Wide-spectrum photoelectric detector based on AlScN

Abstract

The invention discloses a wide spectrum photoelectric detector based on AlScN (AlxScN). The wide-spectrum photoelectric detector based on the AlScN comprises an AlScN light absorption layer, a bottom electrode and a top electrode, the bottom electrode is arranged on the first face of the AlScN light absorption layer, the bottom electrode and the AlScN light absorption layer form Schottky contact, the top electrode is arranged on the second face of the AlScN light absorption layer, the top electrode and the AlScN light absorption layer form ohmic contact, and the AlScN light absorption layer is arranged on the second face of the AlScN light absorption layer. A built-in electric field inside the AlScN light absorption layer can help or restrain drift motion of carriers, so that the wide-spectrum photoelectric detector can work without external bias voltage, and the first face and the second face are arranged back to back. According to the invention, AlScN switchable unit cell spontaneous polarization is utilized to regulate and control a potential barrier and help or inhibit carrier transport at the same time, so that a photovoltaic photoelectric detection technology of optical information is obtained, and the photoelectric detector has the characteristics of wide spectrum detection, high reliability, small size, low energy consumption and the like.

Description

Technical Field

[0001] The present invention particularly relates to a wide-spectrum photoelectric detector based on AlScN, belonging to the technical field of photoelectric detection. Background Art

[0002] Photodetectors (PDs) are a type of sensor that converts light into electrical signals (usually in the form of current or voltage). Today, photodetectors have been widely used in aerospace, aviation, military, scientific research, medicine and health, and industrial production. For example, photodetectors are an important part of optical communication systems. The booming development of the information age has put forward higher and higher requirements on the cost and response speed of photodetectors. Photodetectors with weak light detection capabilities (such as single photon detection) have important application value in astronomy, spectroscopy, laser ranging, missile guidance and other fields. In addition, photodetectors can also be combined with artificial intelligence to give machines human-like facial features and brain functions, which can perceive various phenomena and complete various actions. Photodetectors as receptors can be said to be the most critical part of the entire system. In order to meet the application needs of different fields, people have developed photodetectors with different structures such as PN junction photodiodes, PIN photodiodes, avalanche photodiodes, metal-semiconductor-metal photodetectors (MSM-PDs), etc. Among them, the metal-semiconductor-metal photodetector (MSM-PDs) device has a simple manufacturing process and has the characteristics of high speed and high response due to its own structural characteristics. The performance of optoelectronic devices is evaluated by a series of quality factors, including responsivity, response speed, detectivity, quantum efficiency and noise, which mainly depend on the device structure, but more on the semiconductor optoelectronic materials.

[0003] Traditional metal-semiconductor-metal photodetectors (MSM-PDs) can be divided into photovoltaic and photoconductive types according to their working principles. Photovoltaic detectors are devices made using the photovoltaic effect of semiconductor PN junctions, also known as junction photoelectric devices. There are many varieties, including photocells, photodiodes, phototransistors, etc. This type of detector is used in optical bands such as ultraviolet, visible light, near infrared, mid-wave red and far infrared, and the changes in optical signals are converted into electrical signals for output through photodetectors. Photovoltaic detectors can be used without bias or with reverse bias. Photoconductive detectors are a type of optical detection device made using the photoconductive effect of semiconductor materials. The so-called photoconductive effect refers to a physical phenomenon in which the conductivity of the irradiated material changes due to radiation. Photoconductive detectors are widely used in various fields of military and national economy, especially in visible light or near infrared bands, mainly used for ray measurement and detection, industrial automatic control, photometry, etc.; in infrared bands, they are mainly used for missile guidance, infrared thermal imaging, infrared remote sensing, etc.

[0004] The main differences between photovoltaic detectors and photoconductive detectors are the location where they produce photoelectric conversion, polarity, external bias requirements, response speed, and frequency response characteristics. The location where the photoelectric conversion is produced is different: the photoconductive detector is a mean type, no matter which part of it the light shines on, the conductivity of the light-receiving part will increase; while the photovoltaic detector is a junction type, and only the light that reaches the vicinity of the junction area will produce a photovoltaic effect. Different polarity: the photoconductive detector has no polarity and must be biased externally when working; the photovoltaic detector has a definite positive and negative pole, and can convert the optical signal into an electrical signal without an external bias. Different response speed and frequency response characteristics: the photoelectric effect of the photoconductive detector mainly depends on the majority carrier generation and recombination motion in the non-equilibrium carriers, and the relaxation time is long, so the response speed is slow and the frequency response performance is poor; while the photovoltaic effect of the photovoltaic detector mainly depends on the minority carrier drift motion in the non-equilibrium carriers in the junction area, and the relaxation time is short, so the response speed is fast and the frequency response characteristics are good.

[0005] Conventional metal-semiconductor-metal photodetectors (MSM-PDs) use semiconductors as light absorption layers. When the incident photon energy is lower than the band gap of the semiconductor material, the semiconductor material cannot produce intrinsic excitation, which limits the application of some relatively wide bandgap or wide bandgap semiconductor materials in the detection field of visible and infrared bands. The use of metal hot carrier emission mechanism can break through this limitation. In particular, the emergence of perfect absorbers with metasurface structures in recent years has made it possible to achieve wide-spectrum photodetection with wide-bandgap semiconductor materials. The perfect absorber is a device that can completely absorb incident electromagnetic waves without reflection and transmission. It is a vertical metal-dielectric-metal structure, and its top metal is a metasurface structure, which is used to efficiently excite plasmons and efficiently capture incident light around the metal structure. This special vertical structure can not only generate more hot carriers than flat devices, but also can achieve selective absorption of incident light by designing metasurface structures.

