Homojunction device

Abstract

A homojunction device and a method of fabricating a homojunction device. The homojunction device comprises a programming electrode, a dielectric stack on the programming electrode, the dielectric stack comprising a ferroelectric material and a dielectric layer disposed between the ferroelectric material and the programming electrode; an ambipolar material on the dielectric stack on an opposite side thereof compared to the programming electrode; and a first electrode and a second electrode each electrically connected to the ambipolar material; wherein the ambipolar material extends beyond the ferroelectric material to be in contact with the dielectric layer in a first area of the ambipolar material; wherein the first electrode is electrically connected to the first area of the ambipolar material and the second electrode is electrically connected to a second area of the ambipolar material overlapping the ferroelectric material; and wherein, in the second area, the ambipolar material is programmable to be either p-type or n-type through application of a voltage pulse to the programming electrode for forming a homojunction comprising the first area and the second area of the ambipolar material. 3A

Description

[0001] HOMOJUNCTION DEVICE

[0002] FIELD OF INVENTION

[0003] The present invention relates broadly to a homojunction device and a method of fabricating a homojunction device.

[0004] BACKGROUND

[0005] Any mention and / or discussion of prior art throughout the specification should not be considered, in any way, as an admission that this prior art is well known or forms part of common general knowledge in the field.

[0006] The p-n junction diode is a foundational component in current electronic and optoelectronic devices, playing a pivotal role in tasks like energy conversion and current rectification. Discovered by chance nearly 80 years ago, its significance in the modem semiconductor industry is undeniable, seamlessly connecting the realms of electronics and optics.1,2,3Traditional p-n junctions predominantly utilize bulk semiconductors, such as Si and Ge, and are created by introducing group III or V elements into two distinct areas to achieve p-type or n-type doping, respectively.

[0007] Recently, there has been a surge in interest towards p-n junctions crafted from two-dimensional (2D) materials due to their remarkable mechanical, electrical, and optical characteristics.4,5,6These materials also pave the way for optical interconnect components that are compatible with Si photonics and CMOS, utilizing the back-end-of-the-line processing techniques. There's been a significant push to associate p- and n-type 2D materials closely to ensure a functioning p-n junction, ushering in the development of various optoelectronic and electronic applications like photodetectors, solar cells, light sources, memory storage, and logic rectifiers.

[0008] According to the components of junctions, they can be classified into two types: heterojunctions constructed by two different materials,7,8and homojunctions formed by one material.9,10Although 2D materials based van der Walls (vdW) heterostructure has attracted much attention due to the capability of rationally integrating disparate layers of 2D materials to achieve novel electronic / optoelectronic devices with desirable functions and performance, there are some non-negligible shortcomings in the 2D heterojunctions to be considered, such as chemical intermixing, grain boundaries, and discontinuous band alignments, which may lead to carrier scattering and trapping centers at the heterointerfaces, deteriorating the interface charge transfer efficiency and device performance.10Meanwhile, 2D homojunctions formed by a single 2D material might be more beneficial for carrier transport and separation at the interface owing to the natural matching of their chemical and electronic structures. As a result, 2D homojunctions exhibit outstanding performances, for example, better rectifying characteristics and more efficient photorcsponsc, making them of great value in designing novel functional devices.11,12

[0009] 2D homojunctions can be categorized into p-n homojunctions, hetero-phase homojunctions, and layer-engineered homojunctions, and the preparation strategies of 2D homojunctions include vapor-phase deposition, lithium intercalation, chemical doping, electrostatic doping, and photodoping.10Among all the homojunctions, electrically tunable homojunctions (ETH) by electrostatic doping show advantages in simpler fabrication process and the ability of accommodating an abundance of current states at a physical level.9Typically, electrostatic doping used to regulate the carrier types in ambipolar 2D materials needs persistent gate voltages, leading to some light emission loss at the surface. To achieve reduced power usage, ferroelectric substances are viewed as potential replacements for doping 2D materials, given their ability to have their spontaneous polarization directions altered by external triggers.13

[0010] In SG Patent Application No. 10202113123X, and WO 2023 / 096585 A3, interfacial states are introduced on a ferroelectric Hfo.5Zro.5O2 thin film during an annealing process. Utilizing the synergetic effect of ferroelectric polarization and charge trapping behavior, a multifunctional 2D Fe-FET was demonstrated, exhibiting reliable memory properties, tunable synaptic functions, and rcconfigurablc photodetection behaviors in one single device. Furthermore, the ferroelectric polarization-dependent optoelectronic response was observed, making it promising for the optoelectronic logic device application. The results pave the way for the fabrication of high-density data process systems with various functions.

