ZnTe is a promising material for a variety of optoelectronic devices such as pure green LED because of its direct band gap of 2.26 eV at room temperature. Recently, Al thermal diffusion technique is attracted attention as a potential method to fabricate pn-junction ZnTe LED at low cost. In order to fabricate LEDs with better performance, the Al concentration in the diffusion layer has to be optimized [1]. However, the diffusion properties of Al in ZnTe has been scarcely reported except for a paper which reported the diffusion coefficient of Al estimated from the diffusion depth measured by scanning electron microscope [2]. In this study, we have evaluated the depth profile of Al in the diffusion layer by secondary ion mass spectroscopy (SIMS), and analyzed the diffusion property exactly.

SIMS measurements were performed on Al-diffused ZnTe from the backside of the diffusion layer to evaluate the Al depth profile exactly. According to the Fick's second law of diffusion, the diffusion profile must obey an erfc function. However, the SIMS depth profile deviates from an erfc curve in the Al concentration range below 10¹⁸cm^-3. We employed the Boltzmann-Matano analysis to evaluate the concentration dependent diffusion coefficient of Al in ZnTe, and found that the diffusion coefficient of Al decreases at the Al concentration range below 10¹⁸cm^-3. This result indicates that a rapid decrease in Al concentration is occur at the diffusion front, yielding the steep pn-junction leading the better performance.

This study was supported by Industrial Technology Research Grant Program in 2005 from NEDO of Japan.

[1] T. Tanaka et.al, physica status solidi (b) 243 (2006) 959. [2] M. Hanafusa et.al, J. Appl. Phys. 89 (2001) 1989.

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