Aluminum nitride vacuum detector and preparation method thereof

Abstract

The invention provides an aluminum nitride vacuum detector which can be applied to the technical field of semiconductors and optoelectronic materials. The aluminum nitride epitaxial layer is located on the substrate, a local area of the aluminum nitride epitaxial layer contains silicon atoms, and the projection of the area containing the silicon atoms on the surface of the aluminum nitride epitaxial layer does not completely cover the surface of the aluminum nitride epitaxial layer; the first electrode is located on the surface of a region, containing silicon atoms, of the aluminum nitride epitaxial layer; and the second electrode is located on the surface of the region, not containing the silicon atoms, of the aluminum nitride epitaxial layer. High-concentration silicon impurities are locally injected into the aluminum nitride epitaxial layer, so that good ohmic contact is formed between the aluminum nitride epitaxial layer and the first electrode, Schottky contact is formed between the second electrode and the aluminum nitride epitaxial layer, and the Schottky junction detector which responds faster than an MSM structure detector and does not need higher bias voltage is constructed.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductors and optoelectronic materials, and particularly to an aluminum nitride vacuum detector and a preparation method thereof. Background Art

[0002] Aluminum nitride (AlN) has the characteristics of wide bandgap, high electron mobility, large saturation velocity, good high-temperature resistance and radiation resistance, and is one of the best materials for preparing ultraviolet detectors. At the same time, the bandgap of AlN is 6.1 eV. The vacuum ultraviolet detector made of it has a natural cut-off band edge and responds below 200 nm, without the need for a complex and expensive filtering system. The AlN-based Schottky detector has the advantages of low response time and high quantum efficiency due to its structural characteristics. However, due to the difficulty in achieving good ohmic contact for AlN, it is generally only possible to fabricate a Metal-Semiconductor-Metal (MSM) structure detector that needs to work under a high bias voltage and is difficult to integrate. At the same time, for a detector array fabricated from a vacuum ultraviolet detector, if it is front-illuminated, the light needs to pass through multiple layers such as leads and electrodes to reach the absorption layer, which results in light loss and reduced quantum efficiency. Summary of the Invention

[0003] (I) Technical Problems to be Solved

[0004] To solve at least one of the above problems existing in the aluminum nitride vacuum detector in the prior art, embodiments of the present invention provide an aluminum nitride vacuum detector and a preparation method thereof. By ion-implanting high-concentration silicon (Si) impurities, good ohmic contact between AlN and the electrode is achieved; the other electrode forms a Schottky contact with AlN, constructing a Schottky junction detector that is faster in response and does not require a high bias voltage compared to the MSM structure detector.

[0005] (II) Technical Solutions

[0006] In view of the above technical problems, embodiments of the present invention propose an aluminum nitride vacuum detector and a preparation method thereof.

[0007] According to a first aspect of the present invention, there is provided an aluminum nitride vacuum detector, comprising: a substrate, the material of the substrate including a sapphire substrate; an aluminum nitride epitaxial layer, the aluminum nitride epitaxial layer including a first surface and a second surface, the first surface being located on the substrate, wherein a local region of the aluminum nitride epitaxial layer contains silicon atoms, and the projection of the region containing silicon atoms on the first surface and the second surface does not completely cover the first surface and the second surface; a first electrode, located on the second surface and within the projection region of the region containing silicon atoms on the second surface; and a second electrode, located on the second surface and not within the projection region of the region containing silicon atoms on the second surface.

[0008] In some exemplary embodiments, an ohmic contact is formed between the first electrode and the aluminum nitride epitaxial layer; and a Schottky contact is formed between the second electrode and the aluminum nitride epitaxial layer.

