A conductive semi-transparent solar blind photocathode underlayer

Abstract

The present invention relates to a solar blind photocathode device, comprising: a substrate, a photocathode layer disposed on the substrate, characterized by a conductive underlayer disposed between the substrate and the photocathode layer, wherein the conductive underlayer comprises a first layer of nickel (130) deposited directly on the substrate, and a second layer of aluminum oxide (140) deposited onto the first layer of nickel, wherein the second layer was obtained through natural oxidation of aluminum or direct evaporation of aluminum oxide. Aluminum oxide was configured to form an aluminum oxide interface with the photocathode layer. The conductive underlayer is arranged to provide electrical conductivity for the photocathode while maintaining high quantum efficiency in the deep ultraviolet spectrum.

Description

[0001] Title: A conductive semi-transparent solar blind photocathode underlayer.

[0002] Description:

[0003] TECHNICAL FIELD

[0004] The present invention generally relates to the field of optoelectronic devices, and more particularly to the field of solar blind photocathode devices with enhanced electrical conductivity and quantum efficiency.

[0005] BACKGROUND

[0006] The current state of the art in the field of solar blind photocathodes involves the use of multi-alkali telluride materials such as cesium telluride (CsTe) and rubidium telluride (RbTe) deposited on substrates to achieve high quantum efficiency in the deep ultraviolet spectrum. These devices typically employ conductive grid layers made from materials like chromium, which are deposited using photolithography techniques. These grid layers are crucial for providing the necessary electrical conductivity to the otherwise highly resistive photocathode materials, which can exhibit square resistance values in the Giga-ohm range.

[0007] In addition to grid structures, thin metal films, such as chromium, are also commonly used as conductive underlayers in solar blind photocathodes. In some cases, indium tin oxide (ITO) has been explored as a transparent conductive option, though it is not yet widely adopted due to its high surface resistivity. While these metal and ITO layers improve electrical conductivity, they introduce trade-offs, such as increased absorption of ultraviolet light, which reduces the overall quantum efficiency of the photocathode (see, for example, Braem et al., Nuclear Instruments and Methods in Physics Research A, 2003).

[0008] However, the use of conductive grids in solar blind photocathodes presents several significant disadvantages. Firstly, the fabrication of these grids using photolithography is both complex and costly, significantly increasing the production costs of these devices. Additionally, the grid structures can block a portion of the incoming ultraviolet light, reducing the overall quantum efficiency of the photocathode. Furthermore, the grids provide a level of conductivity that exceeds the requirements for nano-current continuous operation, representing an unnecessary technological overshoot.

[0009] A further disadvantage of the current state of the art is the relatively low quantum efficiency (QE) of the photocathodes when simpler conductive layers, such as thin metal films of nickel, are used. Although nickel films are more cost-effective compared to grid structures, they result in lower QE values. This issue is compounded by the fact that high square resistance in the photocathodes leads to voltage drops and image quality problems, such as dark zones, which are undesirable for applications requiring high-resolution detection.

[0010] It is therefore a goal of the present invention to provide a solar blind photocathode device that combines cost-effective production with enhanced quantum efficiency and sufficient electrical conductivity, thereby overcoming the above-mentioned disadvantages of the prior art at least in part.

[0011] SUMMARY

[0012] In a first aspect, there is provided a solar blind photocathode device, comprising:

[0013] a substrate;

[0014] a photocathode layer disposed on the substrate;

[0015] characterized by:

[0016] a conductive underlayer disposed between the substrate and the photocathode layer, wherein the conductive underlayer comprises:

[0017] a first layer of nickel deposited directly on the substrate; and a second layer of aluminum deposited directly on the first layer of nickel, and

[0018] wherein the conductive underlayer is arranged to provide electrical conductivity for the photocathode while maintaining high quantum efficiency in the deep ultraviolet spectrum.

