Effects of Hydrogen Radical Annealing on Electrical Properties of Amorphous Silicon
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EFFECTS OF HYDROGEN RADICAL ANNEALING ON ELECTRICAL PROPERTIES OF AMORPHOUS SILICON JIN JANG, TAE GONKIM, SONG OK KOH. HYONKYUNSONG, KYUCHANG PARK, MOONHYUNCHUNG,AND SUNG CHUL KIM, Dept. of Physics and Research Institute for Basic Sciences, Kyung Hee University, Dongdaemoon-ku, Seoul 130-701, Korea; JUNG HEA KWONANDJUN DONGKIM, Daewoo Electronics Co Ltd., Inchon, Korea
ABSTRACT We studied the layer by layer deposition technique of a-Si:H film, where the hydrogen radicals are exposed between the deposition of each layer. The effects of each layer thickness and hydrogen radical exposure time on the electrical and optical properties were studied. With the decrease of the each layer thickness, more hydrogen is involved in the network if the structure is still amorphous, but the hydrogen content is very small for microcrystal Si formed by long exposure to hydrogen radicals in between the depositions of thin layers.
INTRODUCTION There has been much work on the improvement of the quality of intrinsic amorphous silicon in order to apply this material to the fabrication of solar cells, thin film transistors and so on. But no big improvement has been obtained in spin density and in reducing the optical band gap without degrading the quality of material. Recently, Shimizu group[l-4] demonstrates that the layer by layer deposition technique, where hydrogen radicals are exposed in between the depositions of each layer, gives rise to the decrease in optical band gap. Shimizu group reports that the in hydrogen content as well as hydrogen content and the optical gap decrease with increasing the substrate temperature and hydrogen radical exposure time, without changing the structure into microcrystal. However, Asano[5] reports that the microstructure of the layer by layer deposited film changes into microcrystal with increasing hydrogen radical exposure time. There are many parameters affecting the structural, electrical, and optical properties of a-Si:H films deposited by layer by layer technique such as deposition time, hydrogen of deposition and hydrogen radical annealing(HRA). radical exposure time, powers substrate temperature and so on. In the present work, we varied the thickness of- each layer, HRA time and the substrate temperature. We used a remote plasma technique for the deposition and the HRA.
EXPERIMENTAL We used a remote plasma CVD technique, where plasma generating region is connected upstream of a remote deposition chamber. The base pressure of the reaction chamber is less than 2 x 10-7 torr. pumped by turbomolecular pump. 20 X silane in hydrogen is introduced While helium passes through the plasma generating region, into the downstream reactor. inside of the cylindrical quartz tube of diameter 3.8 cm, some of them are excited to metastable state. The substrate temperature was varied over a range of 250 - 3300C. and the rf power was applied to the induction coil, turned on the outside of the cylindrical quartz tube. Films of about 0.3 /um in thickness were deposited on both Corning 7059 glass Mat. Res. Soc. Symp
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