Atomic layer deposition of Sn-doped germanium diselenide for an As-free Ovonic threshold switch with low off-current

초록

This work introduces the atomic layer deposition (ALD) of Sn-doped GeSe2 (SnGS2) films for developing arsenic-free Ovonic threshold switch (OTS) devices with low off-current (I-off) and desirable threshold voltage (V-t). The undoped GeSe2 film exhibits high V-t and low endurance characteristics despite its low I-off originating from a large mobility gap. Such problems could be overcome by appropriate doping, and thus, Sn was doped into the GeSe2 film using a supercycle consisting of SnNx and GeSe2 subcycles. The co-injection of NH3 with Se-precursor ([(CH3)(3)Si](2)Se) during the GeSe2 subcycle generated a reactive H2Se intermediate, which enhanced the reactivity and transformed the pre-deposited SnNx to SnSe2. The overall cation-to-anion ratio of the deposited films remained at approximately 1 : 2, with amorphous structure and smooth surface morphology. The planar OTS device using SnGS2 films with a Sn concentration of 9.6%, for which the crystallization temperature was >400 degrees C, showed the lowest V-t of similar to 3.5 V and I-off of similar to 12.5 nA at half V-t and demonstrated switching endurance over 10(6) cycles. Furthermore, a vertical-type OTS device was fabricated using the same SnGS2 film using the excellent step coverage of ALD, exhibiting similar switching characteristics to its planar counterpart.

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