[0006] In recent years, with the continuous progress of science and technology, the demand for device miniaturization and electronic integration has become more and more urgent. People have higher and higher requirements for photoelectric detection technology, and the emergence of a large number of emerging materials has led to rapid development in the performance of photodetectors. Among them, ferroelectric materials have attracted attention due to their strong responsiveness, adjustable polarization, simple structure and other advantages. Ferroelectric materials usually refer to crystalline materials or organic materials with ferroelectric effect. When ferroelectric materials are subjected to electric fields, the spontaneous polarization dipole moment can change with the direction of the external electric field. When the applied electric field is greater than a certain value, after the electric field is removed, the polarization charge inside the material will still be retained, forming a recoverable and lasting electric dipole moment. This phenomenon is called ferroelectric effect. In some ferroelectric materials, people have found that they can produce a stable photovoltaic effect along the direction of polarization. It is generally believed that the photovoltaic effect of ferroelectric materials originates from their spontaneous polarization. One of the remarkable characteristics of ferroelectric photovoltaics is that when the polarization direction changes under the action of the electric field, the photocurrent also changes accordingly, and the direction of the photocurrent inside the ferroelectric material is always opposite to the polarization direction.

[0007] The difference between the ferroelectric photovoltaic effect and the traditional pn junction is that in the traditional pn junction, the photoexcited electron-hole pairs are quickly separated by the built-in field in the pn junction, drifting in opposite directions, and finally reaching the electrode, where they are collected. In theory, the photovoltage generated by the pn junction is limited by the width of the semiconductor bandgap. For the ferroelectric photovoltaic effect, the experimentally obtained photovoltage is proportional to the polarization intensity and the distance between the electrodes, and is not limited by the bandgap width and can reach 10 4 V. When the ferroelectric material contacts the electrode to form a Schottky barrier, the energy band at the interface will bend, and the electron-hole pairs generated under light will be driven by the local electric field near the electrode. The generated photocurrent is largely determined by the depth of the Schottky barrier and the depletion layer. According to this model, the magnitude of the photovoltage generated inside the Schottky barrier is still limited to the band gap of the ferroelectric material. In the early stages of studying the ferroelectric photovoltaic effect, the voltage caused by the Schottky effect was often ignored because it was much lower than the anomalous photovoltage in most ferroelectric crystals. However, the Schottky effect has become increasingly important in ferroelectric thin-film photovoltaic devices because the photovoltaic voltage output in these devices is usually relatively small.

[0008] Generally speaking, in a ferroelectric photovoltaic device with a sandwich structure composed of the same electrode and ferroelectric material, the contribution of the Schottky barrier to the photocurrent does not exist, because the two Schottky junctions formed by the upper and lower identical electrodes and the ferroelectric material are back-to-back and mutually restrain each other, so the generated photovoltage and current cancel each other out. However, if different types of electrodes are used, the photovoltaic effect can be enhanced in a ferroelectric photovoltaic device with a vertical structure. Since the Schottky junction effect is independent of the polarization direction of the ferroelectric material, the contribution of the Schottky junction and the bulk photovoltaic effect to the photocurrent can be distinguished based on this feature. However, some researchers believe that the height of the Schottky barrier can be controlled by applying an electric field to the ferroelectric material to change its polarization direction. Moreover, when the polarization direction of the Schottky barrier and the ferroelectric material changes, the sign of the photovoltage also changes.

[0009] At present, ferroelectrics are often introduced into energy harvesting, non-volatile memory and logic devices. In the field of photoelectric detection, ferroelectrics are integrated into devices to enhance light-matter interaction, band bending and control carrier motion in local space. In some cases, we do not need to load external bias, and only rely on the built-in electric field of ferroelectric materials to achieve the separation of excitons and free electrons or holes, that is, it has a self-powered effect. Some ferroelectrics show large anisotropy in input (such as polarized light absorption rate) and output (such as mobility and conductivity of different crystal phases). More importantly, the local field induced by the ferroelectric polarization effect can suppress the recombination of photogenerated carriers and improve the collection efficiency. In the past, the research on ferroelectric materials focused on traditional bulk perovskite materials. However, due to the critical size effect of traditional ferroelectric materials, the ferroelectric polarization will be broken at the nanoscale, which hinders the application of ferroelectric materials in micro-nano devices. At the same time, there are also problems that cannot be ignored in the stability and device reliability of perovskite ferroelectric materials. Therefore, we look forward to a stable semiconductor ferroelectric material with photovoltaic response that is easy to miniaturize and integrate.

[0010] In order to meet the different requirements of different fields for detector working band, response speed, response rate and other performance, people have carried out a lot of research on MSM-PDs based on different semiconductor materials. The exploration range of MSM-PDs covers from ultraviolet to infrared bands. Among them, MSM-PDs based on GaAs, InGaAs, Si / Ge and other materials are often used to detect visible light and infrared light, and those based on wide-bandgap semiconductors such as GaN, ZnO, AlGaN are used to detect ultraviolet light.

