Effect of growth gas flow rate on the SiC crystal resistivity
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chnique of controlling growth gas flow rate for adjusting crystal resistivity is presented in this paper. The experimental results showed that high growth gas flow rate could affect SiC crystal resistivity remarkably. The SiC crystal resistivity would get higher and higher with increasing growth gas flow rate. The purifying effect of gas flow rate was contributing to resistivity increase at a relatively low flow rate range. As for the high gas flow rate, increase of resistivity might be explained by the well-known site competition effect. Then, one explanation for reducing nitrogen content in the crystal via increasing gas flow rate was put forward. Namely, the Si component in the gas species may more easily go through the graphite crucible at the initial stage to make the growth ambient C-rich when the gas flow rate is ;800 sccm or more and hence suppress nitrogen incorporation into carbon site to increase crystal resistivity. This result is very helpful to grow high purity high resistivity SiC ingots.
I. INTRODUCTION
The outstanding properties of silicon carbide (SiC), such as wide band gap, excellent corrosion, and oxidation resistance, make it attractive as substrate material for electronic and optoelectronic semiconductor devices1–8 and also push it to the frontiers of science due to its potential for diluted magnetic semiconductors applications.9–11 Owing to the scientists’ painstaking working all over the world, SiC bulk crystals have been successfully grown by modified Lely method (sublimation method) since this method was proposed first time in 1978.12 But how to improve the resistivity of high purity crystals still remains a key issue for the large diameter SiC bulk crystals. Generally, high purity high resistivity SiC crystals can be obtained in a growth system with a high vacuum background and a high purity sublimation source at high temperature. However, it is still hard to prepare high resistivity SiC crystals due to the limit of intrinsic growth system vacuum and system obturation extent and the normally existing impurity nitrogen adsorbed in the graphite crucible. This is not only a challenge for mechanical fabrication of growth system but also for vacuum equipments, such as mechanical pump and so on. Meanwhile, purity of the source materials also affects the quality of SiC crystals. Therefore, the growth process for satisfying the above-mentioned conditions and reducing nitrogen in the growth system should be maintained and improved. In Ref. 13, the authors suggested that the hydrogen should be added to the growth atmosphere to grow high purity SiC single crystals, which effectively reduced the a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2012.203 J. Mater. Res., Vol. 28, No. 1, Jan 14, 2013
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nitrogen incorporation. But this technique may be costing and lightly risky. On the other hand, Ying et al.14 had reported the effect of growth gas flow rate on the defects density of SiC single crystals. But the effe
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