A self-driven solar-blind ultraviolet detector based on asymmetric Schottky barrier

Abstract

The invention discloses a self-driven solar-blind ultraviolet detector based on an asymmetric Schottky barrier, which belongs to the technical field of semiconductor device manufacturing. The ultraviolet detector comprises, from bottom to top, a substrate layer, an AlN buffer layer, an Al 0.65 Ga 0.35 N layer, Al 0.4 Ga 0.6 N active layer, Al 0.55 Ga 0.45 N barrier layer and metal electrode layer. The present invention connects Al 0.4 Ga 0.6 Al is inserted between the N active layers 0.55 Ga 0.45 N barrier layer, forming an asymmetric MSM structure, using different barrier heights to induce band bending, forming an asymmetric band, significantly promoting the separation and transport of photogenerated carriers, thereby solving the problem of high power consumption of symmetrical MSM structure detectors and realizing self-driving characteristics. The asymmetric heterostructure formed enhances the Al 0.4 Ga 0.6 The polarization field of the N layer increases the generation of photocurrent, greatly improving the responsiveness at 0 V. In addition, the epitaxial structure manufactured by the present invention has a low screw dislocation density, so that the device obtains an ultra-low dark current, improving the sensitivity of the device.

Description

Technical Field

[0001] The invention relates to a self-driven solar-blind ultraviolet detector based on an asymmetric Schottky barrier, belonging to the technical field of semiconductor device manufacturing. Background Art

[0002] In order to adapt to the rapid development of modern electronic information, optoelectronic devices are gradually developing towards the trend of "miniaturization" and "integration". Therefore, the development of highly sensitive, low-energy, and high-response ultraviolet detectors is the core of future development in this field. Furthermore, the construction of self-driven ultraviolet photodetectors that can work sustainably and do not require external power has become a research focus in the field of photoelectric detection. From the application point of view, self-driven ultraviolet detectors have special advantages such as low energy consumption, energy saving and environmental protection, small device size, and suitability for use under extreme conditions. They are very popular in fields such as forest fire prevention and submarine oil spill monitoring.

[0003] Wide bandgap semiconductor material Al x Ga 1-x N has an adjustable band gap, intrinsic solar-blind properties, high temperature resistance, and excellent chemical and physical stability. x Ga 1-x The polarization property of N helps to form a highly conductive two-dimensional electron gas (2DEG) at the heterojunction interface, thereby improving device performance. Given these significant advantages, AlGaN has become an ideal material for developing high-performance UV detectors. To date, most AlGaN-based UV detectors use an MSM structure due to the advantages of simple and controllable manufacturing process, strong planar integration capability, low noise, and high detection rate. Given that the traditional MSM structure uses the same metal / semiconductor Schottky contact to form symmetrical electrodes, resulting in the mirror symmetry of the Schottky barrier formed at both ends of the metal / semiconductor contact. In this case, the photogenerated electrons / holes in the AlGaN semiconductor layer have no preferred drift direction. In other words, although these symmetrical AlGaN-based MSM structure UV detectors have achieved high light detection performance, most of them require external bias voltages to drive the operation and promote the separation and transport of photogenerated electron-hole pairs. These external power supplies will not only increase the circuit design complexity and processing cost of the UV detection system, but also limit its use in special environments and conditions.

[0004] In order to realize the self-driving of AlGaN-based MSM structure ultraviolet detectors, that is, to drive them to work under zero bias voltage, the usual practice is to design an asymmetric structure to obtain an asymmetric Schottky barrier. The usual practice to achieve an asymmetric Schottky barrier is to deposit different metal contacts at both ends of the device, including using different metal materials and changing the contact area of ​​the metal electrodes. However, the above method is not conducive to the flexibility and wear resistance of the device, and has disadvantages such as high cost and limited difference in the work function of Schottky metals, which hinders the further improvement of the asymmetric Schottky barrier and the further improvement of device performance. Most importantly, the photocurrent of the device is small under zero bias voltage, so the responsivity and detection rate at zero bias are low. Summary of the invention

[0005] In order to solve the problems of high energy consumption and low sensitivity of the current AlGaN-based MSM structure ultraviolet detector, the present invention provides a self-driven solar-blind ultraviolet detector based on an asymmetric Schottky barrier. 0.4 Ga 0.6 Al is inserted between the N active layers 0.55 Ga 0.45 N barrier layer, forming an asymmetric Al with polarization effect 0.55 Ga 0.45 N / A 0.4 Ga 0.6 N / A 0.65 Ga 0.35 N heterostructure, constructing an asymmetric MSM structure, thus realizing a self-driven AlGaN-based MSM solar-blind UV detector, and because of the design of Al with polarization enhancement effect 0.55 Ga 0.45 N / A 0.4 Ga 0.6 N / A 0.65 Ga 0.55 N epitaxial structure, enhancing the absorption layer Al by controlling polarization 0.4 Ga 0.6 The built-in electric field in N causes interface charges due to the polarization effect in the heterostructure, and there is a strong built-in electric field in the AlGaN absorption layer, which promotes the separation of photogenerated electron-hole pairs, thereby increasing the generation of photocurrent and greatly improving the responsivity and detectivity at zero bias.