[0009] In some exemplary embodiments, the first electrode includes a titanium layer, an aluminum layer, a titanium layer, and a gold layer sequentially arranged in a direction perpendicular to the second surface; the second electrode includes a nickel layer and a gold layer with a first area sequentially arranged in a direction perpendicular to the second surface; and a titanium layer, an aluminum layer, a titanium layer, and a gold layer with a second area are sequentially arranged on the gold layer in a direction perpendicular to the second surface, where the first area is greater than the second area.

[0010] In some exemplary embodiments, the thickness of the aluminum nitride epitaxial layer is not greater than 300 nm.

[0011] In some exemplary embodiments, the thickness of the sapphire substrate enables light to enter from one side of the sapphire substrate.

[0012] According to a second aspect of the present invention, a method for preparing an aluminum nitride vacuum detector is provided, including: preparing a sapphire substrate; growing an aluminum nitride epitaxial layer on the sapphire substrate; injecting silicon elements into a local area of the aluminum nitride epitaxial layer; sputtering a first electrode at a position where the silicon element region projects onto the aluminum nitride epitaxial layer; and sputtering a second electrode at a position where the projection of the non-silicon element region onto the aluminum nitride epitaxial layer is located, to obtain an aluminum nitride vacuum detector.

[0013] In some exemplary embodiments, growing an aluminum nitride epitaxial layer on the sapphire substrate includes: using a metalorganic chemical vapor deposition device, using trimethylaluminum as an aluminum source and ammonia as a nitrogen source to grow an aluminum nitride epitaxial layer on the sapphire substrate; annealing the epitaxial wafer with the grown epitaxial layer at a temperature of 900 °C ± 50 °C for 2 min - 4 min; and thinning the sapphire substrate to obtain a thinned epitaxial wafer so that light can enter from one side of the sapphire substrate, where the thickness of the aluminum nitride epitaxial layer is not greater than 300 nm.

[0014] In some exemplary embodiments, injecting silicon elements into a local area of the aluminum nitride epitaxial layer includes: growing an insulating layer and coating a photoresist on one surface of the aluminum nitride epitaxial layer of the thinned epitaxial wafer; performing a first photolithography to etch an ion implantation window on the aluminum nitride epitaxial layer; using an ion implantation process to implant Si atoms with a preset depth in the ion implantation window; and annealing at a temperature of 1300 °C ± 50 °C for 4 min - 6 min under a nitrogen protection atmosphere, where the insulating layer material includes silicon dioxide.

[0015] In some exemplary embodiments, sputtering a first electrode at the projection position of a silicon element region on an aluminum nitride epitaxial layer includes: removing photoresist and silicon dioxide; coating a silicon dioxide insulating layer; through a second photolithography process, etching an ohmic contact window in the silicon element region; sputtering a titanium layer, an aluminum layer, a titanium layer, and a gold layer in the ohmic contact window; and annealing at a temperature of 900°C ± 50°C for 25 s - 30 s.

[0016] In some exemplary embodiments, sputtering a second electrode at the projection position of a non-silicon element region on an aluminum nitride epitaxial layer includes: through a third photolithography process, etching a Schottky contact electrode window in the non-silicon element region on the aluminum nitride epitaxial layer; using an electron beam evaporation process to sequentially deposit a transparent electrode nickel layer and a gold layer in the Schottky contact electrode window; annealing at a temperature of 500°C ± 50°C for 4 min - 6 min with a mixed gas of oxygen and nitrogen as a protective atmosphere; through a fourth photolithography process, etching a metal electrode window in the gold layer transparent electrode; and sputtering a titanium layer, an aluminum layer, a titanium layer, and a gold layer in the metal electrode window.

[0017] (III) Beneficial effects

[0018] As can be seen from the above technical solutions, an aluminum nitride vacuum detector and a preparation method thereof provided by an embodiment of the present invention have at least the following beneficial effects:

[0019] (1) By ion-implanting high-concentration Si impurities, good ohmic contact between AlN and the electrode is achieved; the other electrode forms a Schottky contact with AlN, constructing a Schottky junction detector with a faster response than the relative MSM structure detector and without the need to apply a relatively high bias voltage.