[0011] There are two basic structures of MSM-PDs. The first is a coplanar structure. The coplanar device electrodes are usually composed of discrete metal interdigitated fingers, and the two sets of electrodes are located on the same plane on one side of the semiconductor. In the traditional semiconductor materials used in coplanar MSM-PDs, the electric field is weak deep in the light absorption layer. The generated photogenerated carriers have to be transmitted for a long distance under the action of weak electric fields before reaching the electrodes. The collection of carriers is slow, resulting in reduced device performance. Therefore, in order to enhance the electric field inside the semiconductor region, a Schottky-type MSM-PD consisting of two back-to-back series-connected Schottky diodes has been proposed. Since the built-in electric fields of the two Schottky barriers are in opposite directions and different in magnitude, a net electric field will be generated in the semiconductor, increasing the drift velocity of the carriers. In addition, the interdigitated electrodes with sub-wavelength slits on the top of the coplanar MSM-PDs have weak light absorption capacity, and the absorption of light can be enhanced by improving the device structure. For example, the surface electrode is made into a grating structure, or a Bragg reflector is introduced at the bottom of the semiconductor, or metal nanoparticles are introduced on the surface of the semiconductor. The second type is a vertical structure, where metal electrodes are located on both sides of the semiconductor. Usually, the top electrode must be thin enough so as not to affect the semiconductor's absorption of light signals and facilitate carrier transmission. In vertical MSM-PDs, the distance between the two electrodes is determined by the thickness of the semiconductor. Combined with semiconductor epitaxial growth technology, it is easier to obtain a controllable electrode distance, which is conducive to reducing the carrier transmission distance and thus achieving a higher response speed.

[0012] The MSM-PDs photodetectors that have been studied so far are mainly coplanar photoconductive MSM-PDs. Usually, the distance between the electrodes is far, and the spacing between the electrodes is proportional to the transit time of the photogenerated carriers. Therefore, the response time is long. If the distance between the electrodes is too close, a large dark current will be generated.

[0013] ZnO has excellent optoelectronic properties. Some researchers have used ZnO as the light receiving layer in vertical photovoltaic MSM-PDs. ZnO is intrinsically n-type, and its n-type doping process is mature, but p-type doping is difficult, which hinders the practical application of p-ZnO. Recently, vertical photovoltaic MSM-PDs based on ferroelectric perovskite materials can operate at low bias and zero bias, with low power consumption and fast response. Its structure is usually composed of a transparent top electrode, a perovskite layer, and an opaque bottom electrode. Although perovskites have become excellent photosensitive semiconductors, their application in the field of light detection faces severe challenges. First, due to the solid solution process, this type of material is prone to defects, which causes photodetectors to have recombination losses, greater leakage / dark current, and scalability. Second, their compatibility with traditional semiconductor processes and their stability in terms of ultraviolet irradiation, humidity, temperature and toxicity still have challenges and unresolved issues, limiting their compatibility with existing platforms. Summary of the invention

[0014] The main purpose of the present invention is to provide a wide-spectrum photodetector based on AlScN, thereby overcoming the deficiencies in the prior art.

[0015] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention includes: An embodiment of the present invention provides a wide-spectrum photodetector based on AlScN, comprising: an AlScN light absorption layer, a bottom electrode, and a top electrode, wherein the bottom electrode is arranged on a first surface of the AlScN light absorption layer, and the bottom electrode forms a Schottky contact with the AlScN light absorption layer; the top electrode is arranged on a second surface of the AlScN light absorption layer, and the top electrode forms an ohmic contact with the AlScN light absorption layer; the built-in electric field inside the AlScN light absorption layer can help or suppress the drift motion of carriers, so that the wide-spectrum photodetector can operate without an external bias, wherein the first surface and the second surface are arranged back to back.

[0016] Further, when the first built-in electric field induced by polarization inside the AlScN light absorbing layer is in the same direction as the second built-in electric field of the Schottky barrier formed by the contact between the bottom electrode and the AlScN light absorbing layer, the height of the Schottky barrier increases, the width of the depletion region increases, the hot carriers of the bottom electrode find it difficult to cross the Schottky barrier and enter the AlScN light absorbing layer, the drift motion of the hot electrons in the top electrode is suppressed by the first built-in electric field, and the hot holes in the top electrode reach the bottom electrode with the help of the first built-in electric field and the second built-in electric field inside the AlScN light absorbing layer; When the first built-in electric field induced by the internal polarization of the AlScN light absorbing layer is opposite to the second built-in electric field of the Schottky barrier formed by the contact between the bottom electrode and the AlScN light absorbing layer, the height of the Schottky barrier is reduced, the width of the depletion region is narrowed, and the hot carriers of the top electrode cross the Schottky barrier to reach the bottom electrode with the help of the first built-in electric field.

[0017] Furthermore, the Sc content in the AlScN contained in the AlScN light absorbing layer is 5% to 40%.

[0018] Furthermore, the Sc content in the AlScN contained in the AlScN light absorbing layer is 20% to 32%.

[0019] Furthermore, the bandgap width of the AlScN light absorption layer is 3.4 eV to 5.8 eV.

[0020] Furthermore, the thickness of the AlScN light absorbing layer is 20nm~200nm.

[0021] Furthermore, the top electrode has a super surface structure, and the top electrode can resonate with electromagnetic waves in the visible light band and the infrared band, thereby exciting the formation of hot electrons.

[0022] Furthermore, the surface of the top electrode facing away from the AlScN light absorbing layer has a plurality of circular slots distributed in an array.

