Shallow and Deep Centers in As-Grown and Annealed MgZnO/ZnO Structures with Quantum Wells

Abstract

Shallow and deep centers in ZnO(P)/MgZnO/ZnO/MgZnO/ZnO(Ga) structures grown by pulsed laser deposition on sapphire were studied before and after annealing in oxygen atmosphere at high temperatures of 850°C to 950°C. In both as-grown and annealed structures, microcathodoluminescence spectra in the near-bandgap region demonstrate a blue-shift by 0.13 eV compared with bulk ZnO films, indicating carrier confinement in the MgZnO/ZnO/MgZnO quantum well (QW). Annealing strongly decreases the concentration of shallow uncompensated donors from $10 17 cm À3 to $10 16 cm À3 and makes it possible to probe the region of the QW by capacitance-voltage (C-V) profiling. This profiling confirms charge accumulation in the QW. The dominant electron traps in the as-grown films are the well-known traps with activation energies of 0.3 eV and 0.8 eV. After annealing, the electron traps observed in the structure have activation energies of 0.14 eV, 0.33 eV, and 0.57 eV, with the Fermi level in the n-ZnO(P) pinned by the 0.14-eV traps. The annealing also introduces deep compensating defects that decrease the intensity of bandedge luminescence and produce a deep luminescence defect band at 2.2 eV. In addition, a defect vibrational band becomes visible in Raman spectra near 650 cm À1 . No conversion to p-type conductivity was detected. The results are compared with the data for the structures successfully converted to p-type, and possible reasons for the observed differences are discussed.

Deep-Level Transient Spectroscopy Studies on Four Different Zinc Oxide Morphologies

“…The trap sites created by the defects significantly influence the electrical and optical properties of a semiconductor device [46]. From the scientific literature, we commonly found an electron trap with ∼0.10 eV corresponding to the ZnO crystals [41,[47][48][49]. However, this defect level is still not fully accepted as the signature defect in ZnO.…”

Vapor-Transport Synthesis and Annealing Study of ZnxMg1–xO Nanowire Arrays for Selective, Solar-Blind UV-C Detection

“…Thus, the development of reliable techniques toward synthesizing aligned ZnO nanowires, and appreciably incorporating Mg during synthesis is of great significance. Prior work investigating ZnMgO nanostructures have been reported based on deposition methods, which have ranged from: molecular beam epitaxy, metal–organic chemical vapor deposition, , pulsed-laser deposition, hydrothermal techniques, , radio frequency magnetron cosputtering, and vapor-phase transport. ,, The vapor-phase transport technique yields highly crystalline nanostructures and is a relatively straightforward synthesis route, able to encompass equilibrium formation in one step, rather than necessitating ex situ incorporation. Additionally, understanding the changes in optical and physical properties due to postgrowth thermal treatment of ZnMgO nanowires is of importance toward tuning the cutoff wavelength for solar-blind photodetectors.…”