Abstract
In monocrystalline silicon rich in oxygen, thermal donors are formed at temperatures around 450 °C. These are widely accepted to be electrically active oxygen clusters acting as double donors to the conduction band. Exposure to higher temperatures (650 °C) reportedly eliminates them. Herein, a systematic study of the spatial distribution of thermal donor formation and elimination by heat treatment at 450 and 650 °C in commercial n‐type Czochralski‐silicon wafers with high and low content of interstitial oxygen atoms are reported. Hyperspectral imaging techniques with spectral and spatial resolution are used. Thermal donors form at 450 °C in a ring‐like pattern, significantly enhanced in oxygen‐rich material. The results indicate the formation of at least six different donor clusters, leading to a strong, characteristic spectral response upon photoexcitation. The emission related to direct band‐to‐band recombination (1.100 eV) become systematically stronger upon heat treatment at 450 °C. Subsequent treatment at 650 °C rearrange the spectral response into a single, homogenously distributed, broadband emission with peak energy of 0.767 eV. The emission related to band‐to‐band recombination is significantly reduced. A previously studied emission at 0.807 eV (D1) commonly related to impurities is found, providing evidence that this signal is related to the combination of defects and oxygen.
Highlights
Thermal donor (TD) are reported to introduce donor states placed at different energy levels within the bandgap of silicon.[3]
The Czochralski (Cz) technique is commonly used in the growth cluster size, and that larger clusters form with a long annealing of monocrystalline silicon ingots
The samples were exposed to temperatures in the range of 520–700 C, and the results showed that the free electron concentration from donors was reduced in the sample with high initial TD concentration
Summary
TDs are reported to introduce donor states placed at different energy levels within the bandgap of silicon.[3]. Niewelt et al.[13] did conventional nonspectrally resolved PL imaging of as-cut p-type wafers before and after the formation of TD In both these works, the images were combined with resistivity measurements to obtain a concentration map of Oi. Our group represented by Mehl et al was the first to use and report on hyperspectral PL-imaging methods on Cz-silicon wafers.[14] This work showed that the DRL signal of 0.767 eV was distributed in a ring-like pattern and that regions showing high intensities of the P-line signal could be connected to interstitial oxygen. Hyperspectral PL imaging has been conducted on Cz-silicon wafers that have been exposed to heat treatments at 450 and 650 C with the purpose of studying the spatial distribution of the PL signals related to TDs. The treatments were performed on samples with both high and low interstitial oxygen concentration to compare them. It was expected from the literature referenced previously that the generation rate of TDs would be higher in oxygen-rich material
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