[0019] In a second aspect, there is provided, a method of manufacturing a solar blind photocathode device, comprising the steps of: providing a transparent substrate; depositing a first layer of nickel directly on the substrate; depositing a second layer of aluminum directly on the first layer of nickel, wherein the second layer of aluminum has a thickness configured to naturally oxidize upon exposure to air, forming an aluminum oxide interface; depositing a multi-alkali telluride photocathode layer on the aluminum oxide interface, wherein the conductive underlayer comprising the first and second layers provides electrical conductivity for the photocathode while maintaining high quantum efficiency in the deep ultraviolet spectrum.

[0020] In a third aspect there is provided, a solar blind ultraviolet detection device, comprising:

[0021] a solar blind photocathode device, comprising:

[0022] a substrate (110);

[0023] a photocathode layer (150) disposed on the substrate;

[0024] a conductive underlayer (160) disposed between the substrate and the photocathode layer, wherein the conductive underlayer comprises:

[0025] a first layer of nickel (130) deposited directly on the substrate; and

[0026] a second layer of aluminum oxide (140) deposited directly on the first layer of nickel, and

[0027] wherein the conductive underlayer is arranged to provide electrical conductivity for the photocathode while maintaining high quantum efficiency in the deep ultraviolet spectrum; the solar blind ultraviolet detection device further comprising:

[0028] a ring electrode in electrical contact with the conductive underlayer and configured to provide external connectivity; and

[0029] wherein the device is configured for use in applications requiring selective sensitivity to ultraviolet radiation and insensitivity to visible and infrared radiation.

[0030] The solar blind ultraviolet detection device may in various examples be implemented in one or more of the following applications:

[0031] UV and solar-blind image intensifiers;

[0032] photon counting detectors and modules;

[0033] night vision and low-light imaging devices;

[0034] ultraviolet spectroscopy instruments;

[0035] radiation monitoring equipment; scientific and medical imaging cameras;

[0036] aerospace and satellite-based UV detectors;

[0037] UV detection in fire and explosion sensors;

[0038] fast-gated photocathode detectors for laser-induced fluorescence; range gated imaging devices; and

[0039] UV astronomy instruments.

[0040] One aspect of the present invention relates to a solar blind photocathode device. A solar blind photocathode device may be understood as an optoelectronic device that is designed to detect ultraviolet light while being insensitive to visible and infrared light, thus being "blind" to solar radiation.

[0041] The device comprises a substrate. A substrate may be understood as the underlying material or layer upon which other materials are deposited or constructed. In this context, the substrate provides the foundational support for the subsequent layers of the device.

[0042] The device comprises a photocathode layer disposed on the substrate. A photocathode layer may be understood as a light-sensitive material that emits electrons when exposed to light, thereby generating an electrical signal. This arrangement allows the device to convert ultraviolet light into an electrical signal, facilitating the detection of ultraviolet radiation.

[0043] The device is characterized by a conductive underlayer disposed between the substrate and the photocathode layer. This arrangement includes a first layer of nickel deposited directly on the substrate. A first layer of nickel may be understood as a thin film of nickel metal that is applied onto the substrate. The use of nickel provides a cost-effective and compatible material for the conductive underlayer, which aids in enhancing the overall conductivity of the device.

[0044] An effect of the first layer of nickel is that it offers a reasonable level of electrical conductivity while being chemically compatible with the subsequent aluminum layer. This compatibility ensures that the overall structure of the device remains stable and effective in its function.

[0045] The device further comprises a second layer of aluminum deposited directly on the first layer of nickel. A second layer of aluminum may be understood as a thin film of aluminum metal that is applied onto the layer of nickel. The thickness of this aluminum layer is configured to either naturally oxidize upon exposure to air, forming an aluminum oxide interface with the photocathode layer, or the layer may also be obtained by deposition of a pre-formed aluminum oxide layer, preferably with a thickness in the range of 20 A to 200 A, and most preferably approximately 50 A, to form an aluminum oxide interface with the photocathode layer. This arrangement provides an aluminum oxide interface that is beneficial for the growth and performance of the photocathode layer.

[0046] An effect of the second layer of aluminum is that it enhances the quantum efficiency of the photocathode layer. The natural oxidation of aluminum to form aluminum oxide creates an interface that supports the efficient operation of the photocathode by improving the device's sensitivity to ultraviolet light.

