Mn$_4$Si$_7$–Si$\langle$Mn$\rangle$–Mn$_4$Si$_7$ and Mn$_4$Si$_7$–Si$\langle$Mn$\rangle$–M photodiodes

The current-voltage characteristics of Mn$_4$Si$_7$–Si$\langle$Mn$\rangle$–Mn$_4$Si$_7$ and Mn$_4$Si$_7$–Si$\langle$Mn$\rangle$–M photodiodes are studied experimentally. The current passage mechanism under illumination with $h\nu\ge E_g$ is considered. The role of a contact to Mn$_4$Si$_7$ in the provision of high photosensitivity under illumination of the base by light with $h\nu\ge$ 1.14 eV at low temperatures, 77–220 K, is analyzed. From electrical measurements, electron microscopic data for the Mn$_4$Si$_7$–Si$\langle$Mn$\rangle$ interface, and photocurrent-voltage characteristics, a band diagram under the conditions of photocurrent passage is constructed. The high low-temperature photosensitivity of the diodes $(I_{\mathrm{ph}}/I_{\mathrm{d}}\ge 10^9)$ is explained by the impact-ionization-induced modulation of the base conductivity and injection amplification of holes in the transition layer.