Diamond for Image Intensifier and Photodetection Applications

图像增强器是一种将微光图像增强到人眼可以看到或相机可以检测到的光线水平的设备。像增强器由一个真空管和几个转换和倍增屏组成。入射的光子将击中光敏光电阴极屏幕。光子在光电阴极中被吸收，并产生电子发射到真空中。这些电子被电场加速，以增加它们的能量，并将它们集中在多通道板(MCP)上。由于半导体金刚石具有宽禁带(5.5 eV)，因此它具有一系列特性，使其集成到像增强器器件中，在增强器件性能方面非常有希望。例如，在适当的条件下，钻石表面可以显示负电子亲和力(NEA)，从而实现高的二次电子产额(SEY)，达到大于100的值。通过化学气相沉积(CVD)方法生长的钻石也可以支持非常高的载流子迁移率，并且具有很高的电场击穿强度。考虑到当受到电子照射时，需要13 eV才能在钻石中产生电子-空穴对，因此可以实现钻石内部电子流量的“级联增益”；如果传输的电子从NEA钻石表面出来，这可以导致电子传输增益为&gt；10。金刚石还可以通过掺入硼来进行p型掺杂。现有的MCP技术在入射电子冲击平板沟道区时，可以获得约1.9的二次电子‘增益’。虽然级联导致在MCP出口处的总增益为几千，但这些大的值只出现在二次生成的初始阶段有效的电子中。由于1.9是一个统计值，一些入射电子将不会导致进一步的级联，并且有效地“丢失”了所产生的图像。因此，希望在MCP的入口处和进入MCP的短距离处增加增益电平。当前基于MCP的像增强器的性能的另一个限制涉及从MCP的出口出现的‘热’电子导致的‘焦点’的损失。正是对这些问题的考虑，以及上述钻石的特性，才能开发出几个显著提高现有图像增强器性能的想法，即：[1]钻石前置放大器级。一种薄的钻石薄膜(显示传输电子增益)，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]为增强像增强器的SEY(显示反射增益)，在MCP上涂覆金刚石。显示NEA的薄金刚石层可增强MCP内每次电子碰撞的SEY此外，将像增强器设备内的MCP替换为一层金刚石膜可提供雪崩光电二极管(APD)的替代方案，用于超弱光快速光检测。如果每个膜提供~10的传输增益，那么4层叠层可以提供大约10,000的增益。这将导致一种全新的光电探测器。[3]一种用于微光快速光电探测器中多级电子放大(传输增益)的金刚石膜堆栈

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