Transmission and absorption based photoacoustic methods of determination of the optical absorption spectra of Si samples — Comparison

This paper is a comparison of two photoacoustic methods of determination of the optical absorption coefficient spectra of semiconductors illustrated with results obtained from Si samples. It presents experimental transmission and absorption photoacoustic spectra of Si samples as also the appropriate models leading to the determination of optical absorption coefficient spectra. The idea and the experimental set-up of the analyzed methods are presented in the paper too. From the fitting procedure of theoretical characteristics to experimental transmission and absorption photoacoustic spectra and after computations of the optical absorption coefficient spectra three components of the optical absorption coefficient spectra of Si samples were identified i.e. band to band transitions, Urbach tail and free carrier absorption. Their parameters are given and discussed in the paper. At the end the advantages and disadvantages of both methods are discussed. To the best of our knowledge, no such proof of the correctness of the PA method of determination of optical absorption spectra has been done.     

Photoacoustic spectroscopy analysis of thin semiconductor samples

This paper is an analysis of determination possibility of the optical absorption coefficient spectra of thin semiconductor layers from their normalized photoacoustic amplitude spectra. Influence of multiple reflections of light in thin layers on their photoacoustic and optical absorption coefficient spectra is presented and discussed in detail. Practical formulae for the optical absorption coefficient spectrum as a function of the normalized photoacoustic amplitude spectrum are derived and presented. Next, they were applied for computations of the optical absorption coefficient spectra of thin In₂S₃ thin layers deposited on a glass substrate. This method was experimentally verified with the optical transmission method.     

The photoacoustic spectroscopic investigations of the surface preparation of ZnSe crystals

This paper presents results of the photoacoustic (PA) spectral studies of a series of ZnSe crystals with differently prepared surfaces. All samples exhibited the surface absorption connected with defects states located on their surfaces. The quality of the surface preparation is expressed by the surface absorption coefficient spectra of the samples times the thickness of a damaged layer. In this paper both theoretical and experimental photoacoustic amplitude and phase spectra as also the corresponding computed surface and volume optical absorption coefficient spectra of the samples with differently prepared surfaces are presented and discussed. This is the first attempt of the quantitative evaluation of the surface quality of the samples from the photoacoustic experimental spectra.     

The photoacoustic spectroscopic investigations of the surface preparation of ZnSe crystals with the use of the optimization methods

This paper shows results of the photoacoustic (PA) spectral studies, with the microphone detection, of a series of ZnSe crystals with differently prepared surfaces. All samples exhibited the surface absorption connected with defects states located on their surfaces. The quality of the surface preparation is expressed by the surface absorption coefficient spectra of the samples times the thickness of a damaged layer. In this paper both theoretical and experimental photoacoustic amplitude and phase spectra as also the corresponding computed surface and volume optical absorption coefficient spectra of the samples with differently prepared surfaces are presented and discussed. The procedure of computations of the volume and surface absorption spectra with the use of the optimization method is presented in the paper too.     

Photoacoustic saturation spectra of some semiconducting group IV-A transition metal dichalcogenides

Photoacoustic saturation spectra in some semiconductors as HfSe₂, ZrS₂ and HfS₂ have been measured at energies above the fundamental absorption edge, where the photoacoustic signal is independent of the optical coefficient and the dips detected in the photoacoustic spectra may be ascribed to optical reflection effects inherent to the band structure. The comparison between our experimental data and those obtained by means of conventional and modulatory spectroscopic techniques proves that such method is a useful tool in order to determine the electronic structure of photoacoustically active semiconductors.     

Photoacoustic investigations of the optical absorption spectra of porous silicon layers on a silicon backing

This paper presents a series of experimental photoacoustic spectra of porous silicon layers on crystalline silicon and their numerical analysis performed in the proposed two-layer model. The goal of the analysis was to calculate the optical absorption spectra of porous silicon from the photoacoustic spectra of porous silicon layers on a silicon background. The experimental character of the observed absorption band associated with the porous silicon was revealed. This is the first attempt at a theoretical interpretation of the photoacoustic spectra of porous silicon on a silicon backing.     

Photoacoustic saturation spectra of GaSe,GaTe and InSe layered semiconductors

The photoacoustic spectra in GaSe, GaTe and InSe semiconductors have been measured in the region of energy greater than the fundamental absorption edge. In this range the photoacoustic signal magnitude can be regarded as independent of the absorption coefficient, i.e. photoacoustic spectroscopy in saturation region, and the dips in the spectra are ascribed to the optical reflection effect inherent in semiconductors interband transitions. The photoacoustic signal phase spectra have been also measured; they are shown to be a useful check of the structures observed in the magnitude saturation spectra. The experimental results are in good agreement with the allowed interband transition energies as observed in thermo-reflectance, electroreflectance and normal reflectivity experiments.     

