Generally in electrical studies of the sample like ZnO, with the increase in barrier height the conductivity decreases and thereby the bandgap increases in optical studies of the same sample. Is it not possible that with the increase in barrier height the bandgap decreases?
Dear Ghosh in semiconductor the conduction is due to the carrier concentration which completely depends on band gap. Where as in ZnO the conduction (ie dc conductivity or ac conductivity) is due to ionic conduction between energy gap ie activation energy is responsible for conduction. note: one should understand the deference between band gap and energy gap in ionic conduction.
Dear Sir Satishkumar, if you can explain in more detailed form, it will be very helpful to me.
Some wide band gap materials indeed can be conductive such as FTO, ITO and IZO, which are transparent semiconductors. In well known semiconductors like Si, GaAs the conductivity defined by amount of dopants. In metal oxide it is defined by the ratio between Zn and like ZnxO1-x.
In wide band gap semiconductors, the conductivity is determined by impurity doping (and directly related electrical compensation and mobility reduction caused by defects). For moderate doping levels, measuring the bandgap always produces the same value (the band gap is a constant at constant temperature). However, at very high doping levels when the conduction band starts to fill, optical absorption will give you a higher apparent band gap due to teh Burstein-Moss shift.
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