[0023] Furthermore, the material of the top electrode includes at least one of In, Mo, Pt, Au, Cu, Al, and Ag, or an alloy formed by two or more of the above, but is not limited thereto.

[0024] Furthermore, the bottom electrode is a planar thin film structure.

[0025] Furthermore, the material of the bottom electrode includes at least one of TiN, Al, Ag, Pt, Mo, Cr, and Cu, but is not limited thereto.

[0026] In a more specific embodiment, the AlScN-based wide-spectrum photodetector further includes a substrate, and the bottom electrode is disposed on the substrate.

[0027] Furthermore, the substrate includes one of a sapphire substrate, a Si substrate, and a GaN substrate, but is not limited thereto.

[0028] Compared with the prior art, the advantages of the present invention include: The AlScN-based MSM-PDs photodetector proposed in the embodiment of the present invention is a photovoltaic photodetection technology that utilizes the switchable spontaneous polarization of the AlScN unit cell to regulate the potential barrier while helping or suppressing the transport of carriers, thereby obtaining light information. The present invention combines the advantages and particularities of AlScN and has the characteristics of wide spectrum detection, high reliability, small size, and low energy consumption.

[0029] The vertical MSM-PDs proposed in this paper is a photovoltaic photodetector with a supersurface structure based on AlScN. The polarization-induced built-in electric field of AlScN with ferroelectricity can help or inhibit the collection of carriers and modulate the Schottky barrier height, and the metal supersurface structure on the top will enhance the absorption of light.

[0030] The AlScN-based photodetector proposed in the present invention is a photodetector that can separate photogenerated electron-hole pairs without external bias. The band gap width of AlScN varies between 3.4 and 4.5 eV depending on the Sc content, and can effectively respond to ultraviolet electromagnetic waves. At the same time, a metasurface structure is introduced, and the device as a whole constitutes a perfect absorber. Hot electron injection in the metal can detect electromagnetic waves in the visible and infrared bands, which is of great significance to the development of lightweight, low-power, and multifunctional photodetectors. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1a , Figure 1b They are the phase change model during the polarization switching of AlScN and the hysteresis loop of AlScN; Figure 2a It is a schematic structural diagram of a wide-spectrum photodetector based on AlScN provided in a typical implementation case of the present invention; Figure 2b It is a schematic structural diagram of a top electrode in a wide-spectrum photodetector based on AlScN provided in a typical implementation case of the present invention; Figure 3a , Figure 3b They are respectively schematic diagrams of the working principles of a wide-spectrum photodetector based on AlScN in different polarization directions provided in a typical implementation case of the present invention; Figure 4a , Figure 4b , Figure 4c The simulation results of In / AlScN FDTD with plane waves of wavelengths 820nm, 956nm, and 1194nm respectively; Figure 5a , Figure 5b The current-voltage curves of AlScN materials with Sc contents of 20% and 32% respectively; Figure 6 It is a schematic diagram of the preparation process of a wide-spectrum photodetector based on AlScN provided in a typical implementation case of the present invention. DETAILED DESCRIPTION

[0032] In view of the deficiencies in the prior art, the inventor of this case has proposed the technical solution of the present invention after long-term research and extensive practice. The technical solution, its implementation process and principle, etc. will be further explained in conjunction with the accompanying drawings and specific implementation cases. Unless otherwise specified, the semiconductor epitaxial growth process and equipment, photolithography, etching, annealing and other processes and equipment used in the embodiments of the present invention can be known in the art and are not specifically limited here.

[0033] Group III nitride semiconductors have superior properties such as bandgap, large thermal conductivity, high carrier mobility, small dielectric constant, strong radiation resistance, and good chemical stability. Due to these superior properties, group III nitride semiconductors can be used in extreme environments, solid-state lighting and displays, short-wavelength lasers, and optical detection. Common materials include gallium nitride GaN, aluminum nitride AlN, indium nitride InN, and their ternary and quaternary alloys such as AlGaN, GaInN, AlGaInN, etc. The bandgap width of semiconductor materials can be adjusted by changing the alloy composition. Recent studies have found that the addition of rare earth elements to group III nitrides can produce a ferroelectric effect, and its built-in electric field can reach the MV / cm level, which can be used to regulate carrier transport and polarization processes. Ferroelectric group III nitride semiconductors have stronger advantages than traditional ferroelectric perovskites because they exhibit strong ferroelectricity and stability in harsh environments. At the same time, they can be prepared through traditional semiconductor processes, which reduces the difficulty of integration and adapts to device miniaturization.

[0034] The characteristic of AlScN is that it has spontaneous polarization, and the direction of its spontaneous polarization can be reversed with the reversal of the external field polarity. When the external electric field is removed, its polarization direction can be maintained. The phase change process of AlScN polarization switching is as follows: Figure 1a As shown, the polarization of AlScN and the applied electric field are shown as follows Figure 1b The nonlinear relationship shown is called a hysteresis loop. Figure 1b Where Ec is the coercive field, which is the minimum electric field that causes the ferroelectric polarization to flip, and Pr is the remnant polarization, which is the polarization strength maintained in the ferroelectric crystal when the electric field is zero. At the maximum applied electric field, the ferroelectric polarization reaches saturation, and the ratio of the remnant polarization to the saturation polarization is called the rectangularity of the hysteresis loop. Usually, the ferroelectric properties of a material only exist within a specific temperature range. As the temperature increases, the ferroelectric material will transform into a paraelectric state, and this transition point is called the Curie temperature.