Photoacoustic method of determination of quantum efficiency of luminescence in Mn<Superscript>2+</Superscript> ions in Zn<Subscript>1−x−y</Subscript>Be<Subscript>x</Subscript>Mn<Subscript>y</Subscript>Se crystals

This paper presents step by step the procedure of determination of the quantum efficiency of luminescence of Mn²⁺ ions in the Zn_1−x−yBe_xMn_ySe crystals. The method is based on the photoacoustic spectroscopy approach. In the paper, the experimental spectra of absorbance, transmission, absorption and photoacoustic spectra of the samples are presented and analyzed from the point of view of the possibility of determination of the quantum efficiency of Mn²⁺ ion luminescence at room temperature. It was determined experimentally that in the investigated crystals the quantum efficiency of luminescence in the Mn²⁺ ions is about 35%, 40%, 32% for the absorption peaks at 430 nm, 470 nm, and 510 nm, respectively, for Zn_0.75Be_0.2Mn_0.05Se crystal.     

Numerical analysis of absorption and transmission photoacoustic spectra of silicon samples with differently treated surfaces

This paper presents results of the photoacoustic (PA) spectral studies, of a series of silicon samples with differently prepared surfaces, in two PA experimental configurations, so-called, absorption and transmission ones. The PA amplitude spectra of the samples indicated existence of the damaged surface layers. In the paper, the two layer mathematical models of a sample with a damaged surface layer that were used for numerical interpretation of the amplitude PA spectra of the investigated samples, are presented and discussed.     

Optical properties of xenon implanted CuInSe2 by photoacoustic spectroscopy

A theoretical relation is derived for the normalized photoacoustic amplitude signal of a gas-coupled cell for the case of double-layer solid samples with particular application given to ion implanted semiconductors. Numerical estimates for a solar cell of the type CdS/CuInSe₂ based on experimental measured data of these compounds are given to illustrate the photoacoustic effect originating from double-layer samples. In application to ion implanted semiconductors, we show that the absorption coefficient of the implanted layer can be very easily extracted by photoacoustic spectroscopy if the absorption coefficient of the untreated substrate is known. We also present the optical properties results obtained from the analysis of the effect of xenon implantation into CuInSe₂ single crystals with the energy of 40 keV and a dose of 5×10¹⁶ ions/cm².     

用光声技术研究半导体TiO2,ZnO纳米晶粉的光学特性

应用新型的光声光谱技术,研究了不同种类和不同制备工艺条件的半导体纳米晶粉的光学特性,测量了半导体TiO2、ZnO和掺铝ZnO纳米晶粉的光声光谱,获得了这些半导体纳米晶粉的带隙和光谱吸收系数.研究结果表明,相同种类和相同颗粒形状的半导体纳米晶粉的粒径越小,光学吸收系数越大.半导体纳米晶粉的带隙与相同种类纳米颗粒形状(圆球...     

表面粗糙样品的太赫兹光谱参数提取方法研究

很多物质在太赫兹波段内的光谱参数具有指纹特征,这是太赫兹技术在安检等众多领域有所应用的基础.但是,目前常用的太赫兹时域光谱(THz-TDS)技术提取物质光学参数的Duvillaret算法,要求样品上下表面平行且充分光滑.然而在很多有潜力的实际应用场合中,尤其是对于固体样品,表面粗糙度不可避免,并且不能使用模具压片等实验...     

Numerical analysis of the photoacoustic spectra of silicon samples with differently treated surfaces

This paper presents results of the photoacoustic (PA) spectral studies of a series of silicon samples with differently prepared surfaces. The PA amplitude and phase spectra of the samples indicated existence of the damaged surface layers. In the paper the two layer mathematical model of a sample with a damaged surface layer, that was used for numerical interpretation of the amplitude and phase PA spectra of the investigated samples, is presented and discussed. This model comprises the Urbach edge contribution to the optical absorption coefficient spectrum and it enabled observation of its influence on the PA amplitude spectra of silicon samples.     

