WSe2 / hBN Field-Effect Transistors

1. Device Structure & TLM Patterning

Fig 1a. Sample 1 Optical microscope image showing the WSe2 flake (red outline) transferred onto an hBN flake (yellow outline).

Fig 1b. Sample 2 Optical image of the second fabricated device, maintaining the same heterostructure design.

Fig 1c. TLM Pattern The channel lengths are defined as L = 1, 2, 3, and 5 μm, with a uniform channel width of W = 4 μm across all devices.

2. Transfer Characteristics

Fig 2a. Sample 1 Transfer Curve (I_D - V_G) measured at V_DS = 0.2V for varying channel lengths.

Fig 2b. Sample 2 Transfer Curve Measured under identical conditions, showing consistent field-effect behavior.

3. Transconductance (g_m)

Fig 3a. Sample 1 Transconductance Peak g_m values extracted for each channel length, reaching up to 1.21 μA/V for L = 2 μm.

Fig 3b. Sample 2 Transconductance Demonstrating higher peak g_m values compared to Sample 1, with a maximum of 1.88 μA/V for L = 1 μm.

4. Transfer Length Method (TLM) Analysis

To extract the contact resistance (R_c), the total resistance (R_total) is plotted against the channel length (L) using the following relationship:

Fig 4a. Sample 1 TLM Fitting Linear fit yields a normalized contact resistance of 2R_c W = 43.0 kΩ·μm with an R-square of 0.867.

Fig 4b. Sample 2 TLM Fitting Excellent linearity (R-square 0.995) is observed, yielding a lower contact resistance of 2R_c W = 37.2 kΩ·μm.

5. Field-Effect Mobility (\(\mu_{FE}\))

Field-effect mobility is a critical physical quantity representing how easily charge carriers can move within an electric field. The mobility is extracted from the transconductance (\(g_m\)) using the following equation:

where \(L\) and \(W\) are the channel length and width, respectively. \(C_{ox}\) is the area capacitance of the 90 nm SiO\(_2\) dielectric (\(3.84 \times 10^{-4} \text{ F/m}^2\)). By substituting the extracted \(g_m\) and corresponding \(L\) values for each channel, the mobility is calculated as shown in the table below.