[0011] Embodiments of the present invention seek to provide alternative devices based on ferroelectric polarization-assisted charge trapping.

[0012] SUMMARY

[0013] In accordance with a first aspect of the present invention, there is provided a homojunction device comprising: a programming electrode, a dielectric stack on the programming electrode, the dielectric stack comprising a ferroelectric material and a dielectric layer disposed between the ferroelectric material and the programming electrode; an ambipolar material on the dielectric stack on an opposite side thereof compared to the programming electrode; and a first electrode and a second electrode each electrically connected the ambipolar material; wherein the ambipolar material extends beyond the ferroelectric material to be in contact with the dielectric layer in a first area of the ambipolar material; wherein the first electrode is electrically connected to the first area of the ambipolar material and the second electrode is electrically connected to a second area of the ambipolar material overlapping the ferroelectric material; and wherein, in the second area, the ambipolar material is programmable to be either p-type or n- type through application of a voltage pulse to the programming electrode for forming a homojunction comprising the first area and the second area of the ambipolar material.

[0014] In accordance with a second aspect of the present invention, there is provided a method of fabricating a homojunction device comprising the steps of: providing a programming electrode, providing a dielectric stack on the programming electrode, the dielectric stack comprising a ferroelectric material and a dielectric layer disposed between the ferroelectric material and the programming electrode; providing an ambipolar material on the dielectric stack on an opposite side thereof compared to the programming electrode; and providing a first electrode and a second electrode each electrically connected to the ambipolar material; wherein the ambipolar material extends beyond the ferroelectric material to be in contact with the dielectric layer in a first area of the ambipolar material; wherein the first electrode is disposed in the first area of the ambipolar material and the second electrode is disposed in a second area of the ambipolar material overlapping the ferroelectric material; and wherein, in the second area, the ambipolar material is programmable to be either p-type or n- type through application of a voltage pulse to the programming electrode for forming a homojunction comprising the first area and the second area of the ambipolar material.

[0015] BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Embodiments of the invention will be better understood and readily apparent to one of ordinary skill in the art from the following written description, by way of example only, and in conjunction with the drawings, in which:

[0017] FIG. 1 A shows the top and side view for the crystal structure of CuCrPzSe (CCPS). Within a layer, the Cu, Cr and P-P form separate triangular networks. The polarization direction is indicated in by the arrow.

[0018] FIG. IB shows the optical image of a CCPS flakes. FIG. 1C shows Raman spectra and Raman signal mapping of one of the CCPS flakes in FIG. IB.

[0019] FIG. ID shows a graph of the PFM amplitude hysteresis loop during the switching process for a 400nm thick CCPS.

[0020] FIG. IE shows a graph of the phase hysteresis loop during the switching process for the 400nm thick CCPS flake.

[0021] FIG. IF shows a PFM phase image of the 400 nm CCPS flake after writing “box-in-box” pattern by reverse DC bias (+6 V for inside, -6 V for outside).

[0022] FIG. 2A shows an optical image of a structure for evaluating the WSer / CCPS heterostructure according to an example embodiment.

[0023] FIG. 2B shows the Raman signal mapping of the region marked by dashed box in FIG. 2A, specifically the signal intensity of the peak at about 197cm-1(CCPS peak). Scale bar: 5 pm.

[0024] FIG. 2C shows the Raman signal mapping of the region marked by dashed box in FIG. 2A, specifically the signal intensity of the peak at about 250cm-1(WSe2 peak). Scale bar: 5 pm.

[0025] FIG. 2D shows a schematic of the KPFM set-up for evaluating the WSe2 / CCPS heterostructure according to an example embodiment, with Vbias applied to the sample.

[0026] FIG. 2E shows an AFM image of the WSe2 / CCPS heterostructure according to an example embodiment. Inset: optical image of the sample. Scale bar: 5 pm.

[0027] FIG. 2F shows the spatially mapped Vbias by KPFM characterization of the area marked by dashed box in FIG. 2E and the Vbias profile. Scale bar: 500 nm.

