Abstract
Phase-change memory (PCM) holds great potential in realizing the combination of DRAM-like speeds with non-volatility and large storage capacity for future electronic devices including in-memory computing. However, various (reliability) issues related to e.g. too high programming current (power consumption), resistance drift, data retention (low crystallization temperature), phase separation and density change upon switching stand in the way to make PCM really attractive. GaSb thin films have interesting optical and electrical properties which are attractive for optoelectronic and PCM applications but so far reported stoichiometric GaSb compositions are Sb-rich which produced reliability issues in PCM devices. In this study, we managed to deposit stoichiometric GaSb thin films using pulsed laser deposition (PLD) by varying deposition parameters and conditions. Using electron microscopy, the morphology of deposited films and target surface and the compositional deviation from exact stoichiometry have been investigated. We show that the directional nature of laser-target interaction is directly responsible for film quality in PLD in which particulates with high number density are generated due to directional pillar formation. Suppressing this pillar formation, by a simple 180° target rotation, showed an increase in deposition yield by 60%, exact stoichiometric transfer from target to substrate, and large reduction in particulate density. Moreover, from XRD analysis, we show that exact stoichiometric transfer from target to substrate is crucial for structural integrity of the produced films. Temperature induced structural transformation from resistivity vs. temperature measurements show a high crystallization temperature of 250 °C for stoichiometric GaSb thin film. We believe the exact stoichiometric GaSb thin films with reduced particulate densities and favorable structural and (opto)electronic properties are attractive for future PCM devices.
Highlights
Phase-Change Memory (PCM) architectures are some of the most promising candidates for future data storage devices [1]
To further investigate the properties of these particulate-free and stoichiometric films, structural analysis and electrical resistivity measurements have been performed by X-ray diffraction and Van der Pauw setup
We show that pillars, which are produced by the directional nature of the laser-target inter action, are directly responsible for the thin film quality and particulate formation
Summary
Phase-Change Memory (PCM) architectures are some of the most promising candidates for future data storage devices [1]. Another approach is to go for a completely new phase change material with attractive properties altogether Among those ideal for future PCM devices are GaSb alloys, which attract attention due to their unusual crystallization behavior [17]. It has been shown that particulate generation can be suppressed by using a continuous target rotation to simulate irradiations in opposite directions [33] None of these methods were effective in achieving ab-initio stoichio metric GaSb deposition that contains low particulate densities. To incorporate GaSb into future PCM devices, problems with off-stoichiometric thin film production for both magnetron sputtering and PLD and high particulate densities on the film surface in PLD must be solved. We either did not apply any target rota tion or we rotated the target 180◦ after a certain number of laser pulses using a homemade target holder in addition to the translation (see Supplementary Information, Fig. S1)
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