The deviation of ideality factor from ideal value is because of the presence of large number of trapping states . Higher value is commonly observed in the heterostructures of two different materials having large lattice mismatch.
See Ref: A. Gokarna, N. R. Pavaskar, S. D. Sathaye, V. Ganesan and S. V. Bhoraskar, Journal of Applied Physics 92, 2118-2124 (2002).
A large ideality factor (n >> 1) indicates that the forward biased Schottky-barrier diode current is smaller compared to that predicted by the so-called thermionic emission or over-the-barrier emission of charge carriers. It is correct that a large trap concentration will lead to a large n. The paper cited by Kamran Rasool reports that, but it does not show the temperature dependence of n which is the question here.
An apparent large value of n at low temperature can occur due to ignoring of the voltage drop across the series resistance of a diode. The series resistance increases with decrease in temperature as the resistivity of the undepleted semiconductor material in the diode increases with decrease in temperature.
Emission and capture of electrons by traps in semiconductors fall exponentially with temperature; so the diode current is decreasingly limited by traps at lower temperatures. Hence a high value of n at lower temperatures should not be caused by a large interface trap concentration.
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