[0047] The conductive underlayer, comprising both the first layer of nickel and the second layer of aluminum, is arranged to provide electrical conductivity for the photocathode while maintaining high quantum efficiency in the deep ultraviolet spectrum. This arrangement ensures that the photocathode operates efficiently and effectively, providing reliable detection of ultraviolet light without significant loss of signal quality or efficiency.

[0048] An effect of this combined conductive underlayer is that it reduces the overall production costs and complexity compared to traditional grid-based conductive layers, while still delivering high performance. The use of a thin metal film structure provides sufficient electrical conductivity to prevent lateral voltage drops, or in other words to maintain the same electric potential over the entire surface of the photocathode, and prevent dark zones in the image, thereby enhancing the device's operational reliability and performance. This approach also facilitates a more straightforward manufacturing process, leading to improved production yields and reduced costs.

[0049] In an example, the second layer of aluminum has a thickness configured to form an aluminum oxide interface with the photocathode layer through natural oxidization upon exposure to air. This embodiment leverages the natural properties of aluminum to form a stable and effective aluminum oxide interface, simplifying the manufacturing process while ensuring high quantum efficiency in the deep ultraviolet spectrum.

[0050] In an example, the second layer comprises a pre-formed aluminum oxide layer with a thickness in the range of 20 A to 200 A, and most preferably approximately 50 A, forming an aluminum oxide interface with the photocathode layer. This embodiment provides a controlled aluminum oxide layer, which can be deposited directly onto the nickel layer, ensuring a consistent and reliable interface for the photocathode. The defined thickness range optimizes both conductivity and performance of the photocathode, making this approach particularly suitable for high-precision applications.

[0051] In an example, the photocathode layer comprises a multi-alkali telluride material selected from the group consisting of cesium telluride (CsTe), rubidium telluride (RbTe), and combinations thereof. It may be provided that a multi-alkali telluride material, such as cesium telluride or rubidium telluride, forms the photocathode layer. These materials are known for their high quantum efficiency in the deep ultraviolet spectrum, enhancing the device's sensitivity and performance in detecting ultraviolet light.

[0052] In an example, the second layer of aluminum has a thickness in the range of 10 A to 200 A, preferably in the range of 10 A to 100 A, and most preferably approximately 15 A. It may be provided that the second layer of aluminum has a thickness configured within specific ranges to ensure optimal natural oxidation and formation of an aluminum oxide interface. This feature provides an aluminum oxide layer that enhances the photocathode's efficiency by offering a stable and effective interface for electron emission.

[0053] In an example, the first layer of nickel has a thickness in the range of 5 A to 40 A, preferably in the range of 5 A to 25 A, and most preferably approximately 8 A. It may be provided that the first layer of nickel is deposited with a controlled thickness to balance conductivity and compatibility with the aluminum layer. This feature ensures adequate electrical conductivity while maintaining structural integrity and performance of the photocathode device.

[0054] In an example, the substrate is made of a material selected from the group consisting of quartz, sapphire, fused silica, magnesium fluoride, calcium fluoride or lithium fluoride. It may be provided that the substrate comprises materials like quartz, sapphire, or fused silica, which are known for their excellent transparency and stability in the ultraviolet spectrum. This feature ensures minimal light absorption and high structural integrity, enhancing the overall performance of the device. In an example, the substrate has a transparency greater than 80% in the deep ultraviolet spectrum. It may be provided that the substrate maintains a transparency of over 80% in the deep ultraviolet range. This feature allows maximum ultraviolet light to reach the photocathode layer, improving the device's sensitivity and efficiency in detecting ultraviolet radiation.

[0055] In an example, the conductive underlayer has a square resistance in the range of 1 kQ to 1 MQ, preferably in the range of 10 kQ to 100 kQ. It may be provided that the conductive underlayer has a specific range of square resistance, ensuring adequate conductivity without excessive current leakage. This feature provides optimal electrical performance, preventing lateral voltage drops and ensuring consistent image quality.

[0056] In an example, the aluminum oxide interface is formed by natural oxidation of the second layer of aluminum upon exposure to air. It may be provided that the aluminum oxide interface forms naturally when the second layer of aluminum is exposed to air. This feature simplifies the manufacturing process and ensures a reliable and effective interface for the photocathode layer.

