Search

In an optically excited semiconductor micromechanical structure, photogenerated carriers (plasma waves) can produce elastic deformations (local strains and stresses)–plasmaelastic (PE) deformations. On the other hand, the generation of excess carriers will produce heat due to carrier thermalization and recombination processes. The generated heat can produce other elastic deformations–thermoelastic (TE) deformations. For these two components of elastic deformation, it is possible to consider two types of elastic displacements (two mods of elastic vibrations): elastic expanding and elastic bending. A theoretical model of the photoacoustic (PA) signal for optically excited Si membranes is given, which includes thermal diffusion (TD), TE, and PE mechanisms, in order to study elastic expansion and bending. The relations for the PA amplitude and the phase of elastic expanding and bending in the excited membrane are derived. Analysis of the PA signal indicates that the TD component is dominant for all thicknesses and practically the entire range of observed frequencies. The calculated PA amplitude and phase spectra show that the PA elastic expanding component has a significant influence on the total PA signal at low frequencies. On the other side, the calculated PA spectra show that the PA elastic bending component has a significant influence on the total PA signal at high frequencies. Experimental PA signals of Si membranes were measured using the sample-gas-microphone detection technique with a transmission configuration in relation to the modulation frequency of the optical excitation for different membrane thicknesses. The experimental PA spectra were compared with the theoretical ones. [ABSTRACT FROM AUTHOR]

The model of a photoacoustic gas-microphone signal in the time domain recorded in a transmission configuration using a minimum volume cell is derived. This model takes into account the inertial thermal relaxations of both the sample and the gas filling the cell by means of the generalized hyperbolic theory of heat conduction. With the introduction of electro-thermal analogy for the thin sample and short microphone length cavity, characteristic quantities are defined, which can be used in solving the inverse problem in time-domain photoacoustic in both cases, when thermal relaxations are neglected as well as when they are considered. The derived model that includes thermal relaxation explains the experimentally observed occurrence of overshoots and undershoots as well as an oscillatory approach to the steady values of the recorded signal in high-resolution time-domain photoacoustic measurements of thin semiconductor membranes, which will be presented in detail in Paper II of the paper. [ABSTRACT FROM AUTHOR]

Theoretical model for optically excited two-layer elastic plate, which includes plasmaelastic, thermoelastic, and thermodiffusion mechanisms, is given in order to study the dependence of the photoacoustic (PA) elastic bending signal on the optical, thermal, and elastic properties of thin film-substrate system. Thin film-semiconductor sample (in our case Silicon) is modeled by simultaneous analysis of the plasma, thermal, and elastic wave equations. Multireflection effects in thin film are included in theoretical model and analyzed. Relations for the amplitude and phase of electronic and thermal elastic bending in the optically excited two-layer mechanically-supported circular plate are derived. Theoretical analysis of the thermodiffusion, plasmaelastic, and thermoelastic effects in a sample-gas-microphone photoacoustic detection configuration is given. Two normalization procedures of the photoacoustic elastic bending signal in function of the modulation frequency of the optical excitation are established. Given theoretical model can be used for various photoacoustic detection configurations, for example, in the study of optical, thermal, and elastic properties of the dielectric-semiconductor or metal-semiconductor structure, etc., Theoretical analysis shows that it is possible to develop new noncontact and nondestructive experimental method-PA elastic bending method for thin film study, with possibility to obtain the optical, thermal, and elastic parameters of the film thinner than 1 μm. [ABSTRACT FROM AUTHOR]

The results of the theoretical analysis of the dynamic effects in the optically excited cantilevers were given. Theoretical model for dynamic elastic bending for two-layer cantilevers was derived including electronic and thermal elastic deformation effects which have the main influence on the dynamics of the cantilevers. The influence of the carrier transport characteristics (the carrier diffusion coefficient, the lifetime of photogenerated carriers, and the carrier recombination velocities) to the elastic vibrations of cantilevers was analyzed. Theoretical model was verified by comparing with the experimental results. The results of these investigations are important for sensors, actuators, and resonators based on the cantilevers. [ABSTRACT FROM AUTHOR]

In this paper an interferometric setup called “thermoelastic microscopy” has been used to measure the vibration response of the semiconductor cantilevers under modulated laser thermal source. The small vibration amplitude has been detected well below 10 pm magnitude in accurate adjustment conditions. The results showed that experimental responses have a good agreement with the theoretical ones. Also from the analysis we could conclude that the signal amplitude has a power functional dependence on the modulation frequency and that the phase angle linearly depended on the square root of modulation frequency. [ABSTRACT FROM AUTHOR]

Presents a study that used photoacoustic frequency heat-transmission technique to examine thermal and carrier transport properties in low-doped silicon wafers. Description of the theoretical model; Experimental results; Discussion.

