Determination of Absorption Coefficients and Thermal Diffusivity of Modulated Doped GaAlAs/GaAs Heterostructure by Photothermal Deflection Spectroscopy

M Oueslati,S Aloulou,A Sfaxi,M Fathallah

doi:10.3844/ajassp.2005.1412.1417

Abstract

We report in this study theoretical and experimental studies of photothermal deflection spectroscopy (PDS) for planar doped heterostructures AlGaAs/GaAs. The PDS spectra at T=300K are recorded by varying the wavelength of the excited radiation for different modulation frequencies. They show two different regions related to the fundamental electronic transitions from GaAs and Si doped AlGaAs. The DX levels have been observed approximately at 0.150 eV below the conduction band edge of Si doped Al0.33Ga0.67As (Eg=1.835 eV at 300 K). We give in this study a method of measuring the absorption coefficient of AlGaAs/GaAs heterostructures from the amplitude measurement of PDS signal. The optical absorption coefficient found was between 10 and 105 cm-1 in the energy range 1-2.5eV for samples. The PDS data are compared with those given by conventional transmission technique. The evolution of PDS amplitude spectra by varying the modulation frequency from 5 to 100 Hz (usually called depth profile analysis) and using He-Ne laser probe beam shows that the PDS signal amplitude increases with decreasing the modulated frequency. A numerical procedure is applied to fit the measured amplitude of the PDS signal. The value of thermal diffusivity (Ds=0. 27cm2s-1) shows a very good agreement with results given by spectroscopic ellipsometry.

Highlights

Two dimensional GaAlAs/GaAs structures grown by molecular beam epitaxy (MBE) have been achieved using modulated doping techniques[1]
The structure studied in this work is a two δSi modulated doped GaAlAs/GaAs heterostructure elaborated according to the model proposed by Schubert et al.[3]
In the present study we report results of photo thermal deflection spectroscopy (PDS)[4,5]

Summary

Introduction

Two dimensional GaAlAs/GaAs structures grown by molecular beam epitaxy (MBE) have been achieved using modulated doping techniques[1]. Q is the complex temperature rise above AlGaAs/GaAs modelled doped hetero structure grown the average temperature on the sample surface and its by molecular beam epitaxy on semi-insulating GaAs expression is obtained by solving the one dimensional (001) substrate and elaborated according to the model heat equation in the different environments sample, proposed by Schubert et al.[13].

Results

Conclusion