[0020] (2) The thickness of the aluminum nitride epitaxial layer does not exceed 300 nm. By setting a thin aluminum nitride layer, electron-hole pairs generated by absorbing photons are in the Schottky junction region, which is easy to separate to generate photocurrent. At the same time, the relatively thin aluminum nitride epitaxial layer enables photo-generated carriers to be quickly collected by the metal electrode, achieving a fast response.

[0021] (3) By thinning the sapphire substrate, light can be irradiated from the back of the device, and the light directly enters the absorption layer, avoiding the influence of the light on the wiring and electrodes, reducing light loss, and being suitable for preparing large-scale area array devices. Description of the drawings

[0022] Through the following description of the embodiments of the present invention with reference to the drawings, the above content and other objects, features, and advantages of the present invention will become clearer. In the drawings:

[0023] Figure 1 Schematically shows a structural diagram of a traditional MSM structure AlN vacuum detector;

[0024] Figure 2Schematically shows a structural schematic diagram of an AlN vacuum detector according to an embodiment of the present invention; and

[0025] Figure 3 Schematically shows a flowchart of a preparation method of an AlN vacuum detector according to an embodiment of the present invention. Detailed implementation manners

[0026] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the following further describes the present invention in detail with reference to specific embodiments and the accompanying drawings. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0027] Figure 1 Schematically shows a structural schematic diagram of a traditional MSM - structured AlN vacuum detector.

[0028] As Figure 1 shown, a traditional MSM - structured AlN vacuum detector includes a sapphire substrate, an aluminum nitride buffer layer, an aluminum nitride epitaxial layer, and metal electrodes. When incident light enters the aluminum nitride epitaxial layer through the part between the electrodes, the photon energy is absorbed by AlN, exciting electron - hole pairs. In the MSM structure, due to the Schottky barrier formed between the metal electrode and AlN, electrons and holes move to the two poles respectively under the action of the electric field, forming a photocurrent. In this way, the MSM - structured AlN vacuum detector can convert the optical signal into an electrical signal for output.

[0029] The traditional MSM - structured AlN vacuum detector is greatly affected by surface states and has a serious parasitic photoconductivity effect, which limits its application and development in some fields.

[0030] Figure 2 Schematically shows a structural schematic diagram of an AlN vacuum detector according to an embodiment of the present invention.

[0031] As Figure 2 shown, an AlN vacuum detector according to an embodiment of the present invention includes: a substrate, the material of the substrate includes a sapphire substrate; an aluminum nitride epitaxial layer, the aluminum nitride epitaxial layer includes a first surface and a second surface, the first surface is located on the substrate, wherein a local area of the aluminum nitride epitaxial layer contains silicon atoms, and the projection of the area containing silicon atoms on the first surface and the second surface does not completely cover the first surface and the second surface; a first electrode, located on the second surface and within the projection area of the area containing silicon atoms on the second surface; and a second electrode, located on the second surface and not within the projection area of the area containing silicon atoms on the second surface.

[0032] In the embodiment of the present invention, by ion implanting high-concentration Si impurities, an ohmic contact is formed between the first electrode and the aluminum nitride epitaxial layer; and a Schottky contact is formed between the second electrode and the aluminum nitride epitaxial layer. A Schottky junction detector with a faster response than the MSM structure detector and without the need for a high bias voltage is constructed.

[0033] In some exemplary embodiments, the first electrode includes a titanium layer, an aluminum layer, a titanium layer, and a gold layer sequentially arranged in a direction perpendicular to the second surface. Preferably, the thicknesses of each layer are 15 nm, 250 nm, 50 nm, and 150 nm, respectively.