Optische Bestimmung der Nichtparabolizität des dritten Valenzbandes von Germanium

Measurements of the optical absorption of free holes in germanium produced by direct intraband transitions in the valence band have been made at temperatures of 300–390 °K. The experimental method of the photoabsorption was used which enables the absorption spectra to be determined at intrinsic material without an influence of the absorption edge due to interband transitions between the valence band and the conduction band. An analysis of the spectra gives an experimental determination of the shape of the non parabolic split-off valence band. By comparison withKane's theory a marked difference is found but good agreement with calculations fromFawcett is achieved. The temperature dependence of the shape of the split-off band is discussed concerning the optical absorption measurements on “hot holes” in high electric fields with respect of the non-equilibrium energy distribution of the carriers.     

Reflection,Transmission, and Scattering of Light by Photonic Crystals Based on Opal Films

The spectroscopic methods with angular resolution are used to perform an integrated experimental study of optical phenomena (Bragg's reflection, transmission, and scattering of light) in photonic crystals based on opal films. The anisotropy of optical properties and the influence of the photonic band structure on optical spectra of specimens are detected in all examined cases.     

用模拟退火算法研究非晶硅薄膜的光学性质

在玻璃衬底上采用等离子体增强的化学气相沉积(PECVD)法制备了非晶硅薄膜(A-Si:H)。用紫外-可见-近红外分光光度计测出了其透射光谱。采用模拟退火算法研究了透射光谱,得出了薄膜的厚度、折射率和吸收系数随波长变化的关系式、光学带隙等光学常数,并对该方法的优缺点进行了讨论。     

Determination of the low absorption coefficients of thick semi-conductor samples using rear side photoacoustic spectroscopy detection

Based on the Rosencwaig and Gersho theory, we have theoretically derived the photoacoustic signal in the gaz behind the unilluminated surface of thick samples and presented a simple analytical procedure for determining the low optical absorption spectra of these samples.The rear side photoacoustic spectroscopy (PAS) detection has been employed on thick samples of GaP (0,2-1mm) and optical absorption coefficients in the region between 15 to 200 cm^?1 were measured.Our results are discussed in comparison with those obtained by usual front side PAS detection and spectroscopic ellipsometry.     

多参量光声成像及其在生物医学领域的应用

光声成像兼具声学成像和光学成像两者的优点, 因而成为近十年来发展最迅速的生物医学成像技术之一. 本文介绍了光声成像的特点及其相对于广泛应用的光学成像技术和声学成像技术的优点; 其次, 解释了光声成像的成像原理, 在此基础上介绍了光声断层成像和光声显微镜这两种典型的光声成像方案, 并介绍了它们的技术特点; 然后, 介绍了光声成像对生物组织的生化特性、组织力学特性、血液流速分布、温度分布参数、微结构特性等多信息参量的提取能力, 及其在生物系统的结构成像、功能成像、代谢成像、分子成像、基因成像等多领域的应用; 最后, 展望了光声成像在生物医学领域的应用潜力并讨论了其局限性.     

Optical properties of silver colloidal centers in KCl crystals

The Ag colloidal centers in additively colored KCl: Ag crystals have been studied by optical and electron microscope methods. The transmission electron microscope studies reveal that the colloidal particles are spherical in shape and have a size distribution which can be described by the skewed zeroth order logarithmic distribution (ZOLD) function. The band shape of the experimental absorption spectra of colloidal particles agrees well with that calculated on the basis of Mie theory, if the optical constants are suitably modified and if the particle size distribution is taken into account. If the particle size is so small that the size distribution cannot be measured by electron microscope the optical absorption bands can be used to determine the size distribution parameters provided the distribution is well described by ZOLD, which in turn is used to calculate theoretical extinction bands.     

Absorption measurement of strained SiGe nanostructures deposited by UHV-CVD

In order to obtain a low band gap photocell based on the widely spread silicon technology, e.g. for thermophotovoltaics, SiGe nanostructures can be introduced into a monocrystalline silicon photocell. Beforehand, it is necessary to know the absorption coefficient of the SiGe quantum wells. On a silicon (1 0 0) substrate multiple Si/SiGe quantum well structures were grown by UHV-CVD. The Ge concentration and the well width were used as growth parameters. To obtain significant absorption, the experiment was set up to allow for 200 internal reflections.The total reflection of the light results in a standing electromagnetic wave. The absorption coefficient was obtained from the experimental data taking the geometry and the electric field distribution in the absorbing layer into account. The influence of well width and germanium content on the absorption was investigated with the goal of maximizing the absorption for photons with energies below the band gap energy of silicon. The measurement results are compared with a theoretical model, which takes the band structure of strained SiGe including confinement effects into account.