We show from transport investigations that Ge doped GaAs can be either semimetallic or semiconducting depending on hydrostatic pressure and previous sample illumination. This property results from a unique crossover of two states of the Ge donor in GaAs in their energetic position under pressure. The experimental results obtained make it possible to identify the nature of these Ge‐donor states: The drastic enhancement of the electron mobility after illumination is taken as evidence of the electron transfer from the two‐electron DX− state to a neutral, localized, and unrelaxed state of the Ge donor.
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