REPORT FOR ANALYTICAL CHEMISTS
ELECTRICAL MEASUREMENTS FOR PURE MATERIALS ANALYSES By
LEONARD R. WEISBERG RCA Laboratories,
Princeton,
Leonard Weisberg was born in 1929 in New York City. He received his B.A. degree from Clark University in 1950, Magna Cum Laude, with Honors in Physics, and he was awarded a Ph.D. by Columbia University. From 1953 to 1955, he was a part-time research assistant at the IBM Watson Laboratory in New York, working on the preparations and properties of germanium. Since 1955, he has been with RCA Laboratories, and has specialized in materials research on GaAs and other lll-V compound semiconductors. He is author of 30 publications, and has delivered many invited papers. He is now a member of the Electronic Materials Committee of the AIME, and is also a member of Sigma Xi and the American Physical Society.
New Jersey
\ CONTINUALLY increasing prob•£*- lern for the analytical chemist is the detection of impurities in ultra-pure materials. The need for detection of impurities in a range as low as a part-per-billion is no longer uncommon. However, there arc four techniques of electrical measurements that have great advantages for the analyses of such high purity materials: conductivity and Hall effect (for semiconductors), residual resistivity (for metals), and thermally stimulated currents (for insulators). In this Report, the fundamentals and applications of these four techniques are presented in an introductory fashion. This paper is based on the author's chapter "Non-Specific Methods for Analysis of Solids" in the recently published book Trace Analysis: Physical Methods, George H. Morrison, Ed. (John Wiley, New York, 1965), and further details of these methods can be found there. The advantages and disadvantages of these four methods are listed in Table I. The advantages are quite remarkable—they include almost every feature desirable for analysis. Unfortunately, their Achilles' heel is that they are all non-specific, and this, in turn, leads to the three other disadvantages shown, since the effects of different impurities arc all mixed together. In some applications, this is not crucial, as, for example, in monitoring the steps in the purification of a material, or in establishing the VOL. 38, N O . 1 , JANUARY 1 9 6 6
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REPORT FOR ANALYTICAL CHEMISTS general impurity level of an ultra high purity material. These methods have been used primarily with inorganic solids, al though inorganic liquids are not excluded. We will first discuss the fundamentals of the four methods, and then consider the a p p a r a t u s for, and applications of, each method in turn. The simplicity of both the apparatus and interpretation is a significant feature of these methods.
TABLE I—Advantages and Disadvantages of the Four Electrical Measurement of Techniques Disadvantages No identification of impurities (non specific) Detects only dominant impurities Determines only minimum impurity concentrations. No determination of absolute concentrations
Advantages Very high sensitivity (to 1 ppb) High speed (10 to 100 minutes) High relative precision (10%) Non-destructive Inexpensive apparatus (