[0028] FIG. 2G shows the expected band alignment of isolated WSe2 located on CCPS and SiCh, respectively, according to an example embodiment.

[0029] FIG. 2H shows the band alignment from FIG. 2G if WSe2 is in contact with the respective surfaces of CCPS and SiO2 and reach equilibrium.

[0030] FIG. 3A shows a schematic diagram of a ferroelectric field-effect transistor (FE-FET) device according to an example embodiment.

[0031] FIG. 3B shows the optical image of a FE-FET device according to an example embodiment.

[0032] FIG. 3C shows the transfer characteristics of the memory device in a FE-FET device according to an example embodiment at Vds= 0.1 V.

[0033] FIG. 3D shows the schematic image illustrating the clockwise hysteresis originated from ferroelectric polarization assisted interfacial trapping effect of the memory device in a FE-FET device according to an example embodiment. FIG. 3E shows the schematic image of the anti-clockwise hysteresis in a memory device originated from the switch of the ferroelectric polarization.

[0034] FIG. 3F shows the output characteristics of the memory device in a FE-FET device according to an example embodiment at on state and off state, respectively

[0035] FIG. 3G shows the retention performance of the memory device in a FE-FET device according to an example embodiment. The on state- and off state-currents were separately read after erasing with a -60 V Vg pulse for 1 s and writing with a +60 V Vg pulse for 1 s, respectively. During the reading process, keeping Eds = 0.1 V and Eg =0 V.

[0036] FIG. 3H shows the endurance characteristics of the memory device in a FE-FET device according to an example embodiment. Writing and erasing operations were carried out under cyclic voltage pulses. The reading states were operated under Yds = 0.1 V.

[0037] FIG. 4A shows the schematic diagram of a FE-FET device according to an example embodiment with p-n homojunction.

[0038] FIG. 4B shows the transfer characteristics of the homojunction FE-FET device according to an example embodiment at different Yds (-1 and +1 V).

[0039] FIG. 4C shows the operation diagrams of the homojunction FE-FET device according to an example embodiment when it is programmed to be a p-n homojunction and the band diagrams of the p-n homojunction.

[0040] FIG. 4D shows the output curves of the homojunction FE-FET device according to an example embodiment when it is programmed to be a p-n junction, with Vg - 0, noting that the p-n junction is nonvolatille, which means it can be retained after the Vg pulse is removed.

[0041] FIG. 4E shows the dynamic photoresponse (with light on and off) of the p-n homojunction FE-FET device according to an example embodiment under light with wavelength of 638 nm.

[0042] FIG. 4F shows the dynamic photoresponse (with light on and off) of the p-n homojunction FE- FET device according to an example embodiment under light with wavelength of 473 nm.

[0043] FIG. 4G shows Zds-Vds curves of the p-n junction of the p-n homojunction FE-FET device according to an example embodiment under different Pln. the laser wavelength is 638 nm., with Vg = 0, noting that the p-n junction is nonvolatille, which means it can be retained after the Vg pulse is removed.

[0044] FIG. 4H shows Zds-Vds curves of the p-n junction of the p-n homojunction FE-FET device according to an example embodiment under different Pin, the laser wavelength is 473 nm, with Vg = 0, noting that the p-n junction is nonvolatille, which means it can be retained after the Vg pulse is removed.

[0045] FIG. 41 shows the fitting of relationship between Pmand Zp, where Zpis the short-circuit current derived from FIGs. 4G and 4H. FIG. 5 shows a flow-chart illustrating a method of fabricating a homojunction device according to an example embodiment.

[0046] DETAILED DESCRIPTION

[0047] Example embodiments of the present invention can provide a 2D homojunction device employing a localized doping strategy that can reversibly program the device in a nonvolatile manner. When operating as a p-n homojunction, the device according to an example embodiment exhibits excellent rectifying characteristics and high responsivity under light illumination. Embodiments of the present invention demonstrate great potential towards high- performance photoelectric interconnected circuits.

