[Truncated abstract] Infrared radiation detectors find application in a wide range of military and civilian applications: for example, target identification, astronomy, atmospheric sensing and medical imaging. The greatest sensitivity, response speed, and wavelength range is offered by infrared detectors based on HgCdTe semiconductor material, the growth and characterisation of which is the subject of this thesis. Molecular Beam Epitaxy (MBE) is a versatile method of depositing layers of semiconductor material on a suitable crystalline substrate. In particular, MBE facilitates the growth of multilayer structures, thus allowing bandgap engineered devices to be realised. By modulating the bandgap within the device structure it is possible to improve the sensitivity or increase the operating temperature of photodetectors when compared to devices fabricated on single layer material. Furthermore, dual-band detectors may be fabricated using multi-layered HgCdTe material. The bulk of this thesis is concerned with the development of the MBE process for multilayer growth, from modelling of the growth process to characterisation of the material produced, and measurement of photoconductive devices fabricated on these wafers. In this thesis a previously published model of HgCdTe growth by MBE is reviewed in detail, and is applied to the growth of double layer heterostructures in order to determine the optimum method of changing the mole fraction between layers. The model has been used to predict the change in the temperature of the phase limit when the mole fraction and growth rate change suddenly as is the case during growth of an abrupt heterostructure. Two options for growth of an abrupt heterostructure were examined (a) modulating the CdTe flux and (b) modulating the Te flux. The change in the phase limit temperature between the layers was calculated as being 4:1±C for option (a) and 5:2±C for option (b) when growing a Hg(0:7)Cd(0:3)Te/Hg(0:56)Cd(0:44)Te heterostructure

Die von Gegenständen abgegebene Wärmestrahlung lässt sich mit Hilfe einer Infrarotkamera messen. Die Atmosphäre zwischen dem Gegenstand und dem Objektiv der Kamera beeinflusst die gemessene infrarote Strahlung [Becker and Li (1995)]. In diesem Artikel soll dieser Einfluss der Atmosphäre auf die langwellige Strahlung quantifiziert werden. Dabei wird die Strahlung aus dem oberen Halbraum gemessen, welche den Weg in das begrenzte Sichtfeld der Kamera findet. Die Temperaturstrahlung aus den einzelnen Winkelelementen der Atmosphäre ist abhängig von den Strahlungseigenschaften der einzelnen Luftschichten. Das verwendete Messgerät vom Typ Varioscan 3021-ST bestimmt die Strahlung im Wellenlängenbereich 8 – 14 μm. Verantwortlich für die Absorption der Strahlung ist der atmosphärische Wasserdampf in der Grenzschicht. Bei geringen Entfernungen unter einem Dekameter kann der Einfluss der Atmosphäre auf die Wärmestrahlung vernachlässigt werden. Es wird versucht die Absorptionskoeffizienten für die untere Troposphäre abzuschätzen. Es zeigt sich eine gute Übereinstimmung der Verteilung der Absorptionskoeffizienten mit der Verteilung des atmosphärischen Wasserdampfes. Nach Lozán (2005), befindet sich die Hälfte des atmosphärischen Wasserdampfes unterhalb von 1.5 km Höhe. Weiterhin sind nur 5 % oberhalb von 5 km angesiedelt und sogar nur 1 % in der Stratosphäre anzutreffen. Also lässt sich ein großer Teil des Wasserdampfes mit diesem Messgerät erfassen, wobei ein weiterer Vorteil in der einfachen Transportfähigkeit des Messgerätes zu sehen ist. / With the help of an infrared camera, one can measure the infrared radiation emitted by all bodies. However, the Earth’s atmosphere has a significant effect on the measurements of infrared radiation. In this article, the nature and quantification of these atmospheric effects will be discussed. Therefore we measure the radiation from the upper half space, which is coming to the camera during their field of view. The measurement of thermal radiation from the separate angels of the atmosphere depends on the properties of radiation in the different layers of the Earth’s atmosphere. The measurement Varioscan 3021-ST will account for all the radiation in the wavelength from 8 to 14 μm. The water vapor in the boundary layer is accountable for the absorption of this radiation. Only on small distances under about 100 m the effect of the atmosphere on the long wave radiation is untended. The coefficients of absorption can be estimated for the lower boundary layer. One can see a very good correlation with the atmospheric water vapor. By seeing Lozán (2005), approximately half of the atmospheric water vapor is located under 1.5 km height. Only 5 % are over 5 km and just 1 % is located in die stratosphere. That way a big part of the water vapor can comprise by the measurement. Another advantage is the easy way of transportability of the measurement.