Inorganic semiconductors such as silicon are indispensable in modern electronics because they possess tunable electrical conductivity between that of a metal and that of an insulator. The electrical conductivity of a semiconductor is controlled by its band gap, which is the energy difference between its valence and conduction bands; a narrow band gap results in increased conductivity because it is easier for an electron to move from the valence to the conduction band. However, inorganic semiconductors are brittle, which can lead to device failure and limits their application range, particularly in flexible electronics.