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M.Maliński 1) J.Zakrzewski 2)

Application of the inhomogeneous sample model in the piezoelectric spectroscopy of Zn 1-x Be x Te and Cd 1-x Mn x Te mixed crystals. M.Maliński 1) J.Zakrzewski 2) 1)      Department of Electronics, Technical University of Koszalin Poland

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M.Maliński 1) J.Zakrzewski 2)

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  1. Application of the inhomogeneous sample model in the piezoelectric spectroscopy of Zn1-xBexTe and Cd1-xMnxTe mixed crystals. M.Maliński 1) J.Zakrzewski 2) 1)      Department of Electronics, Technical University of Koszalin Poland 2)Institute of Physics Nicolaus Copernicus University Toruń Poland

  2. ABSTRACT This paper presents the basic details of the inhomogeneous sample model. This is one of the models describing the piezoelectric photothermal (PPT) spectra observed for mixed crystals. The experimental PPT spectra of Zn1-xBexTe and Cd1-xMnxTe mixed crystals presented in this paper exhibited the character of the crystal structure that was interpreted in the model of the inhomogeneous sample. The analysis of the spectra, performed in this model, enabled determination of both the basic optical parameters of two crystal regions, observed in the investigated samples, and the percentage composition of the crystals.

  3. Sample preparation and experimental procedures. Single crystals of AII-BVI semiconductors were grown from the melt by the high pressure Bridgman method under argon overpressure. The crystals were cut into 0.1 cm thick plates , mechanically polished and chemically etched. Some samples were annealed in zinc vapour at the temperature 1230K for several hours. The piezoelectric photothermal (PPT) spectra were measured in the rear configuration with the PZT transducer attached to the back side of the sample. For the measurements the open acoustic cell was used. The signal was detected with the lock-in amplifier. All PPT spectra were measured at room temperature.

  4. The inhomogeneous sample model. Fig1. Schematic diagram of a sample in the inhomogeneous sample model. I and II denote two crystal regions  is the thickness of a surface inactive layer, backing means in the case of investigated samples a steal hemisphere between the sample and a PZT transducer. ForE exc< Eg ForE exc> Eg

  5. The set of average values of the parameters obtained for Zn1-xBexTe mixed crystals when x=0.07 Eg1=2.32 eV Eg2=2.38 eV 01=100 cm-1 02=80 cm-1 1=0.5 2=1 A01=1500 cm-1eV-1/2A01=1500 cm-1eV-1/2 =0.2 cm2/s =0.006 cm

  6. Computations of the PPT spectra of mixed crystals l=0.1 cm =0.2, R=-1, f=126 Hz 1=0.006 cm, 2=0 cm Jackson & Amer Piezoelectric Equation

  7. Resulting PPT spectra for k=0.4 & 1=0.006 cm, 2=0 cm

  8. The experimental PPT spectra of Zn1-xBexTe mixed crystals PPT amplitude spectra of ZnTe at a) f=16 Hz b) f=36 Hz. Circles are experimental results, solid lines are theoretical curves computed in a model of a single layer =0 cm.

  9. The experimental and theoretical amplitude PPT spectra of Zn0.93Be0.07Te mixed crystals Amplitude PPT spectra for 3 Hz. Eg1=2.37 eV Eg2=2.42 eV k=0.42. Circles –experimental results , solid line theoretical curve. Amplitude PPT spectra for 16 Hz Eg1=2.31 eV, Eg2=2.37 eV k=0.42. Circles-experimental results, solid line- theoretical curve.

  10. The experimental PPT spectra of Zn1-xBexTe mixed crystals Amplitude PPT spectra for 76 Hz Eg1=2.31 eV, Eg2=2.35 eV k=0.25. Circles-experimental results, solid line- theoretical curve. Amplitude PPT spectra for 36 Hz Eg1=2.32 eV, Eg2=2.38 eV k=0.25. Circles-experimental results, solid line- theoretical curve

  11. The experimental and theoretical amplitude PPT spectra of Zn0.93Be0.07Te mixed crystals Amplitude PPT spectra for 126 Hz Eg1=2.30 eV, Eg2=2.35 eV k=0.4. Circles-experimental results, solid line- theoretical curve.

  12. The amplitude PPT spectra of CdTe sample Amplitude PPT spectra of CdTe sample at f=76 Hz. Circles-experimental results, solid line is the theoretical curve computed for the parameters: Eg=1.51 eV, =0.03 cm2/s, =0.019 cm, 0=130 cm-1, =0.9. Amplitude PPT spectra of Cd0.51Mn0.49Te mixed crystal for f=76 Hz, l=0.1 cm. Fitting parameters: : Eg1=2.035 eV, 01=130 cm-1,1=0.5, A01=1500 ,Eg2=2.105 eV, 02=150 cm-1,2=0.9,A02=1500 , =0.1 cm2/s, 1=0.005 cm, 2=0 cm. R=1, k=0.3.

  13. The influence of the reflections from the backing on the PPT spectra. Amplitude characteristics of CdTe crystal at different frequencies of modulation: f=16 Hz-solid line, f=36 Hz- dadot line, f=76 Hz- dotted line and f=126 Hz- dash line.=0.03 cm2/s, R=-0.6. Amplitude characteristics of CdTe crystal at different frequencies of modulation: f=16 Hz-solid line, f=36 Hz- dadot line, f=76 Hz- dotted line and f=126 Hz- dash line but computed for =0.3 cm2/s , R= -0.6.

  14. CONCLUSIONS • The inhomogeneous sample model enables the determination of the percentage composition of the crystal. • It’s possible to describe the surface of the sample in the inactive layer model. • The control of uniformity of crystals is possible with the PPT method. • PPT spectroscopy enables thermal and optical characterisation of samples.

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