M. Maliński

A linear relationship between the Hall carrier concentration and the effective absorption coefficient measured by means of photothermal radiometry in IR semi-transparent n-type CdMgSe mixed crystals

In this work we demonstrate the ability to measure the effective infrared absorption coefficient in semiconductors by a photothermal infrared radiometry (PTR) experiment, and its correlation with the Hall carrier concentration. The amplitude and phase of the PTR signal were measured for Cd1?xMgxSe mixed crystals, with the magnesium content varying from x = 0 to x = 0.15. The PTR experiments were performed at room temperature in thermal reflection and transmission configurations using a mercury cadmium telluride infrared detector. The PTR data were analyzed in the frame of the one-dimensional heat transport model for infrared semi-transparent crystals. Based on the variation of the normalized PTR phase and amplitude on the modulation frequency, the thermal diffusivity and the effective infrared absorption coefficient were obtained by fitting the theoretical expression to experimental data and compared with the Hall carrier concentration determined by supplementary Hall experiments. A linear relationship between the effective infrared absorption coefficient and the Hall carrier concentration was found which is explained in the frame of the Drude theory. The uncertainty of the measured slope was 6%. The value of the slope depends on (1) the sample IR absorption spectrum and (2) the spectral range of the infrared detector. It has to be pointed out that this method is suitable for use in an industrial environment for a fast and contactless carrier concentration measurement. This method can be used for the characterization of other semiconductors after a calibration procedure is carried out. In addition, the PTR technique yields information on the thermal properties in the same experiment.

Minority carrier recombination lifetimes in n-type CdMgSe mixed crystals measured by means of the photothermal infrared radiometry

Minority recombination lifetimes of n-type CdMgSe mixed crystals were estimated by using infrared photothermal radiometry (PTR) amplitude and phase frequency spectra. The results obtained by the PTR method indicate that the lifetimes of optically generated carriers in CdSe and CdxMg1−xSe crystals are about 0.1 μs. The diffusion length of minority carrier in n-type CdSe single crystal was found to be 4.42 μm and it is in a good agreement with the literature value. It was found that with the increasing thermal-to-plasma component coefficient A the carrier concentration increases as expected from PTR theory.

Photoacoustic studies of Zn1-xBexSe mixed crystals: two-layer approach

Abstract Using the photoacoustic spectroscopy, the following composition-dependent material parameters of Zn 1− x Be x Se mixed crystals were determined: thermal diffusivity, optical absorption coefficient spectra in the region of high absorption and in the Urbachs edge region, the energy gap values and the thermal and compositional broadening of the absorption bands. The quality of the surface of the samples and its influence on the determination of these parameters was checked and discussed.

Design and optimisation of the photoacoustic cell for nondestructive photoacoustic spectroscopy

This paper describes the design and optimisation of the photoacoustic (PA) cell for nondestructive PA spectroscopy. The results of numerical calculations of the acoustic properties of the PA cell are compared with experimental measurements with respect to the frequency response and the quality factor of the cell. The method of designing and optimising of the PA cell is presented. Advantages and disadvantages of this study are discussed.

Theoretical and Experimental Studies of a Plasma Wave Contribution to the Photoacoustic Signal for Si Samples

This paper presents results of theoretical and experimental photoacoustic studies performed on Si samples. The aim of these investigations was to find and examine the best experimental configuration for detection and measurement of plasma waves. The parameter of plasma waves that was examined and determined was a lifetime of excess carriers. This paper prooves that there is one best configuration for observation and detection of plasma waves with the photoacoustic method and describes the method of extraction of a lifetime of carriers in this configuration.

Photoacoustic method of determination of quantum efficiency of luminescence in Mn2+ ions in Zn1−x−yBexMnySe crystals

This paper presents step by step the procedure of determination of the quantum efficiency of luminescence of Mn2+ ions in the Zn1−x−yBexMnySe 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 Zn0.75Be0.2Mn0.05Se crystal.

Energy efficiency of near infrared cobalt luminscence in ZnSe:Co determined by a photoacoustic method

The paper presents results of computations of the energy efficiency of the cobalt luminescence in ZnSe:Co determined by the photoacoustic method. The transmission spectra, photoacoustic experimental and theoretical spectra, and the frequency dependence on the photoacoustic amplitude characteristics are presented. From them, the energy efficiency of Co2+ the near infrared luminescence (3200 nm) was computed in the frame of new proposed photoacoustic model of computations of the luminescence energy efficiency.

A modified approach to the analysis of piezoelectric photothermal spectra

In this paper a modified approach to the problem of interpretation of the piezoelectric photothermal (PPT) spectra is presented. The theory includes computations of the temperature distributions in the samples i.e. the instantaneous temperature, temperature amplitude and phase distributions obtained from the presented temperature distribution equation. Application of the modified Jackson and Amer equation resulted in computations of the amplitude and phase spectra of the piezoelectric signals as a function of the photon energy of the exciting light. The computations of the PPT spectra carried out for the series of semiconductor materials, such as GaAs, InSe and p and n-type Si, led to the new interpretation of the peaks, dips and humps observed in experiments. The inactive layer model and its influence on the interpretation of the PPT spectra is presented and discussed.

Effect of Surface States on Piezoelectric Photothermal Specta of Silicon Single Crystals

The effect of surface states on the piezoelectric photothermal (PPT) spectra of p- and n-type, oriented, single crystal silicon was investigated. We showed that a PPT signal bearing a lower energy edge around 1.04 eV at room temperature was due to the bulk effect. This bulk signal was greatly affected by another signal bearing a broad peak around 1.18±0.01 eV. The broad peaked signal was found to be due to the surface states. The variation in amplitude and phase of the 1.18±0.01 eV signal revealed that the surface states were affected by the ambient illumination and low-temperature thermal annealing at 350 K. The results also indicated that a very low absorption coefficient in indirect semiconductors can be effectively observed by using the proposed PPTS technique.

Influence of light intensity on the lifetime of carriers in silicon investigated by a photoacoustic method

Abstract The paper presents experimental results of the lifetime of light induced excess carriers in the n−type silicon. The lifetimes of carriers of silicon crystals were analysed as a function of the intensity of light illuminating the sample. As a measurement method of the lifetime of carriers, the photoacoustic method in a transmission configuration with different surfaces was used. The dependence character was next analysed in the frame of the Shockley Reed Hall statistics in approximation of the light low intensity.