Dynamic biasing leads to Joule heating–which is one of the major causes of electrical breakdown. Such events generate a high surge current and significantly affect the electrical performance of the device, resulting in permanent damage in severe cases. Our findings revealed that Gr/Si diode could absorb high surge current, has a fast reverse recovery time (~10ns), and a highly robust junction (V_R-BD~80V) at higher dynamic switching. Benefitting from these advantage, we demonstrated a strategy to protect 2D material-based devices from electrical stress. It has been observed that electrical input spikes are the primary reasons for electrical failure in 2D heterostructures.

The ultra-fast response of the Gr/Si Schottky diode can effectively bypass electrical spikes beyond thresholds and increase the lifetime of the 2D-PN diodes (i.e., WSe₂/MoS₂). This study provides an overall picture of the failure mechanisms of Gr-based Schottky diode under dynamic biasing conditions, leading to protection circuits for 2D heterostructures and extending the device lifetime.

The Gr/Si protective diode in parallel with a 2D heterostructure (MoS₂/WSe₂) diode is shown in Figure 1(a). The Raman spectra of WSe₂, WSe₂/MoS_2, and MoS₂ heterostructure and the optical image are shown in Figure 1(b-f) with the thickness of WSe₂/MoS₂ (~30/~15 nm). The accumulated charges during forwarding biasing give rise to the initial surge current while switching the polarity. These accumulated charges are directly proportional to the forwarding biasing, which increases the initial overshoot current in both directions (forward and reverse). This initial overshoot current was adversely affecting the lifetime of the device. The higher the forward voltage, the large the accumulated charge at the interface, taking longer to reach the steady state. Our findings showed that with increasing input bias, the initial peak current rises, which contributes to the overall heating of the device and causes device failure.

When the Gr/Si diode is connected in parallel with the 2D PN diode, any surges or spikes in the circuit will appear on both devices simultaneously. Due to ultrafast response time and high current absorbing ability, the Gr/Si diode will absorb spikes and protect 2D sensitive devices. We simultaneously monitor the current of the 2D-PN and Schottky diode to observe the amount of current distributed at both devices. The Gr/Si Schottky diode routes excessive current to the circuit ground without letting it reach the sensitive circuit (2D-PN diode). The temporal current through 2D PN and Gr/Si Schottky diode with three configurations are presented in Figure. 1(g-i).

In case I, the testing condition shows both devices are connected in parallel configurations (Figure 1(g)). It is evident from the result that in the presence of electrical stress (V_in) in the circuit, Gr/Si silicon Schottky diode reacts more quickly after reaching its threshold voltage and absorbs most of the initial current. In the configuration presented in case II with a voltage clamping source of 3V connected in series with the Schottky diode, Gr/Si Schottky diode does not conduct in either biasing.

Figure. 1. (a) Cross-section view of Gr/Si protection diode coupled with 2D-PN diode. (b-d) Raman spectra of WSe₂, WSe₂/MoS_2, and MoS₂ heterostructure (e, f) Optical image of the Gr/Si Schottky and 2D-PN diode heterostructure. (g-i) The current temporal response through 2D PN and Gr/Si Schottky diode with three configurations

In that way, Gr/Si diode will wake up only when input biasing or unwanted spikes exceed 3.5V. Until then, the 2D PN will safely perform rectification per its designed parameters (Figure 1(h)). In case III, when there are overvoltage’s in the circuits or spikes in the input, the Gr/Si diode turns on immediately, and a more significant portion of the current will pass through the Gr/Si diode instead of the 2D-PN diode, which helps in reduction of the electrical stress at 2D-PN diode and avoids breakdown as depicted in Figure. 1(i). A keen observation revealed that when the 2D PN diode is measured separately, the initial spike current was more prominent at switching input bias when compared with the cases I-III, which justifies that the Gr/Si diode passes the majority of current through it.

For a broader perspective, future electronics will be based on thin film materials capable of performing multiple tasks. It can be made possible by engineering their geometrical structure, interlayer charge dynamics, and selective excitonic properties to be employed in retinomorphic and neuromorphic sensing and computing. These developments have emerged artificial neural networks as a baseline for computationally complex real-world problems. We expect a rapid interest in developing such nanoelectronics-based devices with the help of 2D materials, thin film transistors, and TMDCs. Several types of research have investigated the failure mechanism in low-dimensional materials such as MoS₂, WSe₂, black-phosphorus (BP), carbon nanotubes (CNTs), graphene nanoribbons (GNR) and thin film graphene.

 Broadening the scope of the Gr/Si Schottky diode, the excellent charge absorption capability of the device finds its innovative application for on-chip protection of surge-initiated failures of sensitive 2D materials-based devices.  

When the Gr/Si diode is connected in parallel with the 2D PN diode, any surges or spikes in the circuit will appear on both devices simultaneously. Due to ultrafast response time and high current absorbing ability, the Gr/Si diode will absorb spikes and protect 2D sensitive devices. We simultaneously monitor the current of the 2D-PN and Schottky diode to observe the amount of current distributed at both devices. The Gr/Si Schottky diode routes excessive current to the circuit ground without letting it reach the sensitive circuit (2D-PN diode). The temporal current through 2D PN and Gr/Si Schottky diode with three configurations are presented in Fig. 7(g-i). In case I, the testing condition shows both devices are connected in parallel configurations (Fig. 7(g)). It is evident from the result that in the presence of electrical stress (Vin) in the circuit, Gr/Si silicon Schottky diode reacts more quickly after reaching its threshold voltage and absorbs most of the initial current. In the configuration presented in case II with a voltage clamping source of 3V connected in series with the Schottky diode, Gr/Si Schottky diode does not conduct in either biasing. In that way, Gr/Si diode will wake up only when input biasing or unwanted spikes exceed 3.5V. Until then, the 2D PN will safely perform rectification per its designed parameters (Fig. 7(h)). In case III, when there are overvoltage’s in the circuits or spikes in the input, the Gr/Si diode turns on immediately, and a more significant portion of the current will pass through the Gr/Si diode instead of the 2D-PN diode, which helps in reduction of the electrical stress at 2D-PN diode and avoids breakdown as depicted in Fig. 7(i). A keen observation revealed that when the 2D PN diode is measured separately, the initial spike current was more prominent at switching input bias when compared with the cases I-III, which justifies that the Gr/Si diode passes the majority of current through it.