Kumar, Arunandan and Srivastava, Ritu and Tyagi, Priyanka and Mehta, D. S. and Kamalasanan, M. N.
(2011)
Effect of doping of 8-hydroxyquinolinatolithium on electron transport in tris(8-hydroxyquinolinato)aluminum.
Journal of Applied Physics, 109 (11).
114511 .
ISSN 1089-7550
Abstract
Effect of doping of 8-hydroxyquinolinatolithium (Liq) on the electron transport properties of tris(8-hydroxyquinolinato)aluminum (Alq3) has been investigated as a function of temperature and doping concentration by fabricating electron only devices. It has been observed that current density in the devices increases with the doping of Liq up to a doping concentration of 33 wt. % and then decreases. Current density-voltage (J-V) characteristics of 0, 15, and 33 wt. % Liq doped Alq3 devices were found to be bulk limited and analyzed on the basis of trap charge limited conduction model. The J-V characteristics of 50 and 100 wt. % Liq doped Alq3 devices were found to be injection limited and were analyzed using the Fowler-Nordheim model. The increase in current density with doping up to 33 wt. % was found to be due to an increase in electron mobility upon doping, whereas the decrease in current density above 33 wt. % was due to the switching of transport mechanism from bulk limited to injection limited type due to an increase in barrier height. Electron mobility and variance of energy distribution have been measured by using transient electroluminescence technique to support our analysis. Electron mobility for pure Alq3 was found to be 1 × 10−6 cm2/V s, which increased to 3 × 10−5 cm2/V s upon doping with 33 wt. % Liq. The measured values of variance were 95, 87.5, 80, 72, and 65 meV for 0, 15, 33, 50, and 100 wt. % Liq doped Alq3 respectively. The increase in electron mobility upon doping has been attributed to a decrease in energetic disorder upon doping as evidenced by the decrease in variance. The increase in barrier height for the higher doping concentration was due to the disorder related correction σ2/2kT in the barrier height, which decreases with the increase in doping concentration.
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