FIELD OF THE INVENTION
The present invention relates generally to semiconductors and mixed-dimensional heterostructure nano-devices with multi-functionality. More specifically, but not exclusively, the present invention concerns a gate-tunable and anti-ambipolar phototransistor is devised based on 1D p-type GaAsSb nanowire/2D n-type MoS2 nanoflake mixed-dimensional van der Waals (vdW) heterojunctions.
BACKGROUND OF THE INVENTION
In the past decade, the emergence of 2D vdW heterostructures has expanded the possibility of diverse nanoscale functional devices through integrating the disparate materials with artificially stacked architecture. Prominent among these vdW nanodevices are the discovery of anti-ambipolar transistors, which could be deemed as deriving from the field-effect transistor (FET) channel composed of p-type and n-type semiconductors and p-n diode in series, as presented in FIG. 1a. It presents a convex shape transfer characteristics that the channel electrical conductance peaks at a specific gate bias, which is exactly distinct from the transfer curves of unipolar FETs and regular ambipolar devices (FIG. 1B). This special characteristic is quite advantageous to implement complicated electronic functions merely by a single device in logic circuits, optoelectronics and spiking neurons.
The anti-ambipolar transistors based on lateral p-n heterojunctions possess gate-tunable rectification characteristics, which can be used to develop gate-tunable rectifier circuits and photodiodes. Since the anti-ambipolar devices enable both positive and negative transconductance, the p/n-type components can be readily modulated by a capacitively coupled gate bias. Nevertheless, the studies of photodetection on such nanodevice geometries with external gate modulation are still largely lacking. This may be due to the challenging fabrication of anti-ambipolar heterodiodes with reliable and exceptional performances. First, the turn-on voltages (Von) and carrier densities of both the p/n-type transistors should be precisely controlled. Second, it requires the limit of device dimensions and local gating. Last but not least, high-quality and strongly coupled heterointerface is also crucial to produce efficient charge transfer.
Here, a gate-tunable high-performance anti-ambipolar phototransistor based on 1D p-type III-V semiconductor nanowire/n-type 2D transition metal dichalcogenide (TMD) nanoflake heterojunctions has been first developed, as shown in FIGS. 2A-2B. The reduced dimensionality of GaAsSb nanowires (NWs) can distinctly decrease the active region in the heterostructures. Meanwhile, owing to the wave-guiding effect, NWs also play a functional role in light trapping to enhance light-to-current conversion efficiency substantially. In terms of unique physical properties of MoS2, the nature of dangling-bond-free surface enables the formation of hybrid vdW heterostructures when integrated with differently dimensioned materials. And the high intrinsic carrier mobility of both integrated constituents has a beneficial effect on shortening the carrier-transit time within the heterostructure device channel. In general, the synergistic effect in the mixed-dimensional heterostructures would bring great significance in constructing anti-ambipolar optoelectronics with diverse functionalities.
The electronic performance of the heterojunction device was evaluated with the n-contact grounded. An obviously anti-ambipolar response could be observed from the transfer characteristics under a forward source-drain bias of 2 V (FIG. 3A), demonstrating the gate-tunability of the current through the p-n heterojunction. Meanwhile, the gate leakage current (below 40 pA) is negligible as compared with the channel current. The unique transfer characteristics results from the FET channel comprising of a p-type and n-type semiconductors in series, in which the total current reaches maximum when both transistors are turned on (near Vgs=−40 V) and declines to a minimum when either device is off (Vgs=−60 V and 40 V). As indicated from the optoelectronic performance in FIGS. 3b and c, with the optimum gate modulation (Vgs=−40 V), the heterostructure photodiode delivered a respectable performance with a responsivity of 11.7 A W−1, a detectivity of 1.64×1011 Jones and an EQE value of 2.74×103% at Vds of −2 V under 532 nm illumination. Importantly, the rise and decay times are as efficient as around 50 μs (FIG. 3D). All these results demonstrate the superiority and multi-functionality of the anti-ambipolar device structure consisting of p-type III-V semiconductor NW and n-type 2D TMD nanoflake FETs in series.
Thus, what is needed are anti-ambipolar transistors devised to have the potential application in three-terminal device units, including frequency doubling, binary phase shift keying, and ternary logic inverter, which can reduce the number of circuit elements and the circuit design compared to conventional FET technologies. In addition, what is needed is an anti-ambipolar device that can be utilized as a gate-tunable phototransistors, i.e., the optoelectronic properties can be well tailored by the external applied gate bias.
SUMMARY OF THE INVENTION
Aspects of the present invention provide a gate-tunable and anti-ambipolar phototransistor is devised based on 1D p-type GaAsSb nanowire/2D n-type MoS2 nanoflake mixed-dimensional van der Waals (vdW) heterojunctions apparatus and a method for creating same.
