Growth Of High-quality Epitaxial Films Research Articles

Advances in pulsed laser deposition of nitrides and their integration with oxides

Pulsed laser deposition (PLD) is emerging as the fastest thin film prototyping tool for a variety of multicomponent ceramic films. There could be significant payoffs in applying this technique for the growth of GaN and related wide bandgap semiconductor films and heterostructures (primarily for their potential applications in optoelectronics and high-temperature high-power electronics), on account of PLD's speed and flexibility. The present work describes the pulsed laser deposition of GaN and other participating electronic and optoelectronic materials such as AlN, TiN, and ZnO on sapphire. A pulsed KrF excimer laser was used for ablation of the sintered stoichiometric GaN, AlN, and TiN targets. The processing parameters such as laser fluence, substrate temperature, background gas pressure, and pulse repetition rate have been optimized for growth of high-quality epitaxial films. The films were characterized by X-ray diffraction, Rutherford backscattering spectrometry, ion channeling, high-resolution transmission electron microscopy, atomic force microscopy, UV–visible spectroscopy, and electrical resistivity measurement. We also discuss pulsed laser deposition of multilayer heterostructures of TiN/AlN/TiN (as capacitors for high-temperature electronics), ZnO heteroepitaxy and its integration with GaN for fabrication of novel devices.

Influence of oxygen background pressure on crystalline quality of SrTiO3 films grown on MgO by pulsed laser deposition

We have systematically investigated the effect of oxygen partial pressure (PO2) on the crystalline quality of SrTiO3 films grown on MgO (001) substrates using pulsed laser deposition and established optimized conditions for the growth of high-quality epitaxial films. The crystalline quality is found to improve significantly in the O2 pressure range of 0.5–1 mTorr, compared to the films deposited at higher pressures of 10–100 mTorr. The x-ray diffraction rocking curves for the films grown at PO2 of 1 mTorr and 100 mTorr yielded full width at half-maximum (FWHM) of 0.7° and 1.4°, respectively. The in-plane x-ray φ scans showed epitaxial cube-on-cube alignment of the films. Channeling yields χmin were found to be <5% for the 1 mTorr films and ∼14% for 100 mTorr films. Thermal annealing of the SrTiO3 films in oxygen further improves the quality, and the 1 mTorr films give FWHM of 0.13° and χmin of 1.7%. In-plane misorientations of the annealed SrTiO3 films calculated using results of transmission electron microscopy are ±0.7° for 1 mTorr and ±1.7° for the 10 mTorr film. The high temperature superconducting (high-Tc) Y1Ba2Cu3O7−δ films grown on these SrTiO3/MgO substrates showed a χmin of 2.0% and transition temperature of ∼92 K, indicating that SrTiO3 buffer layers on MgO can be used for growth of high-quality Y1Ba2Cu3O7−δ thin film heterostructures for use in high-Tc devices and next generation microelectronics devices requiring films with high dielectric constants.