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称为价带，而最低的未被填满的能带是导带。导电带和价带之间的能量差称为带隙。当来自价带的电子被吸收能量等于或大于带隙的光而激发到导带时，电荷的变化就会引起电流。因此，带隙是半导体光电探测器设计中最重要的参数。虽然可见波长的光电探测器广泛使用，但红外波长的探测器明显不太成熟，而且更昂贵。目前可用的带隙选择有限，阻碍了红外探测器的发展。在这项工作中，我们将引入一种新的方法，通过将铋（Bi）原子结合到现有的半导体中，如InAs和InGaAs，来实现宽范围的带隙能量，从而在相应的宽波长范围内检测红外信号。实现这一目标将导致一系列新的红外探测器，这些探测器可以对应用产生变革性影响，包括夜视成像，医疗诊断传感器，环境监视器以及制造过程中的精确温度测量。我们还将利用铋合金在雪崩光电二极管（apd）中设计无噪声电荷放大过程。当一个电子离开价带时，就会产生一个空穴。因此，一个电子和一个空穴就形成了半导体中的一对电荷。导电带和价带的性质将决定电子和空穴如何从外加电场获得能量。在诸如InAs之类的材料中，当施加电压时，电子以更快的速率获得能量，并且以更高的速度运动。因此，InAs是高速电子器件的优良材料，也可用于在apd中提供内部信号放大。当设计得当时，InAs APD中的高能电子确保放大过程（称为冲击电离）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Bi加入到InAs中以改变价带，这样只有电子将从电场中获得显著的能量。这种抑制高能空穴的能力将使我们能够在广泛的电场范围内设计非常高增益的APD，同时抑制与冲击电离相关的噪声。通过仔细控制Ga和Bi原子的比例，我们还将开发一系列适合探测大范围红外波长的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精心组建的团队与廷德尔国家研究所以及LAND仪器，激光组件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带结构的模型将被开发出来，以便我们可以使用它们来设计高性能红外探测器和apd。这些新设计的设备将与我们的工业合作伙伴一起评估其应用范围，从制造中的温度测量到利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.