[0006] A self-driven solar-blind ultraviolet detector based on an asymmetric Schottky barrier, the self-driven solar-blind ultraviolet detector comprises, from bottom to top, a substrate layer, an AlN buffer layer, a heterostructure layer and a metal electrode layer; wherein the heterostructure layer comprises three high-aluminum component layers: Al 0.65 Ga 0.35 N buffer layer, Al 0.4 Ga 0.6N active layer and Al 0.55 Ga 0.45 N barrier layer; and one side electrode of the self-driven solar-blind ultraviolet detector is composed of Al in three layers of high aluminum component layers. 0.55 Ga 0.45 The N barrier layer and the metal electrode layer are composed, and the other electrode is composed only of the metal electrode layer.

[0007] Optionally, the electrodes on both sides of the self-driven solar-blind ultraviolet detector are interdigitated electrodes, and the metal electrode layer on one side of the electrode is connected to the Al in the three-layer high aluminum component layer. 0.4 Ga 0.6 The N active layer forms a Schottky contact, and the metal electrode layer on the other side of the electrode is connected to the Al in the three-layer high aluminum component layer. 0.55 Ga 0.45 The N barrier layer forms a Schottky contact.

[0008] Optionally, the finger-shaped electrodes on both sides are symmetrically arranged, the finger width is 25±5 μm, the finger length is 500 μm, and the spacing between adjacent fingers is 10±5 μm.

[0009] Optionally, Al in the three high aluminum component layers 0.65 Ga 0.35 The thickness of N layer is 1.5 μm, and Al 0.4 Ga 0.6 The thickness of the N active layer is 300nm, and the Al 0.55 Ga 0.45 The thickness of the N barrier layer is 50 nm.

[0010] Optionally, the thickness of the AlN buffer layer is 2 μm.

[0011] Optionally, the material of the metal electrode layer is Ni / Au composite metal.

[0012] Optionally, the substrate layer material is sapphire.

[0013] The present application provides a method for preparing a self-driven solar-blind ultraviolet detector based on an asymmetric Schottky barrier, wherein the method obtains a self-driven solar-blind ultraviolet detector by growing a device epitaxial heterostructure on a substrate layer, and the method comprises:

[0014] Step 1: growing an AlN buffer layer on a substrate layer;

[0015] Step 2: Undoped Al 0.65 Ga 0.35 N is deposited on the AlN buffer layer to form Al 0.65 Ga 0.35 N buffer layer;

[0016] Step 3: Al 0.65 Ga0.35 After the N layer is grown, the Al 0.65 Ga 0.35 Undoped Al is deposited on the N buffer layer 0.4 Ga 0.6 N, forming Al 0.4 Ga 0.6 N active layer;

[0017] Step 4: Al 0.4 Ga 0.6 After the N layer is grown, the Al 0.4 Ga 0.6 Undoped Al is deposited on the N active layer 0.55 Ga 0.45 N, forming Al 0.55 Ga 0.45 N barrier layer, while forming Al with polarization enhancement effect 0.55 Ga 0.45 N / A 0.4 Ga 0.6 N / A 0.65 Ga 0.35 N heterostructure;

[0018] Step 5: 0.55 Ga 0.45 The N barrier layer is subjected to mesa isolation etching to form the asymmetric heterostructure;

[0019] Step 6: Deposit a metal electrode layer in a symmetrical interdigitated shape to form a Schottky electrode.

[0020] Optionally, the growth of the device epitaxial heterostructure on the substrate layer adopts a metal organic chemical vapor deposition (MOCVD) method.

[0021] Optionally, in step 5, inductively coupled plasma and BCl3 / Cl2 gas are used to perform mesa etching.

[0022] The beneficial effects of the present invention are:

[0023] (1) The AlGaN-based solar-blind ultraviolet detector of the asymmetric heterostructure of the present invention utilizes an asymmetric polarization-enhanced Al 0.55 Ga 0.45 N / A 0.4 Ga 0.6 N / A 0.65 Ga 0.35N heterostructure, due to the formation of different barrier heights at the two Schottky contacts, induces band bending and constitutes an asymmetric band structure, so that there is an internal potential difference between the two electrodes, providing a built-in electric field for photogenerated carriers, significantly promoting carrier separation and transport, and generating photocurrent even in the absence of a bias voltage, thus realizing self-driven detection and solving the high energy consumption disadvantage of traditional MSM structure ultraviolet detectors.

