High-purity gallium analysis by inductively coupled plasma mass spectrometry
Abstract
The mobility of Two-dimensional Electron Gas in AlGaAs/GaAs heterostructures that are grown in the Molecular Beam Epitaxy (MBE) can be increased by purification of the gallium used to grow the films. To attain 200 million cm2/Vs mobility, the impurity concentration of gallium should be reduced to below 1 ppb. The commercial 7N (99.99999%) gallium with 100 ppb total impurity is currently used in the MBE at Purdue University and is being purified by zone refining. To evaluate the commercial 7N gallium and establish the methodology for the impurity measurement after zone refining, germanium, iron, and zinc in 6N and 7N gallium were measured by Inductively Coupled Plasma Mass Spectrometry (ICP-MS). The germanium concentration was 4.4 ppb in 6N gallium and 690 ppb in 7N gallium, which exceeds the total nominal impurity concentration, but is similar to independent analysis by Glow Discharge Mass Spectrometry (GDMS) which gave 440 ppb germanium. The measured concentrations of iron and zinc were below the detection limit of 1 ppb because of the spectral interference and the matrix effect due to high relative concentration of gallium. In order to reduce the gallium concentration in the sample, an organic solvent extraction process and ICP-MS parameter optimization are proposed.
Degree
M.S.M.S.E.
Advisors
Trumble, Purdue University.
Subject Area
Organic chemistry|Materials science
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