Presents information on a study which investigated the possibility of simultaneous determination of thermal and transport properties of thin films using a photoacoustic method. Properties of amorphous GeSe thin films; Determination of thermal diffusivity and transport properties fo the GeSe thin films; Carrier density distribution.

The dynamic thermoelastic and electronic deformation bending in various micromechanical systems were investigated. The elastic bending effect was investigated as a function of modulation frequency including the generation and propagation processes of the plasma, thermal, and elastic waves. The theoretical model for two microstructures (circular plate and cantilever beam) was given and the relations for dynamic elastic bending were derived. The elastic bending was calculated and analyzed for both type of microplates. This investigation is important for the analysis of the possibility to use these semiconducting optically driven microstructures as sensors and actuators. [ABSTRACT FROM AUTHOR]

A method of investigation of semiconductors and metal-semiconductor structures based on two techniques: The elastic bending technique and pyropiezoelectric (PPE) technique was presented. The method was demonstrated on a metal -- semiconductor -- metal (MSM) structure, which is attached to a PPE detector. Two different ac voltages can be measured: One on the electrodes of MSM structure -- the ac-photovoltage, and another on the electrodes of the PPE detector -- the PPE voltage. The ac photovoltage is a consequence of the photogenerated plasma processes in the sample (MSM structure). Photogenerated plasma waves in a semiconductor are followed by the thermal and elastic waves (the elastic bending). Then, the pyroelectric voltage is a consequence of the thermal processes and the piezoelectric voltage is a consequence of elastic bending in the sample-PPE detector system. A theoretical model for a metal -- semiconductor -- metal-pyro(piezo)electric system is given including the space-charge regions and electronic states on the semiconductor surfaces, thermodiffusion, thermoelastic, and electronic deformation effects in a semiconductor. The photoelectric and pyropiezoelectric effects are investigated by analyzing the ac voltages as a function of the modulation frequency of excitation beam. [ABSTRACT FROM AUTHOR]

The system of partially coupled plasma, thermal, and elastic wave equations and conditions for neglecting the coupling between them is analyzed. The treatment considers a semiconductor elastic medium with isotropic and homogeneous thermal and elastic properties. The solution of the coupled system of plasma, thermal and elastic equations is a very complex problem. In most practical cases partially coupled treatment is sufficient. Conditions where it is possible to neglect the coupling between the plasma, thermal, and elastic waves are considered in this work. Special cases for coupled thermal and elastic waves (the thermoelastic problem) and coupled plasma and elastic waves (the electronic deformation) are taken into consideration. An approximate quantitative analysis of the coupling effects is given. [ABSTRACT FROM AUTHOR]

The spectral and dynamic characteristics of surface energy states (SES) on a Si wafer are investigated by photoacoustic (PA) spectroscopy. The PA spectra were measured as a function of the wavelength and modulation frequency of the excitation optical beam by the PA spectrometer. The PA amplitude spectra of Si samples of various surface quality were studied at room temperature in the spectral range of the excitation optical energy beam from 0.7 to 1.5 eV and for various modulation frequencies. The difference in PA amplitude spectra of an as-received Si wafer and a Si wafer with a mechanically roughened surface for various modulation frequencies indicates the energy distribution and the dynamics of the SES. A change in the PA amplitude signal for various modulation frequencies indicates the temporal distribution of the SES for a fixed energy of excitation. [ABSTRACT FROM AUTHOR]

The contribution of free carrier transport processes to the photoacoustic effect in doped A[SUPIV]B[SUPVI]compounds was investigated using the photoacoustic (PA) frequency modulated transmission technique as a valuable tool in the study of thermal and carrier transport processes in semiconductors. The PA signals were measured and analyzed as a function of the modulation frequency in a specially constructed PA cell. The multiparametric fitting procedure was used to obtain some thermal and electronic transport parameters of doped and pure A[SUPIV]B[SUPVI]compounds. [ABSTRACT FROM AUTHOR]