[0024] (2) The present invention constructs three layers of high aluminum component, using Al with polarization enhancement effect 0.55 Ga 0.45 N / A 0.4 Ga 0.6 N / A 0.65 Ga 0.55 N epitaxial structure, by controlling polarization to enhance the built-in electric field of the absorption layer, due to the polarization effect in the heterostructure caused by the interface charge, there is a strong built-in electric field in the AlGaN absorption layer, thereby promoting the separation of photogenerated electron-hole pairs, thereby increasing the generation of photocurrent. Compared with the existing self-driven MSM ultraviolet photodetector, the responsivity and detection rate at zero bias are greatly improved.

[0025] (3) The self-driven solar-blind ultraviolet detector of the present invention uses AlN / sapphire substrate, so that the screw dislocation density of the epitaxial structure is low, about 2.45×10 8 cm -2 , reducing leakage channels, the device has ultra-low dark current, and improves the sensitivity of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0027] Figure 1 It is a schematic diagram of the layer structure of the self-driven solar-blind ultraviolet detector based on asymmetric Schottky barrier provided by the present invention.

[0028] Figure 2 It is an IV curve characteristic diagram of the device of the present invention under room temperature without illumination and under 280nm illumination at a bias voltage of -10 to 10V.

[0029] Figure 3 It is a photocurrent response curve and a spectrum response curve diagram of the ultraviolet detector of the present invention under no bias voltage (0V).

[0030] Figure 4This is a structural comparison diagram of the asymmetric MSM structure ultraviolet detector A of the present invention and the reference device B.

[0031] Figure 5 It is a spectral response curve diagram of the asymmetric MSM structure ultraviolet detector of the present invention and the symmetric MSM structure ultraviolet detector of the reference device at 0V. DETAILED DESCRIPTION

[0032] In order to make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0033] Embodiment 1:

[0034] This embodiment provides a self-driven solar-blind ultraviolet detector based on an asymmetric Schottky barrier. Figure 1 The ultraviolet detector includes, from top to bottom, a substrate layer, an AlN buffer layer, a heterogeneous structure layer, and a metal electrode layer; wherein the heterogeneous structure layer includes three high-aluminum component layers: Al 0.65 Ga 0.35 N buffer layer, Al 0.4 Ga 0.6 N active layer and Al 0.55 Ga 0.45 N barrier layer; and one side electrode of the self-driven solar-blind ultraviolet detector is composed of Al in three layers of high aluminum component layers. 0.55 Ga 0.45 The N barrier layer and the metal electrode layer are composed, and the other electrode is composed only of the metal electrode layer.

[0035] The electrodes on both sides are interdigitated electrodes, and the metal electrode layer on one side of the electrode is connected to the Al in the three-layer high aluminum component layer. 0.4 Ga 0.6 The N active layer forms a Schottky contact, and the metal electrode layer on the other side of the electrode is connected to the Al in the three-layer high aluminum component layer. 0.55 Ga 0.45 The N barrier layer forms a Schottky contact.

[0036] This application considers one of the main defects in AlGaN materials, namely screw dislocation, and adopts AlN / sapphire substrate, which greatly reduces the screw dislocation density of the epitaxial structure and improves the sensitivity of the device. In the AlN / sapphire substrate, the substrate layer is a sapphire substrate, the thickness of the AlN buffer layer is 2μm, and the Al 0.65 Ga 0.35 The N buffer layer is not doped and has a thickness of 1.5 μm. Then a 300 nm thick Al 0.4 Ga 0.6 N active layer and 50nm thick Al 0.55 Ga 0.45The N barrier layer is used to form a heterostructure. The material of the metal electrode layer is Ni / Au composite metal.

[0037] Mesa etching was performed using inductively coupled plasma with BCl3 / Cl2 gas to remove the remaining Al 0.55 Ga 0.45 N barrier layer, obtained Al 0.55 Ga 0.45 N table, Al table structure 0.55 Ga 0.45 The width of N is 25 μm. 0.55 Ga 0.45 N / A 0.4 Ga 0.6 N / A 0.65 Ga 0.55 Asymmetric heterostructure of N.

[0038] The interdigitated electrodes on both sides of the ultraviolet detector are symmetrically arranged, the interdigitated width is 25±5μm, the interdigitated length is 500μm, and the spacing between adjacent interdigitated electrodes is 10±5μm.

