Conduction mechanism of an infrared emitting diode: impedance spectroscopy and current–voltage analysis

The bias dependent complex impedance spectra of a conventional GaAs based infrared emitting diode have been studied in the temperature range 150–300 K. It is found that for bias voltages lower than 0.7 V, the device behaves like a pure capacitor. However for $V_{\mathrm{dc}}\ge$ 0.7 V, an equivalent circuit model composed of a parallel resistor $(R_p)$ and capacitor $(C_p)$ network connected with a series resistance $(R_s)$ can be used to describe the individual impedance contributions from interfacial and bulk regions of the diode. Fitting of experimental data to the proposed ac model reveal that the value of parallel device capacitance $C_p$ increases with temperature whereas the parallel resistance $R_p$ component decreases. The tendency of parallel resistance and parallel capacitance as a function of temperature is expected that thermally activated current transport mechanism dominates in the forward bias, which coincides with the analysing results of the dark forward current-voltage (I–V) characteristics. The temperature dependent I–V variations suggest that recombination in the depletion region has a paramount role.