Realising a solid state photomultiplier and infrared detectors through bismide containing semiconductors

半导体通常用于成像传感器和太阳能电池，因为它们可以直接将光转换为电流。被完全占据的电子能量的最高带被称为价带，而最低的未填充能带是导带。导带和价带之间的能量差称为带隙。当来自价带的电子通过吸收能量等于或大于带隙的光而被激发到导带中时，电荷的变化引起电流。因此，带隙是半导体光电探测器设计中最重要的参数。虽然可见光波长光电探测器是广泛可用的，但红外波长的探测器明显不太成熟且更昂贵。红外探测器的发展一直受到当前有限的带隙选择的阻碍。在这项工作中，我们将介绍一种新的方法，通过将铋（Bi）原子到现有的半导体，如InAs和InGaAs，实现宽范围的带隙能量，以检测在相应的宽波长范围内的红外信号。实现这一目标将产生一系列新的红外探测器，这些探测器可以对夜视成像、医疗诊断传感器、环境监测器等应用产生变革性影响，并用于制造过程中的精确温度测量。 我们还将利用Bi合金在称为雪崩光电二极管（APD）的光电二极管中设计无噪声电荷放大过程。当一个电子离开价带时，就会产生一个空态（空穴）。因此，在半导体中，电子和空穴作为一对电荷产生。导带和价带的性质将决定电子和空穴如何从外加电场中获得能量。在InAs等材料中，当施加电压时，电子以更快的速率获得能量，并且也以更高的速度行进。因此，InAs是用于高速电子器件以及用于在APD中提供内部信号放大的优良材料。如果设计得当，InAs APD中的高能电子可确保放大过程（称为碰撞电离）是相干的，因此产生的放大噪声可以忽略不计。在这项工作中，我们将把铋到砷化铟改变价带，使只有电子将获得显着的能量从电场。这种抑制高能空穴的能力将使我们能够在宽范围的电场中设计非常高增益的APD，同时抑制与碰撞电离相关的噪声。通过仔细控制Ga和Bi原子的分数，我们还将开发一系列适用于检测宽范围红外波长的InGaAsBi APD。 拟议的研究将引入一类新的含Bi红外探测器和APD，将由来自谢菲尔德大学和萨里大学的世界领先研究人员组成的精心组建的团队与廷德尔国家研究所以及来自LAND Instruments，Laser Components和英国量子技术中心的合作伙伴合作进行增强量子成像。我们的工作将从制定生长条件（如温度和原子通量）开始，以获得高质量的InGaAsBi晶体。在密集的晶体生长计划之后，我们将开发将生长的InGaAsBi半导体制造成器件的程序，用于广泛的测量以提取关键材料参数。一个准确描述InGaAsBi能带结构的模型将被开发，以便我们可以使用它们来设计高性能的红外探测器和APD。这些新设计的器件将与我们的工业合作伙伴一起进行评估，从制造中的温度测量到使用光的量子特性的新型成像技术。

Semiconductors are commonly used in imaging sensors and solar cells, as they can directly convert light into an electrical current. The highest band of electron energies that are fully occupied is known as the valence band while the lowest unfilled energy band is the conduction band. The energy difference between the conduction and valence bands is known as the bandgap. When electrons from the valence band are excited into the conduction band by absorbing light with energy equals to or greater than the bandgap, the change of charges induces an electrical current. Consequently the bandgap is the most important parameter in the design of semiconductor photodetectors. While visible wavelength photodetectors are widely available, detectors for infrared wavelengths are significantly less mature and more costly. Progress in infrared detectors has been hindered by the limited choice of bandgaps currently available. In this work we will introduce a novel approach, by incorporating Bismuth (Bi) atoms into existing semiconductors such as InAs and InGaAs, to achieve a wide range of bandgap energies to detect infrared signals across a correspondingly wide wavelength range. Achieving this will lead to a new range of infrared detectors that can have transformative impact on applications including night vision imaging, medical diagnostic sensors, environmental monitors and for accurate temperature measurements in manufacturing processes. We will also exploit Bi-alloys to engineer a noiseless charge amplification process in photodiodes known as avalanche photodiodes (APDs). When an electron leaves the valence band a vacant state (a hole) is created. Therefore an electron and a hole are created as a pair of charges in semiconductors. Properties of the conduction and valence bands will determine how electrons and holes gain energy from an applied electric field. In materials such as InAs, electrons gain energy at a much faster rate and travel at higher velocity too, when a voltage is applied. Therefore InAs is an excellent material for high speed electronic devices and also for providing internal signal amplification in APDs. When designed appropriately, the energetic electrons in InAs APD ensure that the amplification process, known as impact ionisation, is coherent so that negligible amplification noise is generated. In this work we will incorporate Bi into InAs to alter the valence band such that only electrons will gain significant energy from the electric field. This ability to suppress energetic holes will allow us to design very high gain APD across a wide range of electric field while concomitantly suppressing the noise associated with impact ionisation. By carefully controlling the fraction of Ga and Bi atoms, we will also develop a range of InGaAsBi APDs suitable for detecting a wide range of infrared wavelengths. The proposed research to introduce a new class of Bi-containing infrared detectors and APDs, will be carried out by a carefully assembled team of world leading researchers from Universities of Sheffield and Surrey, in collaboration with the Tyndall National Institute, as well as partners from LAND Instruments, Laser Components and the UK Quantum Technology Hubs in Enhanced Quantum Imaging. Our work will start with a focus on formulating growth conditions (such as temperature and atomic fluxes) to obtain high quality InGaAsBi crystals. Following an intensive crystal growth programme, we will develop procedures to fabricate the grown InGaAsBi semiconductors into devices for a wide range of measurements to extract key material parameters. A model that accurately describes the bandstructure of InGaAsBi will be developed so that we can use them to design high performance infrared detectors and APDs. These newly engineered devices will be evaluated with our industrial partners for applications ranging from temperature measurements in manufacturing to novel imaging techniques using quantum properties of light.