Effect of grain boundaries on carrier lifetime in chemical-vapor-deposited diamond film

• Published in: Applied physics letters 2000-09, Vol.77 (10), p.1425-1427
• Main Authors: Yoneda, Hitoki, Tokuyama, Kazutatsu, Yamazaki, Riichi, Ueda, Ken-ichi, Yamamoto, Hironori, Baba, Kazuhiro
• Format: Article
• Language: English
• ISSN: 0003-6951; 1077-3118
• DOI: 10.1063/1.1308054

Using the reflective measurements, the effect of grain boundaries on the lifetime of photogenerated carriers was investigated for chemical-vapor-deposited (CVD) diamond films. To investigate the effect of grain boundaries on the carrier dynamics, photons having energy lower than the band gap energy of a single crystal of diamond were used for pumping. For a 4.8 eV photon, the measured lifetime was several tens of picoseconds, and that was consistent with photoconductive current measurements. However, a dramatic decrease of the carrier lifetime was observed in the case of 3.2 eV irradiation. The variation of the lifetime inside the single grain was measured by a microscopic pump–probe method. The carrier lifetime near the grain boundary decreased from 5 to 8 ps at the center to 0.35–0.5 ps. This decreased lifetime and the carrier generation efficiency with lower energy photon had a negative correlation. To explain this mechanism, we considered the decrease in lifetime to be related to the density of the imperfection or mid-band gap states inside the single-CVD-polycrystalline grain.