Temperature-Dependent and Gate-Tunable Rectification in a Black Phosphorus/WS₂ van der Waals Heterojunction Diode

Dastgeer, Ghulam,Khan, Muhammad Farooq,Nazir, Ghazanfar,Afzal, Amir Muhammad,Aftab, Sikandar,Naqvi, Bilal Abbas,Cha, Janghwan,Min, Kyung-Ah,Jamil, Yasir,Jung, Jongwan,Hong, Suklyun,Eom, Jonghwa American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.15

<P>Heterostructures comprising two-dimensional (2D) semiconductors fabricated by individual stacking exhibit interesting characteristics owing to their 2D nature and atomically sharp interface. As an emerging 2D material, black phosphorus (BP) nanosheets have drawn much attention because of their small band gap semiconductor characteristics along with high mobility. Stacking structures composed of p-type BP and n-type transition metal dichalcogenides can produce an atomically sharp interface with van der Waals interaction which leads to p-n diode functionality. In this study, for the first time, we fabricated a heterojunction p-n diode composed of BP and WS<SUB>2</SUB>. The rectification effects are examined for monolayer, bilayer, trilayer, and multilayer WS<SUB>2</SUB> flakes in our BP/WS<SUB>2</SUB> van der Waals heterojunction diodes and also verified by density function theory calculations. We report superior functionalities as compared to other van der Waals heterojunction, such as efficient gate-dependent static rectification of 2.6 × 10<SUP>4</SUP>, temperature dependence, thickness dependence of rectification, and ideality factor of the device. The temperature dependence of Zener breakdown voltage and avalanche breakdown voltage were analyzed in the same device. Additionally, superior optoelectronic characteristics such as photoresponsivity of 500 mA/W and external quantum efficiency of 103% are achieved in the BP/WS<SUB>2</SUB> van der Waals p-n diode, which is unprecedented for BP/transition metal dichalcogenides heterostructures. The BP/WS<SUB>2</SUB> van der Waals p-n diodes have a profound potential to fabricate rectifiers, solar cells, and photovoltaic diodes in 2D semiconductor electronics and optoelectronics.</P> [FIG OMISSION]</BR>

Distinct Detection of Thermally Induced Spin Voltage in Pt/WS₂/Ni₈₁Fe₁₉ by the Inverse Spin Hall Effect

Dastgeer, Ghulam,Shehzad, Muhammad Arslan,Eom, Jonghwa American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.51

<P>Conversion of heat into a spin current by means of the spin Seebeck effect (SSE) is one of the exciting topics in spin caloritronics. By use of this technique, the excess heat may be transformed into a valuable electric voltage by coupling SSE with the inverse spin Hall effect (ISHE). In this study, a thermal gradient and an in-plane magnetic field are used as the driving power to mobilize the spin electrons to produce SSE. A spin voltage is detected by ISHE in the Ni<SUB>81</SUB>Fe<SUB>19</SUB> heterostructure by means of a WS<SUB>2</SUB>/Pt strip. Using WS<SUB>2</SUB> sheets of different thicknesses, we obtained a large spin Seebeck coefficient of 0.72 μV/K, which is 12 times greater than the conventional spin Seebeck coefficient observed in Pt/Ni<SUB>81</SUB>Fe<SUB>19</SUB> bilayer devices. We observe the thickness dependence of tungsten disulfide (WS<SUB>2</SUB>) flakes and the polarity reversal of pure SSE signals that are measured without influence from the other thermoelectric effects in our Pt/WS<SUB>2</SUB>/Ni<SUB>81</SUB>Fe<SUB>19</SUB> device-the most intriguing feature of this study. Without the electric charge conduction, the spins are distributed over a longer distance that is greater than the spin diffusion length of the Ni<SUB>81</SUB>Fe<SUB>19</SUB> layer. Such features are strongly desired for designing the efficient spin-caloritronics devices that may be used in the thermoelectric spin generators and the temperature sensors such as thermocouples.</P> [FIG OMISSION]</BR>

Black Phosphorus-IGZO van der Waals Diode with Low-Resistivity Metal Contacts

Dastgeer, Ghulam,Khan, Muhammad Farooq,Cha, Janghwan,Afzal, Amir Muhammad,Min, Keun Hong,Ko, Byung Min,Liu, Hailiang,Hong, Suklyun,Eom, Jonghwa American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.11