[0034] In some exemplary embodiments, the second electrode includes a nickel layer and a gold layer with a first area sequentially arranged in a direction perpendicular to the second surface, preferably with thicknesses of 10 nm and 10 nm, respectively; and a titanium layer, an aluminum layer, a titanium layer, and a gold layer with a second area sequentially arranged on the gold layer in a direction perpendicular to the second surface, preferably with thicknesses of 15 nm, 250 nm, 50 nm, and 150 nm, respectively. Wherein, the first area is larger than the second area.

[0035] Preferably, the thickness of the aluminum nitride epitaxial layer is not greater than 300 nm. The thin-layer design of the aluminum nitride epitaxial layer enables the electron-hole pairs generated by photon absorption to be in the Schottky junction region, which is easy to separate to generate photocurrent. At the same time, the relatively thin aluminum nitride epitaxial layer enables the photo-generated carriers to be quickly collected by the metal electrodes, achieving a fast response.

[0036] Preferably, the thickness of the sapphire substrate can allow light to enter from one side of the sapphire substrate. By thinning the sapphire substrate, light can be irradiated from the back of the device, and the light directly enters the absorption layer, avoiding the influence of the wiring and electrodes on the light, reducing light loss, and being suitable for the preparation of large-scale area array devices.

[0037] Based on the AlN vacuum detector of claim 1, combined with Figure 3 introduce Figure 1 the preparation method of the AlN vacuum detector shown.

[0038] Figure 3 Schematically shows a flow chart of a preparation method of an AlN vacuum detector according to an embodiment of the present invention.

[0039] As Figure 3 shown, a preparation method of an AlN vacuum detector according to an embodiment of the present invention includes step S110 - step S150.

[0040] In step S110, a sapphire substrate is prepared.

[0041] In step S120, an aluminum nitride epitaxial layer is grown on the sapphire substrate.

[0042] For example, using a metalorganic chemical vapor deposition (MOCVD) apparatus, trimethylaluminum (TMAl) is used as the aluminum source and ammonia gas (NH 3 ) is used as the nitrogen source to grow an aluminum nitride epitaxial layer on a sapphire substrate; the epitaxial wafer with the grown epitaxial layer is annealed at a temperature of 900°C ± 50°C for 2 min - 4 min; and the sapphire substrate is thinned to obtain a thinned epitaxial wafer, so that light can enter from one side of the sapphire substrate, wherein the thickness of the aluminum nitride epitaxial layer is not greater than 300 nm.

[0043] In the embodiment of the present invention, by thinning the sapphire substrate, light can be irradiated from the back of the device, and the light directly enters the absorption layer, avoiding the influence of the light by the wiring and the electrodes, reducing the light loss, and being applicable to the preparation of large-scale area array devices.

[0044] In step S130, silicon elements are implanted into a local area of the aluminum nitride epitaxial layer.

[0045] For example, an insulating layer is grown and photoresist is coated on one side surface of the aluminum nitride epitaxial layer of the thinned epitaxial wafer; first photolithography is performed to etch an ion implantation window on the aluminum nitride epitaxial layer; Si atoms with a preset depth are implanted into the ion implantation window by using an ion implantation process; and annealing is performed at a temperature of 1300°C ± 50°C for 4 min - 6 min in a nitrogen gas protective atmosphere, wherein the insulating layer material includes silicon dioxide.

[0046] In the embodiment of the present invention, by ion-implanting high-concentration Si impurities, good ohmic contact between AlN and the electrode is achieved; another electrode forms a Schottky contact with AlN, and a Schottky junction detector with a faster response and without the need to apply a relatively high bias voltage compared to the MSM structure detector is constructed.

[0047] In step S140, a first electrode is sputtered at the projection position of the silicon element region on the aluminum nitride epitaxial layer.

[0048] For example, the photoresist and silicon dioxide used in step S130 are removed; a silicon dioxide insulating layer is coated, and an ohmic contact window is etched in the silicon element region by second photolithography; a titanium layer, an aluminum layer, a titanium layer, and a gold layer are sputtered in the ohmic contact window; and annealing is performed at a temperature of 900°C ± 50°C for 25 s - 30 s.