[0057] In an example, the photocathode layer is deposited using a chemical vapor deposition process. It may be provided that the photocathode layer is deposited via a chemical vapor deposition process, which allows precise control over the thickness and uniformity of the layer. This feature ensures high-quality deposition, enhancing the performance and reliability of the photocathode device.

[0058] In an example, the conductive underlayer provides electrical conductivity for the photocathode layer to enable a fast gating option below 3 nanoseconds. It may be provided that the conductive underlayer supports fast gating options below 3 nanoseconds. This feature enables the device to operate at high speeds, which is critical for applications requiring rapid response times and high temporal resolution.

[0059] In an example, the device is configured to be used in a solar blind nongating product group for enhanced quantum efficiency and cost-effective production. It may be provided that the device is intended for use in solar blind non-gating applications, offering improved quantum efficiency and reduced production costs. This feature ensures the device is both effective and economical, making it suitable for widespread use in various ultraviolet detection applications. In an example, the device comprises a ring electrode to provide electrical conductivity for the photocathode device. A ring electrode may be understood as an electrode in the form of a ring or circular structure surrounding the device to enhance electrical conductivity across the photocathode layer or over the transparent substrate This arrangement enables uniform conductivity across the photocathode device, supporting effective operation in applications requiring stable electrical performance. An effect of this arrangement is that it allows the photocathode layer to maintain efficient electron emission without current fluctuations.

[0060] In an example, the ring electrode has a circumference that is larger than a circumference of the photocathode layer defining a flange arranged for sealing the photocathode device in a vacuum envelope. A flange may be understood as a projecting rim or edge on a component, often used to ensure secure attachment or sealing within an assembly. This arrangement provides an enhanced seal for the photocathode device, protecting the photocathode layer and maintaining an optimal vacuum environment, which is beneficial for sustaining the long-term performance and sensitivity of the photocathode. An effect of this configuration is that it preserves the high quantum efficiency of the photocathode over extended use, as it minimizes exposure to atmospheric conditions that could otherwise degrade the photocathode’s performance.

[0061] In an example of the method aspect of the present disclosure, the step of depositing the second layer of aluminum, comprises depositing the aluminum with a thickness configured to form an aluminum oxide interface with the photocathode layer through natural oxidization upon exposure to air.

[0062] In an example of the method aspect of the present disclosure, the step of depositing the second layer of aluminum, comprises deposing a pre-formed aluminum oxide layer.

[0063] In an example of the method aspect of the present disclosure, the deposited pre-formed aluminum oxide layer has a thickness in the range of 20 A to 200 A, and most preferably approximately 50 A, forming an aluminum oxide interface with the photocathode layer.

[0064] The method may further comprise a step of integrating a ring electrode into the solar blind photocathode device, for example directly onto the photocathode layer, the transparent substrate or the conductive underlayer, in order to provide electrical conductivity for the photocathode layer. This step of integrating a ring electrode may be understood as incorporating a circular conductive component that surrounds and enhances the photocathode's conductivity. An effect of this arrangement is that it ensures consistent current distribution across the photocathode layer, thereby enhancing the device's electrical performance.

[0065] According to an example of the method, the integration of the ring electrode comprises configuring it with a circumference larger than that of the photocathode layer, defining a flange arranged for sealing the photocathode device in a photocathode vacuum envelope. This flange provides a secure seal for the photocathode device within the vacuum envelope, crucial for maintaining an ideal operational environment for the photocathode layer. An effect of this sealing arrangement is that it stabilizes the photocathode’s performance by minimizing atmospheric exposure, thus ensuring sustained device efficiency and quantum performance over prolonged use.

[0066] The above mentioned and other features and advantages of the invention are illustrated in the following description with reference to the enclosed drawings which are provided by way of illustration only and which are not limitative to the present invention.

