Investigation of n-ZnO/p-porous GaAs/p++-GaAs heterostructure for photodetection applications

In this work, we have investigated n-ZnO/p-porous GaAs/p(++)-GaAs heterostructure for low-cost photodetector applications. Solution-based deposition process was used to synthesize ZnO thin film on porous GaAs layer formed by anodic etching. Energy dispersive x-ray spectroscopy (EDX) was used for chemical characterization and revealed that the deposited ZnO film was oxygen rich. Scanning electron microscopy (SEM) analysis demonstrated a porous surface morphology of the ZnO film and the infiltration of a part of the deposited film inside the porous GaAs matrix. The transport mechanisms of the n-ZnO/p-porous_GaAs/p(++)-GaAs heterostructure were investigated via current-voltage (I-V) measurements in the dark at room temperature. I-V characteristic showed rectification behavior, and the maximum value of the rectification ratio is 53 at +/- 1.78 V. A series resistance R-s = 15 Omega and an ideality factor, n = 8, were obtained by using the Cheung function. The Forward I-V curve in Log-Log scales follows a power law dependence characteristic of trap-assisted space charge limited conduction. In the reverse bias voltages, we found that the thermionic emission theory in the presence of an interface layer reproduces the current-voltage characteristic. A potential barrier height of phi(B)= 580 meV and an ideality factor n = 1.06 were obtained. For more investigations, we carried out impedance spectroscopy measurements. From the Cole-Cole impedance curves of the reverse-biased device, we demonstrated the formation of two depletion regions operating in opposite directions to the applied voltage. Conductance-frequency (G-f) experimental results agree with Jonsher's law, proving that charge transport processes across device interfaces occur by jumping between localized states. The analysis of I-V characteristic under illumination demonstrates that the n-ZnO/p-porous GaAs/p(++)-GaAs device can be used for photodetection applications. The measured photocurrent reaches a value of 39 mA for an applied voltage of 1.48 V. The photocurrent spectrum showed a signal without applied voltage and confirmed the presence of an internal electric field that self-polarizes the device.