S. Oktyabrsky

Aluminum nitride films on different orientations of sapphire and silicon

The details of epitaxial growth and microstrictural characteristics of AlN films grown on sapphire (0001), (1012) and Si (100), (111) substrates were investigated using plan‐view and cross‐sectional high‐resolution transmission electron microscopy and x‐ray diffraction techniques. The films were grown by metalorganic chemical vapor deposition using TMA1+NH3+N2 gas mixtures. Different degrees of epitaxy were observed for the films grown on α‐Al2O3 and Si substrates in different orientations. The epitaxial relationship for (0001) sapphire was found to be (0001)AlN∥(0001)sap with in‐plane orientation relationship of [0110]AlN∥[1210]sap. This is equivalent to a 30° rotation in the basal (0001) plane. For (1012) sapphire substrates, the epitaxial relationship was determined to be (1120)AlN∥(1012)sap with the in‐plane alignment of [0001]AlN∥[1011]sap. The AlN films on (0001) α‐Al2O3 were found to contain inverted domain boundaries and a/3〈1120〉 threading dislocations with the estimated density of 1010 ...

Characteristics of stacking faults in AlN thin films

We have investigated growth characteristics and atomic structure of defects in AlN thin films grown by the metalorganic chemical vapor deposition technique on the (1012) r plane of α-Al2O3. The AlN films were single crystal and exhibited the following epitaxial relationship: (1120)AlN∥(1012)sap with the in-plane alignment of [0001]AlN∥[1011]sap. Using high-resolution electron microscopy and multislice image simulation, the predominant defects in AlN thin films grown on the r plane of α-Al2O3 were found to be low-energy intrinsic stacking faults of type I1 lying in the basal plane. This fault, with a 1/6[2023] resultant displacement vector, can be formed by removing one (0002) plane and then shearing the remaining half-crystal by displacement of 1/3[1010]. The faults appear as a single face-centered-cubic stack ABC inserted into the normal …ABAB… hexagonal sequence. We discuss the possible role of these defects in optical properties of semiconductor 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 mic...

Misfit dislocations in low-temperature grown Ge/Si heterostructures

Abstract We have investigated the initial stages of two-dimensional epitaxial growth of Ge on (001)Si substrates using pulsed laser deposition. The Ge films grow epitaxially above 170°C and switched from two- to three-dimensional growth mode above 350°C. The evolution of the dislocation network as a function of film thickness was studied by high-resolution transmission electron microscopy (TEM) in the films grown at 300°C and at relatively high growth rates to suppress the three-dimensional nucleation and obtain low rate of inelastic misfit relaxation. The relaxation process begins with generation of 60° slip dislocations with a strongly non-equilibrium inhomogeneous distribution which seems to be controlled by additional stress resulting from random surface undulations. When the film is just 8 nm thick, 90% of misfit stress is already relaxed by mostly 60° dislocations which demonstrate a distinct tendency of pairing of parallel dislocations from different glide planes. As the thickness of the film incre...

New mechanism of formation of stacking faults in Gd(001)Si heterostructures

Abstract Initial stages of misfit relaxation process in Ge epitaxial films grown in two-dimensional (layer-by-layer) mode on Si(001) have been investigated by high-resolution transmission electron microscopy. Special emphasis is placed on the dislocation interactions leading to rearrangements in a non-equilibrium dislocation network driven by elastic interaction between parallel 60° dislocation segments. One of the dislocation reactions between closely spaced misfit segments which cannot combine to form a 90° pure edge dislocation is analysed in detail. On the basis of our experimental observations, we propose a model for the formation of stacking faults in heterostructures. We discuss the energetics of various dislocation reactions involved and splitting of 60° dislocations to create stacking faults.

Role of silver doping in oxygen incorporation of oxide thin film

A distinctive characteristic of silver in oxygen incorporation of oxide thin films during pulsed laser ablation has been discovered. Optical emission spectroscopy studies of laser-induced plume of Ag-target indicates the presence of AgO species whose concentration increases with an increase in oxygen partial pressure. The formation of AgO in laser-plume has been found to be very useful for the realization of high temperature superconducting YBa2Cu3O7-delta (YBCO) and giant magnetoresistive La0.7MnO3-delta (LMO) thin films with dramatically superior quality if the target materials contained a small amount of silver. The improvement in the quality of these films is brought about by the supply of atomic oxygen to oxide lattices during their formation. This becomes possible due to the fact that Ag, after it is ablated with other constituent materials in the target, gets moderately oxidized in an oxygen atmosphere and the oxidized species dissociate back into Ag and nascent O at the substrate surface. The nascent oxygen is very highly reactive and is easily assimilated into the lattice of these compounds

CHARACTERIZATION OF HIGHLY ORIENTED (110) TIN FILMS GROWN ON EPITAXIAL GE/SI(001) HETEROSTRUCTURES

The characteristics of epitaxial growth of titanium nitride films on Ge/Si(001) have been studied. The growth of titanium nitride and germanium films on (001)Si was carried out in situ in a high vacuum chamber ( −7 Torr) using a multitarget stage in a pulsed laser deposition system. Electrical resistivity, stoichiometry, crystallinity, and epitaxial relationships as a function of deposition temperature have been studied. Electrical resistivity of the titanium nitride films grown at deposition temperatures in the range of 450 °C–750 °C was measured using a four-point probe. The stoichiometry of these films was investigated using Auger electron spectroscopy and Raman spectroscopy. The crystalline quality and epitaxial nature of TiN films grown at different substrate temperatures were characterized using x-ray diffraction and transmission electron microscopy. Highly oriented titanium nitride films with (110) orientation were obtained on Ge(001) film when the substrate temperature was maintained between 550 °C and 650 °C. The epitaxial growth of the titanium nitride films was found to be a function of two-dimensional or three-dimensional growth mode of germanium film on silicon (001) substrate. Titanium nitride films grown at a substrate temperature of 650 °C exhibited the lowest room temperature resistivity (26 μΩ-cm), highest nitrogen content (close to stoichiometry), and the best epitaxiality with the Ge(001) films on Si(001). The epitaxial relationships for the TiN/Ge/Si(001) heterostructure are found to be [001]TiN‖ [110]Ge‖ [110]Si and [110]TiN‖ [110] Ge‖ [110]Si. To explain the epitaxial growth in a large mismatch system (∼28%) such as TiN/Ge(001), the domain matching mechanism is proposed. Domains of size four (001)TiN by seventeen (220)TiN in the titanium nitride film match closely with domains of size three (220)Ge by sixteen (220)Ge in the germanium film, respectively. The lattice matching epitaxy involving a 4% mismatch between Ge and Si provides a mechanism for epitaxial growth of Ge on Si(001).