[0067] BRIEF DESCRIPTION OF THE DRAWINGS

[0068] The present disclosure will be explained in more detail below by means of examples of a device and method according to the present disclosure shown in the drawings, in which:

[0069] Fig. 1 shows a solar blind photocathode device according to an aspect of the present invention;

[0070] Fig. 2 shows method steps of manufacturing a solar blind photocathode device according to an aspect of the present invention.

[0071] DETAILED DESCRIPTION

[0072] The present invention will now be described in detail with reference to the accompanying drawings, which illustrate exemplary embodiments of the solar blind photocathode device (100) and the method of manufacturing the same. It is to be understood that these embodiments are provided by way of example only and are not intended to limit the scope of the present invention. The following detailed description should be read in conjunction with the claims and the figures.

[0073] As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items. Expressions such as “at least one of,” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list.

[0074] The terms “a substrate has a transparency greater than” a given percentage is understood to mean that the light transmittance of the substrate is greater than said percentage. This light transmittance may in particular be measured as described in European standard EN 410:2011.

[0075] The square resistance measurement is known. It may be implemented, for example, according to the method described in the international standards ASTM F390 or ASTM F76. As used herein, the terms “square resistance” and “sheet resistance” will be used with the same definition, i.e. , the square resistance is equal to the resistivity divided by a film thickness.

[0076] As the inventive concept allows for various changes and numerous embodiments, particular embodiments will be illustrated in the drawings and described in more detail in the written description. Effects, features, and a method of achieving the inventive concept will be obvious by referring to exemplary embodiments of the inventive concept with reference to the accompanying drawings. The inventive concept may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein.

[0077] In the embodiments described in the present specification, an expression utilized in the singular encompasses the expression of the plural, unless it has a clearly different meaning in the context. Also, it is to be understood that the terms such as “including,” “having,” and / or “comprising” are intended to indicate the presence of the stated features or components, and are not intended to preclude the presence or addition of one or more other features or components.

[0078] It will be understood that when a layer, region, or component is referred to as being “on” or “onto” another layer, region, or component, it may be directly or indirectly formed on the other layer, region, or component. That is, for example, intervening layer(s), region(s), or component(s) may be present.

[0079] Sizes of components in the drawings may be exaggerated for convenience of explanation. In other words, since sizes and thicknesses of components in the drawings are arbitrarily illustrated for convenience of explanation, the following embodiments of the present disclosure are not limited thereto.

[0080] Referring to Fig. 1, a schematic cross sectional view is shown of a photocathode assembly according to an embodiment of the present disclosure. Fig. 1 shows the solar blind photocathode device 100 comprises a substrate 110, a conductive underlayer 160 disposed directly on the substrate, and a photocathode layer 150 disposed on the conductive underlayer. In this embodiment, the substrate 110 is a transparent material selected from quartz, sapphire, fused silica, magnesium fluoride, calcium fluoride or lithium fluoride each of which offers excellent transparency in the deep ultraviolet (UV) spectrum, ensuring minimal light absorption and providing structural integrity. The transparency of the substrate 110 is preferably greater than 80% in the deep UV range, allowing sufficient ultraviolet light to pass through to the photocathode layer 150 to achieve high quantum efficiency. It is understood that the photocathode device according to one embodiment of the invention is a transmissionmode photocathode device.

[0081] The conductive underlayer 160, disposed between the substrate 110 and the photocathode layer 150, consists of two distinct layers. A first layer of nickel 130 is deposited directly onto the substrate 110. The thickness of the first layer of nickel 130 is carefully controlled to ensure adequate electrical conductivity while maintaining the overall transparency of the substrate. In one example, the thickness of the first nickel layer 130 is in the range of 5 A to 40 A, preferably in the range of 5 A to 25 A, and most preferably approximately 8 A. This thin nickel layer provides a cost-effective solution for enhancing conductivity while minimizing the impact on quantum efficiency.

[0082] Directly on top of the first layer of nickel 130, a second layer of aluminum 140 is deposited. The aluminum layer 140 is configured to naturally oxidize upon exposure to air, forming an aluminum oxide interface with the photocathode layer 150. This oxidation process occurs at ambient conditions and results in the formation of a stable aluminum oxide (AI2O3) layer, which is highly compatible with the multi-alkali telluride photocathode materials used in the device. The thickness of the second layer of aluminum 140 is critical to the device's performance and is controlled within a range of 10 A to 200 A, preferably in the range of 10 A to 100 A, and most preferably approximately 15 A. This thickness ensures optimal natural oxidation while preserving the device's quantum efficiency in the deep ultraviolet spectrum.