[0035] The present invention proposes a wide-spectrum photodetector based on AlScN based on three basic effects, namely, ferroelectric polarization, photovoltaic effect, and metal plasmon, couples AlScN with a vertical MSM architecture, and increases the absorption range and absorption efficiency of incident light by patterning the top electrode. At the same time, compared with the photovoltaic photodetector currently prepared based on perovskite materials, the AlScN used in the present invention does not need to be doped, the bandgap width of the AlScN material depends on the Al or Sc content, the detector preparation is compatible with the semiconductor process, and the complexity of the integrated process is reduced. At the same time, the oxygen vacancies in AlScN are much lower than those in oxygen-containing perovskite materials, the nitrogen vacancy formation energy is higher, and it has stronger stability and durability. In addition, the strong built-in electric field embodied by AlScN helps to transport or block carriers in the AlScN layer, with a fast response speed and lower dark current. Finally, since metal hot electrons are introduced into the device, when visible light is irradiated on the patterned metal, the hot electrons generated in the metal enter the AlScN layer, are separated under the action of the ferroelectric depolarization field, and thus the spectral response range is broadened.

[0036] In a more specific implementation, see Figure 2a , Figure 2b A wide-spectrum photodetector based on AlScN, the wide-spectrum photodetector is a metal-semiconductor-metal (MSM) structure, comprising a substrate and a bottom electrode, an AlScN light absorption layer, and a top electrode stacked in sequence on the substrate, the bottom electrode and the AlScN light absorption layer form a Schottky contact, the top electrode and the AlScN light absorption layer form an ohmic contact, the top electrode is a patterned metasurface structure, for the patterned top electrode forming the ohmic contact, when an electromagnetic wave with a wavelength in the visible light band is irradiated on the top electrode, due to the metal plasmon The non-radiative decay of the AlScN light absorption layer generates hot carriers with a certain energy, which enter the AlScN light absorption layer (or enter the AlScN light absorption layer through the tunneling effect, or light directly excites electrons at the metal Fermi level to jump to the bottom of the AlScN conduction band) and enter the bottom electrode under the action of the depolarization field; when the electromagnetic wave energy is greater than the band gap width of AlScN, the electromagnetic wave should be in the ultraviolet band. At this time, the electromagnetic wave should penetrate the metal into the AlScN light absorption layer, excite the valence band electrons to enter the conduction band, and form electron-hole pairs, which are then separated and drifted to the electrodes on both sides under the action of the built-in electric field.

[0037] Specifically, the top electrode, AlScN light absorption layer and bottom electrode in a wide spectrum photodetector based on AlScN provided by an embodiment of the present invention constitute a perfect absorber of a metal-dielectric-metal structure, and the patterned top electrode resonates with visible and infrared electromagnetic waves to excite hot electrons, thereby achieving the purpose of increasing the spectrum detection width. In the present invention, the role of the perfect absorber is to absorb electromagnetic waves in the required band as much as possible without reflection, and convert the optical signal in the required band into an electrical signal. The patterned top electrode can broaden the absorption bandwidth and obtain a higher photoelectric conversion efficiency.

[0038] It should be noted that when electromagnetic waves hit an object, they can be transmitted, reflected, absorbed and scattered. Assuming that the scattering caused by roughness can be ignored, the surface absorptivity A=1-RT, R is the reflectivity, and T is the transmittance. The bottom side of the object can be covered with metal to reduce the transmittance, and to reduce the reflectivity, the relative dielectric constant ε of the material needs to be adjusted. r and magnetic permeability μ r , metasurface materials can do this. When both the reflectivity and transmittance are reduced, the light absorption rate is improved.

[0039] Specifically, the surface of the top electrode facing away from the AlScN light absorbing layer has a plurality of circular slots distributed in an array. Exemplarily, the thickness of the top electrode is 100 nm, the depth of the circular slots is 98 nm, the diameter of the circular slots is 150 nm, and the spacing is 80 nm.

[0040] The built-in electric field inside the AlScN light absorption layer used in the present invention can help or inhibit the drift motion of carriers. Therefore, the wide-spectrum photodetector provided by the present invention can work without an external bias. In addition, due to the switchability of ferroelectric polarization, the wide-spectrum photodetector provided by the present invention has two working modes: like Figure 3a As shown, when the first built-in electric field induced by the polarization of the AlScN light absorbing layer itself is in the same direction as the second built-in electric field of the Schottky barrier formed by the contact between the bottom electrode and the AlScN light absorbing layer, the height of the Schottky barrier increases and the width of the depletion region increases. Therefore, it is difficult for the hot carriers of the bottom electrode to cross the Schottky barrier and enter the AlScN light absorbing layer. On the side of the top electrode, since the vector directions of the first and second built-in electric fields point to the bottom electrode, the hot electrons in the top electrode are blocked by the first and second built-in electric fields, and the hot holes can reach the bottom electrode with the help of the first and second built-in electric fields.

[0041] like Figure 3bAs shown, when the first built-in electric field induced by the polarization of the AlScN light absorption layer itself is opposite to the second built-in electric field of the Schottky barrier formed by the contact between the bottom electrode and the AlScN light absorption layer, the height of the Schottky barrier is reduced, the width of the depletion region is narrowed, and the hot carriers of the top electrode can easily cross the Schottky barrier and reach the bottom electrode with the help of the first built-in electric field.

