Ultra high detectivity single carrier multiplication InAs avalanche photodiodes for IR optical detection

在红外（IR）波长中检测非常低的光水平的能力，低到单个光子有许多应用，从依赖于单个光子检测的高度安全通信，测量生物分子识别中的非常弱的荧光，到基于激光测距的高分辨率三维成像。传统的半导体光电二极管不具备这些光子匮乏应用所需的灵敏度。因此，有必要使用具有内部放大或增益的光电二极管，称为雪崩光电二极管（apd），将信号从少数光子转换为可被外部电子器件检测到的大电流。在大多数半导体中，这种放大过程也会引入多余的噪声。然而，硅apd能够产生高增益和低过量噪声，因此已在许多应用中使用，以提供在可见波长内的单个光子的检测。这是因为，在硅中，增益主要由电子倍增过程提供，从而减少了多余的噪声。不幸的是，在过去的20年里，尽管有各种各样的建议来实现类似硅的APD，但没有任何商业IR APD具有与硅相似或更好的性能。这一令人兴奋的提案将通过开发基于InAs的新型apd来解决这一空白，InAs是一种具有独特带结构特征的半导体，可以实现高增益，并且可以忽略不计比硅低的多余噪声。该提案旨在提供具有极高性能的红外apd，能够检测波长范围为1100 nm至3000 nm的单个光子。例如，他们可以为红外应用提供低成本高性能的大幅面成像阵列，如激光雷达，这种技术可以提供出色的图像和距离测量，无创血糖传感，大气二氧化碳浓度监测以及眼睛安全的自由空间光通信。因此，我们期望我们的apd能够产生新的应用，并提供极具竞争力的IR apd。基于对InAs带结构的理解，我们的apd将被设计成只有电子会受到冲击电离，从而产生高雪崩增益，而过量噪声可以忽略不计。除了出色的增益外，我们的设备还可以在低电压下工作，使其与现成的读出电路兼容。这将为高灵敏度和经济实惠的红外相机铺平道路。为了提高开发和增益特性，我们将在GaAs衬底上生长一种新型的InAsSb apd，它比InAs衬底更大，更便宜。如果成功，将实现与商用GaAs电子产品的集成。为了推动我们的InAs apd在上述应用程序中的开发，我们将；1)优化晶体生长方法，获得低杂质、高质量的InAs材料。II)开发制造和表面钝化技术，以产生具有低泄漏电流的器件，从而提高灵敏度。III)在InAs器件中引入离子种类和进行掺杂扩散以控制电场的先驱技术，从而实现高可靠性。4)控制生长条件，如温度和原子压力，以实现在GaAs上生长InAsSb apd时低晶体缺陷的形成。这个令人兴奋的项目将由一个高技能的研究团队进行，包括英国大学（谢菲尔德，赫瑞瓦特和萨里），美国大学（弗吉尼亚）和英国公司（Selex-Galileo和Thales Optronics），他们在传感应用的研究和开发方面具有多年的经验。因此，该项目的产出之一是为研究团体提供领先的红外传感器技术，以促进新的研究，并使该行业保持在红外传感器市场的领先地位。

The ability to detect very low light level in the infrared (IR) wavelengths, down to a single photon has numerous applications ranging from enabling highly secured communication that relies on detection of a single photon, measurement of very weak fluorescence in biomolecule identification to high resolution 3 dimensional imaging based on laser ranging. Conventional semiconductor photodiodes do not have the sensitivity required for these photon-starved applications. Therefore it is necessary to use photodiodes designed with internal amplification or gain, called avalanche photodiodes (APDs), to convert the signal from a few photons to a large current that can be detected by an external electronics. In most semiconductors this amplification process also introduces excess noise. However Silicon APDs were able to produce high gain with low excess noise and therefore have been used in many applications to provide detection down to a single photon in the visible wavelengths. This is because, in Silicon the gain is provided predominantly by the electron multiplication process which reduces the excess noise. Unfortunately no commercial IR APD with performance similar to, or better than, Silicon is available despite various proposals to achieve Silicon-like APDs over the last 20 years. This exciting proposal will address this void by developing a new class of APDs based on InAs, a semiconductor with unique band structure features, to achieve high gain with negligible excess noise that is lower than that of Silicon. This proposal aims to provide IR APDs with extremely high performance, capable of detecting a single photon in the wavelength range of 1100 nm to 3000 nm. For instance they can provide low cost high performance large format imaging arrays for IR applications such as LIDAR, a technique that can provide excellent images and range measurements, non-invasive blood glucose sensing, atmospheric CO2 concentration monitoring as well as eye-safe free space optical communication. We therefore expect our APDs to generate new applications and provide highly competitive IR APDs. Based on the understanding of the InAs bandstructure, our APDs will be designed such that only electron will undergo impact ionisation to produce high avalanche gain with negligible excess noise. In addition to excellent gain, our devices can be operated at low voltage, making them compatible with off-the-shelf readout circuits. This could pave the way to a highly sensitive and affordable IR camera. To enhance the exploitation and the gain characteristics we will grow a novel InAsSb APDs on GaAs substrate which is significantly larger and cheaper than InAs substrate. This, if successful, will enable integration with commercial GaAs electronics. To propel our InAs APDs towards exploitation in the applications mentioned above we will;I) Optimise the crystal growth method to achieve high quality InAs materials with low level of impurities.II) Develop fabrication and surface passivation techniques to yield devices with low leakage current, leading to higher sensitivity.III) Pioneer techniques to implant ion species and to perform dopant diffusion to control the electric field in the InAs devices leading to high reliability.IV) Control growth conditions such as temperature and atomic pressure to achieve low crystal defect formation during the growth of InAsSb APDs on GaAs.This exciting project will be carried out by a highly skilled research team, comprising UK universities (Sheffield, Heriot-Watt and Surrey), American university (Virginia) and UK companies (Selex-Galileo and Thales Optronics) with years of experience in research and development of sensing applications. Thus, one of the outputs of the project is to provide a leading IR sensor technology to the research communities to facilitate new research and to the industry to maintain a lead in the IR sensor market.