© The Author(s) 2025. Published by Science Press and EDP Sciences.

INTRODUCTION

As the most widely used transistor at present, silicon-based metal-oxide-semiconductor field-effect transistor (MOSFET) has been constrained by the evolution of Moore’s Law, the whole size continues to shrink and is approaching the physical limit, resulting in a sharp increase in power consumption [1–6]. Junction field-effect transistor (JFET) without the dielectric layer has become one of the effective alternative solutions to MOSFET, which can perfectly avoid strong phonon scattering between the channel material and the dielectric layer [7–10]. By adjusting the depletion layer width formed by the heterojunction, the channel current is controlled to achieve ON and OFF states. More importantly, the subthreshold swing (SS) for MOSFET is defined as [11]

$SS={\left[\frac{\partial \left({\text{log}}_{10}{I}_{\text{DS}}\right)}{\partial V_{\text{GS}}}\times \frac{\partial {\phi }_{\text{s}}}{\partial V_{\text{GS}}}\right]}^{-1},$

while

$\frac{\partial {\phi }_{\text{s}}}{\partial V_{\text{GS}}}=\frac{C_{\frac{\text{gate}}{\text{channel}}}}{C_{\frac{\text{gate}}{\text{channel}}}+C_{\frac{\text{source}}{\text{channel}}}},$

where I_DS and V_GS represent the source-drain current and the gate-source voltage of the transistor, respectively. Due to the dielectric-free configuration and the higher doping concentration of the gate compared to the channel, the JFET behaves similar to a MOSFET with a very large gate capacitance. Since the capacitance from the source to the channel is much smaller than that from the gate to the channel, the SS of JFET can approach the Boltzmann limit of 60 mV dec⁻¹ easily [8]. Unlike silicon-based transistors, two-dimensional (2D) transition metal dichalcogenides (TMDCs) have become attractive channel materials for constructing low-power electronics due to their atom-scale thickness, dangling-bond-free surface, tunable bandgap, and high carrier mobility [12–14]. However, there are still certain technical challenges in achieving a 2D JFET that simultaneously possesses high mobility, high on-off ratio, and ultra-low SS due to the limited heterojunction depletion region and barrier height [15–18]. Lim et al. [19] reported a MoTe₂/MoS₂ van der Waals (vdWs) JFET and realized a near-zero threshold voltage. However, the performance of the p-channel is far inferior to that of the n-channel, leading to a small gate adjustment capability. An appropriate doping strategy can effectively increase the carrier concentration and enhance the performance of the JFETs [20]. The standard doping methods include chemical doping and molecular doping [21]. Chemical doping is mainly achieved by adding dopants to the material surface. Since dopants are inherently dispersed in the form of particles, localized non-uniform doping is inevitable [22]. Such non-uniformity introduces local fields, leading to uneven regulation of barrier height and, consequently, a tendency to induce leakage current. Molecular doping is also called absorbate-induced doping that depends on the surface charge transfer of organic molecular materials to a semiconductor [9,23,24]. Compared with the chemical doping method, molecular doping also encounters difficulties in removing organic molecules and instability in doping. Therefore, there is an urgent need to develop a stable and uniform doping control method to obtain high-performance and low-power transistors.

Here, we fabricated a uniformly Au-doped MoS₂/MoTe₂ van der Waals JFET, and MoTe₂ is used as the gate while MoS₂ serves as the n-channel. Compared with the undoped MoS₂/MoTe₂ JFET (Figure 1a), the MoTe₂ needs to be transferred onto the pre-deposited Au completely to obtain uniformly electrostatic doping (Figure 1b). The band diagram in Figure 1c indicated that the work function of Au is 5.1 eV, the bottom of the conduction band and the top of the valence band of MoTe₂ (MoS₂) are about −3.8 eV (−4.2 eV) and −4.8 eV (−5.4 eV) [25–27]. The band diagram of the MoTe₂ and MoS₂ after contact is displayed in Figure 1d. When the two materials come into contact, the minority carrier holes in MoTe₂ are injected into MoS₂, while the minority carrier electrons in MoS₂ are injected into MoTe₂. Eventually, the movement of carriers reaches an equilibrium state, and the valence band offset of the MoS₂/MoTe₂ heterojunction is about 0.6 eV (ΔE_V1). The Schottky barrier height between Au and MoTe₂ refers to the difference in work function of Au to the electron affinity of MoTe₂, which is about 0.3 eV (ΔE_V2). The bottom Au-doping effect will bring the Fermi level of MoTe₂ closer to the valence band without inducing the additional local state, thereby increasing the barrier height (ΔE_V3) of the MoS₂/MoTe₂ heterojunction, and the ΔE_V3 is approximately equal to ΔE_V1 plus ΔE_V2 (Figure 1e). Thus, the n-type JFETs can achieve effective pinch-off for the MoS₂ channel, exhibiting an obviously enhanced current on-off ratio and enlarged the mobility compared to the undoped MoS₂/MoTe₂ JFET (Figure 1f, g).

