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Absorption spectra as a function of temperature for sample B, a CdO film with . Inset: absorption spectra for samples A, B, and C at 100 K.
Absorption edge energy or “optical gap” as a function of temperature for the three CdO films with different carrier concentrations. The points are the experimental data and the lines are model calculations. The optical gap decreases with temperature with Varshni parameters, and . The zero-temperature fundamental bandgap and band edge effective mass used in the model in the limit of zero carrier density are 2.31 eV and , respectively.
Schematic representation of the band structure close to the -point in CdO, illustrating the phenomena that influence the bandgap and band edge effective mass: (a) an empty conduction band at 0 K; (b) an empty conduction band undergoing a bandgap reduction due to temperature effects; and (c) the effects of conduction band filling ( ) and bandgap renormalization ( ). The former directly influences the latter with the high free electron densities leading to increased B-M shift of the band edge and larger reduction of the bandgap due to many body interactions. The resulting gap for allowed interband transitions defines the temperature-dependent optical edge, , at non-zero wavevectors.
Carrier concentration (a) and mobility (b) as a function of temperature for three CdO samples.
The fundamental direct -point bandgap variations with respect to temperature in CdO.
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