Measurement and Mapping of Materials Parameters for Gallium Arsenide Wafers by Infrared Transmission Topography

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Polished wafers of semiinsulating (SI) undoped GaAs or of doped conducting GaAs are important for manufacture of monolithic microwave integrated circuits or of junction light emitters. For SI wafers, the EL2 defect causes the SI state, and variation in EL2 density can cause on-wafer variations in device isolation and other device properties. With conducting materials, crystalline dislocations cause dark-line defects and other recombination centers that limit carrier lifetime in fabricated lasers. High free carrier concentration leads to low series resistance ohmic contacts and is very desirable in semiconductor lasers. In the process of evaluating these materials, we have found that infrared transmission measurements can provide dense data on device-pertinent materials parameters for correlation to device parameters [1]. Our custom color maps of these materials parameters keyed to color histograms of the measurement data can provide informative presentations of very large data sets for comparison to device measurements [1,2]. For example, we discuss nondestructive neutral and total EL2 density measurements in SI GaAs [1] and nondestructive dislocation density and free carrier concentration measurements in GaAs:Si [2], both by infrared topography. When test devices can be fabricated at known positions on the materials evaluation wafer (or on a nearby wafer from the same boule), sensitive comparison of materials evaluation data to measured device performance can be achieved. We show that topographic color maps allow meaningful comparisons of the materials measurements to device measurements at different spacings.


This paper was presented at the 6th Annual Conference on Defect and Recognition and Image Processing in Semiconductors, December 3-6, 1995 in Boulder, CO.

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