Showing papers by "Andrej Yu. Kuznetsov published in 2007"

Properties of phosphorus doped ZnO

Abstract: We report the electrical and optical properties of P-doped epitaxial ZnO thin films grown heteroepitaxially on sapphire substrates or homoepitaxially on ZnO wafers grown by the hydrothermal method, respectively. As-grown heteroepitaxial thin films exhibit semi-insulating to strongly n-conducting behavior depending on the P-content and the oxygen partial pressure applied during deposition. New features are observed in the recombination spectra compared to nominally undoped ZnO thin films. The spectral position of these new features also depends on the growth conditions making a clear correlation between P-incorporation and particular spectral features feasible. For the homoepitaxially grown thin films lateral scanning capacitance microscopy measurements revealed areas of both n- and p-type majority carriers.

Recombination centers in as-grown and electron-irradiated ZnO substrates

Abstract: Optical detection of magnetic resonance (ODMR) was used to study defects in ZnO substrates irradiated with 3 MeV electrons at room temperature. The Zn vacancy and some other ODMR centers were detected. Among these, the Zn vacancy and two other centers, labeled as LU3 and LU4, were also commonly observed in different types of as-grown ZnO substrates. The LU3 and LU4 are related to intrinsic defects and act as dominating recombination centers in irradiated and as-grown ZnO. © 2007 American Institute of Physics.

Hydrothermally Grown Single-Crystalline Zinc Oxide; Characterization and Modification

Abstract: An overview of our recent results on characterization and modification of high-resistivity n-type bulk zinc oxide samples, grown by hydrothermal techniques, is given. Three specific topics are addressed; (i) the role of lithium (Li) as an electrically compensating impurity, (ii) extrinsic n-type doping by hydrogen implantation, and (iii) influence of annealing conditions on deep band emission. In (i), furnace annealing of as-grown samples at temperatures above ∼800 °C is shown to cause out-diffusion of residual Li impurities and concurrently, the resistivity decreases. After annealing at 1400 °C, a resistivity close to 10−1 Ωcm is obtained and the Li content is reduced from above 1017 cm−3 to the mid 1015 cm−3 range, providing evidence for the crucial role of Li as an electrically compensating impurity. For ion-implanted samples, vacancy clusters evolve during post-implant flash lamp annealing (20 ms duration) and these clusters appear to trap and deactivate Li with a resulting improvement of the n-type conductivity. However, these clusters have a limited stability and start to dissociate already after 1h at 900 °C, accompanied by a decrease in the conductivity. For topic (ii), n-type doping by hydrogen implantation is shown to enhance the conductivity by about 5 orders of magnitude already in the as-implanted state. Despite substantial loss of hydrogen, the conductivity remains stable, or even increases, after annealing up to ≥600 °C, and necessary conditions for doping by hydrogen are discussed. In (iii), the origin of the commonly observed deep band emission from monocrystalline zinc oxide is investigated using a concept of annealing as-grown samples in different atmospheres. A strong influence by the atmosphere and temperature is observed and the results can be interpreted in terms of dominant effects on the emission by vacancy-related defects.

Study of defect engineering in the initial stage of SIMOX processing

Abstract: Defect engineering for SiO2 precipitation was investigated during ion beam synthesis in the first stage of SIMOX processing. Vacancy defects were created in Si: (i) by a buried nanocavity layer pre-fabricated by He implantation and annealing and (ii) by excess vacancy generation during oxide synthesis induced by an additional simultaneous high-energy Si implantation. A narrow nanocavity layer was found to be an excellent nucleation site that effectively assists SiO2 formation. Such cavity layer must be adjusted to the excess vacancy profile of the O implant. The excess vacancy generation by simultaneous dual implantation avoids defect formation in Si. However, it is inappropriate to form a narrow oxide layer due to the too broad distribution of excess vacancies.

Hydrogen Migration in Single Crystalline ZnO

Abstract: Hydrogen has been proposed as one of the contributors to the native n-type doping in as-grown Zinc Oxide and can also be used as an active (intentional) n-type dopant. In this work we have employed Secondary Ion Mass Spectrometry (SIMS) to study deuterium diffusion profiles in single crystalline ZnO. The samples used are hydrothermally grown, high-resistive (10 kΩ cm) monocrystalline ZnO implanted with deuterium to a dose of 1×1015 cm−2 yielding a peak concentration of approximately 5 × 1018 cm−3 at a depth of 2.2 µm. Diffusion profiles have been studied after 30 minutes isochronal heat treatments from 100oC up to 400oC in steps of 50oC. The observed redistribution can be explained by employing a diffusion model which includes trapping of 2H by Li-impurities and an activation energy of 0.85 eV is extracted for the diffusion of 2H.