[0042] Specifically, the Sc content in the AlScN contained in the AlScN light absorption layer is 5%~40%, preferably 20%~32%. Specifically, the bandgap width of the AlScN light absorption layer is 3.4 eV~5.8eV, and the thickness of the AlScN light absorption layer is 20nm~200nm. When the Sc content is greater than 40%, the crystalline material will be converted into a salt rock ore structure, and the ferroelectric effect will inevitably not occur. The present invention uses AlScN with a Sc content of 5%~40%, which can achieve a faster carrier separation speed. Most importantly, when the Sc content is 5%~40%, the present invention can make the voltage required for polarization reversal lower under a thinner AlScN light absorption layer, that is, the required regulation voltage is lower, the energy saving effect is better, and the device performance is stronger.

[0043] Specifically, the material of the substrate can be sapphire, Si or GaN, etc., the material of the bottom electrode can be TiN or Al, Ag, Pt, Mo, Cr, Cu, etc., and the material of the patterned top electrode can be In or Mo, Pt, Au, Cu, Al, Ag, etc. More specifically, different bottom electrodes can be selected according to needs or application requirements to form different contact barriers; different top electrodes can be selected and different top electrode patterns can be designed to obtain different light absorption frequencies and light absorption effects.

[0044] Specifically, an embodiment of the present invention provides an AlScN-based wide-spectrum photodetector mainly based on the photovoltaic effect of ferroelectric materials and the local electric field generated by ferroelectric polarization, that is, the built-in electric field. Ferroelectric materials have a photovoltaic effect and can generate photoelectric voltage and photocurrent under illumination. The photovoltaic effect is not limited by the bandgap width, so ferroelectric materials can generate a large photoelectric voltage at a specific wavelength. Local electric field generated by ferroelectric polarization: The residual polarization of ferroelectric materials can form a strong local electric field inside the material. This local electric field can be used to regulate the concentration of carriers, thereby improving the photoelectric detection capability of low-dimensional materials. Separation and transmission of carriers: In a ferroelectric self-powered photodetector, the electron-hole pairs generated by light excitation are effectively separated and transmitted under the action of the local electric field generated by the ferroelectric material, thereby generating a photocurrent. This mechanism enables the detector to work without an external bias. Non-volatile modulation: The polarization state of ferroelectric materials can be reversed by an external electric field, but after the external electric field is removed, the residual polarization can remain stable, which means that the effect of the ferroelectric local field is non-volatile and remains even after the gate voltage is removed, thereby reducing the power consumption of optoelectronic devices.

[0045] Specifically, the top electrode in the present invention has a patterned structure, the purpose of which is to absorb light to provide hot carriers, which are then injected into the AlScN light absorbing layer and migrate under the action of the built-in electric field in the AlScN light absorbing layer to form current.

[0046] See also Figure 4a , Figure 4b , Figure 4c , Figure 4a , Figure 4b , Figure 4c The simulation results of In / AlScN FDTD under plane wave irradiation with wavelengths of 820nm, 956nm, and 1194nm respectively. It can be seen that under irradiation with different wavelengths, electric field concentration (red part) appears at the interface between the In metal surface and the AlScN layer, which indicates that the metasurface structure makes it easy for hot carriers generated by plasmon resonance to be generated on the In metal surface and injected into the AlScN layer.

[0047] There is a complex relationship between the bandgap width of AlScN and the Sc content, which is affected by many factors such as the change in band structure, lattice constant, electronic structure, phase change, etc. caused by Sc doping. The photoelectric performance of AlScN can be optimized by precisely controlling the Sc doping content. When the Sc doping content is between 5% and 40%, AlScN has a ferroelectric effect. Ferroelectric materials have a natural internal electric field after polarization, and this electric field can change with the change of polarization direction. In addition, when the Sc content is higher than 5% to 20%, the external bias voltage required to change the polarization direction of AlScN is large. When the Sc content is higher than 32%, although the voltage required to change the polarization direction becomes smaller, the excessive introduction of Sc causes an increase in material defects, which will lead to a decrease in device performance and reliability. Therefore, the preferred Sc content is 20% to 32%.

[0048] like Figure 5a As shown in the figure, when the Sc content is 20%, the AlScN material shows obvious resistance change (a situation in which the resistance changes due to the change of polarization direction and polarization degree of the ferroelectric material. For example, a certain ferroelectric device is polarized to the left in a high resistance state and to the right in a low resistance state. The greater the polarization degree, the more obvious the resistance state. Therefore, the current in the figure has different values ​​at the same voltage. The fundamental reason is the change of ferroelectric polarization). The greater the voltage, that is, the lower the Sc content, the greater the voltage required to change the ferroelectric polarization state (the figure shows that 14V is required), as shown in the figure. Figure 5b As shown in the figure, when the Sc content increases to 32%, the voltage is reduced to 5V, but the leakage of the material is larger, which means that there are more defects and it is easy for photogenerated carriers to be captured by defects.

