Diamond for Image Intensifier and Photodetection Applications

图像增强器是一种将低亮度图像增强到人眼可以看到或相机可以检测到的亮度水平的设备。像增强器由一个真空管和几个转换和倍增屏组成。一个入射光子将击中一个光敏光电阴极屏幕。光子在光电阴极中被吸收，并引起电子发射到真空中。这些电子被电场加速以增加它们的能量并将它们聚焦在多通道板（MCP）上。作为宽带隙（5.5eV）半导体金刚石提供了一系列特性，使其集成到图像增强器件中在增强器件性能方面非常有前途。例如，在适当的条件下，金刚石的表面可以显示负电子亲和力（NEA），允许实现高的二次电子产额（SEY），其中实现大于100的值。通过化学气相沉积（CVD）方法生长的金刚石还可以支持非常高的载流子迁移率并且具有高电场击穿强度。考虑到当被电子照射时在金刚石中产生电子-空穴对需要13 eV，可以实现金刚石内的电子通量的“级联增益”;如果透射的电子从NEA金刚石表面出现，则这可以导致>10的电子透射增益。金刚石也可以通过加入硼进行p型掺杂。现有的MCP技术在进入的电子撞击板的沟道区域时导致约1.9的二次电子“增益”。虽然级联在MCP的出口处导致几千的总体增益，但是这些大的值仅针对在二次生成的初始阶段中有效的电子出现。由于1.9是一个统计值，因此一些进入的电子不会导致进一步的级联，并且实际上“丢失”了，从而降低了所得图像的质量。对当前基于MCP的图像增强器的性能的另一个限制涉及由从MCP的出口出现的“热”电子引起的“聚焦”损失。正是对这些问题的考虑，沿着上述金刚石的性质，允许开发用于显著增强现有图像增强器的性能的几个想法，即：[1]金刚石前置放大器级。薄金刚石膜（显示透射电子增益），用于在光生电子进入图像增强器的MCP之前对其进行预放大。[2]金刚石涂层的MCP增强SEY（显示反射增益）的图像增强器。显示NEA的薄金刚石层，以增强MCP内每个电子碰撞的SEY。此外，用金刚石膜的“堆叠”代替图像增强器装置内的MCP，可以提供雪崩光电二极管（APD）的替代方案，用于超低光快速光电检测。如果每个膜提供约10的透射增益，则4层堆叠可以提供约10，000的增益。这将导致全新一代的光电探测器。[3]用于低光快光电探测器内的多级电子放大（传输增益）的金刚石膜叠层

An image intensifier is a device that intensifies low light-level images to light levels that can be seen with the human eye or can be detected by a camera. An image intensifier consists of a vacuum tube with several conversion and multiplication screens. An incident photon will hit a light sensitive photo-cathode screen. Photons are absorbed in the photocathode and give rise to emission of electrons into the vacuum. These electrons are accelerated by an electric field to increase their energy and focus them on the multi channel plate (MCP).As a wide band gap (5.5eV) semiconductor diamond offers a range of properties that make its integration into image intensifier devices very promising in terms of enhanced device performance. For example, under appropriate conditions the surface of diamond can display a negative electron affinity (NEA), allowing for high secondary electron yields (SEY) to be achieved, with values greater than 100 being achieved. Diamond, grown by chemical vapour deposition (CVD) methods, can also support very high carrier mobilities and has a high electric field breakdown strength. Given that it takes 13eV to create electron-hole pairs in diamond when irradiated by electrons 'cascade gain' of an electron flux within diamond can be achieved; this can lead to an electron transmission gain of >10 if the transmitted electrons emerge from an NEA diamond surface. Diamond can also be doped p-type by the inclusion of boron.Existing MCP technology leads to a secondary electron 'gain' of around 1.9 when incoming electrons impact the channel regions of the plate. Whilst cascading results in over-all gains of a few thousand at the exit of the MCP, these large values only arise for the electrons that are effective in the initial stages of secondary generation. As 1.9 is a statistical value some incoming electrons will not result in further cascade and are effectively 'lost' degrading the resultant image. It is thus desirable that gain levels are increased at the entrance to the MCP and for a short distance into the MCP.Another limitation to the performance of current MCP-based image intensifiers involves the loss of 'focus' caused by the emergence of 'hot' electrons from the exit of the MCP. It is the consideration of these issues, along with the properties of diamond described above that allows for the development of several ideas for considerably enhancing the performance of existing image intensifiers, namely:[1] A diamond pre-amplifier stage. A thin diamond membrane (displaying transmission electron gain), to pre-amplify the photo-generated electrons prior to their entry into the MCP for image intensifiers. [2] Diamond coating the MCP for enhanced SEY (displaying reflective gain) for image intensifiers. A thin diamond layer displaying NEA to enhance the SEY for each electron collision within the MCPIn addition the replacement of the MCP within an image intensifier device with a 'stack' of diamond membranes may offer an alternative to Avalanche Photodiodes (APD) for ultra-low light fast photodetection. If each membrane offers a transmission gain of ~10, then a 4-layer stack may offer a gain of some 10,000. This would lead to a completely new generation of photodetectors.[3] A diamond membrane stack for multi-stage electron amplification (transmission gain) within a low light fast photodetector