Apparatus for accurate measurement of the optical and electronic properties of narrow bandgap semiconductors

吸收或发射波长在1.25至25微米范围内的中红外光的材料对于许多应用变得越来越重要。 许多生物分子和化学物质的主要吸收在这个范围内，光学方法可以用于以灵敏和选择性的方式检测它们。 该波长范围内的特征温度为160至3200 K，因此这些材料非常适合在室温（300 K）下进行热成像，以及使用热光伏器件（~ 1500 K）捕获工业过程中的废热。 更高效率的太阳能电池也可以通过捕获该范围内的红外辐射来制造。 用于此目的的重要材料是III-V族和II-VI族化合物半导体，其中一些具有窄的能隙和相应的长波长灵敏度。 许多化合物半导体材料可以以非常受控的方式生长，一次一个原子层，以产生高质量的单晶层。 它们的成分可以在生长过程中改变，以制造复杂的多层结构，这些结构可以进一步加工，以制造激光器，探测器和光伏器件。 我们正在开发在硅等衬底上生长此类材料的新方法，以降低成本，并促进其与通常使用硅制造的电子和光学器件的集成。 为了进一步发展，能够准确地表征生长的材料以确定它们的能隙和光学性质是至关重要的。 这对于该光谱范围内的半导体来说尤其具有挑战性，因为来自环境热源的强背景以及空气及其成分的吸收。 基于荧光的光学和差分技术用于测量小的特征，同时消除内在和外在的背景效应，以高精度和分辨率测量该光谱范围内的能隙。 这些方法基于傅里叶变换光谱学，其以最有效的方式使用所有捕获的光来确定能谱。 这些方法最近才在长波长上得到证实，该系统将是加拿大的第一个此类系统。

Materials that absorb or emit light in the mid-infrared, with wavelengths in the range of 1.25 to 25 microns, are becoming increasingly important for a number of applications.  The primary absorption of many biomolecular and chemical species is in this range and optical methods can be used to detect them in a sensitive and selective way.  The characteristic temperatures in this wavelength range are 160 to 3200K and so these materials are ideal for thermal imaging at room temperature (300K) and for capturing waste heat from industrial processes using thermophotovoltaic devices (~1500K).  Higher efficiency solar cells can be made by also capturing infrared radiation in this range.  Important materials for this purpose are III-V and II-VI compound semiconductors, some of which have narrow energy gaps and correspondingly long wavelength sensitivity.  Many compound semiconductor materials can be grown in a very controlled way, one atomic layer at a time, to produce high quality single crystal layers.  Their composition can be altered during the growth process to make complex multi-layer structures that can be further processed to make lasers, detectors and photovoltaic devices.  We are developing new methods for growing such materials on substrates such as Silicon to reduce cost and to facilitate their integration with electronic and optical devices that are already commonly made using Silicon.  To further this development, it is crucial to be able to accurately characterize the grown materials to determine their energy gaps and optical properties.  This is particularly challenging for semiconductors in this spectral range because of the strong background from ambient thermal sources and absorption by air and its constituents.  Vacuum-based optics and differential techniques are used to measure small signatures, while eliminating intrinsic and extrinsic background effects, to measure the energy gaps in this spectral range with high accuracy and resolution.  These methods are based on Fourier transform spectroscopy which uses all of the captured light in the most efficient manner to determine an energy spectrum.  These methods have only been demonstrated very recently at long wavelengths and this system will be the first of its kind in Canada.