Figure 1 Comparisons of schematic diagrams, band structures and electrical properties between conventional and uniformly doped MoS2/MoTe2 JFET. (a, b) Schematic diagrams and atomic structures of the two JFETs. The red and green spheres represent MoS2, the blue and green spheres represent MoTe2, and the yellow spheres represent Au atoms. (c) The band diagrams of Au, MoTe2, and MoS2 before contact. (d, e) Band diagrams of the undoped (d) and Au-doped (e) MoS2/MoTe2 heterojunction. The ΔEV1 is the valence band offset when the MoS2/MoTe2 pn junction formed, which is about 0.6 eV. The ΔEV2 is the Schottky barrier height between Au and MoTe2, which is about 0.3 eV. The ΔEV3 is the valence band offset of the Au-doped MoS2/MoTe2 pn junction, while the ΔEV3 is approximately equal to ΔEV1 plus ΔEV2. (f) Transfer characteristics comparison with the VGS of 2 V. (g) The mobilities of undoped and doped JFETs with the VGS at 2 V.

MATERIALS AND METHODS

Fabrication of Au-doped and undoped MoS₂/MoTe₂ vdWs JFETs

Mechanical exfoliation was used to obtain few-layer MoS₂ and MoTe₂. The bulk MoS₂ and MoTe₂ were purchased from 6 Carbon Technology (Shenzhen). The vdWs MoS₂/MoTe₂ heterostructure was built using a precise transfer platform (Metatest, E1-T) with the dry-accurate transfer method. First, a 10 nm-thick Au film is deposited on the substrate. Subsequently, MoS₂ and MoTe₂ flakes with thicknesses of approximately 4 and 8 nm, respectively, are obtained via mechanical exfoliation. Next, the MoTe₂ flake is transferred onto the Au film surface using a precision transfer platform. Following this, the MoS₂ flake is stacked onto the MoTe₂ surface in a perpendicularly crossed orientation. During this step, it is essential to ensure that the selected MoTe₂ flake exhibits a uniform size comparable to that of the bottom electrode (Au film) and fully covers it to prevent direct contact between MoS₂ and the bottom electrode, which would cause short-circuit failure of the device. The precise transfer technology enables a super-clean interface of the vdWs integrated MoS₂/MoTe₂ heterojunction. Finally, the electrode pattern was formed by electron beam exposure, and contact metals were deposited via a high-vacuum electron-beam evaporation system (KYKY). A 10/50 nm Pd/Au electrode is deposited on the MoTe₂ surface, while a 60 nm-thick Au electrode is deposited on the MoS₂ surface.

Characterization

Optical microscopy was used to determine the morphology of MoS₂ and MoTe₂ crystals (Olympus BX-51M). Kelvin probe force microscope (KPFM) and atomic force microscope (AFM) images were measured under the AFM (Bruker dimension ICON). A Pt/Ir-coated conductive tip (SCM-PIT-V2, Bruker Nano Inc.,) was chosen to probe the morphology and thickness of MoS₂ and MoTe₂ under the ScanAsyst mode, while AM-KPFM measurement was performed in the tapping mode using the same model tip with a resonant frequency of 75 kHz and a tip radius of 25 nm. Raman spectrum was performed under the confocal microscope (JY-HR800) at room temperature with a power of 20 mW and a 532 nm laser. The laser spot size was about 1 mm². The electrical properties were realized by the semiconductor analysis system (Keithley 4200).