[0049] In step S150, a second electrode is sputtered at the projection position of the non-silicon element region on the aluminum nitride epitaxial layer to obtain an aluminum nitride vacuum detector.

[0050] For example, through the third photolithography, a Schottky contact electrode window is etched in the non-silicon element region on the aluminum nitride epitaxial layer; using the electron beam evaporation process, a transparent electrode nickel layer and a gold layer are sequentially evaporated on the Schottky contact electrode window; with a mixed gas of oxygen and nitrogen as the protective atmosphere, annealing is carried out at a temperature of 500 °C ± 50 °C for 4 min - 6 min; through the fourth photolithography, a metal electrode window is etched on the gold layer transparent electrode; and a titanium layer, an aluminum layer, a titanium layer, and a gold layer are sputtered on the metal electrode window.

[0051] Example 1: A preparation method of a back-illuminated AlN vacuum detector with good ohmic contact.

[0052] (1) Epitaxial wafer preparation: Using MOCVD equipment, with TMAl and NH 3 respectively as the precursors of Al and N, a 300-nm-thick AlN epitaxial layer is grown on a sapphire substrate. The epitaxial wafer is annealed in a high-temperature annealing furnace at a temperature of 900 °C for 3 min. And the sapphire substrate of the epitaxial wafer is thinned.

[0053] (2) Process preparation: After cleaning the epitaxial wafer, an insulating layer is grown and photoresist is coated. Through the first photolithography, an ion implantation window is etched. Using the ion implantation process, high-concentration Si atoms are implanted about 40 nm deep in the window, with N 2 as the protective atmosphere, annealing is carried out at a temperature of 1300 °C for 5 min.

[0054] (3) Remove the photoresist and insulating layer in step (2), re-cover the SiO 2 insulating layer, through the second photolithography, an ohmic contact window is etched in the silicon-containing region. Sputter a titanium layer, an aluminum layer, a titanium layer, and a gold layer (Ti / Al / Ti / Au) with thicknesses of 15 nm, 250 nm, 50 nm, and 150 nm respectively, and perform distributed annealing with N 2 as the protective atmosphere, one-step annealing, annealing temperature 530 °C and annealing time 300 s, two-step annealing, annealing temperature 900 °C, annealing time 30 s.

[0055] (4) Through the third photolithography, a Schottky contact electrode window is etched in the silicon-free region. Use electron beam evaporation to sequentially deposit a transparent electrode Ni and Au, both with a thickness of 10 nm. In the mixed atmosphere of O 2 and N 2 annealing is carried out at 500 °C for 5 min. Through the fourth photolithography, a metal electrode window is etched on the transparent electrode Au, and Ti / Al / Ti / Au is sputtered on the metal electrode window with thicknesses of 15 nm, 250 nm, 50 nm, and 150 nm respectively.

[0056] In the above specific embodiments, the object, technical solution and beneficial effects of the present invention have been further described in detail. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. An aluminum nitride vacuum detector, characterized in that: include: A substrate, wherein the material of the substrate is a sapphire substrate; An aluminum nitride epitaxial layer, the aluminum nitride epitaxial layer comprising a first surface and a second surface, the first surface being located on the substrate, wherein a local region of the aluminum nitride epitaxial layer comprises silicon atoms, and projections of the region comprising silicon atoms on the first surface and the second surface do not completely cover the first surface and the second surface; A first electrode is located on the second surface and is located in a projection area of ​​a region containing silicon atoms on the second surface; and The second electrode is located on the second surface and is not located in a projection area of ​​a region containing silicon atoms on the second surface.

2. The aluminum nitride vacuum detector according to claim 1, characterized in that: An ohmic contact is formed between the first electrode and the aluminum nitride epitaxial layer; and A Schottky contact is formed between the second electrode and the aluminum nitride epitaxial layer.