[0049] In a more specific embodiment, a method for preparing a wide-spectrum photodetector based on AlScN comprises the following steps: First, the substrate is ultrasonically cleaned, and then a bottom electrode with a thickness of 120nm-1um is formed on the substrate using an epitaxial growth process (TiN and any metal electrode can be used, such as Pt, Al, Ag, Ni, etc.); then the electrode is in-situ annealed, and an AlScN ferroelectric film is grown (the thickness is adjusted in the range of 20~200nm according to the requirements), and then a top electrode material is formed on the AlScN ferroelectric film, and then positive photoresist AZ5214 is sprayed on to pattern the top electrode through photolithography and development technology (any photolithography machine model The sample can be any size, and different resolution photolithography machines can be selected according to the requirements of the unit device size for actual applications). After coating and photolithography, use the photoresist as a mask and use the NLD etcher to etch away the top electrode materials other than those without patterning. After etching, soak the sample in an acetone solution for 12 hours, use a rubber-tipped dropper to gently blow on the surface in the solution, and ultrasonicate for 30s×4 to completely remove the photoresist to obtain the device structure; finally, rinse with isopropanol and deionized water several times respectively, blow dry the sample with nitrogen, and then anneal in a nitrogen atmosphere. After cooling, the preparation is completed.

[0050] Example This embodiment provides a method for preparing a wide-spectrum photodetector based on AlScN. This embodiment can adjust the contact type by selecting different metal electrodes. This embodiment uses a pulsed laser deposition device (PLD), an MA6 double-sided alignment lithography machine, a DC magnetron sputtering device, an NLD etcher, etc. to prepare a wide-spectrum photodetector based on AlScN. The preparation mainly uses the MA6 double-sided alignment lithography machine, a pulsed laser deposition device (PLD), and other instruments.

[0051] See also Figure 6 The main process steps of a wide spectrum photodetector based on AlScN are: substrate cleaning, pulsed laser deposition system (PLD) growth of TiN thin film electrode, pulsed laser deposition equipment growth of AlScN thin film, DC magnetron sputtering system growth of In top electrode, glue coating, photolithography, development, lift-off, NLD etcher etching. Specifically include the following steps: 1) Substrate preparation: The substrate used in the embodiment of the present invention is a sapphire substrate oriented to the c-axis (0001), with a thickness of 0.4 mm and a length and width of 10 mm×10 mm.

[0052] Since the metal film is grown on the substrate surface using pulsed laser deposition equipment, the roughness and smoothness of the substrate surface directly determines the uniformity and smoothness of the subsequent coated film. If the surface is not clean, it may cause the film to fall off during subsequent processes or cleaning.

[0053] In view of the above reasons, the substrate cleaning steps usually taken are as follows: first, take a glass beaker and a polytetrafluoroethylene flower basket of appropriate capacity, rinse them repeatedly with deionized water, and use a nitrogen gun to blow dry the excess water on the inner wall of the beaker and the flower basket; then take out the sample and put it in the flower basket, add acetone solution to the beaker, immerse the flower basket and the sample in the solution and then put it into an ultrasonic cleaner for cleaning for 5 minutes, and repeat this operation 3 times; then replace the isopropanol solution to clean the substrate for 5 minutes, repeat 3 times, and the other operations are the same as the previous step; finally, rinse the substrate repeatedly with deionized water, blow dry it with nitrogen, and put it in the sample box.

[0054] 2) A TiN bottom electrode is grown on the substrate using a pulsed laser deposition system (PLD).

[0055] The TiN bottom electrode with a thickness of 120 nm was grown using the PLD system. The growth rate was 0.72 nm / min, the growth time was 167 mins, the growth temperature was 650℃, the laser frequency of the PLD system was 2 Hz, and the laser energy was 350 mJ.

[0056] 3) Pulsed laser deposition system (PLD) grows AlScN ferroelectric thin films.

[0057] The AlScN ferroelectric film with a thickness of 100 nm was grown using the PLD system. The growth rate was 2 nm / min, the growth time was 50 mins, the operating temperature was 420℃, the laser frequency of the PLD system was 2 Hz, and the laser energy was 300 mJ.

[0058] 4) Magnetron sputtering of In top electrode.

[0059] The In film was sputtered using a DC magnetron sputtering system with a thickness of 100 nm.

[0060] 5) Photolithography and development: Spray positive photoresist AZ5214 and use MA6 double-sided alignment photolithography machine (in fact, any model of photolithography machine can be used, depending on the size of the unit device) to make the required device size. The specific photolithography parameters are as follows: surface pretreatment and adhesive (HMDS) coating; AZ5214 coating forward rotation of 600 rpm for 5 s, backward rotation of 3000 rpm for 30 s; Hard mode, 0.8 s; development using 3038, 45 s (start shaking after 10 s), DI water fixation for 1 min, blow dry with nitrogen gun; microscopy objective 5x, 20x.

[0061] 6) ICP (reactive coupled plasma) etching: Use photoresist as a mask to etch out the patterned In electrode.

[0062] 7) Removal of residual photoresist: Since the etching process does not completely etch away the photoresist, the sample needs to be immersed in an acetone solution for 12 hours, and a rubber-tipped dropper is used to gently blow on the surface in the solution, and ultrasonically applied for 30 seconds to completely remove the photoresist, and then immersed and cleaned with isopropyl alcohol and water, and finally dried with nitrogen.

[0063] 8) Magnetron sputtering In film: Magnetron sputtering of 5 nm In film.

[0064] 9) Device annealing: Annealing was performed using a PLD system in a nitrogen atmosphere with a nitrogen pressure of 5 Pa, a temperature of 150°C, and a time of 8 h.

[0065] The present invention designs a wide-spectrum photodetector based on AlScN based on the three principles of ferroelectric polarization, surface plasmon resonance and photovoltaic effect. The wide-spectrum photodetector based on AlScN provided by the embodiment of the present invention does not need to add a transport layer for electrons and holes, simplifies the device structure, and at the same time, there are no oxygen vacancies in AlScN, and the nitrogen vacancy formation energy is high, so it has excellent fatigue resistance and device uniformity. It does not contain heavy metals such as lead and is environmentally friendly.