RESULTS AND DISCUSSION

To investigate the influence of uniform doping on MoTe₂, we conducted a comparative experiment on the performance of MoTe₂ field-effect transistors (FETs) doped with Au and without Au (Figure 2a). The fabrication process can be found in the Section MATERIALS AND METHODS. To enhance the device performance of Au-doped MoS₂/MoTe₂ heterojunctions, it is critical to minimize the non-overlapping regions of Au, MoS₂, and MoTe₂ in the JFET, which inherently complicates AFM height measurements. Therefore, we roughly estimate the thicknesses of MoS₂ and MoTe₂ based on their colors. A series of samples was selected based on their characteristic colors, and their corresponding thicknesses were measured (Figure S1). Subsequently, during device fabrication, materials with specific colors were consistently chosen to ensure controlled thicknesses. To ensure the optimal contact of MoTe₂ with metal, we fabricated three MoTe₂ FETs with 10 nm/50 nm-thick Cr/Au, 60 nm-thick Au and 10 nm/50 nm-thick Pd/Au electrodes, respectively (Figures S2–S4). The output characteristics of all three devices showed good ohmic contact but exhibited distinct charge transport behavior. The MoTe₂ FET with Cr/Au contact exhibited electron-dominated transport (Figure S2), while the MoTe₂ FET with Au contact showed a symmetrical bipolar behavior (Figure S3). In contrast, the MoTe₂ FET with Pd/Au contact exhibited hole-dominated transport behavior, characterized by a positive shift in the gate voltage turn-on point and enhanced hole concentrations (Figure S4). The higher metal work function of Pd made the metal Fermi level closer to the valence band edge of MoTe₂, which reduced the hole injection barrier and promoted hole transport. Therefore, the Pd/Au electrodes are selected to fabricate MoTe₂ FETs to achieve good hole-dominated transport behavior in the following devices. The transfer characteristics of the Pd/Au contacted MoTe₂ FETs in Figure 2b show prominent p-type transfer characteristics of both uniform doped and undoped MoTe₂ FETs. Still, the inflection point of the transfer curve of the uniformly Au-doped MoTe₂ FET is located at a more positive gate voltage, proving the hole concentration is significantly higher than that of the undoped MoTe₂ FET. Although the Au film did not completely cover the entire layer of MoTe₂, the output characteristics of the MoTe₂ FETs in Figure S5 exhibited good ohmic contacts in both undoped and Au-doped MoTe₂, indicating that the doping of the MoTe₂ channel was relatively uniform. This may be because although Au doping can achieve local charge injection into MoTe₂, the carriers migrate toward the source and drain electrodes simultaneously, eventually making the electrical transport of the transistor exhibit ohmic contact. To further determine the doping effect, Raman characterization of MoTe₂ on SiO₂ and on Au film was performed, equipped with the 532 nm wavelength laser, respectively, as shown in Figure 2c. The 186 and 231 cm⁻¹ in the spectra of 2H-MoTe₂ correspond to the A_1g and $E_{2\text{g}}^1$ mode, respectively [28]. Additionally, the difference of the A_1g peak is enlarged for analysis. Compared with MoTe₂ on SiO₂, Raman spectra of MoTe₂ on Au exhibit an evident blue shift by 1 cm⁻¹, while the shift of $E_{2\text{g}}^1$ peak cannot be observed obviously. In MoTe₂ characteristic Raman peaks, the $E_{2\text{g}}^1$ represents the in-plane vibrational mode, while the A_1g represents the out-of-plane vibration mode. The $E_{2\text{g}}^1$ mode is quite sensitive to uniaxial strains, while the strain effect cannot affect the A_1g mode [29,30]. On the other hand, doping can change the A_1g mode of vibration but has no impact on the $E_{2\text{g}}^1$ vibrational mode. According to the blueshift of the A_1g peak in Figure 2c, it can be proved that Au indeed has a hole-doped effect on MoTe₂. In addition, we also used the KPFM to characterize the potential difference of MoTe₂ contacted with and without Au. Contact potential difference (CPD) usually indicates the difference in work function between the sample and AFM tip [31]. Significant changes in the surface potential between Au-doped MoTe₂ and undoped MoTe₂ are distinguished (Figure 2d). The potential line profile across the heterostructure edge corresponds to the white line in Figure 2d, implying a Fermi level difference of 40 mV, indicating that the Fermi level of MoTe₂ lying on the Au film moves downward. As shown in Figure 2f, the energy bands of the undoped and the Au-doped MoTe₂/MoS₂ heterojunction indicate that the barrier height of the latter one is higher, which can greatly enhance the depletion region of the heterojunction.

