Photocurrent saturation and negative differential photoconductivity in Мn$_4$Si$_7$–Si$\langle$Mn$\rangle$–Мn$_4$Si$_7$ and Мn$_4$Si$_7$–Si$\langle$Mn$\rangle$–М heterojunctions

A mechanism behind the saturation of the photocurrent and occurrence of negative differential photoconductivity in Мn$_4$Si$_7$–Si$\langle$Mn$\rangle$–Мn$_4$Si$_7$ and Мn$_4$Si$_7$–Si$\langle$Mn$\rangle$–М heterojunctions is found. Мn$_4$Si$_7$–Si$\langle$Mn$\rangle$–Мn$_4$Si$_7$ and Мn$_4$Si$_7$–Si$\langle$Mn$\rangle$–М structures are studied with a model of back-to-back diodes. Photocurrent-voltage characteristics are taken at high constant and pulsed applied biases. It is found that the nonlinearity of the photocurrent-voltage characteristics and photoconductivity kinetics are due to the quenching of photoconductivity by Joule self-heating.