InAsNSb Dilute Nitride Materials for Mid-infrared Devices & Applications

我们的目标是在“稀氮化”半导体材料的性能上取得突破，以开发能够工作在中红外光谱范围内的新型光源和光电探测器。3-5um波长范围具有重要的技术意义，因为它用于远程气体传感、测距和夜视、用于医疗诊断的生物医学成像以及光学光谱中的灵敏检测等应用。然而，有效的、负担得起的光源和光电探测器的可获得性限制了仪器的发展，这直接由目前可用的半导体材料决定。通过在InAs(Sb)中引入少量(~1%)的N，我们已经证明了使用一种新的(稀氮化物)半导体来获得中红外是可能的，我们现在正在寻求设计它的能带结构，以便显著地增强材料的光学性质，并提高光探测和发射的量子效率。为了开发新的光电探测器，我们将利用导带对N能级与宿主InAsSb晶格的扩展态的共振相互作用的敏感性来定制光响应，并为电子加速和雪崩倍增创造一个接近理想的情况，从而产生更大的可探测信号。为了最大限度地减少导致过大噪声和暗电流的有害过程，这与探测器中的雪崩倍增和光检测竞争，我们将安排雪崩倍增仅由一种载流子类型(在我们的情况下是电子)启动。许多应用依赖于对仅由几个光子组成的非常微弱的信号的检测。传统的光电二极管灵敏度有限，特别是在需要高速检测的情况下。在光子匮乏的应用中，雪崩光电二极管(APD)可以提供一种有效的解决方案。然而，目前在中红外光谱范围内的有效雪崩倍增只能通过使用稀有的半导体合金来实现。由此产生的探测器需要冷却，因此使得基于CMT的APD对于除军事应用之外的所有应用都昂贵得令人望而却步。与现有技术相比，基于稀氮化物材料的APDS具有制造简单、噪声低、工作电压低、制造成本低和室温操作以及单极电子电离等显著优势。同样，我们将能够开发更有效的中红外光源。通过调整InAsN(Sb)量子阱中的N含量，并仔细地调整残余应变和载流子限制，我们将能够在提高光产生效率的同时击败竞争的非辐射复合过程。然后，这些新颖的量子井将形成产生光的有源区的基础，无论是在LED还是在半导体激光器中。目前中红外LED在室温下的效率较低，随着我们即将提供的改进，我们预计将按照我们的领导开发出具有显著更高直流输出功率的设备。采用我们的应变稀氮化物量子阱的中红外二极管激光器也有望表现出更低的阈值电流，并可能提供现有技术的负担得起的替代方案，特别是在3-4微米的光谱范围内。我们将生产原型光电探测器和LED，并分别用它们来演示上述雪崩行为和量子效率的提高。我们将与NPL、SELEX、CST和INSTRO的合作伙伴密切合作，验证我们的稀氮化物材料和结构，以评估在实际应用中使用的性能，并帮助确保采用我们的技术。

We aim to achieve a breakthrough in the performance of "dilute nitride" semiconductor materials to enable the development of novel light sources and photodetectors which can operate in the mid-infrared spectral range. The 3-5 um wavelength range is technologically important because it is used for applications including; remote gas sensing, range-finding and night vision, bio-medical imaging for diagnosis in healthcare and sensitive detection in optical spectroscopy. However, the development of instrumentation is limited by the availability of efficient, affordable light sources and photodetectors, which is directly determined by the semiconductor materials which are currently available. By introducing small amounts (~ 1%) of N into InAs(Sb) we have shown that it is possible to access the mid-infrared using a new (dilute nitride) semiconductor and we are now seeking to engineer its band structure in order to significantly enhance the material's optical properties and increase quantum efficiency for light detection and emission. To enable the development of new photodetectors we will exploit the sensitivity of the conduction band to the resonant interaction of the N-level with the extended states of the host InAsSb crystal lattice to tailor the photoresponse and create a near ideal situation for electron acceleration and avalanche multiplication, resulting in a much larger detectable signal. To minimise the unwanted processes causing excessive noise and dark current, which compete with the avalanche multiplication and light detection in the detector, we shall arrange for the avalanche multiplication to be initiated by only one carrier type (electrons in our case). Many applications rely on the detection of very weak signals consisting of only a few photons. Conventional photodiodes have a limited sensitivity, especially if high speed detection is needed. In applications which are "photon starved", avalanche photodiodes (APDs) can provide an effective solution. However, at present effective avalanche multiplication in the mid-infrared spectral range can only be obtained by using exotic CdHgTe (CMT) semiconductor alloys. The resulting detectors require cooling, thus making CMT-based APDs prohibitively expensive for all except military applications. Simpler fabrication, low noise, low operating voltage, inexpensive manufacturing and room temperature operation, together with monopolar electron ionisation are all significant advantages of APDs based on the dilute nitride materials compared to existing technologies. Similarly, we shall enable the development of more efficient mid-infrared light sources. By adjusting the N content within InAsN(Sb) quantum wells and carefully tailoring the residual strain and carrier confinement, we shall be able to defeat competing non-radiative recombination processes whilst simultaneously enhancing the light generation efficiency. These novel quantum wells would then form the basis of the active region from where the light is generated, either within an LED or a diode laser. Currently mid-infrared LED efficiency is low at room temperature, and with the improvements which we shall deliver; we envisage that devices with significantly higher dc output power will be developed following our lead. Mid-infrared diode lasers incorporating our strained dilute nitride quantum wells are also expected to exhibit a reduced threshold current and could offer an affordable alternative to existing technology, especially in the 3-4 um spectral range. We will produce prototype photodetectors and LEDs and use these to demonstrate the above-mentioned avalanche behaviour and quantum efficiency improvements respectively. We shall validate our dilute nitride materials and structures in close collaboration with our collaborators at NPL, SELEX, CST and INSTRO to evaluate performance for use in practical applications and help ensure uptake of our technology.