Figure 2 Multi-angle comparisons of uniformly Au-doped and undoped MoTe2 FETs. (a) Optical image of the two MoTe2 FETs. (b) Drain voltage dependent transfer characteristic curves. (c) Raman curves of uniformly doped and undoped MoTe2. (d) Surface potential image of MoTe2 on Au and SiO2 substrates. (e) Potential line profile across the edge of the Au corresponding to the white line in (d). The inset is the optical microscope image of MoTe2 layer stack on the Au film and the insulating silicon substrate. (f) Band alignment of MoTe2/MoS2 heterojunction with the undoped MoTe2 (left) and the doped MoTe2 (right). (g) Rectification curves of doped and undoped MoS2/MoTe2 pn junction. (h) Band diagrams of the uniformly doped (blue) and undoped (grey) MoS2 along the channel length.

Furthermore, the diode characteristics of the gate-channel heterojunction are essential in determining the eventual performance of the JFETs. The rectification characteristics of the pn junction are systematically measured, as shown in Figure 2g. It was found that the rectification ratio (RR) of the doped JFET can be achieved at 10⁴, which is significantly higher than that of the undoped JFET of 2×10². Similar results are also obtained for the output characteristics, as shown in Figures S6 and S7. It is further proved that the uniformly doped heterojunction has good rectification characteristics, laying a foundation for the subsequent excellent device performance. The band structure of uniformly doped (blue) and undoped (gray) MoS₂ is also drawn in Figure 2h. Under the same gate voltage, the energy band of doped MoS₂ is more bent up than that of the undoped MoS₂, which can be easily depleted.

As mentioned above, theoretically, JFET is superior to MOSFET in the sub-threshold region due to its dielectric-free device structure. Figure 3a is an optical microscope image of a uniformly doped MoS₂/MoTe₂ JFET. The electrical properties of the JFET under different gate voltages were measured, as shown in Figure 3b. At zero gate voltage, the output characteristic curve is easily saturated. As the gate voltage gradually increases, the saturation speed of the output characteristic curve gradually slows down. Based on the output characteristic curves of the JFET, they can be divided into the linear region, pinch-off region, and saturation region. In the linear region, the source-drain voltage of V_DS is small, the longitudinal electric field dominates the channel. The electric field intensity in the channel is low and uniformly distributed. The mobility is close to the intrinsic mobility of the material. At this point, carrier scattering is mainly determined by lattice vibrations and impurity scattering, and is only weakly affected by the electric field intensity, so the mobility approximates a constant. In the pinch-off region, as V_DS increases, the electric field intensity on the side of the channel close to the drain electrode increases significantly, leading to pinch-off of the channel in this region. As a result, the carrier drift velocity begins to deviate from the linear relationship, and the mobility decreases noticeably with the increase of electric field intensity. In the saturation region, the pinch-off region of the channel expands toward the source, and the average electric field intensity of the entire channel further increases. At this time, the drain current I_DS no longer changes significantly with V_DS, and the carrier drift velocity approaches the saturation velocity. Here, with the increase of electric field intensity, the mobility exhibits an approximately inverse proportional decay and tends to stabilize [8]. Figure 3c, d shows the typical transfer characteristics of MoS₂/MoTe₂ JFET under different source-drain voltages by a logarithmic diagram and a linear diagram, respectively. As shown in Figure 3c, the n-type transport behavior of the JFET was obtained with a switching ratio of about 10⁷. The SS can be expressed as the reciprocal of the slope of the subthreshold region of the transfer characteristic, where $SS=\partial V_{\text{GS}}/\partial \text{lg}{I}_{\text{DS}}$. The smaller the SS value, the stronger the gate voltage’s ability to regulate the channel current [32]. Notably, the I_DS-V_GS slope in the subthreshold region is about 62.5 mV dec⁻¹, close to the theoretical limit. Additionally, gate leakage current measurements of the doped JFET revealed values of about 10⁻¹² A, which reveals that uniform doping not only significantly decreased the SS, but also substantially reduced the gate leakage current. The pinch-off voltage (V_p) refers to the critical voltage at which the channel is completely depleted when the V_GS reaches a specific value, causing the I_DS approach to zero. During measurement, the V_DS needs to be kept constant. When I_DS decreases to below 1 pA as V_GS changes, the corresponding V_GS is the V_p [8,32]. As shown in Figure 3d, the pinch-off voltage of V_p is only −0.1 V through the intersection of the linear partial reverse extension line and the transverse gate voltage. To quantitatively study the performance of MoS₂/MoTe₂ JFET in the subthreshold region, SS and I_DS are plotted as the gate voltage functions (Figure 3e). It is obvious that the values of SS are close to the ideal value of 60 mV dec⁻¹. The transconductance (g_m) is a parameter that represents the current gain influenced by the gate voltage, which is calculated by Eq. (1) and shown in Figure 3f. The maximum transconductance of the Au-doped MoS₂/MoTe₂ JFET can reach 7.68 μS at V_DS=1 V.

