Abstract

Atomically thin (or two-dimensional, 2D) transition metal dichalcogenide (TMD) semiconductors possess ideal attributes for meeting industry scaling targets for transistor channel technology. The realization of ultra-scaled field effect transistors (FETs) will require industry compatible gate dielectrics with very low equivalent oxide thickness (EOT) values. Dielectric substrates such as SiO2, Al₂O₃ and HfO₂ unintentionally dope 2D TMDs and create interfacial defect states that lead to non-ideal FET characteristics – such as variable threshold voltage. Despite their importance, the electronic properties of 2D TMD/dielectric interface have not been extensively studied. Here we show that zirconium oxide (ZrO₂) – a well-known industry compatible high dielectric constant (k) oxide – forms an ultra-clean interface with MoS2. Our detailed soft and hard X-ray photoelectron spectroscopy (XPS) analysis reveals that SiO₂ and HfO₂ substrates introduce significant doping of MoS₂ while ZrO₂ exhibits no measurable interactions with MoS₂ – consistent with density functional theory calculations. Because of the ultra-clean MoS₂/ZrO₂ dielectric interface, back gated monolayer MoS₂ FETs using ZrO₂ as dielectric show extremely stable and positive threshold voltage of 0.36 ± 0.3 V, low subthreshold swing of 75 mV/dec, and high ON currents of > 400 µA. We also demonstrate P-type 2D WSe₂ FETs with high ON state currents of > 200 µA/µm via suppression of electron doping using ZrO₂ dielectrics. Atomic resolution imaging and of ZrO₂ deposited on top of MoS₂ also reveals a defect free interface, which enables top gate FETs with equivalent oxide thickness of 0.86 nm and SS values of 80 mV/dec. Furthermore, we demonstrate that the ultraclean interface between ZrO₂ and monolayer MoS₂ enables effective modulation of the threshold voltage in top gate FETs by gate metal work function engineering. Our results show that ZrO₂ holds tremendous promise as an industry compatible high k dielectric for electronics based 2D TMD semiconductors.

Abstract

Atomically thin (or two-dimensional, 2D) transition metal dichalcogenide (TMD) semiconductors possess ideal attributes for meeting industry scaling targets for transistor channel technology. The realization of ultra-scaled field effect transistors (FETs) will require industry compatible gate dielectrics with very low equivalent oxide thickness (EOT) values. Dielectric substrates such as SiO2, Al₂O₃ and HfO₂ unintentionally dope 2D TMDs and create interfacial defect states that lead to non-ideal FET characteristics – such as variable threshold voltage. Despite their importance, the electronic properties of 2D TMD/dielectric interface have not been extensively studied. Here we show that zirconium oxide (ZrO₂) – a well-known industry compatible high dielectric constant (k) oxide – forms an ultra-clean interface with MoS2. Our detailed soft and hard X-ray photoelectron spectroscopy (XPS) analysis reveals that SiO₂ and HfO₂ substrates introduce significant doping of MoS₂ while ZrO₂ exhibits no measurable interactions with MoS₂ – consistent with density functional theory calculations. Because of the ultra-clean MoS₂/ZrO₂ dielectric interface, back gated monolayer MoS₂ FETs using ZrO₂ as dielectric show extremely stable and positive threshold voltage of 0.36 ± 0.3 V, low subthreshold swing of 75 mV/dec, and high ON currents of > 400 µA. We also demonstrate P-type 2D WSe₂ FETs with high ON state currents of > 200 µA/µm via suppression of electron doping using ZrO₂ dielectrics. Atomic resolution imaging and of ZrO₂ deposited on top of MoS₂ also reveals a defect free interface, which enables top gate FETs with equivalent oxide thickness of 0.86 nm and SS values of 80 mV/dec. Furthermore, we demonstrate that the ultraclean interface between ZrO₂ and monolayer MoS₂ enables effective modulation of the threshold voltage in top gate FETs by gate metal work function engineering. Our results show that ZrO₂ holds tremendous promise as an industry compatible high k dielectric for electronics based 2D TMD semiconductors.

