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ION-BEAM-HYDROGENATED AMORPHOUS SILICON Y. S. Tsuo, X. J. Deng, Y. Xu, A. K. Barua , S. Asher and S. jolar Energy Research Institute, Golden, Colorado 80401 Indian Association for the Cultivation of Science, Calcutta,

K. Deb India 700032

ABSTRACT A Kaufman ion-beam source has been used to study the rehydrogenation and postdeposition hydrogenation of amorphous silicon. In the rehydrogenation study, hydrogen atoms were implanted into glow-dischargedeposited amorphous silicon materials in which the hydrogen content had been driven out by heating. In the posthydrogenation study, amorphous silicon samples with no hydrogen content detectable by infrared absorption and no photoconductivity were used as the starting material. These materials were deposited by thermal CVD, magnetron sputtering, or RF glow discharge. INTRODUCTION Most high-quality amorphous silicon hydrogen alloys (a-Si:H) are hydrogenated during deposition. For example, in the commonly used plasmaassisted chemical vapor deposition (CVD) (or glow discharge) a-Si:H deposition process [1], the main precursors in high-quality film deposition are believed to be the SiH3 radicals. Processes of silicon-network building, hydrogen incorporation, and hydrogen elimination at the growing film's surface determine the deposited film's hydrogen content and bonding configurations. Methods of introducing hydrogen into amorphous silicon (a-Si) after deposition, independent of the deposition reaction chemistry, will likely permit more control of the hydrogen content and bonding configurations. Postdeposition hydrogenation (posthydrogenation) also provides more freedom to choose the methods and conditions of the amorphous silicon deposition. For example, high-temperature deposition or annealing can be used to improve the density and adhesion of a-Si before hydrogenation, and high-deposition-rate methods can be used for the a-Si deposition. Posthydrogenation techniques can also add flexibility in the development of new a-Si:H device structures and fabrication techniques. In addition, it has been reported [2-6] that posthydrogenated a-Si:H suffers much less light-induced degradation, known as the Staebler-Wronski effect [7], than conventionally deposited a-Si:H. Studies reported in the literature on the posthydrogenation of undoped a-Si [8) have so far failed to produce a-Si:H films with photosensitivities comparable to those of conventional a-Si:H hydrogenated during deposition. The disadvantages of posthydrogenation techniques include non-uniform hydrogen depth profiles [9] and sputter-induced damages introduced during the posthydrogenation. Some possible reasons for the lack of success of posthydrogenation techniques also include insufficient hydrogenation, a poor a-Si starting material structure, and impurity contamination. The rehydrogenation process, first reported by Pankove [101, provides a means of testing the effectiveness of a posthydrogenation technique independent of the starting a-Si material structure and purity. In a rehydrogenation process, hydrogen atoms are