<P>There have been a few studies of heterojunctions composed of two-dimensional transition-metal dichalcogenides (TMDs) and an oxide layer, but such studies of high-performance electric and optoelectronic devices are essential. Such heterojunctions with low-resistivity metal contacts are needed by the electronics industry to fabricate efficient diodes and photovoltaic devices. Here, a van der Waals heterojunction composed of p-type black phosphorus (p-BP) and n-type indium-gallium-zinc oxide (n-IGZO) films with low-resistivity metal contacts is reported, and it demonstrates high rectification. The low off-state leakage current in the thick IGZO film accounts for the high rectification ratio in a sharp interface of p-BP/n-IGZO devices. For electrostatic gate control, an ionic liquid is introduced to achieve a high rectification ratio of 9.1 × 10<SUP>4</SUP>. The photovoltaic measurements of p-BP/n-IGZO show fast rise and decay times, significant open-circuit voltage and short-circuit current, and a high photoresponsivity of 418 mA/W with a substantial external quantum efficiency of 12.1%. The electric and optoelectronic characteristics of TMDs/oxide layer van der Waals heterojunctions are attractive for industrial applications in the near future.</P> [FIG OMISSION]</BR>

Temperature and bias dependent magnetoresistance in a vertical spin valve CoFe/TiO₂/CoFe based structure

Ehsan Elahi,Ghulam Dastgeer,Pradeep Raj Sharma,Abdul Subhan Siddiqui,Hwayong Noh 한국자기학회 2021 한국자기학회 학술연구발표회 논문개요집 Vol.31 No.2

The metal-oxides spin valve junctions are the building blocks for spintronic devices and to utilize for miniaturized magnetic sensors. Here, we describe the fabrication and characterization of vertical spin valve based on CoFe/TiO₂/CoFe structure. CoFe was deposited on Si/SiO₂ substrate and TiO₂(1 nm) deposited on CoFe directly by an e-beam evaporator, in a high vacuum. A reasonable positive magnetoresistance (MR) is obtained via this vertical spin valve at low temperatures. We have observed a maximum value of MR about 0.33% at 28K and 0.20% at 300K. At various current bias, a significant variation in MR is observed. The value of MR was high at lower current (15 μA) and then decreased for the higher bias current which saturates at 40 μA. The decrement in MR at higher bias current can be accredited to the excitation of magnons, to band bending, and probably to the contribution of interface states at higher currents. This trend was also observed in other previous reports. The linear I-V curve demonstrates the ohmic trend of the TiO₂ and FM contacts. The demonstrated device identifies TiO₂ as favorable spacer material in spin valve and opens the way to integrate high-performance memory storage devices.

Comparison of Electrical and Photoelectrical Properties of ReS₂ Field-Effect Transistors on Different Dielectric Substrates

Nazir, Ghazanfar,Rehman, Malik Abdul,Khan, Muhammad Farooq,Dastgeer, Ghulam,Aftab, Sikandar,Afzal, Amir Muhammad,Seo, Yongho,Eom, Jonghwa American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.38

<P>As one of the newly discovered transition-metal dichalcogenides (TMDs), rhenium disulfide (ReS<SUB>2</SUB>) has been investigated mostly because of its unique characteristics such as the direct band gap nature even in bulk form, which is not prominent in other TMDs (e.g., MoS<SUB>2</SUB>, WSe<SUB>2</SUB>, etc.). However, this material possesses a low mobility and an on/off ratio, which restrict its usage in high-speed and fast switching applications. Low mobilities or on/off ratios can also be caused by substrate scattering as well as environmental effects. In this study, we used few-layer ReS<SUB>2</SUB> (FL-ReS<SUB>2</SUB>) as a channel material to investigate the substrate-dependent mobility, current on/off ratio, Schottky barrier height (SBH), and trap density of states of different dielectric substrates. The hexagonal boron nitride (h-BN)/FL-ReS<SUB>2</SUB>/h-BN structure was observed to exhibit a high mobility of 45 cm<SUP>2</SUP> V<SUP>-1</SUP> s<SUP>-1</SUP>, current on/off ratio of about 10<SUP>7</SUP>, the lowest SBH of about 12 mV at a zero back-gate voltage (<I>V</I><SUB>bg</SUB>), and a low trap density of states of about 5 × 10<SUP>13</SUP> cm<SUP>-3</SUP>. These quantities are reasonably superior compared to the FL-ReS<SUB>2</SUB> devices on SiO<SUB>2</SUB> substrates. We also observed a nearly 5-fold improvement in the photoresponsivity and external quantum efficiency values for the FL-ReS<SUB>2</SUB> devices on h-BN substrates. We believe that the photonic characteristics of TMDs can be improved by using h-BN as the substrate and capping layer.</P> [FIG OMISSION]</BR>

Optimization of Plasma Display Panel by Fluid Simulations

M.S. Hur,C.H. Shon,H.C. Kim,S. Dastgeer,J.K. Lee 한국진공학회 2000 한국진공학회 학술발표회초록집 Vol.- No.-