[0039] Embodiment 2

[0040] This embodiment provides a method for preparing a self-driven solar-blind ultraviolet detector based on an asymmetric Schottky barrier, which is used to prepare a self-driven solar-blind ultraviolet detector with an asymmetric heterostructure provided in Embodiment 1. The preparation method grows a device epitaxial heterostructure on a sapphire substrate by metal organic chemical vapor deposition (MOCVD), comprising:

[0041] Step 1: growing an AlN buffer layer on a substrate layer;

[0042] Step 2: Undoped Al 0.65 Ga 0.35 The N layer is deposited on the AlN buffer layer;

[0043] Step 3: Al 0.65 Ga 0.35 After the N layer is grown, the Al 0.65 Ga 0.35 Undoped Al is deposited on the N layer 0.4 Ga 0.6 N, forming Al 0.4 Ga 0.6 N active layer;

[0044] Step 4: Al 0.4 Ga 0.6 After the N layer is grown, the Al 0.4 Ga 0.6 Undoped Al is deposited on the N layer 0.55 Ga0.45 N, forming Al 0.55 Ga 0.45 N barrier layer, forming Al 0.55 Ga 0.45 N / A 0.4 Ga 0.6 N / A 0.65 Ga 0.55 N heterostructure;

[0045] Step 5: Using Inductively Coupled Plasma with BCl3 / Cl2 Gas to Treat Al 0.55 Ga 0.45 The N barrier layer is etched to isolate the mesa and form an asymmetric Al 0.55 Ga 0.45 N / A 0.4 Ga 0.6 N / A 0.65 Ga 0.55 N heterostructure;

[0046] Step 6: After the mesa isolation etch, a standard Ni / Au (50 / 150nm) Schottky metal stack was deposited.

[0047] In order to further illustrate the beneficial effects of the self-driven solar-blind ultraviolet detector with asymmetric Schottky barrier provided by the present invention, a series of experiments were conducted. The experimental results are shown in FIG. Figures 2 to 5 shown.

[0048] Figure 2 The IV curves of the UV detector of the present invention in a dark environment and under 280nm monochromatic light illumination are shown. The dark current measured at room temperature is less than 1.0×10 -11 A, at 5V bias voltage, can be as low as 1.8×10 -13 A. The photocurrent at 5V bias voltage is 2.8×10 -9 A. Therefore, it can be seen from the test results that the self-driven solar-blind ultraviolet detector device provided in this application has a relatively ideal light-to-dark current ratio, which is about 1.6×10 4 .

[0049] Figure 3 The photocurrent response curve of the self-driven solar-blind UV detector in the unbiased state and the spectral response curve after calibration are shown. It can be seen that the device achieves the maximum photocurrent at 280nm and is clearly cut off at 285nm, which is similar to Al 0.4 Ga 0.6 The bandgap bandwidth of the N absorption layer is consistent. In addition, at 0V, the responsivity of the self-driven solar-blind UV detector device is 0.04A / W, and the detection rate is 3.1×10 12Jones, realizing the self-driving function. This is because the asymmetric heterostructure with polarization enhancement effect constitutes an asymmetric MSM structure device, so that different barrier heights provide an asymmetric energy band and enhance the Al 0.4 Ga 0.6 N The built-in electric field of the active layer.

[0050] In order to highlight the metal electrode layer on one side of the electrode of the self-driven solar-blind ultraviolet detector provided by the present application and the Al in the three-layer high-aluminum component layer 0.4 Ga 0.6 The N active layer forms a Schottky contact, and the metal electrode layer on the other side of the electrode is connected to the Al in the three-layer high aluminum component layer. 0.55 Ga 0.45 The beneficial effect brought by the formation of Schottky contact by the N barrier layer, this embodiment also prepares a symmetrical structure device B, and compares it with the self-driven solar-blind ultraviolet detector provided by the present application. The difference between the symmetrical structure device B and the device of the present application is that the electrodes on both sides are connected to Al 0.55 Ga 0.45 N barrier layer forms Schottky contact, please refer to Figure 4 .

[0051] Figure 5 The comparison results of the light response curves of the self-driven day-blind ultraviolet detector device A and the symmetrical structure device B provided in the present application at 0V are shown. From the comparison results, it can be obviously concluded that the response spectrum of the self-driven day-blind ultraviolet detector device A provided in the present application has an obvious response broad peak at 250-280nm, that is, it has an obvious response broad peak to day-blind ultraviolet rays, but the light response curve of the device B at 0V does not have an obvious response peak.

