Hydrogen in Compound Semiconductors
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HYDROGEN IN COMPOUND SEMICONDUCTORS
N. M. JOHNSON Xerox Palo Alto Research Center, Palo Alto, CA 94304
ABSTRACT Phenomena associated with hydrogen in compound semiconductors include the formation of complexes with both dopant impurities and deep-level defects, the generation of hydrogen-related deep-level defects, and the migration of isolated hydrogen as a charged species. In addition to reviewing these phenomena, this paper describes the depletion-layer technique for determining thermal dissociation energies of hydrogen-impurity complexes and presents an updated tabulation of the parameters that have thus far been obtained from experimental studies to quantitatively describe hydrogen-dopant complexes and hydrogen migration in GaAs.
INTRODUCTION The properties of hydrogen in semiconductors are of both fundamental and technological interest. Hydrogen has the distinction of being the lightest element in the periodic table and the most abundant element in the universe. Fundamental interest in hydrogen in semiconductors relates to the first feature since hydrogen is both a highly-mobile, interstitially-migrating impurity even near room temperature and a highly chemically reactive species. While both features underlie the technological interest, the abundance of hydrogen underscores the necessity of understanding its properties in semiconductor materials, particularly in compound semiconductors. There is steadily accumulating evidence that hydrogen is a major contaminant in compound semiconductors when it is unwittingly introduced during crystal growth and device processing. Controlled introduction of hydrogen, on the other hand, offers a potentially powerful processing strategy for device fabrication. To illustrate, exploratory device studies have utilized hydrogen passivation of dopant impurities in GaAs as a deliberate processing step in the fabrication of laser diodes (1] and field-effect transistors [2]. In addition, hydrogen passivates the technologically-important deep-level defects designated as the "EL2" center in GaAs [3] and the "DX" center in AIGaAs [4]. Current research on hydrogen in compound semiconductors is directed towards obtaining information on the migration, chemical kinetics, and microscopic structure of hydrogen and its complexes. A fundamental understanding of these properties will be essential both to minimize adverse effects of hydrogen contamination and to control and optimize hydrogenation as a device-processing technique. The amount of research on hydrogen in compound semiconductors is substantial and increasing at a brisk pace, although scientific consensus has yet to be attained on many issues. Several recent review articles [5-71 and conference Mat. Res. Soc. Symp. Proc. Vol. 262. @1992 Materials Research Society
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proceedings [8-10], all or in part, have dealt with the subject. In this paper, two approaches are employed to provide an overview of the issues and achievements in the field. First, the several phenomena that have been observed with hydrogen in compound semiconductor
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