APPLICATIONS OF THERMOACOUSTIC TECHNIQUES FOR THERMAL, OPTICAL AND MECHANICAL CHARACTERIZATION OF MATERIALS, STRUCTURES AND DEVICES Mirosław Maliński Department of Electronics and Computer Studies Technical Univeristy of Koszalin, Poland

Contents Introduction Multi-layer optically opaque systems Optically semitransparent systems Determination of thermal parameters of materials Determination of recombination parameters of carriers Determination of air-tightness of packagings Investigation of the quality of the surface of samples Investigation of composition of crystals and their quality Determination of internal quantum efficiency

Introduction Thermoacoustics uses both frequency and spectral amplitude and phase characteristics for determination of several parameters of samples and structures This presentation is limited to the analysis of FA characteristics measured with a microphone or piezoelectric methods

The idea of a thermoacoustic method Generation of periodical heat in the sample by absorbed light or dissipation of electric power Propagation of induced thermal waves in the sample Detection of the amplitude and phase of a thermal wave with one of the methods e.g. microphone, IR or piezoelectric or… Detection of one of the effects connected with the periodical temperature distribution e.g. thermal expantion, thermoelastic bending, IR emission, overpressure

Schematic diagram of a sample

Temperature spatial distribution

Example temperature distributions R=1 (left) R= -1 (right) : 1 - t=0, 2- t=T/4, 3- t=T/2, 4 - t=3T/4.l=0.1 cm,  =0.1 cm 2 /s,  =100 cm -1, f=16 Hz.

Photoacoustic signals Microphone detection Piezoelectric detection

Experimental set-up

Multilayer optically opaque systems

Theoretical frequency domain dependencies of a phase of a photoacoustic signal for a transistor structure of a thickness l 1 =230  m, a lead frame of the thickness l 3 =350  m for different values of air delaminations: 1–  m, 2– 0.05  m, 3–  m, 4– 0.1  m, 5– 0.15  m, 6– 0.2  m.

Multilayer optically opaque systems Correlation of the phase of the PA signal and the force of detachment of the transistor structure from a lead frame. Solid line is a theoretical curve, circles are experimental points, BC 237 transistor structures Phase(S) = (180/  )arg (S 1 ( d 2 = 0  m)p + S 2 (d 2 = 0.1  m)(1-p) ) Force necessary for detachment is proportional to the parameter p

Optically semitransparent systems Schematic diagram of a thin semitransparent layer on the semitransparent backing Application – characterization of thin semiconductor films on semiconductor thick substrates

Optically semitransparent systems

Optically semitransparent systems GaAs on Si Amplitude and phase photoacoustic frequency characteristics of a l 1 = 10  m thick layer on the thick substrate. Parameters taken for computations:  1 =0 cm -1,  2 =10000 cm -1 (solid line),  1 =10 4 cm -1,  2 =10 3 cm -1 ( dash line),  1 =0.3 cm 2 /s,  2 =0.9 cm 2 /s, GaAs/Si FREQUENCY [Hz] AMPLITUDE [a.u] FREQUENCY [Hz} PHASE [degs]

Optically semitransparent systems SCL in Si Theoretical influence of a SCL on the photoacoustic amplitude and phase characteristics in the front configuration. Parameters:  =0.01 cm 2 /s, thickness of the layer l 1 =5  m – dash line, l 1 =10  m – dotted line, l 1 =15  m – solid line,  1 =0 cm -1,  2 =1000 cm -1, R 12 =0.

Optically semitransparent systems PS on Si substrate The phase frequency characteristics of the PS/Si structure in the reflection configuration. Diamonds and circles are for exc =514 nm and exc =670 nm. Parameters of PS layer  =0.016cm 2 /s, k c = cal(cmKs) -1,  1 (514nm)=1900 cm -1,  1 (670nm)=903 cm -1.