[0048] In an example embodiment it is demonstrated that by vdW stacking an ambipolar material / ferroelectrics heterostructure, e.g. a transition-metal dichalcogenides (TMDjs / ferroelectrics heterostructure, a nonvolatile memory with a high on / off ratio, large memory window, good endurance, and long retention time can be realized by the synergetic effect of ferroelectric polarization and charge trapping behavior. By using an ambipolar material, in an example embodiment a 2D semiconductor WSe2 (multilayer), acting as the channel, a lateral homojunction in WSe2 can be modulated by the voltage pulses at the control gate and be further retained by the charge trapping behavior at the interface. When operating as a p-n homojunction, the device according to an example embodiment exhibits excellent rectifying characteristics and high responsivity under light illumination. Embodiments of the present invention demonstrate great potential towards high-performance photoelectric interconnected circuits.

[0049] FIG. 1A shows the crystal structure of ferroelectric (FE) CuCrP2Se (CCPS) as a non-limiting example of a ferroelectric material for use in example embodiments. CCPS has CuSs, CrSe, and P2S6 units forming triangular networks. The Cr ions and the P-P pairs arc almost centered within a layer, whereas the Cu ions are off-centered. The Cu ions all occupy the upper (Cu’) or lower (Cu”) position, resulting in two different FE states. Since the interlayer coupling is vdW interaction, it is possible to exfoliate the CCPS bulk to monolayer and few-layer counterparts. FIG. IB shows the optical images of CCPS flakes e.g. 110 with different thickness, which were be achieved by exfoliation of the CCPS bulk. The Raman spectra and Raman signal mapping of one of the CCPS flakes in FIG. 1A is shown in FIG. 1C. The CCPS presents three characteristic peaks at about 193cm-1, 259 cm-1, and 371 cm-1.

[0050] To verify the thin-film ferroelectricity, the CCPS flakes were investigated using piezoresponse force microscopy (PFM). The PFM amplitude reflects the absolute magnitude of the local piezoelectric response, while the phase indicates the polarization direction in each individual domain. By definition, a ferroelectric material should possess spontaneous polarization that is switchable. Local switching tests were carried out by applying a bias between the conductive PFM tip and the heavily doped Si substrate. The switching spectroscopic loops were recorded under resonance-enhanced PFM mode by applying an AC electric field. The well-defined butterfly loops of the PFM amplitude signals (see FIG. ID) and the distinct 180° switching of the phase signals (see FIG. IE) indicate the robust ferroelectric polarization in the CCPS ultrathin flakes. FIG. IF displays the PFM phase images of CCPS flakes after writing box-in- box patterns with reversed DC bias in the centre. Clear phase contrast further confirms the switching of polarization in CCPS.

[0051] To evaluate the feasibility of applying CCPS in 2D devices according to example embodiments, the properties of the TMDs / CCPS interface were investigated by constructing a WScz / h-BN / CCPS hctcrostructurc, as shown in FIG. 2A, as a non-limiting example material combination for use in example embodiments. A CCPS flake 201 was first exfoliated onto a Si / SiO2 substrate 200, then a h-BN flake 202 and a WSc2 flake 204 were transferred onto the CCPS flake 201 sequentially. Finally, part of the WSe2 flake 204 lies directly on SiO2 200, i.e. with physical contact therebetween, part of the WSe2 flake 204 lies on the CCPS flake 201, and part of WSc2 flake 204 lies on h-BN / CCPS (i.e. on a stack of the h-BN flake 202 and the CCPS flake 201. The h-BN flake 202 is used to isolate WSC2 and CCPS in order to evaluate the contact between WSc2 and CCPS.

[0052] FIG. 2B.C show Raman signal mapping of WSc; peak and CCPS peak of the region marked by white dashed box in in FIG. 2A. The CCPS signal intensity shows significant decay at the region covered by WScz (FIG. 2B), and notably the WSe2; signal intensity at WSeVCCPS heterostructure region is weaker comparing to that at WSe2 / h-BN / CCPS and WSe2 / SiC>2 regions (FIG. 2C), revealing some anomalous interface effects of WSeVCCPS junctions.

[0053] Kelvin probe force microscopy (KPFM) measurement of WSe2 / CCPS heterostructure was conducted with the set-up shown in FIG. 2D. The lift mode with a constant tip height (h = 40nm) was used and the DC component of a bias voltage (Vbias) was applied to the sample. As KPFM typically requires the sample to be sufficiently conducting, we made an electrode on WSe2 to add Vbias on the sample.