Figure 3 Electrical properties of Au-doped MoS2/MoTe2 JFET with MoS2 serves as channel material and MoTe2 serves as gate materials. (a) Optical microscope image of the MoS2/MoTe2 JFET. (b) Output characteristic curves of the MoS2/MoTe2 JFET. The three working stages represent (i) linear region, (ii) pinch-off region, and (iii) saturation region. (c) Drain voltage dependent transfer characteristic curves. (d) Linear plot of the transfer characteristic curves. The pinch-off voltage VP of the JFET is −0.10 V. (e) The SS extracted at different VDS at room temperature. (f) The gm as a function of gate voltage at the VDS of 1 and 2 V. (g–i) Cross-sectional view of the depletion region of the JFET at three stages of (g) linear region, (h) pinch-off region, and (i) saturation region, corresponding to the output characteristics in (b). The d represents the distance between the edge of the Au and MoS2 in the JFET.

$\begin{array}{c}{g}_{\text{m}}=\frac{\partial I_{\text{DS}}}{\partial V_{\text{GS}}}\end{array}$(1)

The mobility of the JFET is defined as the average drift velocity of carriers under a unit electric field. Specifically, it refers to the movement efficiency of carriers in the channel region under the combined action of the transverse electric field formed by the gate voltage and the longitudinal electric field formed by the source-drain voltage. Here, the maximum mobility of JFET is extracted utilizing the following calculation formula when the JFET is in the saturation region and the transconductance reaches the maximum value [33]:

$\begin{array}{c}\mu =\frac{L{g}_{\text{m}}}{q{N}_{\text{d}}tW}\end{array}$(2)

where N_d is the number of carrier concentrations of charges per cubic centimeter, which is estimated by the Hall measurement. q is the electronic charge. t, W, and L are the thickness, width, and length of the channel, respectively. N_d can be estimated through the Hall effect by measuring the electron carrier density at zero gate voltage, which is estimated as 2.5×10¹⁶ cm⁻³ at 300 K. Ultimately, the mobility curve of this device is attained, and the peak value of the mobility achieves 350 cm² V⁻¹ s⁻¹, which is similar to the typical MoS₂ MOSFET.

To obtain a comprehensive understanding of the working mechanism of the Au-doped MoS₂/MoTe₂ JFETs, the schematic diagrams of the junction depletion region driven by both V_GS and V_DS are shown in Figure 3g–i. As mentioned above, to improve the performance of Au-doped MoS₂/MoTe₂ heterojunction devices, it is essential to reduce the non-overlapping areas of Au, MoS₂, and MoTe₂ as much as possible. Therefore, the distance (d) between the edge of the Au film and MoS₂ layer in Figure 3g should be as small as possible. At the same time, the Au film must not come into contact with MoS₂ to prevent short circuits. Similar to MOSFET, JFET has an asymmetric depletion region. When the device operates in the linear region corresponding to Figure 3b(i), due to the small depletion region, the carrier in MoS₂ can inject from the source electrode to the drain electrode fluently. Because of the presence of a voltage gradient in the channel, the source voltage is higher than the drain voltage, which results in a lower barrier. The junction potential near the drain is lower, thereby tilting the depletion region toward the drain (Figure 3g). This effect becomes more pronounced as V_DS increases up the V_GS−V_P due to the change in the electric field strength distribution in the channel, as shown in Figure 3h. When V_GS−V_P=V_DS, the channel is completely shut down, and the device operates in the pinch-off region corresponding the Figure 3b(ii). As the V_DS continues to increase, and then V_GS−V_P​<V_DS, the pinch-off region extends further, as shown in Figure 3i. The inclined depletion region causes the JFET to reach the saturation region state, and the device exhibits stable I_DS with the increase of V_DS [16,34]. Compared with the undoped-MoS₂/MoTe₂ JFET, the underlying Au film will increase the work function of MoTe₂, making its Fermi level closer to the valence band. As a result, the barrier height between MoTe₂ and MoS₂ will be increased, and therefore, accelerating the depletion rate of the MoS₂ channel.