[0066] The AlScN-based MSM-PDs photodetector proposed in the embodiment of the present invention is a photovoltaic photodetection technology that utilizes the switchable spontaneous polarization of the AlScN unit cell to regulate the potential barrier while helping or suppressing the transport of carriers, thereby obtaining light information. The present invention combines the advantages and particularities of AlScN and has the characteristics of wide spectrum detection, high reliability, small size, and low energy consumption.

[0067] The vertical MSM-PDs proposed in this paper is a photovoltaic photodetector with a supersurface structure based on AlScN. The polarization-induced built-in electric field of AlScN with ferroelectricity can help or inhibit the collection of carriers and modulate the Schottky barrier height, and the metal supersurface structure on the top will enhance the absorption of light.

[0068] The AlScN-based photodetector proposed in the present invention is a photodetector that can separate photogenerated electron-hole pairs without external bias. The bandgap width of AlScN varies between 3.4 and 5.8 eV depending on the Sc content, and can effectively respond to ultraviolet electromagnetic waves. At the same time, a super-surface structure is introduced, and the device as a whole constitutes a perfect absorber; hot electron injection in the metal can detect electromagnetic waves in the visible and infrared bands, which is of great significance to the development of lightweight, low-power, and multifunctional photodetectors. In theoretical design, by changing the electrode pattern of different work functions and the thickness of the ferroelectric layer, a low-energy consumption, low-recombination, low-dark current, fast-response, high-contrast wide-spectrum detection device that can be applied to different scenarios can be realized. The present invention is compatible with nitride semiconductor processes, so the device can be expanded and integrated in different nitride electronic systems, thereby simplifying the difficulty of nitride on-chip integration.

[0069] It should be understood that the above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A wide spectrum photodetector based on AlScN, characterized in that: include: An AlScN light absorbing layer, a bottom electrode and a top electrode, wherein the bottom electrode is arranged on the first surface of the AlScN light absorbing layer, and the bottom electrode forms a Schottky contact with the AlScN light absorbing layer; the top electrode is arranged on the second surface of the AlScN light absorbing layer, and the top electrode forms an ohmic contact with the AlScN light absorbing layer; the built-in electric field inside the AlScN light absorbing layer can help or inhibit the drift motion of carriers, so that the wide-spectrum photodetector can work without an external bias, wherein the first surface and the second surface are arranged back to back.

2. The AlScN-based wide-spectrum photodetector according to claim 1, characterized in that: When the first built-in electric field induced by polarization inside the AlScN light absorbing layer is in the same direction as the second built-in electric field of the Schottky barrier formed by the contact between the bottom electrode and the AlScN light absorbing layer, the height of the Schottky barrier increases, the width of the depletion region increases, the hot carriers of the bottom electrode find it difficult to cross the Schottky barrier and enter the AlScN light absorbing layer, the drift motion of the hot electrons in the top electrode is suppressed by the first built-in electric field, and the hot holes in the top electrode reach the bottom electrode with the help of the first built-in electric field and the second built-in electric field inside the AlScN light absorbing layer; When the first built-in electric field induced by the internal polarization of the AlScN light absorbing layer is opposite to the second built-in electric field of the Schottky barrier formed by the contact between the bottom electrode and the AlScN light absorbing layer, the height of the Schottky barrier is reduced, the width of the depletion region is narrowed, and the hot carriers of the top electrode cross the Schottky barrier to reach the bottom electrode with the help of the first built-in electric field.

3. The AlScN-based wide-spectrum photodetector according to claim 1 or 2, characterized in that: The Sc content in the AlScN contained in the AlScN light absorption layer is 5% to 40%; Preferably, the Sc content in the AlScN contained in the AlScN light absorbing layer is 20% to 32%.

4. The AlScN-based wide-spectrum photodetector according to claim 3, characterized in that: The bandgap width of the AlScN light absorption layer is 3.4 eV to 5.8 eV.

5. The AlScN-based wide-spectrum photodetector according to claim 1 or 2, characterized in that: The thickness of the AlScN light absorbing layer is 20nm-200nm.

6. The AlScN-based wide-spectrum photodetector according to claim 1, characterized in that: The top electrode has a super surface structure, and the top electrode can resonate with electromagnetic waves in the visible light band and the infrared band, thereby exciting and forming hot electrons.

7. The AlScN-based wide-spectrum photodetector according to claim 6, characterized in that: The surface of the top electrode facing away from the AlScN light absorbing layer has a plurality of circular slots distributed in an array.

8. The AlScN-based wide-spectrum photodetector according to claim 1 or 6, characterized in that: The material of the top electrode includes at least one of In, Mo, Pt, Au, Cu, Al, and Ag, or an alloy formed by two or more thereof.

9. The AlScN-based wide-spectrum photodetector according to claim 1, characterized in that: The bottom electrode is a planar thin film structure; Preferably, the material of the bottom electrode includes at least one of TiN, Al, Ag, Pt, Mo, Cr, and Cu.

10. The AlScN-based wide-spectrum photodetector according to claim 1, characterized in that: Also includes: a substrate, the bottom electrode being disposed on the substrate; Preferably, the substrate includes one of a sapphire substrate, a Si substrate, and a GaN substrate.

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