[0054] FIG. 2E shows the atomic force microscopy (AFM) image of the heterostructure in FIG. 2D. One can observe some small bubbles resulting from the transfer process. The Kelvin probe force microscopy (KPFM) measurement was then carried out of the region marked by the dotted box in FIG. 2E. FIG. 2F shows the mapping of Vbias that was applied to the sample and the corresponding averaged Vbias profile. The magnitude of Vbias is related to the work function of the sample and that of the tip, so KPFM measurements allow direct interpretation of the conduction band offset from the Vbias contrast. FIG. 2F therefore implies that AE = -140 meV for the experimental condition, that is, Ecfor WSe2 on CCPS is positioned higher than that on SiCh. The band offset implies that a lateral homojunction is formed in WSe2 when it lies on different substrates, in this example SiC>2 and CCPS, respectively. As a result, one can draw the energy band diagrams of isolated WSei located on CCPS and SiO2 and lateral homojunction in WSe2 after reaching equilibrium, as shown in FIG. 2G,H. The nonvolatile memory behavior of a homojunction device according to an example embodiment, here in the form of form of a 2D ferroelectric field-effect transistor (FE-FET) device 300 based on a vdW stack of TMDs / fcrroclcctrics hetero structure, was examined first. As shown in FIG. 3A, on the left side of the 2D FE-FET device 300 a memory device was constructed by utilizing the SiCh of a Sith / Si substrate 302 and a CCPS flake304 as the gate dielectric and dry transferring a WScj flake 306 as the channel. The Si of the SiOi / Si substrate 302 was used as the gate electrode, whereas Au / Ti source and drain electrodes 308, 310 were deposited on the WScz flake 306.

[0055] FIG. 3C displays the transfer characteristics of the memory device, where it shows obvious electron-dominated clockwise hysteresis behavior under forward and backward gate voltage sweeping. It is worth mentioning that the results of conductance tuning in the 2D semiconductor channel by ferroelectric polarization are different from the behaviors in previous reports, which mostly show the anticlockwise hysteresis for the n-type channel. Clockwise hysteresis observed in previous studies were typically attributed to the adsorption of molecules, oxide traps close to the 2D channel, intrinsic traps, etc. As a result, it is proposed that the ferroelectric polarization-assisted interface traps between the 2D channel, in the example embodiment the WScz flake 306, and CCPS flake 304 arc the possible origin for the observed clockwise hysteresis.

[0056] A schematic illustration of the hysteresis originated from ferroelectric polarization assisted interfacial trapping effect and pure ferroelectric polarization switching arc shown in FIGs. 3D,E respectively. For the device switched purely by ferroelectric polarization (FIG. 3E), the negative gate voltage sets the ferroelectric polarization to the downward direction (Pdown), which depletes the electrons in the channel and sets the device to the off state; while the positive gate voltage sets the ferroelectric polarization to the upward direction (Pup), which causes the accumulation of electrons in the channel and sets the device to the on state. As a result, the memory device exhibits transfer characteristics with anti-clockwise hysteresis.

[0057] On the other hand, in the structure according to embodiments of the present invention, the dominant carrier trapping behavior at the interface traps leads to clockwise hysteresis in transfer characteristics, as shown in FIG. 3C, and as schematically illustrated in FIG. 3D. The negative gate voltage attracts holes into interface trap states (indicated generally at numeral 311) from the channel and sets the ferroelectric polarization to the downward direction (Pdown). After releasing the gate bias, the downward ferroelectric polarization maintains and attract the trapped holes at the interface, further inducing electron accumulation in the channel and setting the device to the on state. Similarly, the positive gate voltage leads to the depletion of electrons and accumulation of holes in the channel. As a result, the memory device in the 2D FE-FET device 300 (FIG. 3A) according to an example embodiment exhibits transfer characteristics with clockwise hysteresis.

[0058] The nonvolatile memory performance of the memory device in the 2D FE-FET device 300 (FIG. 3A) according to an example embodiment was further investigated. Excellent charge retention ability and good endurance are important parameters to evaluate the performance of nonvolatile memory. Output characteristics of the memory device under on and off states arc demonstrated in FIG. 3F. The low resistance state (LRS, on state) and high resistance state (HRS, off state) obtained in the memory device under different CCPS polarizations exhibit a high on / off ratio up to 104. FIG. 3G shows the retention performance of the memory device in the 2D FE-FET device 300 according to an example embodiment. After applying one positive or negative Vgpulse, the reading currents of the two states both exhibited limited degradation even after 104s. FIG. 3H shows the reliable endurance cycle of the memory device in the 2D FE-FET device 300 (FIG. 3A) according to an example embodiment. Cyclic Vgpulses (±50 V, 1 s) were set before reading at Vg= 0 V, Vds =100 mV. The on state and off state reading currents arc almost unchanged after over 200 cycles and the on / off ratio maintains over 104during the operation.