To intuitively present the advantages of the doping effect, the electrical properties of the undoped MoS₂/MoTe₂ JFET are tested. The thicknesses of MoS₂ and MoTe₂ used are consistent with that of the uniform doped devices with a MoTe₂ of 8 nm (Figure S8). The obtained output characteristics are shown in Figure 4a, and also have three typical working stages of linear region, pitch-off region, and saturation region. Figure 4b, c also shows the transfer characteristic curves of the logarithmic and linear relationship of the V_GS-I_DS. According to Figure 4b, the current on-off ratio and SS are about 10⁵ and 113 mV dec⁻¹, respectively. By extracting the linear part, the pinch-off voltage of V_p is about −0.18 V. Similarly, the values of SS curves under different bias voltages are about 100 mV dec⁻¹ in Figure 4d, which is far from the ideal subthreshold. Finally, the saturated mobility of undoped MoS₂/MoTe₂ JFET is calculated, and the peak mobility is about 130 cm² V⁻¹ s⁻¹ (Figure 4e). Due to the dangling-free surface of the 2D vdWs heterojunction, the interface capture state of the JFET caused by defects can be minimized. However, due to the bipolar nature of MoTe₂, the barrier height formed with MoS₂ is not high enough to allow sufficient effective electrons and holes to be transmitted. Uniform doping increases the barrier height of the MoS₂/MoTe₂ heterojunction, enhances the rectification characteristics of the junction, and reduces the gate leakage current, thus improving the performance of the MoS₂/MoTe₂ JFET. To more intuitively compare the electrical properties of MoS₂/MoTe₂ JFET with and without Au-doping, the critical parameters of the two JFETs are displayed intuitively in Figure 4f. It can be seen that the current on-off ratio, gate leakage current, subthreshold swing, pinch-off voltage, and mobility have been significantly modified, and SS is directly decreased to near the ideal value. Table S1 lists the key parameter comparisons of vdW-integrated or 2D TMDCs-based JFETs. The bottom line shown in the table is the related parameters of MoS₂/MoTe₂ JFET in this experiment after electrostatic doping of MoTe₂. Compared with other JFETs, the device in this experiment showed a prominent outcome whether SS, V_P, I_G, current on-off ratio and carrier mobility.

Figure 4 Electrical properties of undoped MoS2/MoTe2 JFET. (a) Output characteristics with increased gate voltage from 0 to 1 V. (b) Drain voltage dependent transfer characteristic curves. The current on-off ratio is about 105. (c) Linear plot of the transfer characteristics. The extracted pinch-off voltage VP is −0.18 V. (d) The SS extracted at three VDS of 1, 2, and 3 V. The minimum value of 113 mV dec−1 was extracted. (e) The gm as a function of gate voltage of the JFET at the VDS of 1, 2, and 3 V. (f) Multiple comparisons of key parameters of the uniformly doped and undoped MoS2/MoTe2 JFETs.

CONCLUSIONS

In summary, we propose a uniform doping method for pre-depositing high-work-function Au under MoTe₂ to optimize the performance of 2D MoS₂/MoTe₂ JFET. The JFET shows a near-ideal subthreshold swing of 62.5 mV dec⁻¹ and an ultra-low gate leakage current of 10⁻¹² A with MoS₂ as the channel. The proposed JFET based on vdW p-n heterojunction performs better than previous studies in the same structure, especially in the subthreshold region, which proposes a promising way for future low-power electronic devices.

Data availability

The original data are available from corresponding authors upon reasonable request.

Acknowledgments

We are grateful to Yanlei Wang of Renmin University of China for constructive discussions. We are grateful to Yali Yang of University of Science and Technology Beijing for constructive discussions.

Funding

This work was supported by the National Natural Science Foundation of China (52350301, 52250398, 92463308, 62322402, 52188101, 52225206, 92163205, 62204012, 52303362, 62304019, 52302162 and 52402169), the National Key Research and Development Program of China (2022YFA1203803, 2024YFA1212600 and 2023YFF1500401), the Beijing Nova Program (20220484145 and 20230484478), the Young Elite Scientists Sponsorship Program by China Association for Science and Technology (2022QNRC001), the Fundamental Research Funds for the Central Universities (FRF-TP-22-004C2, FRF-06500207, FRF-TP-22-004A1, FRF-IDRY-22-016 and FRF-IDRY-23-038), the State Key Lab for Advanced Metals and Materials (2023-Z05), the Postdoctoral Fellowship Program of the China Postdoctoral Science Foudation (GZC20230233), and the special support from the Postdoctoral Science Foundation (2023TQ0007).