[0083] The photocathode layer 150, which is disposed on the aluminum oxide interface formed by the second layer of aluminum 140, is comprised of a multi-alkali telluride material selected from cesium telluride (CsTe), rubidium telluride (RbTe), or combinations thereof. These materials are known for their high quantum efficiency in the deep ultraviolet range, typically covering wavelengths from 200 nm to 270 nm. The multi-alkali telluride photocathode layer 150 is deposited using a chemical vapor deposition (CVD) process, which allows for precise control over the layer thickness and uniformity. The resulting photocathode layer 150 emits photoelectrons when exposed to ultraviolet light, thus enabling the device to generate an electrical signal for ultraviolet detection while remaining insensitive to visible and infrared light, ensuring solar blindness.

[0084] An effect of the combined conductive underlayer 160 is that it provides sufficient electrical conductivity for the photocathode layer 150 while maintaining high quantum efficiency. The first layer of nickel 130 contributes to the overall electrical performance, and the aluminum oxide formed by the second layer of aluminum 140 enhances the quantum efficiency by preventing undesirable alloy formation, such as the NiTe alloy, which would otherwise degrade the device's performance. This configuration offers a significant improvement over prior art solutions, such as chromium grid structures, by reducing production costs and complexity while delivering high performance.

[0085] Fig. 1, also shows a ring electrode 120, which is in electrical contact with the conductive underlayer 160 and encircling the photocathode layer 150. This ring electrode is configured to provide enhanced electrical conductivity across the photocathode device and is preferably dimensioned with a circumference larger than that of the photocathode layer 150 itself, thereby defining a flange for sealing the photocathode device within a vacuum envelope.

[0086] Referring to Fig. 2, the method 200 of manufacturing the solar blind photocathode device 100 involves a series of well-defined steps to ensure the creation of a high-performance device with enhanced quantum efficiency and adequate electrical conductivity. The method begins by providing a transparent substrate 210, such as quartz, sapphire, or fused silica. These materials are selected for their high transparency in the deep ultraviolet spectrum, which is essential for achieving high quantum efficiency in the final device. The substrate 210 is cleaned and prepared to ensure a smooth surface for the subsequent deposition of conductive layers.

[0087] In a next step 220, the method may also involve the deposition of a ring electrode onto the device, and more particularly, onto the substrate, to provide enhanced electrical conductivity for the photocathode layer. The ring electrode may comprise or be comprised of chromium, which is preferably deposited trough vapor deposition. The ring electrode is applied to encircle the photocathode layer and is preferably configured with a circumference larger than that of the photocathode layer itself, thereby defining a flange that serves as a sealing interface within a photocathode vacuum envelope. This ring electrode may be deposited using an electrically conductive material compatible with the photocathode and the underlying conductive layers, ensuring stable electrical performance across the device. The flange arrangement created by the oversized circumference of the ring electrode facilitates a secure vacuum seal around the photocathode assembly, which is essential for maintaining optimal operating conditions. This configuration not only enhances the device's structural integrity but also preserves the high quantum efficiency of the photocathode by minimizing exposure to atmospheric conditions, thus enabling reliable and long-term performance in ultraviolet detection applications.

[0088] In the next step, a first layer of nickel 230 is deposited directly onto the substrate 210 using a physical vapor deposition (PVD) process, such as sputtering or evaporation. The thickness of the nickel layer 230 is carefully controlled to fall within the range of 5 A to 40 A, with an optimal thickness of approximately 8 A. This nickel layer 230 provides the necessary electrical conductivity for the device while maintaining the substrate's transparency and preventing significant absorption of ultraviolet light.