3. The aluminum nitride vacuum detector according to claim 1, characterized in that: The first electrode comprises a titanium layer, an aluminum layer, a titanium layer and a gold layer arranged in sequence along a direction perpendicular to the second surface; The second electrode includes a nickel layer and a gold layer with a first area arranged in sequence along a direction perpendicular to the second surface; and a titanium layer, an aluminum layer, a titanium layer and a gold layer with a second area arranged in sequence on the gold layer along a direction perpendicular to the second surface, wherein the first area is larger than the second area.

4. The aluminum nitride vacuum detector according to claim 1, characterized in that: The thickness of the aluminum nitride epitaxial layer is not greater than 300 nm.

5. The aluminum nitride vacuum detector according to claim 1, characterized in that: The thickness of the sapphire substrate enables light to enter from one side of the sapphire substrate.

6. A method for preparing an aluminum nitride vacuum detector, characterized in that: The method comprises: Preparing a sapphire substrate; growing an aluminum nitride epitaxial layer on the sapphire substrate; Implanting silicon into a local area of ​​the aluminum nitride epitaxial layer; sputtering a first electrode at a projection position of the silicon element region on the aluminum nitride epitaxial layer; and A second electrode is sputtered at a projection position of the non-silicon element region on the aluminum nitride epitaxial layer to obtain an aluminum nitride vacuum detector.

7. The preparation method according to claim 6, characterized in that: The step of growing an aluminum nitride epitaxial layer on the sapphire substrate comprises: Using metal organic chemical vapor deposition equipment, trimethylaluminum is used as an aluminum source and ammonia is used as a nitrogen source to grow an aluminum nitride epitaxial layer on a sapphire substrate; Annealing the epitaxial wafer with the epitaxial layer grown thereon at 900°C±50°C for 2min-4min; and The sapphire substrate is thinned to obtain a thinned epitaxial wafer so that light can enter from one side of the sapphire substrate. Wherein, the thickness of the aluminum nitride epitaxial layer is not greater than 300 nm.

8. The preparation method according to claim 7, characterized in that: The step of injecting silicon into a local area of ​​the aluminum nitride epitaxial layer comprises: Growing an insulating layer on the surface of one side of the aluminum nitride epitaxial layer of the thinned epitaxial wafer and coating it with photoresist; Performing a first photolithography to carve an ion implantation window on the aluminum nitride epitaxial layer; Implanting Si atoms to a preset depth in the ion implantation window using an ion implantation process; and Annealing was performed at 1300℃±50℃ for 4min-6min with nitrogen as protective atmosphere. Wherein, the insulating layer material includes silicon dioxide.

9. The preparation method according to claim 8, characterized in that: The step of sputtering the first electrode at the projection position of the silicon element region on the aluminum nitride epitaxial layer comprises: Removal of photoresist and silicon dioxide; Coating with a silicon dioxide insulating layer; Through the second photolithography, an ohmic contact window is carved in the silicon element area; sputtering a titanium layer, an aluminum layer, a titanium layer, and a gold layer on the ohmic contact window; and Anneal at 900℃±50℃ for 25s-30s.

10. The preparation method according to claim 9, characterized in that: The sputtering of the second electrode at the projection position of the non-silicon element region on the aluminum nitride epitaxial layer comprises: Carving out a Schottky contact electrode window in the non-silicon element region on the aluminum nitride epitaxial layer through a third photolithography; Using an electron beam evaporation process, sequentially evaporating a transparent electrode nickel layer and a gold layer on the Schottky contact electrode window; Anneal for 4-6 minutes at 500°C ± 50°C with a mixture of oxygen and nitrogen as the protective atmosphere; Through the fourth photolithography, a metal electrode window is engraved on the gold layer transparent electrode; and A titanium layer, an aluminum layer, a titanium layer and a gold layer are sputtered on the metal electrode window.

Images