In one aspect, provided herein is a mixed-dimensional heterojunction device, including at least one substrate layer, at least one nanowire positioned on a portion of the at least one substrate layer, at least one first contact positioned over at least a portion of the at least one substrate layer and at least a portion of the at least one nanowire, a nanoflake positioned on at least a portion of the at least one substrate layer and at least a portion of the at least one nanowire, and at least one second contact positioned on at least a portion of the at least one substrate layer and at least a portion of the nanoflake.
In another aspect, provided herein is method of mixed-dimensional heterojunction device including obtaining a substrate and obtaining a prepared nanowire. The method also including transferring the nanowire onto the substrate and depositing a first contact over the substrate and at least a portion of the nanowire. The method further includes forming nanoflake over a portion of the substrate and a portion of the nanowire and depositing a second contact over the substrate and at least a portion of the nanoflake.
These, and other objects, features and advantages of this invention will become apparent from the following detailed description of the various aspects of the invention taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF DRAWINGS
The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and together with the detailed description herein, serve to explain the principles of the invention. The drawings are only for purposes of illustrating preferred embodiments and are not to be construed as limiting the invention. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion. The foregoing and other objects, features and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
FIG. 1A is an electrical configuration of ant anti-ambipolar transistor, including p-type and n-type FETs and p-n diode in series, in accordance with an aspect of the present disclosure;
FIG. 1B is a schematic of transfer characteristics of anti-ambipolar transistors, in accordance with an aspect of the present disclosure;
FIG. 2A is a schematic of the 1D GaAsSb nanowire/3D MoS2 nanoflake anti-ambipolar phototransistor, in accordance with an aspect of the present disclosure;
FIG. 2B is an optical image of the 1D GaAsSb nanowire/3D MoS2 nanoflake anti-ambipolar phototransistor, in accordance with an aspect of the present disclosure;
FIG. 3A is a graph of transfer characteristics of the 1D GaAsSb nanowire/2D MoS2 nanoflake anti-ambipolar transistor, in accordance with an aspect of the present disclosure;
FIG. 3B is a graph of responsivity and detectivity, in accordance with an aspect of the present disclosure;
FIG. 3C is a graph of external quantum efficiency (“EQE”), in accordance with an aspect of the present disclosure;
FIG. 3D is a graph of high resolution photoresponse of the anti-ambipolar phototransistor under 532 nm laser illumination, in accordance with an aspect of the present disclosure;
FIG. 4 is a schematic illustration of the fabrication procedures of 1D GaAsSb nanowire/2D MoS2 nanoflake anti-ambipolar transistor, in accordance with an aspect of the present disclosure;
FIG. 5A is a graph of Raman spectra measured on the GaAsSb NW, MoS2 nanosheet and the GaAsSb/MoS2 p-n heterojunction, in accordance with an aspect of the present disclosure;
FIG. 5B is a graph comparison of the Raman spectra in the marked area of panel in FIG. 5A in detail, in accordance with an aspect of the present disclosure;
FIG. 5C is a graph of photoluminescence spectra of MoS2 and GaAsSb/MoS2 heterostructure, in accordance with an aspect of the present disclosure;
FIG. 5D is a PL mapping measured at the wavelength of 686 nm on the GaAsSb/MoS2 heterostructure, in accordance with an aspect of the present disclosure;
FIG. 6A is a graph of output characteristics of the GaAsSb/MoS2 heterostructure device, in accordance with an aspect of the present disclosure;
FIG. 6B is a graph of ideality factors and the knee voltage values extracted from the I-V curves shown in FIG. 6A, in accordance with an aspect of the present disclosure;
FIG. 7A is a graph of time-resolved photoresponse of the GaAsSb/MoS2 heterostructure device as a function of Vgs (532 nm light with power density of 3.62 mW mm−2), in accordance with an aspect of the present disclosure;
FIG. 7B is a graph showing the reproducible on/off switching under the chopped light illumination using logarithmic y-axis, in accordance with an aspect of the present disclosure;
FIG. 7C is a graph of current-voltage curves from −0.2 to 0.25 V under various illumination intensities, in accordance with an aspect of the present disclosure; and
FIG. 7D is a graph of responsivity and detectivity as a function of illumination intensity, in accordance with an aspect of the present disclosure.
DETAILED DESCRIPTION FOR CARRYING OUT THE INVENTION
Generally stated, disclosed herein is a gate-tunable and anti-ambipolar phototransistor is devised based on 1D p-type gallium arsenide antimonide (GaAsSb) nanowire/2D n-type molybdenum disulfide (MoS2) nanoflake mixed-dimensional van der Waals (vdW) heterojunctions. Further, methods making the phototransistors are disclosed.
