Drift transport of charge carriers in silicon $p^+$–$n$–$n^+$ structures at temperatures $\le$ 100 mK

For the first time, the transient current technique is used to study the drift transport of charge carriers in silicon $p^+$–$n$–$n^+$ structures at temperatures $T\le$ 100 mK. The pulse current responses of the structure caused by the drift of laser-generated electrons and holes in the region of the electric field up to 10$^4$ V/cm are measured. It is found that the space charge concentration in the $n$-region decreases to a few percent of the phosphorus atom concentration. This fact indicates that the influence of phonons on the electron tunneling through the potential barrier of phosphorus atoms, reduced according to the Poole–Frenkel effect, becomes ineffective already at $T<$ 1.1 K. The combination of the $p^+$–$n$–$n^+$ structure properties converts $n$-Si into an electrically neutral insulator with a small space charge and high carrier mobilities, which is important for building sensitive elements with internal thermal gain for a neutrino detector.