The M2 Phase of Free‐Standing Ga‐Doped VO ₂ Single Crystals Over Wide Temperature Ranges

ABSTRACT For more than six decades, VO 2 has been one of the most impressive electronic materials due to its spectacular insulator metal transition (IMT) close to room temperature, accompanied by a structural transition and significant changes in optical properties which provided a list of potential applications such as electrical and optical switches, electrical and optical memories, smart windows, neural devices and thermal actuators. Despite a comprehensive investigation effort invested by scientists and engineers, as of today, there is no useful device on sale made of VO 2 . The main cause is cracks induced by the large strain‐stress developed upon cycling through IMT of clamped samples. Another weakness is the high sensitivity of VO 2 to foreign cations and deviations from oxygen stoichiometry, which may induce multiple coexisting phases. To become useful in device technology, the phase diagram of doped VO 2 should be adjusted to provide a wide range of temperatures below IMT in which the material is single‐phase and not under strain or stress induced by the substrate and contacts. Low‐ current R(T), DC, and pulsed I – V measurements conducted on free‐standing Ga‐doped VO 2 single crystals provided encouraging results and proved the advantage of Ga over, e.g., Al doping.