Referring to the drawings, wherein like reference numerals are used to indicate like or analogous components throughout the several views, and with particular reference to FIGS. 4-7D there is illustrated a 1D GaAsSb nanowire/2D MoS2 nanoflake anti-ambipolar transistor 100 and the method of fabricating the heterojunction or 1D GaAsSb nanowire/2D MoS2 nanoflake anti-ambipolar transistor 100.
The transistor or mixed-dimensional heterojunction device 100 includes at least one substrate layer 102. The substrate layer 102 includes at least one layer, for example, a silicon (Si) wafer and a silicon dioxide layer (SiO2) positioned over the silicon wafer. The SiO2 layer may be, for example, thermally grown. The at least one nanowire 104 positioned on a portion of the at least one substrate layer 102. The nanowire 104 is, for example, a III-V compound alloy. The nanowire 104 may be, for example, a p-type, n-type, or ambipolar transistor. The nanowire 104 may be, for example, binary, ternary, or quaternary. At least one first contact 106 may be positioned over at least a portion of the at least one substrate layer 102 and at least a portion of the at least one nanowire 104. A nanoflake 108 is positioned on at least a portion of the at least one substrate layer 102 and at least a portion of the at least one nanowire 104. The nanowire 104 may be positioned beneath the at least one first contact 106 and the nanoflake 108. Alternatively, the nanowire 104 may be positioned on the at least one first contact 106 and the nanoflake 108. The at least one second contact 110 is positioned on at least a portion of the at least one substrate layer 102 and at least a portion of the nanoflake 108. In an embodiment, the nanowire 104 directly contacts the at least one first contact 106, at least a first portion of the nanoflake 108 directly contacts the at least one nanowire 104, and at least a second portion of the nanoflake 107 directly contacts the second contact 110.
With continued reference to FIGS. 4-7D, the heterojunction fabrication method includes obtaining a substrate 102 and obtaining a prepared nanowire 104. The method also includes transferring the nanowire 104 onto the substrate 102. In addition, the method includes depositing a first contact 106 over the substrate 102 and at least a portion of the nanowire 104. Further, the method includes forming nanoflake 108 over a portion of the substrate 102 and a portion of the nanowire 104. Finally, the method includes depositing a second contact 110 over the substrate 102 and at least a portion of the nanoflake 108.
As best seen in FIG. 4 is the detailed fabrication method for the heterojunction 100. The method includes transferring the prepared GaAsSb nanowires (NWs) 104 on the SiO2/Si substrates 102 by using a dry transfer technique. The SiO2/Si substrates 102 may be, for example, approximately 270 nm thick. Next, the method includes standard photolithography and e-beam evaporation to define and deposit the nickel (Ni) contact 106. The Ni contact 106 may be, for example, 60 nm thick. The MoS2 nanoflake 108 is then mechanically exfoliated by polydimethylsiloxane (PDMS) and transferred accurately onto the GaAsSb NW 104 using micromanipulation transfer system, forming the GaAsSb/MoS2 vdW heterojunction 100. Then, a gold (Au) electrode 110 on top of the MoS2 100 may be patterned by electron beam lithography and thermal evaporation. The Au electrode 110 may be, for example, approximately 60 nm.
After fabrication, the coupling effect and charge transfer at interface can be verified via the optical measurements. Referring now to FIG. 5A, the Raman spectra collected from the MoS2 nanosheet and the overlapped heterojunction are shown. The in-plane E2g1 (384.8 cm−1) and out-of-plane A1g modes (410.2 cm−1) are explicitly shown in the MoS2 Raman spectrum measured from shaded region 120 in FIG. 5A. It can be seen that the Raman signals from the overlapped heterostructure region are a sum of the two individual signals obtained separately from the p-type GaAsSb and the n-type MoS2, which confirms the formation of vertically stacked p-GaAsSb and n-MoS2 heterojunction. Compared with the individual MoS2 displayed in FIG. 5B, the E2g1 and A1g characteristic peaks in overlapped MoS2 are red-shifted, implying the electron transfer from GaAsSb to the MoS2 layer at the interface. Since the x-axis unit of the Raman spectrum is wavenumber (cm−1), which is reciprocal to the wavelength, here the red-shift corresponds to the decrease in the wavenumber. Specifically, the Raman peaks of GaAsSb—MoS2 shift towards left relative to those of MoS2 in FIG. 5B. Hence, strong interfacial coupling is confirmed in the vdW hybrid heterojunction.