[0089] Following the deposition of the nickel layer 230, a second layer of aluminum 240 is deposited directly onto the nickel layer using the same PVD process. The thickness of the aluminum layer 240 is controlled within the range of 10 A to 200 A, with a preferred thickness of approximately 15 A. The aluminum layer 240 is exposed to air, where it naturally oxidizes to form an aluminum oxide interface. This oxidation process enhances the photocathode's performance by providing a stable and compatible interface for the multi-alkali telluride photocathode layer 250 to be deposited in subsequent steps.

[0090] After the aluminum layer 240 has naturally oxidized, a multi-alkali telluride photocathode layer 250, composed of materials such as cesium telluride (CsTe) or rubidium telluride (RbTe), is deposited onto the aluminum oxide interface. This photocathode layer 250 is deposited using a chemical vapor deposition (CVD) process, which allows for precise control over the material composition and thickness. The resulting photocathode layer 250 is responsible for the ultraviolet light detection functionality of the device, converting incoming UV radiation into photoelectrons that generate an electrical signal.

[0091] The conductive underlayer, comprising the first nickel layer 230 and the second aluminum layer 240, provides sufficient electrical conductivity to ensure that the photocathode operates efficiently. The conductivity is carefully tuned to achieve a square resistance in the range of 1 kQ to 1 MQ, with a preferred range of 10 kQ to 100 kQ. This range ensures that the device operates without significant voltage drops or dark zones, thereby improving image quality and ensuring consistent performance in ultraviolet detection.

[0092] Accordingly, the method provides a solar blind photocathode device with enhanced quantum efficiency and electrical conductivity. The combination of a nickel / aluminum underlayer with a multi-alkali telluride photocathode layer provides a cost-effective solution to the challenges faced by existing devices, such as high production costs and suboptimal quantum efficiency. This method facilitates the production of high-performance solar blind photocathodes suitable for a wide range of ultraviolet detection applications.

[0093] The foregoing description of the embodiments of the invention has been presented for purposes of illustration and description and is not intended to be exhaustive or to limit the claimed invention to the precise form disclosed. Those of skill in the art will readily appreciate that many modifications and variations to the claimed invention are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various photocathode embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined exclusively by the following claims, and equivalents thereof.

Claims

CLAIMS1. A solar blind photocathode device (100), comprising:a substrate (110);a photocathode layer (150) disposed on the substrate; characterized by:a conductive underlayer (160) disposed between the substrate and the photocathode layer, wherein the conductive underlayer comprises:a first layer of nickel (130) deposited directly on the substrate; and a second layer of aluminum oxide (140) deposited directly on the first layer of nickel, andwherein the conductive underlayer is arranged to provide electrical conductivity for the photocathode while maintaining high quantum efficiency in the deep ultraviolet spectrum.

2. The solar blind photocathode device according to claim 1, wherein the photocathode layer comprises a multi-alkali telluride material selected from the group consisting of cesium telluride (CsTe), rubidium telluride (RbTe), and combinations thereof.

3. The solar blind photocathode device according to any of the previous claims, wherein the second layer of aluminum has a thickness in the range of 10 A to 200 A, preferably in the range of 10 A to 100 A, and most preferably approximately 15 A.

4. The solar blind photocathode device according to any of the previous claims, wherein the first layer of nickel has a thickness in the range of 5 A to 40 A, preferably in the range of 5 A to 25 A, and most preferably approximately 8 A.

5. The solar blind photocathode device according to any of the previous claims, wherein the substrate is made of a material selected from the group consisting of quartz, sapphire, and fused silica.

6. The solar blind photocathode device according to any of the previous claims, wherein the substrate has a transparency greater than 80% in the deep ultraviolet spectrum.

7. The solar blind photocathode device according to any of the previous claims, wherein the conductive underlayer has a square resistance in the range of 1 kQ to 1 MQ, preferably in the range of 10 kQ to 100 kQ.

8. The solar blind photocathode device according to any of the previous claims, wherein the aluminum oxide interface is formed by natural oxidation of the second layer of aluminum upon exposure to air.

9. The solar blind photocathode device according to any of the previous claims, wherein the photocathode layer is deposited using a chemical vapor deposition process.

