Diode characteristics of ZnO/ZnMgO nanowire p-n junctions grown on Si by molecular beam epitaxy

Abstract

In this paper we focus on fundamental studies of ZnO/ZnMgO nanowire p-n junctions grown by MBE on Si substrate for UV light emitting sources. A lot of attention is paid on investigation of defects responsible for optical emission form the nanowires. Electro-optical properties of the diodes as well as deep level traps have been studied by means of photoluminescence (PL) and deep level transient spectroscopy (DLTS). To perform electrical measurements of the aforementioned nanowire structures p-n junctions of n-ZnMgO/p-Si were fabricated and their quality has been verified in measurements of I-V and C-V characteristics. PL experiments were conducted in the near- UV and visible spectral range. They provided information on the excitonic transitions associated with quantum wells (QWs). Moreover, a broad emission peak located at ~ 2.3 eV (~540 nm) assigned to deep-level-emission (DLE) was also observed. The origin of the DLE band in the PL spectra has been further analyzed by means of electrical methods. The C-V results proved that the depletion region of the studied diodes is located on the n-type side of the p-n junction. The DLTS measurements revealed the presence of electron traps related with ZnO. The parameters of the traps, such as activation energies and capture cross sections, were determined and the source of their origin has been discussed. The results obtained within this work helped us to understand the impact of defects/QWs on electrical and optical properties of the studied nanowire n-ZnMgO/p-Si diodes.