Optically semitransparent systems PS on Si substrate d 1 =50  m on the Si substrate of the thickness d 2 =500  m. The anodisation current I=100mA for the time t=10 min

Determination of thermal parameters

Determination of thermal parameters –piezoelectric method ZnSe crystal l = cm  =0.01 cm 2 /s ( solid line),  = 0.05 cm 2 /s, 0.1 cm 2 /s, 0.2 cm 2 /s. Zn 0.83 Be 0.17 Se l= cm  =0.05 cm 2 /s,  =0.01 cm 2 /s,  =0.1 cm 2 /s and  = 0.2 cm 2 /s

Determination of thermal parameters –microphone method Si sample l=240  m and  =0.6 cm 2 /s. Description of lines: line 1 – R = 1, line 2 – R = 0.9, line 3 – R = 0.76, line 4 – R = 0.5. Circles and diamonds are experimental lines, lines are theoretical curves.

Determination of thermal parameters Dependance of the thermal conductivity of SiGe on the composition CONCENTRATION of Si in SiGe THERMAL CONDUCTIVITY [W/mK]

Determination of recombination parameters in TWI-PW model

Determination of recombination parameters Computations of Ge samples:  = 0.4 cm 2 /s, l = 0.1 cm,  = 20  s, D = 44 cm 2 /s, V = 500 cm/s a)  = 0.1  s and D = 22 cm 2 /s b).

Determination of recombination parameters SiGe:  =0.37 cm 2 /s, L=0.1 cm, E 1 =2.0 eV, E 2 =1.4 eV, E g =1.1 eV, D=44 cm 2 /s, V=800 cm/s,  = 100  s  FREQUENCY [Hz] AMPLITUDE RATIO [a.u.]  FREQUENCY [Hz] PHASE SHIFT [degs]

Air-tightness measurements

Air-tightness measurements- theoretical model Parameters taken for computation:  = 17  10-6 [Ns/m2], L = 6-4 [m], M = 28  10-3 [kg/mole], V 2 = 2.16  10-6 [m3], V 2 /V 1 = 3.19, r = 20  m...60  m,  = 1.3 [kg/m3], N a = 6  [mole-1], T = 300 K, k = 1.38  [J/K].

Air-tightness measurements -poster 1) r = 108  m;2) r = 91  m;3) r = 78  m; 4) r = 69  m;5) r = 42  m; 6) r =24  m; L.Majchrzak, M.Maliński ‘Analysis of a Thermoacoustic Approach for the Evaluation of Hermeticity of Packaging of Electronic Devices’ XXIV IMAPS Poland Conf log (f) AMPLITUDE RATIO [1]

Determination of the quality of the surface p-type Si Theoretical and experimental piezoelectric spectra of p-Si at RT d= cm, d= cm.

Determination of the surface quality Amplitude PPT spectra of CdTe sample at f = 76 Hz. Circles – experimental results, and a solid line is the theoretical curve: E g = 1.51 eV,  = 0.03 cm 2  s -1,  = cm,  0 = 130 cm -1,  = 0.9.

Composition of mixed crystals The correlation of the energy gap value of the Zn 1-x Be x Te mixed crystal and the mole fraction of beryllium x in the crystal

Composition of mixed crystals Zn 0.93 Be 0.07 Te E g1 = 2.31eV, E g2 = eV, k = 0.4,  = 0.2 cm 2 /s, f = 36 Hz,  = cm, R = 1 ENERGY [eV] AMPLITUDE [j.u.] ENERGY [eV] – – 100 PHASE [deg]

Internal quantum efficiency Schematic diagram of the absorption and irradiative and radiative recombination processes involved in a generation of the photoacoustic signal.

Internal quantum efficiency ZnTe RT at 76 Hz and 126 Hz, internal quantum efficiency of irradiative recombination  R =0.75

Conclusions Frequency FA characteristics are a useful tool bringing information about: Multilayer optically opaque systems Optically semitransparent systems Thermal parameters of materials Recombination parameters of carriers Air-tightness of packagings Determination of the quality of the surface and composition Determination of the internal quantum efficiency

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