[0059] As the good memory behavior of the memory device in the 2D FE-FET device 300 according to an example embodiment utilizing vdW stack of the TMDs / fcrroclcctrics hctcrostructurc was confirmed, the hctcrostructurc was used to achieve a programmable homojunction device according to an example embodiment, by employing a localized doping strategy. As shown in FIG. 4A, for the 2D FE-FET device 300, half of the channel, here WScz flake 306, lies on CCPS flake 304, while the other half lies on SiCh. As a result, only one side of the channel can be modulated by the underlying ferroelectrics, while the other side advantageously cannot be affected by the programming media. In FIG. 4A, the left-side channel can be programmed into p-typc / n-typc by the control gate and then it can retain the polarity by the synergetic effect of ferroelectric polarization and charge (clcctron / holc) trapping in the memory device part of the 2D FE-FET device 300, as described above. Since the channel on the right in FIG. 4A is not affected by the programming media, it then forms different homojunctions with the channel on the left according to example embodiments, depending on different states of the programming media. Specifically in this example embodiment, the channel on the right will always be n- typc, because WSc2 is electron-dominant. Therefore, if the left side of the channel is set to be p-type, the junction is a p-n junction. If the left side is set to be n-type, the junction is an n-n junction.

[0060] In more detail, in order to achieve a p-n homojunction, an ambipolar material is used as the channel in the 2D FE-FET device 300 according to an example embodiment. As shown in FIG. 4B, the homojunction device according to an example embodiment exhibits two distinctly different transfer characteristics as Vds varies from -1 V to +1 V, due to the ferroelectrics induced homojunction in the device according to an example embodiment.

[0061] Accordingly, after applying a positive programming pulse to the memory device in the 2D FE- FET device 300 (FIG. 4A) according to an example embodiment, the left-side channel is programmed into p-type and retains the polarity by the CCPS induced interface charge trapping, as described above. As a result, the homojunction becomes a p-n junction (FIG. 4C), which exhibits a typical 1-V curve of a p-n diode (FIG. 4D).

[0062] The dynamic optoelectronic properties of the p-n homojunction in the 2D FE-FET device 300 according to an example embodiment under the illumination of laser beam at a wavelength of 638 nrn or 473 nm (indicated at numerals 312 and 314, respectively in FIG. 4A) arc shown in FIG. 4E and FIG. 4F, respectively, with varying power density (An) of the laser beam. The static optoelectronic properties of the p-n homojunction arc shown in FIG. 4G and FIG. 4H. The I-V curves shift upwards with increasing incident laser power, and obvious open-circuit voltage can be observed to be from ~0.3 V to -0.5 V, further verifying the formation of the p- n junction. The relationship between photocurrent (Zp), measured at Vds = 0, and Pin extracted from FIG. 4E and 4F is shown in FIG. 41 at numeral 404 and 406, respectively. The experimental data arc fitted with equation 1 = P“, where a equals 1 for an ideal p-n junction photodiode with photocurrent depending linearly on the illumination power density. An a value of 1.05 and 0.95 was obtained for the device according to an example embodiment under blue and red light illumination, respectively, implying that / pshows a good linear behavior when altering Pin over several orders of magnitude.

[0063] In an example embodiment, a homojunction device is provided comprising a programming electrode, a dielectric stack on the programming electrode, the dielectric stack comprising a ferroelectric material and a dielectric layer disposed between the ferroelectric material and the programming electrode; an ambipolar material on the dielectric stack on an opposite side thereof compared to the programming electrode; and a first electrode and a second electrode each electrically connected to the ambipolar material; wherein the ambipolar material extends beyond the ferroelectric material to be in contact with the dielectric layer in a first area of the ambipolar material; wherein the first electrode is electrically connected to the first area of the ambipolar material and the second electrode is electrically connected to a second area of the ambipolar material overlapping the ferroelectric material; and wherein, in the second area, the ambipolar material is programmable to be either p-typc or n-typc through application of a voltage pulse to the programming electrode for forming a homojunction comprising the first area and the second area of the ambipolar material.

