An investigation of the photoconductivity of Ge-doped material under hydrostatic pressure revealed, in addition to the well-known persistent photoconductivity that was due to the DX state, another giant photoconductivity that was caused by a neutral localized so-called A1 state of the donor. It was found that the top of the barrier for electron recapture to the A1 state was pinned to the conduction band edge and that the capture cross-section was surprisingly small. An investigation was also made of the situation where the top of the capture barrier for the DX state approached the conduction band edge under pressure. It became pinned at higher pressures; which was another manifestation of weak hybridization of the A1.

C.Skierbiszewski, W.Jantsch, Z.Wilamowski, K.Lübke, T.Suski: Materials Science Forum, 1995, 196-201, 1025-30