  We fabricated an etched hole quantum dot in a Si-doped (311)A AlGaAs/GaAs
heterostructure to study disorder effects via magnetoconductance fluctuations
(MCF) at millikelvin temperatures. Recent experiments in electron quantum dots
have shown that the MCF is sensitive to the disorder potential created by
remote ionised impurities. We utilize this to study the temporal/thermal
stability of Si acceptors in p-type AlGaAs/GaAs heterostructures. In
particular, we use a surface gate to cause charge migration between Si acceptor
sites at T = 40 mK, and detect the ensuing changes in the disorder potential
using the MCF. We show that Si acceptors are metastable at T = 40 mK and that
raising the device to a temperature T = 4.2 K and returning to T = 40 mK is
sufficient to produce complete decorrelation of the MCF. The same decorrelation
occurs at T ~ 165 K for electron quantum dots; by comparing with the known trap
energy for Si DX centers, we estimate that the shallow acceptor traps in our
heterostructures have an activation energy EA ~ 3 meV. Our method can be used
to study charge noise and dopant stability towards optimisation of
semiconductor materials and devices.
