Role of the impurity wave function on the relaxation of photoexcited carriers in heavily doped $\chem{SiC}$

S. Dhar; S. Ghosh

doi:doi:10.1209/epl/i2002-00477-3

DOI: 10.1209/epl/i2002-00477-3

Europhys. Lett., 57 (3) , pp. 416-422 (2002)

Role of the impurity wave function on the relaxation of photoexcited carriers in heavily doped $\chem{SiC}$

S. Dhar and S. Ghosh

School of Physical Sciences, Jawaharlal Nehru University - New Delhi 110067, India

(Received 16 February 2001; accepted in final form 8 November 2001)

Abstract
Relaxation of photoexcited carriers has been investigated in heavily doped n-type $\chem{6H}$ - $\chem{SiC}$ . It has been observed that, as the photoexcitation is terminated, the photoexcited carriers decay following a simple exponential law with time constant $\tau$ . When the electron concentration in SiC is very high, such that the insulator-to-metal transition is traversed and the Fermi level lies inside the conduction band, $\tau$ increases anomalously with temperature. However, when the electron concentration is less than this critical concentration, such that the Fermi level lies inside the forbidden gap, $\tau$ becomes temperature independent and does not show anomalous behavior. This anomalous decay has been explained by an effective-mass-like model of the impurity with the wave packet centered away from the minima of the conduction band in the Brillouin zone. The enhanced lifetime of the photoexcited carriers with temperature correlates with a corresponding decrease of the recombination probability of photoexcited carriers with different region of impurity wave function in k-space. It has been shown that the impurity wave function can be determined from this temperature-dependent recombination rate of photoexcited electrons.

PACS
71.55.-i - Impurity and defect levels.
72.40.+w - Photoconduction and photovoltaic effects.
72.60.+g - Mixed conductivity and conductivity transitions.

© EDP Sciences 2002