| Abstrakt: |
Epitaxial HgCdTe HgCdTe grown by molecular-beam epitaxy (MBE) molecular-beam epitaxy (MBE) is the material of choice for advanced infrared (IR) detection and imaging devices. Its bandgap is easily tunable over the entire IR range with only very small changes in lattice constant, offering the possibility of multilayer device structures and thus an unlimited choice of device designs, and it yields devices with quantum efficiencies as high as 0.99. Despite a number of unresolved challenges in achieving its ultimate promise for industrial application, the great achievements in the MBE growth of HgCdTe are made evident by its routine use in the industrial manufacture of focal-plane arrays (FPAs). focal-plane array (FPA) MBE growth can be continuously monitored in situ by reflection high-energy electron diffraction, spectroscopic ellipsometry (SE), and other characterization tools, providing instantaneous feedback on the influence of growth conditions on film structure. This allows the growth of a large range of unique structures such as superlattices (SLs), quantum well devices, lasers, and advanced design devices such as multicolor and high-operating-temperature IR sensors and focal-plane arrays. This chapter considers the theory and practice of MBE growth of HgCdTe and HgTe/CdTe superlattices and the use of HgCdTe in IR devices, emphasizing such incompletely resolved issues as the choice and preparation of substrates, dislocation reduction, p-doping, and the uses of SE. The theory of MBE growth is summarized briefly in Sect. 32.2, followed by a lengthy discussion of substrate-related issues in Sect. 32.3, including a summary of the relative merits and demerits of different substrate materials. The growth hardware is discussed very briefly in Sect. 32.4, followed by a discussion of the in situ characterization tools used for monitoring and control of the growth in Sect. 32.5 and of the growth procedure for HgCdTe in Sect. 32.6. A discussion of the doping of HgCdTe, including the serious issues still surrounding p-type doping, is given in Sect. 32.7. The properties achievable in MBE-grown HgCdTe are summarized in Sect. 32.8, with emphasis on the types of defects common in MBE-grown material, their effects on device performance, and possible methods to reduce the present defect densities. The use of MBE-grown HgTe/CdTe SLs for IR absorbers in lieu of HgCdTe alloy material is considered in Sect. 32.9. Finally, a brief discussion of the devices enabled by the MBE growth of HgCdTe and of their fabrication is given in Sects. 32.10 and 32.11, and a brief concluding summary of the chapter is given in Sect. 32.12. [ABSTRACT FROM AUTHOR] |
