Electrical Behavior of Lead Telluride at Elevated Temperature

Author

Shiuan-Yuw Yang, Marquette University

Date of Award

5-1990

Document Type

Dissertation - Restricted

Degree Name

Doctor of Philosophy (PhD)

Department

Electrical and Computer Engineering

First Advisor

Martin A. Seitz

Second Advisor

Susan C. Schneider

Third Advisor

Raymond A. Fournelle

Fourth Advisor

Shrinivas G. Joshi

Fifth Advisor

Robert N. Blumenthal

Abstract

The solidus lines of PbTe have not been accurately predicted. Large uncertainties about the intrinsic carrier concentration, n_i, the state of ionization of native defects, z, and the equilibrium constant of native defects, k_s, of lead telluride at elevated temperature still exists. This research study was carried out to measure the electrical conductivity and Hall coefficient from which these intrinsic parameters (n_i, z, k_s) at high temperatures can be determined. Hence, a more accurate prediction of the solidus lines of PbTe and a better understanding of its electrical behavior at elevated temperature can be achieved. Using a direct current magnet field with a direct current passing through a p-type PbTe single crystal, grown using the Bridgman method, the electrical conductivity and Hall coefficient were measured directly from room temperature to 923°K. The Hall coefficient was also measured at specific elevated temperatures (873°K) while controlling the partial pressure of tellurium. The results of this study indicate that the intrinsic carrier concentration, n_i, measured directly at 873°K, 893°K, and 923°K was observed to increase with increasing temperature, but scatter only slightly when the tellurium partial pressure was widely varied. This agrees with the assumption that intrinsic carrier concentration is independent of composition, but strongly dependent on temperature. The equilibrium constant of native defects, k_s, was determined to be 1 ⨯ 10⁺¹⁷ cm^-3 at 873°K. At elevated temperature, 873°K, the native defects of PbTe were found to be doubly-ionized, z = 2. Therefore two intrinsic adjustable parameters become known, this can result in more accurate values of net carrier concentration on the solidus line while fitting is conducted. A good knowledge of phase diagram and defect equilibrium is important for the preparation of high quality single crystals with controlled carrier type and carrier concentration.