Abstract

Atomically thin (or two-dimensional, 2D) transition metal dichalcogenide (TMD) semiconductors possess ideal attributes for meeting industry scaling targets for transistor channel technology. The realization of ultra-scaled field effect transistors (FETs) will require industry compatible gate dielectrics with very low equivalent oxide thickness (EOT) values. Dielectric substrates such as SiO2, Al₂O₃ and HfO₂ unintentionally dope 2D TMDs and create interfacial defect states that lead to non-ideal FET characteristics – such as variable threshold voltage. Despite their importance, the electronic properties of 2D TMD/dielectric interface have not been extensively studied. Here we show that zirconium oxide (ZrO₂) – a well-known industry compatible high dielectric constant (k) oxide – forms an ultra-clean interface with MoS2. Our detailed soft and hard X-ray photoelectron spectroscopy (XPS) analysis reveals that SiO₂ and HfO₂ substrates introduce significant doping of MoS₂ while ZrO₂ exhibits no measurable interactions with MoS₂ – consistent with density functional theory calculations. Because of the ultra-clean MoS₂/ZrO₂ dielectric interface, back gated monolayer MoS₂ FETs using ZrO₂ as dielectric show extremely stable and positive threshold voltage of 0.36 ± 0.3 V, low subthreshold swing of 75 mV/dec, and high ON currents of > 400 µA. We also demonstrate P-type 2D WSe₂ FETs with high ON state currents of > 200 µA/µm via suppression of electron doping using ZrO₂ dielectrics. Atomic resolution imaging and of ZrO₂ deposited on top of MoS₂ also reveals a defect free interface, which enables top gate FETs with equivalent oxide thickness of 0.86 nm and SS values of 80 mV/dec. Furthermore, we demonstrate that the ultraclean interface between ZrO₂ and monolayer MoS₂ enables effective modulation of the threshold voltage in top gate FETs by gate metal work function engineering. Our results show that ZrO₂ holds tremendous promise as an industry compatible high k dielectric for electronics based 2D TMD semiconductors.

Abstract

Atomically thin (or two-dimensional, 2D) transition metal dichalcogenide (TMD) semiconductors possess ideal attributes for meeting industry scaling targets for transistor channel technology. The realization of ultra-scaled field effect transistors (FETs) will require industry compatible gate dielectrics with very low equivalent oxide thickness (EOT) values. Dielectric substrates such as SiO2, Al₂O₃ and HfO₂ unintentionally dope 2D TMDs and create interfacial defect states that lead to non-ideal FET characteristics – such as variable threshold voltage. Despite their importance, the electronic properties of 2D TMD/dielectric interface have not been extensively studied. Here we show that zirconium oxide (ZrO₂) – a well-known industry compatible high dielectric constant (k) oxide – forms an ultra-clean interface with MoS2. Our detailed soft and hard X-ray photoelectron spectroscopy (XPS) analysis reveals that SiO₂ and HfO₂ substrates introduce significant doping of MoS₂ while ZrO₂ exhibits no measurable interactions with MoS₂ – consistent with density functional theory calculations. Because of the ultra-clean MoS₂/ZrO₂ dielectric interface, back gated monolayer MoS₂ FETs using ZrO₂ as dielectric show extremely stable and positive threshold voltage of 0.36 ± 0.3 V, low subthreshold swing of 75 mV/dec, and high ON currents of > 400 µA. We also demonstrate P-type 2D WSe₂ FETs with high ON state currents of > 200 µA/µm via suppression of electron doping using ZrO₂ dielectrics. Atomic resolution imaging and of ZrO₂ deposited on top of MoS₂ also reveals a defect free interface, which enables top gate FETs with equivalent oxide thickness of 0.86 nm and SS values of 80 mV/dec. Furthermore, we demonstrate that the ultraclean interface between ZrO₂ and monolayer MoS₂ enables effective modulation of the threshold voltage in top gate FETs by gate metal work function engineering. Our results show that ZrO₂ holds tremendous promise as an industry compatible high k dielectric for electronics based 2D TMD semiconductors.