UBC Theses and Dissertations
Electrical and structural characterization of GaAs and Al Ga₋ As gr Xu, Li
The electrical and structural properties of GaAs and Al[formula omitted]Ga₁-[formula omitted]As grown by molecular beam epitaxy have been studied, including cross section morphology, aluminum mole fraction, and electrical transport properties. The film cross section has been investigated by selective etching, and microscopy. The selectively etched samples were examined with an alpha step instrument, a scanning electron microscope, and a scanning tunneling microscope which is a new approach. The aluminium mole fraction of Al[formula omitted]Ga₁-[formula omitted]As in grown layers have been measured with x-ray diffraction. A Rigaku x-ray diffractometer designed for powders was extended to single crystals. A new way of calculating the Al mole fraction from the x-ray diffraction spectrum was developed. The electrical transport properties including carrier concentration, Hall coefficients, resistivity and Hall mobility have been measured and calculated from 4 K to 300 K by means of the Van der Pauw method. Sample patterning was found to be necessary for accurate and reproducible measurements. A variety of samples was measured, including doped and undoped GaAs films. The two-band theory was used to interpret the measurement results. The temperature dependence of electron concentration in the conduction band was fit with an exponential function. From the fit, we obtained the activation energy of the impurity. The residual impurity in the MBE system was found to be mainly silicon.
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