Hall effect studies in germanium doped AlxGa1−xAs

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Abstract
Germanium doping of AlxGa1−xAs has been studied over the range x=0.22–0.40 by measuring the Hall effect in epitaxial layers grown by liquid phase epitaxy. Hall measurements were carried out in the temperature range 70–300 K and the resulting mobilities and carrier densities were analyzed as a function of temperature. These analyses have shown that the Hall to drift mobility ratio in this material, previously assumed to be around unity, is ∼0.6 and that Ge produces two acceptor levels in AlxGa1−xAs. The dominant acceptor level has an activation energy which increases monotonically with x and has a value of ∼160 meV at x=0.40. A shallow level of much lower concentration has also been found at an energy of 20–40 meV above the valence band edge. In addition we have found the level of compensation in our material to be low.