new mechanism of nonlinear contributions due to trap-state-related CDW dynamics in semiconductors superposed on the well-known nonlinear electron-hole recombination interactions that give rise to non-zero HePCR signals. The implications of this notch phenomenon are discussed in terms of its importance in providing physical insights into photocarrier dynamic interactions with traps, leading to identification of active CDW trap-state numbers and precision measurements of their kinetic parameters, carrier capture and emission coefficients, and quantitative trap densities that determine the optoelectronic quality of semiconductors.

Accurate electronic transport characterization of B+ ion-implanted silicon wafers with self-normalized nonlinear photocarrier radiometry

A self-normalized photocarrier radiometry (PCR) is proposed to characterize the electronic transport properties (minority carrier lifetime, carrier diffusion coefficient, and surface recombination velocity) of B+ ion-implanted silicon wafers via multi-parameter estimation. In self-normalized PCR the amplitude and phase measured from the implanted surface are normalized by that measured from the matte rear surface (non-implanted substrate) of the ion-implanted silicon wafer to eliminate the need to measure the instrumental frequency response which is a major error source of the multi-parameter estimation. Two- and single-layer nonlinear PCR models are employed respectively to describe the PCR signals measured from the implanted and matte rear surfaces of the wafers. The self-normalized PCR is applied to the simultaneous determination of the electronic transport parameters and the thickness of the implanted layer of the ion-implanted silicon wafers. Experimentally, the frequency dependences of PCR amplitude and phase measured from the implanted and rear surfaces under 830-nm excitation at 40.5 mW are measured for seven B+ ion-implanted silicon wafers with different implantation doses. The electronic transport parameters and thicknesses of the implanted layers are then determined by multi-parameter fitting the self-normalized PCR amplitude and phase to corresponding nonlinear PCR models, as well as determined by the conventional PCR via measuring the instrumental frequency response and subtracting its influence on the measured PCR signals of the ion-implanted wafers for comparison. The lower variances of multi-parameter fitting and improved uncertainties of the fitted transport parameters in the self-normalized PCR as compared to that in the conventional PCR corroborate the improved accuracy and reliability of the self-normalized PCR for the simultaneous determination of the electronic transport parameters of ion-implanted silicon wafers.

Surface recombination velocity on wet-cleaned silicon wafers using heterodyne lock-in ca rrierography imaging: measurement uniqueness investigation

Characterization of semiconductor surface quality is important for evaluating the surface preparation methods. In this work, three wet-cleaned silicon wafers with different surface conditions were inspected using heterodyne lock-in carrierography (HeLIC) imaging simultaneously with homodyne photocarrier radiometry (HoPCR). The surface recombination velocity was measured at various queue times after the wet-clean treatment using HeLIC and was found to be consistent with values obtained using HoPCR. The results show that HeLIC can provide a reliable quantitative imaging tool for evaluating the surface conditions of wet-cleaned silicon wafers.

Determination of doping concentration of heavily doped silicon wafers using photon reabsorption in photocarrier radiometry

A contactless and non-destructive method for the determination of the doping concentration of heavily doped silicon wafers is proposed. The method is based on a comparison between photocarrier radiometry signals acquired from different surfaces of samples and a comprehensive mathematical model by exploiting photon reabsorption in photocarrier radiometry measurements. With the proposed mathematical model, the influence of experimental and sample parameters on the measurement of the doping concentration is analyzed in detail. The uncertainties and limitations of the method are also discussed. Furthermore, an experimental configuration is proposed.

Electronic transport characterization of B+ ion-implanted silicon wafers with nonlinear photocarrier radiometry

A nonlinear photocarrier radiometry (PCR) based quantitative defect characterization method is applied to determine the electronic transport parameters of the implantation layer of B+ ion-implanted silicon wafers with different implantation doses. A rigorous two-layer nonlinear PCR model is employed to fit the experimental modulation frequency dependences of PCR amplitude and phase to determine the transport parameters, that is, the carrier lifetime, carrier diffusion coefficient, and front surface recombination velocity of the implantation layer via multiparameter fitting. In the multiparameter fitting, the effects of the implantation layer thickness determination on the extraction of the electronic transport properties of the implantation layer are discussed via setting the thickness as a free parameter in the multiparameter fitting and fixed parameters determined by Monte Carlo based TRIM calculation. The fitted implantation layer thicknesses are in good agreement with that determined via TRIM calculation with a modified electronic damage threshold. Monotonic dependences of the transport properties of the implantation layers on the implantation dose are observed, and the effects of impurity density on the transport properties of the implantation layers are discussed. Good agreements between the experimental implantation dose dependence of the nonlinearity coefficient and corresponding theoretical calculations with the determined transport parameters are obtained. These results show that the two-layer nonlinear PCR model is accurate for quantitatively characterizing the transport properties and thickness of the ion-implantation layers of silicon wafers, and the nonlinear PCR technique is appropriate for precise defect characterization in the semiconductor manufacturing processes.