10. The solar blind photocathode device according to any of the previous claims, wherein the conductive underlayer provides electrical conductivity for the photocathode layer to enable a fast gating option below 3 nanoseconds.

11. The solar blind photocathode device according to any of the previous claims, wherein the device is configured to be used in a solar blind non-gating product group for enhanced quantum efficiency and cost-effective production.

12. The solar blind photocathode device according to any of the previous claims, wherein the device comprises a ring electrode to provide electrical conductivity for the photocathode device.

13. The solar blind photocathode device according to claim 12, wherein the ring electrode has a circumference that is larger than a circumference of the photocathode layer defining a flange arranged for sealing the photocathode device in a photocathode vacuum envelope.

14. A method of manufacturing a solar blind photocathode device, comprising the steps of:providing a transparent substrate (210);depositing a first layer of nickel (230) directly on the substrate; depositing a second layer of aluminum or aluminumoxide (240) directly on the first layer of nickel,wherein the second layer of aluminum has a thickness configured to, form an aluminum oxide interface with the photocathode layer;depositing a multi-alkali telluride photocathode layer (250) on the aluminum oxide interface,wherein the conductive underlayer comprising the first and second layers provides electrical conductivity for the photocathode while maintaining high quantum efficiency in the deep ultraviolet spectrum.

15. The method of claim 14, wherein the step of depositing the second layer of aluminum, comprises depositing the aluminum with a thickness configured to form an aluminum oxide interface with the photocathode layer through natural oxidization upon exposure to air.

16. The solar blind photocathode device according to claim 14, wherein the step of depositing the second layer of aluminum, comprises deposing a pre-formed aluminum oxide layer.

17. The solar blind photocathode device according to claim 16, wherein the deposited pre-formed aluminum oxide layer has a thickness in the range of 20 A to 200 A, and most preferably approximately 50 A, forming an aluminum oxide interface with the photocathode layer.

18. The method according to any of the claims 14-17, wherein the step of depositing the first layer of nickel comprises depositing a layer with a thickness in the range of 5 A to 40 A, preferably in the range of 5 A to 25 A, and most preferably approximately 8 A.

19. The method according to any of the claims 14-18, wherein the step of depositing the second layer of aluminum comprises depositing a layer with a thickness in the range of 10 A to 200 A, preferably in the range of 10 A to 100 A, and most preferably approximately 15 A.

20. The method according to any of the claims 14-19, wherein the deposition of the nickel and aluminum layers is performed using a physical vapor deposition process.

21. The method according to any of the claims 14-20, further comprising a step of integrating a ring electrode (220) into the solar blind photocathode device to provide electrical conductivity for the photocathode layer.

22. The method according to claim 21, wherein the step of integrating the ring electrode (220) comprises configuring the ring electrode with a circumference larger than that of the photocathode layer, defining a flange arranged for sealing the photocathode device in a photocathode vacuum envelope.

23. A solar blind ultraviolet detection device, comprising:a solar blind photocathode device, comprising:a substrate (110);a photocathode layer (150) disposed on the substrate;a conductive underlayer (160) disposed between the substrate and the photocathode layer, wherein the conductive underlayer comprises:a first layer of nickel (130) deposited directly on the substrate; anda second layer of aluminum oxide (140) deposited directly on the first layer of nickel, andwherein the conductive underlayer is arranged to provide electrical conductivity for the photocathode while maintaining high quantum efficiency in the deep ultraviolet spectrum; the solar blind ultraviolet detection device further comprising:a ring electrode in electrical contact with the conductive underlayer and configured to provide external connectivity; andwherein the device is configured for use in applications requiring selective sensitivity to ultraviolet radiation and insensitivity to visible and infrared radiation.

24. The solar blind ultraviolet detection device according to claim 23, wherein the device is implemented in one or more of the following applications:UV and solar-blind image intensifiers;photon counting detectors and modules;night vision and low-light imaging devices;ultraviolet spectroscopy instruments;radiation monitoring equipment;scientific and medical imaging cameras;aerospace and satellite-based UV detectors;UV detection in fire and explosion sensors;fast-gated photocathode detectors for laser-induced fluorescence; range gated imaging devices; andUV astronomy instruments.

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