Author contributions

X.Z., Z.Z. and Y.Z. initiated and supervised the project. H.Y. and X.L. designed the research, analyzed the data, and wrote the manuscript. X.W. carried out the Raman and AFM measurement. Z.C. made revisions to the language of the manuscript. All authors have approved the final version of the manuscript.

Conflict of interest

The authors declare no conflict of interest.

Supplementary information

Supplementary file provided by the authors. Access here

References

All Figures

Figure 1 Comparisons of schematic diagrams, band structures and electrical properties between conventional and uniformly doped MoS2/MoTe2 JFET. (a, b) Schematic diagrams and atomic structures of the two JFETs. The red and green spheres represent MoS2, the blue and green spheres represent MoTe2, and the yellow spheres represent Au atoms. (c) The band diagrams of Au, MoTe2, and MoS2 before contact. (d, e) Band diagrams of the undoped (d) and Au-doped (e) MoS2/MoTe2 heterojunction. The ΔEV1 is the valence band offset when the MoS2/MoTe2 pn junction formed, which is about 0.6 eV. The ΔEV2 is the Schottky barrier height between Au and MoTe2, which is about 0.3 eV. The ΔEV3 is the valence band offset of the Au-doped MoS2/MoTe2 pn junction, while the ΔEV3 is approximately equal to ΔEV1 plus ΔEV2. (f) Transfer characteristics comparison with the VGS of 2 V. (g) The mobilities of undoped and doped JFETs with the VGS at 2 V.

In the text

Figure 2 Multi-angle comparisons of uniformly Au-doped and undoped MoTe2 FETs. (a) Optical image of the two MoTe2 FETs. (b) Drain voltage dependent transfer characteristic curves. (c) Raman curves of uniformly doped and undoped MoTe2. (d) Surface potential image of MoTe2 on Au and SiO2 substrates. (e) Potential line profile across the edge of the Au corresponding to the white line in (d). The inset is the optical microscope image of MoTe2 layer stack on the Au film and the insulating silicon substrate. (f) Band alignment of MoTe2/MoS2 heterojunction with the undoped MoTe2 (left) and the doped MoTe2 (right). (g) Rectification curves of doped and undoped MoS2/MoTe2 pn junction. (h) Band diagrams of the uniformly doped (blue) and undoped (grey) MoS2 along the channel length.

In the text

Figure 3 Electrical properties of Au-doped MoS2/MoTe2 JFET with MoS2 serves as channel material and MoTe2 serves as gate materials. (a) Optical microscope image of the MoS2/MoTe2 JFET. (b) Output characteristic curves of the MoS2/MoTe2 JFET. The three working stages represent (i) linear region, (ii) pinch-off region, and (iii) saturation region. (c) Drain voltage dependent transfer characteristic curves. (d) Linear plot of the transfer characteristic curves. The pinch-off voltage VP of the JFET is −0.10 V. (e) The SS extracted at different VDS at room temperature. (f) The gm as a function of gate voltage at the VDS of 1 and 2 V. (g–i) Cross-sectional view of the depletion region of the JFET at three stages of (g) linear region, (h) pinch-off region, and (i) saturation region, corresponding to the output characteristics in (b). The d represents the distance between the edge of the Au and MoS2 in the JFET.

In the text

Figure 4 Electrical properties of undoped MoS2/MoTe2 JFET. (a) Output characteristics with increased gate voltage from 0 to 1 V. (b) Drain voltage dependent transfer characteristic curves. The current on-off ratio is about 105. (c) Linear plot of the transfer characteristics. The extracted pinch-off voltage VP is −0.18 V. (d) The SS extracted at three VDS of 1, 2, and 3 V. The minimum value of 113 mV dec−1 was extracted. (e) The gm as a function of gate voltage of the JFET at the VDS of 1, 2, and 3 V. (f) Multiple comparisons of key parameters of the uniformly doped and undoped MoS2/MoTe2 JFETs.

In the text