Influence of Nonlinearity on Electronic Transport Characterization of Ion-Implanted Silicon Wafers with Photocarrier Radiometry

Two-layer linear and nonlinear models were employed to investigate the influence of the nonlinear dependence of photocarrier radiometry (PCR) signal on excitation power for ion-implanted silicon wafers on the determination of carrier transport parameters of ion-implanted layers in the frequency domain. Three silicon wafers were measured at 830 nm excitation wavelength, with the ion-implantation dose of 1011, 1013, and 1016 cm−2, respectively. The effect of nonlinear coefficient on the multi-parameter fitting for electronic transport parameter determination was analyzed via theoretical simulations and experimental measurements. Both simulation and experimental results showed that the multi-parameter fitted results obtained via the linear PCR model (ignoring the nonlinearity) were significantly different from that obtained via the nonlinear PCR model (taking into account the nonlinearity). With the linear PCR model, the fitting errors in the determination of transport parameters of ion-implanted layers were highly sensitive to the nonlinearity coefficient. For low-implantation-dose silicon wafers with high nonlinearity coefficients close to 2, the square variance increased drastically, and the fitting errors were non-acceptably high. Comparison of the electronic transport parameters determined via the two-layer linear and nonlinear PCR models clearly showed that two-layer nonlinear PCR model is much more suitable than the linear model for describing the PCR signals and is more accurately for characterizing the carrier transport parameters of ion-implanted silicon wafers.

Nonlinear two-layer model for photocarrier radiometry of ion-implanted silicon wafers

A nonlinear two-layer model was developed to describe and analyze Photocarrier Radiometric (PCR) signals of ion-implanted Si wafers which are intrinsically nonlinear with excitation laser power. The thickness of the implantation layer and the optical/electronic damage threshold for different implantation doses were estimated using the Monte Carlo method and the effective medium approximation theory, respectively, which can provide key parameter values for the model to calculate the nonlinearity coefficient, defined as the slope of PCR amplitude versus excitation power in log-log scale. Experimentally, the nonlinearity coefficients of seven c-Si wafers with implantation doses from 1011 to 1016 cm-2 were measured at two different excitation wavelengths (830 and 405 nm), and good agreement between theory and experiment was found. Results show that the nonlinearity coefficient has a negative correlation with the implantation dose, and the coefficient measured at 405 nm is consistently smaller than that measured at 830 nm for each sample. Compared with the conventional PCR models, the nonlinear two-layer model proposed here is more coincident with experimental facts, thus enabling PCR to provide more accurate quantitative characterization of the carrier recombination and transport properties of ion-implanted semiconductor wafers.

Quantitative Analysis of the Degradation Behavior of Silicon Solar Cell Irradiated by 1 MeV Electron Beams Using Photocarrier Radiometry Combined with Lock-in Carrierography

Silicon solar cells with cover glass irradiated by 1 MeV electron beams at various fluences were investigated using photocarrier radiometry (PCR) combined with lock-in carrierography (LIC, spectrally gated dynamic photoluminescence). The minority carrier transport properties (i.e., minority carrier lifetime τ, diffusion coefficient D, surface recombination velocities S) and the degradation of these properties were studied using PCR. The relative damage coefficient obtained by LIC was consistent with the PCR measurement. The local series resistance of the solar cell before and after irradiation was characterized by LIC. The results showed that the series resistance increased with electron fluences.

Carrier Transport Parameter Imaging in a Multicrystalline Silicon Solar Cell by Laser-Induced Photocarrier Radiometry

The distribution of minority carrier transport parameters (i.e., minority carrier lifetime, diffusion coefficient, and two surfaces recombination velocities) of multicrystalline silicon (mc-Si) solar cell was investigated using laser-induced photocarrier radiometry (PCR). Images of the amplitude and phase of the PCR measurements clearly showed the crystal boundaries of the mc-Si solar cell. The distribution of minority carrier transport parameters was obtained by best fitting the experimental results to the theoretical two-layer carrier density wave model of solar cells. The best-fitting results demonstrated that there was great difference in the minority carrier transport parameters among various grains.

Photocarrier Radiometry for Non-contact Evaluation of Monocrystalline Silicon Solar Cell Under Low-Energy (&lt; 200 keV) Proton Irradiation

A three-layer theoretical model is developed for the characterization of the electronic transport properties (lifetime τ, diffusion coefficient D, and surface recombination velocity s) with energetic particle irradiation on solar cells using non-contact photocarrier radiometry. Monte Carlo (MC) simulation is carried out to obtain the depth profiles of the proton irradiation layer at different low energies (< 200 keV). The monocrystalline silicon (c-Si) solar cells are investigated under different low-energy proton irradiation, and the carrier transport parameters of the three layers are obtained by best-fitting of the experimental results. The results show that the low-energy protons have little influence on the transport parameters of the non-irradiated layer, but high influences on both of the p and n-region irradiation layers which are consisted of MC simulation.

Temperature- and Size-Dependent Exciton Dynamics in PbS Colloidal Quantum Dot Thin Films Using Combined Photoluminescence Spectroscopy and Photocarrier Radiometry

Lead salt colloidal quantum dots (CQDs) are promising active components for applications in electronic and optoelectronic devices such as photodetectors, light-emitting diodes, and solar cells. Detailed understanding of exciton dynamics in these nanocrystalline films is crucial for their practical applications. Photocarrier radiometry (PCR) is a dynamic spectrally integrated frequency-domain photoluminescence (PL) method, the spectral bandwidth of which is gated to eliminate thermal infrared photons due to nonradiative recombination. On the other hand, PL spectroscopy is a steady-state method that offers complementary spectrally resolved information. Combined PL temperature spectra and PCR temperature and frequency measurements were applied to PbS CQD thin films capped with oleic acid. Enhanced PL intensities at high temperatures originating in thermally activated exciton transfer from trap to exciton states were found in two samples consisting of two different sizes of quantum dots. A theoretical exciton...