OPTICAL STUDY OF NEW THERMAL DONORS IN SILICON

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1. We have measured infrared absorption at 4K of phosphorus-doped CZ Si crystals annealed at 470ﾟC for long durations. We have observed many sharp absorption peaks arising from the electronic transitions from the ground states to excited states of the shallow levels of several species of thermal donor (TD). The present work has been made to investigate the relationship between the annihilation behavior of these TD peaks and the generation behavior of new thermal donor (NTD) during the prolonged annealing and the effects of carbon on this relationship and also to discuss the mechanism of the generaton and annihilation of TD and NTD and the mechanism of their electrical activation.2. The results obtained are as follows. The same infrared absorption peaks were observed regardless of the carbon density. This means that the same TD species were formed independently of the carbon density. However, the formation of TD was suppressed by the presence of carbon. More remarkably, the annihilation of TD occurred anomalously rapidly in carbon-rich crystals, accompanying the annihilation of substitutional carbon. An important feature is the close correlation of these annihilation with the formation of NTD.3. We propose the following hypothesis. Si self-interstitials created during the oxygen aggregation process eject substitutional carbon into an interstitial site and this interstitial carbon rapidly diffuses to TD to decorate them so as to form electrically inactive clusters, which act as the embryos of NTD.In other words, oxygen atoms diffuse to these neutral embryos to grow the clusters and cause the generation of electrically active donors, NTD.