Diffusion and Defects in Elementary and Compound Semiconductors
Vacancies in III-V compounds induced by dopant diffusion
In opto-electronic devices based on, e.g., GaP and GaAs, diffusion of Zn at high temperatures is commonly used
to establish p-type doping layers. However, the diffusion mechanism of Zn (or other acceptors) in
III-V compounds is still poorly understood. Since long it has been believed that Ga vacancies may
play an important role in GaP and GaAs during Zn incorporation from the vapour phase. However, serious
inconsistencies with other data led us explore the alternative possibility that vacancies of the group V
sublattice (VP or VGa) could be crucially involved. Indeed, positron annihilation
experiments on Zn diffused GaP samples reveal a surprisingly high concentration of vacancies with properties
characteristic of VP. It was checked by reference experiments without Zn that the observed effects
are not merely due to the high temperature treatment. Similarly, recent investigations by positron annihilation
lifetime spectroscopy on GaAs yield strong evidence for the abundant presence of VAs after Zn
diffusion.
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