Noncontact electrical characterization of epitaxial HgCdTe

Abstract

It is important to be able to nondestructively characterize (‘‘screen’’) the electrical properties of those areas of HgCdTe epitaxial material that will later be made into devices. This paper compares several noncontact techniques for measuring resistivity, carrier concentration, and mobility with the standard Hall-effect technique. The noncontact techniques examined are far-infrared reflection, Raman scattering, eddy–current absorption, and electroreflectance. Of these techniques, far-infrared reflection was found to be the best noncontact technique for measuring resistivity, carrier concentration, and mobility. Resistivity values were within a factor of 2 of Hall-effect values, while carrier concentration and mobility values that depend on an assumed effective mass were within a factor of 3. In Raman scattering, interference between the free-carrier plasmon–phonon mode and other modes makes it an inaccurate method for estimating carrier concentration. Eddy–current absorption is useful for quickly measuring epitaxial layer resistivities to within a factor of 3 of Hall-effect values, while electroreflectance gives a relative value for the surface doping density, which is useful in layer profiling.

Raman spectroscopic study of HgCdTe epilayers for infrared detector array fabrication

“…Polishing process is adopted to prepare high quality HgCdTe epilayer surface prior to the fabrication of detector arrays and monitored by suitable non-contact, non-destructive and fast characterization tools in the production environment [1]. Spectroscopic techniques like ellipsometry, photoluminescence, and electrolyte Electro-reflectance used for this purpose are generally functions of the electronic states of the solid [2][3][4][5]. These measurements can be complimented by spatial mapping using micro-Raman spectroscopy to reveal the undesirable surface features which are likely to yield bad pixel clusters.…”

Optical vibration modes in Hg1-xZnxTe solid solutions near q=0

“…Reflectivity measurements in the far infrared are not sensitive to surface defects and have been used to investigate vibrations modes of low wave vector. The knowledge of the dielectric function is important to use infrared reflectivity to characterize the free carriers when their concentration is high enough to give a measurable contribution [10]. First results for materials of low Zn composition (x 0.3) have already been presented [11].…”