Controlled growth of long-wavelength SiGe/Si multiple quantum well resonant-cavity photodetectors

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Abstract
Recently, resonantly enhanced photoresponse in the > 7 micrometers range has been demonstrated for long wavelength SiGe/Si multi-quantum well infrared photodetectors using reflection from a thick buried SiO2 layer. The SiGe/Si detector structures were grown epitaxially on bond-and-etch- back silicon-on-insulator substrates, with the separation of the reflecting oxide and detector surface determining the wavelength of resonant detection. Difficulties were, however, encountered in producing the desired cavity width. In this paper we show the origin to be a thickness-dependent error in the pyrometer measurement of wafer temperature caused by interference in the cavity of radiation to which the pyrometer is sensitive. Judicious choice of substrate oxide thickness is shown to reduce the effect. In-situ real- time monitoring of epitaxial growth rate and thickness using spectroscopic ellipsometry (SE) is demonstrated to be a more flexible solution. Thickness dependent oscillations in the SE spectra allow accurate position of the MQW and end- pointing of the cavity width to give optimum resonant enhancement effect. Use of surface sensitive regions of the SE spectra also allow monitoring of the repeatability of the individual MQW periods. Detectors grown using SE exhibit superior peak responsivities within 0.1 micrometers of the design wavelength.

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