Electronic state transition in cooperatively interacting point-defects in semiconductor crystals

Electron state transition of deep level point defects in a semiconductor crystal was studied. Low-temperature grown GaAs produced excess antisite As (As_Ga) which produces localized spin when doped with Be. A nearly abrupt decrease of 1.7% of the resistance is detected at a temperature around 4 K which is consistent with abrupt decrease of magnetization. These observations are explained as a result of cooperative transition of electron states of As_Ga defects. First-principal calculations of the electron state of an As_Ga atom with a shallow acceptor Be show that at the transition an As_Ga⁺ ion is displaced to the interstitial site and becomes a neutral atom and finally results in formation of a hole producing enhancement in conductivity.