[0064] The ambipolar material may comprise an ambipolar material flake.

[0065] The ambipolar material may comprise WSc2, M0TC2, or black phosphorus (BP).

[0066] The ferroelectric material may comprise a ferroelectric material flake.

[0067] The ferroelectric material may comprise CuCrP2Se, or Hafnium-zirconium oxide (HZO).

[0068] The dielectric layer may comprise SiO2, HfO2, orAFO ,.

[0069] A hetero structure comprising the first area of the ambipolar material, the ferroelectric material, and the dielectric layer may exhibit a clockwise current versus VG hysteresis.

[0070] Ferroelectric polarization-assisted traps may be present at an interface between the ambipolar material and the ferroelectric material.

[0071] The device may exhibit self-powered photodetection.

[0072] The homojunction may be switchable between a p-n junction and a n-n junction. FIG. 5 shows a flow-chart 500 illustrating a method of fabricating a homojunction device according to an example embodiment. At step 502, a programming electrode is provided. At step 504, a dielectric stack is provided on the programming electrode, the dielectric stack comprising a ferroelectric material and a dielectric layer disposed between the ferroelectric material and the programming electrode. At step 506. an ambipolar material is provided on the dielectric stack on an opposite side thereof compared to the programming electrode. At step 508. a first electrode and a second electrode each electrically connected to the ambipolar material arc provided, wherein the ambipolar material extends beyond the ferroelectric material to be in contact with the dielectric layer in a first area of the ambipolar material; wherein the first electrode is electrically connected to the first area of the ambipolar material and the second electrode is electrically connected to a second area of the ambipolar material overlapping the ferroelectric material; and wherein, in the second area, the ambipolar material is programmable to be cither p-typc or n-typc through application of a voltage pulse to the programming electrode for forming a homojunction comprising the first area and the second area of the ambipolar material.

[0073] The ambipolar material may comprise an ambipolar material flake.

[0074] The ambipolar material may comprise WSc2, MoTc2, or black phosphorus (BP).

[0075] The ferroelectric material may comprise a ferroelectric material flake.

[0076] The ferroelectric material may comprise CuCrP2Se, or Hafnium-zirconium oxide (HZO).

[0077] The dielectric layer may comprise Sith. Hfth. orAFO ,.

[0078] A hetero structure comprising the first area of the ambipolar material, the ferroelectric material, and the dielectric layer may exhibit a clockwise current versus VG hysteresis.

[0079] Ferroelectric polarization-assisted traps may be present at an interface between the ambipolar material and the ferroelectric material.

[0080] The homojunction device may exhibit self-powered photodetection.

[0081] The homojunction device may be switchable between a p-n junction and a n-n junction.

[0082] Embodiments of the present invention can have one or more of the following features and associated benefits / advantages:

[0083] It will be appreciated by a person skilled in the art that numerous variations and / or modifications may be made to the present invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects to be illustrative and not restrictive. Also, the invention includes any combination of features described for different embodiments, including in the summary section, even if the feature or combination of features is not explicitly specified in the claims or the detailed description of the present embodiments.

[0084] For example, while WSez was used for the ambipolar material in the example embodiment described herein, other ambipolar materials, such as MoTe2 or black phosphorus (BP) can be used in different embodiments.

[0085] As another example, while SiCh was used as part of the gate dielectric in the example embodiment described herein, other dielectrics such as HfCh. AI2O3 can be used in different embodiments.

[0086] As another example, while CuCrP2Se, was used as ferroelectric material in the example embodiment described herein, other ferroelectric materials such as Hafnium-zirconium oxide (HZO) can be used in different embodiments.

[0087] In general, in the following claims, the terms used should not be construed to limit the systems and methods to the specific embodiments disclosed in the specification and the claims, but should be construed to include all processing systems that operate under the claims. Accordingly, the systems and methods are not limited by the disclosure, but instead the scope of the systems and methods is to be determined entirely by the claims.