A photoluminescence (“PL”) test may be carried out using a laser with a spot diameter to further investigate the interlayer coupling effect at the GaAsSb/MoS2 interface. The laser may be, for example, a 532 nm laser with a spot diameter of ˜1 μm. By contrast, the photoluminescence at the overlapped region is obviously quenched for both emission peaks (acquired at the shaded region 122 in FIG. 5A). The strong suppression of photoluminescence for the MoS2 segment stacked on GaAsSb NW is also apparently demonstrated from the corresponding PL mapping image in FIG. 5D. The PL mapping image may be, for example, taken at a wavelength of approximately 686 nm. In principle, the charge transfer will lead to the increased non-radiative recombination and consequently the quenched light emission from all transitions. Accordingly, the observation of reduced photoluminescence from both A1 and B1, as shown in FIG. 5C, exciton resonances indicates the efficient separation of photogenerated carriers across the heterojunction, verifying the type II GaAsSb/MoS2 band alignment formed at the interface.
Referring now to FIGS. 6A-6B, the output curves of the GaAsSb/MoS2 heterostructure device 100 could demonstrate the gate-tunability of the p-n junction as the gate bias varies from −60 V to 40 V. Concretely, the heterojunction transitions from a nearly insulating state at negative extreme of the Vgs range to a highly rectifying output behavior at Vgs=−40 V, followed by the growing series-resistance with further increase of gate bias. The rectification ratio could, for example, be tuned from 17 to 6×102 by the electrostatic doping of Vgs from −40 V˜40 V, among which the highest value is attained at Vgs of −40 V. In this heterojunction, the utilization of gate is then verified to have capability of tailoring the doping concentration of both semiconductors, thereby enabling tunability of built-in voltage and rectifying behavior. Furthermore, as shown in FIG. 6B and based on the I-V plots, the gate dependence of ideality factor and knee voltage (Vknee) is evaluated and compiled. With the increase of Vgs, the ideality factors witness a monoclinic ascending trend from 2.64 to 3.32, whereas a contrary tendency is observed for the knee voltage. The extracted Vknee of 0.7 V at Vgs=−40 V is almost equal to that of the conventional Si p-n junction.
The time resolved photocurrent as a function of applied back-gate voltage light illumination is shown in FIG. 7A. The light illumination may be, for example, 532 nm light illumination. In all curves, the current rises rapidly when the laser is introduced and decays promptly when the laser shutter is closed. Besides, the photocurrent increases starkly as Vgs varies from 40 to −40 V and finally reaches a saturation at −60 V. The change in photocurrent can be attributed to the band structure adjustment in each semiconductor, which occurs in response to the external applied Vgs. An obvious decrease in the photocurrent indicates a weakened band bending or built-in voltage at the heterointerface under higher Vgs. The device structure is then verified to be capable of modulating the optoelectronic properties with gate bias.
Referring now to FIGS. 7B-7D, the heterostructure device also shows a remarkable photovoltaic response at Vgs of −40 V when operated at a zero source-drain bias under irradiation. The irradiation may be, for example, 532 nm. The dark current of the device is as low as ˜100 fA from the reproducible on/off switching behaviors as shown in FIG. 7B, which yields a high on-off current ratio of ˜1×104 at a light intensity of 3.624 mW mm−2. As shown in FIG. 7C, the photovoltaic effect revealed from the Vds-Vds curves indicates that the open-circuit voltage (Voc) increases gradually with light intensity and can reach up to ˜0.2 V at 3.624 mW mm−2. The extracted R and D* values are demonstrated in FIG. 7D, both of which show an overall upward trend with the increasing light intensity due to the drop of recombination rate at high power intensity. All these impressive features signify the versality of mixed-dimensional vdW heterostructures, bringing prospects for next-generation electronics and optoelectronics.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprise” (and any form of comprise, such as “comprises” and “comprising”), “have” (and any form of have, such as “has”, and “having”), “include” (and any form of include, such as “includes” and “including”), and “contain” (and any form of contain, such as “contains” and “containing”) are open-ended linking verbs. As a result, a method or device that “comprises,” “has,” “includes,” or “contains” one or more steps or elements possesses those one or more steps or elements, but is not limited to possessing only those one or more steps or elements. Likewise, a step of a method or an element of a device that “comprises,” “has,” “includes,” or “contains” one or more features possesses those one or more features, but is not limited to possessing only those one or more features. Furthermore, a device or structure that is configured in a certain way is configured in at least that way, but may also be configured in ways that are not listed.
The invention has been described with reference to the preferred embodiments. It will be understood that the architectural and operational embodiments described herein are exemplary of a plurality of possible arrangements to provide the same general features, characteristics, and general system operation. Modifications and alterations will occur to others upon a reading and understanding of the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations.
Patent Application
20240213391