[0052] In summary, the ultraviolet detector of the present invention can realize self-driving characteristics, low dark current, and high zero-bias responsivity. Therefore, this structural design makes up for the high power consumption of horizontally symmetrical MSM structure devices, and the responsivity is greatly improved.

[0053] Some steps in the embodiments of the present invention may be implemented using software, and the corresponding software program may be stored in a readable storage medium, such as a CD or a hard disk.

[0054] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A self-driven solar-blind ultraviolet detector based on an asymmetric Schottky barrier, characterized in that: The self-driven solar-blind ultraviolet detector includes, from bottom to top, a substrate layer, an AlN buffer layer, a heterostructure layer and a metal electrode layer; wherein the heterostructure layer includes three high-aluminum component layers: Al 0.65 Ga 0.35 N buffer layer, Al 0.4 Ga 0.6 N active layer and Al 0.55 Ga 0.45 N barrier layer; and one side electrode of the self-driven solar-blind ultraviolet detector is composed of Al in three layers of high aluminum component layers. 0.55 Ga 0.45 The N barrier layer and the metal electrode layer are composed of the Al in the three high aluminum component layers. 0.4 Ga 0.6 The N active layer forms a Schottky contact, and the electrode on the other side is only composed of a metal electrode layer, and the metal electrode layer is connected to the Al in the three high aluminum component layers. 0.55 Ga 0.45 The N barrier layer forms a Schottky contact.

2. The self-driven solar-blind ultraviolet detector according to claim 1, characterized in that: The electrodes on both sides of the self-driven solar-blind ultraviolet detector are interdigitated electrodes, and the metal electrode layer on one side of the electrode is connected to the Al in the three-layer high-aluminum component layer. 0.4 Ga 0.6 The N active layer forms a Schottky contact, and the metal electrode layer on the other side of the electrode is connected to the Al in the three-layer high aluminum component layer. 0.55 Ga 0.45 The N barrier layer forms a Schottky contact.

3. The self-driven solar-blind ultraviolet detector according to claim 2, characterized in that: The interdigitated electrodes on both sides are symmetrically arranged, the interdigitated width is 25±5 μm, the interdigitated length is 500 μm, and the spacing between adjacent interdigitated electrodes is 10±5 μm.

4. The self-driven solar-blind ultraviolet detector according to claim 1, characterized in that: The three layers of high aluminum component Al 0.65 Ga 0.35 The thickness of N layer is 1.5 μm, and Al 0.4 Ga 0.6 The thickness of the N active layer is 300nm, and the Al 0.55 Ga 0.45 The thickness of the N barrier layer is 50 nm.

5. The self-driven solar-blind ultraviolet detector according to claim 1, characterized in that: The thickness of the AlN buffer layer is 2 μm.

6. The self-driven solar-blind ultraviolet detector according to claim 1, characterized in that: The material of the metal electrode layer is Ni / Au composite metal.

7. The self-driven solar-blind ultraviolet detector according to claim 1, characterized in that: The substrate layer material is sapphire.

8. A method for preparing a self-driven solar-blind ultraviolet detector based on an asymmetric Schottky barrier, characterized in that: The method obtains a self-driven solar-blind ultraviolet detector by growing a device epitaxial heterostructure on a substrate layer, and the method comprises: Step 1: growing an AlN buffer layer on a substrate layer; Step 2: Undoped Al 0.65 Ga 0.35 N is deposited on the AlN buffer layer to form Al 0.65 Ga 0.35 N buffer layer; Step 3: Al 0.65 Ga 0.35 After the N layer is grown, the Al 0.65 Ga 0.35 Undoped Al is deposited on the N buffer layer 0.4 Ga 0.6 N, forming Al 0.4 Ga 0.6 N active layer; Step 4: Al 0.4 Ga 0.6 After the N layer is grown, the Al 0.4 Ga 0.6 Undoped Al is deposited on the N active layer 0.55 Ga 0.45 N, forming Al 0.55 Ga 0.45 N barrier layer, while forming Al with polarization enhancement effect 0.55 Ga 0.45 N / A 0.4 Ga 0.6 N / A 0.65 Ga 0.35 N heterostructure; Step 5: 0.55 Ga 0.45 The N barrier layer is subjected to mesa isolation etching to form an asymmetric heterostructure; Step 6: Deposit a metal electrode layer in a symmetrical interdigitated shape to form a Schottky electrode.

9. The method according to claim 8, characterized in that The device epitaxial heterostructure is grown on the substrate layer by using a metal organic chemical vapor deposition (MOCVD) method.

10. The method according to claim 8, characterized in that In step 5, inductively coupled plasma and BCl3 / Cl2 gas are used to perform mesa etching.

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