[0088] Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise," "comprising," and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in a sense of "including, but not limited to." Words using the singular or plural number also include the plural or singular number respectively. Additionally, the words "herein," "hereunder," "above," "below," and words of similar import refer to this application as a whole and not to any particular portions of this application. When the word "or" is used in reference to a list of two or more items, that word covers all of the following interpretations of the word: any of the items in the list, all of the items in the list and any combination of the items in the list. References

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Claims

CLAIMS1. A homojunction device comprising: a programming electrode, a dielectric stack on the programming electrode, the dielectric stack comprising a ferroelectric material and a dielectric layer disposed between the ferroelectric material and the programming electrode; an ambipolar material on the dielectric stack on an opposite side thereof compared to the programming electrode; and a first electrode and a second electrode each electrically connected to the ambipolar material; wherein the ambipolar material extends beyond the ferroelectric material to be in contact with the dielectric layer in a first area of the ambipolar material; wherein the first electrode is electrically connected to the first area of the ambipolar material and the second electrode is electrically connected to a second area of the ambipolar material overlapping the ferroelectric material; and wherein, in the second area, the ambipolar material is programmable to be either p-type or n- type through application of a voltage pulse to the programming electrode for forming a homojunction comprising the first area and the second area of the ambipolar material.

2. The device of claim 1, wherein the ambipolar material comprises an ambipolar material flake.

3. The device of claims 1 or 2, wherein the ambipolar material comprises WSe2, MoTe2, or black phosphorus (BP).

4. The device of any one of the preceding claims, wherein the ferroelectric material comprises a ferroelectric material flake.

5. The device of any one of the preceding claims, wherein the ferroelectric material comprises CuCriLSc,. or Hafnium-zirconium oxide (HZO).

6. The device of any one of the preceding claims, wherein the dielectric layer comprises SiC , HfO2, orAl2O3.

7. The device of any one of the preceding claims, wherein a heterostructure comprising the first area of the ambipolar material, the ferroelectric material, and the dielectric layer exhibits a clockwise current versus VG hysteresis.

8. The device of claim 7, wherein ferroelectric polarization-assisted traps are present at an interface between the ambipolar material and the ferroelectric material.

9. The device of any one of the preceding claims, exhibiting self-powered photodetection.

10. The device of any one of the preceding claims, wherein the homojunction is switchable between a p-n junction and a n-n junction.

11. A method of fabricating a homojunction device comprising the steps of: providing a programming electrode, providing a dielectric stack on the programming electrode, the dielectric stack comprising a ferroelectric material and a dielectric layer disposed between the ferroelectric material and the programming electrode; providing an ambipolar material on the dielectric stack on an opposite side thereof compared to the programming electrode; and providing a first electrode and a second electrode each electrically connected to the ambipolar material; wherein the ambipolar material extends beyond the ferroelectric material to be in contact with the dielectric layer in a first area of the ambipolar material; wherein the first electrode is electrically connected to the first area of the ambipolar material and the second electrode electrically connected to a second area of the ambipolar material overlapping the ferroelectric material; and wherein, in the second area, the ambipolar material is programmable to be either p-type or n- type through application of a voltage pulse to the programming electrode for forming a homojunction comprising the first area and the second area of the ambipolar material.

12. The method of claim 1 1 , wherein the ambipolar material comprises an ambipolar material flake.

13. The method of claims 1 1 or 12, wherein the ambipolar material comprises WSe2, MoTe2, or black phosphorus (BP).

14. The method of any one of claim 1 1 to 13, wherein the ferroelectric material comprises a ferroelectric material flake.

15. The method of any one of the claims 1 1 to 14, wherein the ferroelectric material comprises CuCrP2Se, or Hafnium-zirconium oxide (HZO).

16. The method of any one of claims 11 to 15, wherein the dielectric layer comprises SiCh, HfO2, orAl2O3.

17. The method of any one of claims 11 to 16, wherein a hetero structure comprising the first area of the ambipolar material, the ferroelectric material, and the dielectric layer exhibits a clockwise current versus VG hysteresis.

18. The method of claim 17, wherein ferroelectric polarization-assisted traps arc present at an interface between the ambipolar material and the ferroelectric material.

19. The method of any one of claims 11 to 18, wherein the homojunction device exhibits self- powered photodetection.

20. The method of any one of claims 11 to 19, wherein the homojunction device is switchable between a p-n junction and a n-n junction.

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