Deep-level transient spectroscopy analysis of interface defects in Ce:ZnO/p-Si heterostructures

This study reports the investigation of the effect of cerium (Ce) dopant concentration on defect levels in Ce-doped ZnO/p-type Si (p-Si) heterojunctions (HJs) by deep-level transient spectroscopy (DLTS). Undoped ZnO (uZnO) and Ce-doped ZnO (Ce:ZnO) were synthesized at different molar ratios using the sol-gel method, and n-Ce:ZnO/p-Si heterojunctions were fabricated on p-Si via spin coating. According to energy dispersive x-ray spectroscopy (EDS) data, no foreign atoms are present in the synthesized nanoparticles. A critical observation is that the oxygen content increases with Ce doping. Scanning electron microscopy (SEM) images revealed uniform spherical grains, with a decrease in grain size as Ce dopant concentration increased. X-ray diffraction (XRD) confirmed a hexagonal wurtzite crystal structure for all nanostructures. I-V measurements documented that the structures have a good rectifying behavior and that the structure exhibiting the best diode character is the Ce:ZnO/p-Si heterostructure containing 2 mol% Ce with an ideality factor of 3.36. DLTS revealed that Ce doping deepened defect levels below the conduction band edge (Ec), with trap level positions calculated as Ec - 0.079, Ec - 0.311, Ec - 0.290, and Ec - 0.386 eV for undoped, 1, 2, and 5 mol% Ce-doped ZnO/p-Si, respectively. The trap concentration decreases with the addition of Ce into the ZnO lattice. The study underlines the tunability of the electrical properties of ZnO/p-Si HJs through Ce doping and the optimizability of their efficiency.