Erik B. Svedberg

Influence of growth rate on the structure of thick GaN layers grown by HVPE

Thick GaN films grown by hydride vapour phase epitaxy have been investigated by cathodoluminecsence, X-ray diffraction, and photoluminescence. Cross-sectional studies of thick GaN layers grown on sapphire without buffers reveal three zones: a highly disordered interface region; a columnar defective region and a good quality main region of the layer. The influence of the highly doped columnar region on the surface morphology and crystal structure of the layers has been studied. We show that the columnar region influences the material quality more strongly in thinner films. Thicker layers exhibit improved morphology with lower surface pit density and better crystal quality shown in photoluminescence and X-ray diffraction spectra. The relationship between the near-interface columnar structures and surface pits is revealed. A strong effect of the growth rate on the structure of thick layers is found. The results suggest that GaN layers with optimum crystalline quality may be obtained by varying the growth rate during growth.

Interface structure of hydride vapor phase epitaxial GaN grown with high-temperature reactively sputtered AlN buffer

Thick hydride vapor phase epitaxy GaN layers have been grown on a-plane sapphire using high-temperature ion-assisted reactively sputtered AlN as a buffer layer. Transmission electron microscopy and atomic force microscopy were carried out to study the formation of the two interfaces sapphire/AlN and AlN/GaN, and their influence on the microstructure of both the buffer layer and the main GaN layer. It was demonstrated that the high-temperature reactively sputtered buffer layer provides a good alternative for hydride vapor phase epitaxy growth of GaN layers. In particular, the buffer promotes a specific interface ordering mechanism different from that observed on low-temperature buffers.

Temperature stable Pd ohmic contacts to p-type 4H-SiC formed at low temperatures

The formation of low resistivity Pd-based ohmic contacts to p-type 4H-SiC below 750/spl deg/C are reported herein. The electrical properties of the contacts were examined using I-V measurements and the transmission-line model (TLM) technique. Contact resistivity as a function of annealing was investigated over the temperature range of 600/spl deg/C-700/spl deg/C. The lowest contact resistivity (5.5/spl times/10/sup -5/ /spl Omega/cm/sup 2/) was obtained after annealing at 700/spl deg/C for 5 min. Atomic force microscopy of the as-deposited Pd layer showed a root-mean-square roughness of /spl sim/8 nm, while after annealing at 700/spl deg/C, agglomeration occurred, increasing the roughness to 111 nm. Auger electron spectroscopy depth profiles revealed that with annealing, interdiffusion had resulted in the formation of Pd-rich silicides. However, X-ray diffraction and Rutherford backscattering showed that the majority of the film was still (unreacted) Pd. The thermal stability and reliability of the Pd contacts were examined by aging and temperature dependence electrical tests. The contacts annealed at 700/spl deg/C were stable at prolonged heating at a constant temperature of 500/spl deg/C and they showed thermal stability in air at operating temperatures up to 450/spl deg/C. This stability was not found for contacts formed at lower temperatures of 600/spl deg/C or 650/spl deg/C.

Thick Hydride Vapour Phase Epitaxial GaN Layers Grown on Sapphire with Different Buffers

We report a comparative study of the crystalline quality of thick GaN layers grown by hydride vapour phase epitaxy, using a nitridation and a GaCl pretreatment of the sapphire as well as a reactive sputtered AlN buffer and metalorganic chemical vapour deposition grown GaN ‘template’ layers. The structure quality was investigated using X-ray diffraction measurement and cathodoluminescence spectroscopy and imaging of cross-section of the films. The morphology of the layers was revealed by optical and atomic force microscopy. A distinct reduction of both the columnar near-interface region and the domain formation were observed in layers grown on AlN and GaN ‘template’ buffers resulting in improved bulk quality and significant smoother film surfaces.

Asymmetric interface broadening in epitaxial Mo/W (001) superlattices grown by magnetron sputtering

The interfacial structure in epitaxial Mo/W(001) superlattices, grown by magnetron sputtering on MgO(001) substrates has been studied. The films were grown in Ar and Kr discharges at a substrate temperature of 700 °C, and the as-deposited samples were analyzed by x-ray diffraction and found to be epitaxial with no high-angle grain boundaries. The degree of interfacial intermixing, caused by fluxes of different energetic species impinging on the growth surface, was estimated using a combination of Monte Carlo binary collision computer codes and a gas scattering computational model. In the Ar discharge case, large asymmetries in the Mo/W and W/Mo interfaces were found, with the W/Mo interface being more than a factor of 2 broader than the Mo/W interface. Simulations of x-ray reflectivity curves using the calculated interface profiles as input parameters without any additional fitting parameters agreed very well with measured data. The overall good fit between the calculated and measured reflectivity curves ...

Time-resolved measurements of the formation of single-domain epitaxial Ni films on MgO( 111) substrates using in-situ RHEED analysis

Abstract The mechanisms behind the formation of smooth 〈111〉 oriented single domain epitaxial Ni films grown on MgO(111) substrates by ultra-high vacuum dc magnetron sputtering were studied using time-resolved in-situ reflection high energy electron diffraction (RHEED) measurements. The results show that whether a single- or a two-domain 〈111〉 oriented film forms is decided already during the deposition of the first two or three monolayers of Ni, and that the Ni appears to nucleate as strained islands during this initial growth. This implies that an interaction between the atoms in the second Ni layer and the second and third atomic layers of the substrate must exist, making the Ni atoms always choose the same stacking sequence at a growth temperature of 300°C. Prior to growth, the MgO(111) surface is smooth, non-faceted and without reconstructions.

Epitaxial growth of UHV magnetron sputtered Mo thin films on MgO(001) substrates, oxygen segregation and surface reconstructions

Studies of epitaxial growth of Mo thin films on MgO(001) substrates by ultrahigh Vacuum (UHV) d.c. magnetron sputter deposition have shown independently by in situ low energy electron diffraction ( ...

Structure evolution in Ag/Ni multilayers grown by ultra high vacuum DC magnetron sputtering

Abstract Ag/Ni multilayers have been grown by ultra high vacuum d.c. magnetron sputtering onto oxidized Si(001) substrates held at room temperature. Films were grown in both Ar and Kr discharges at different sputtering pressures p. The effects of the different discharge pressures and post-deposition annealing were investigated. The structure evolution was studied using atomic force microscopy (AFM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD pole figure analysis show that all films exhibit a pronounced 〉111〈 fiber texture. Sputtering using low pressures resulted in a reduction of the surface roughness, compared to films grown at higher pressures, and films with rms roughness values as low as 1–2 nm were obtained. XRD analysis show that also the definition of the layer interfaces and the crystallinity of the films improved when the pressure was lowered and when using Ar instead of Kr. The increase in surface roughness with discharge pressure is explained by a reduced adatom mobility on the growing film surface at higher pressures and a wider range of incidence angles of the adatoms when arriving at the surface due to gas scattering. The improved crystalline quality when using Ar instead of Kr is explained using similar arguments. Short post-deposition annealing at 280°C resulted in improved layer definitions as well as improved intralayer order whereas prolonged annealing or annealing at 390°C resulted in agglomeration of Ag precipitates and loss of the compositional modulation. A qualitative model based on the immiscibility of the Ag-Ni system and different diffusivities of Ag and Ni, is proposed.

Method for seed and underlayer optimization of perpendicular magnetic recording media

A set of seed and underlayers for thin film perpendicular recording media has been optimized using a technique involving simultaneous thickness and composition gradients on a single test wafer. Magnetron sputtering under ultrahigh vacuum conditions in Ar gas was used for the deposition of the layers. The structure being optimized consisted of a Ta seed layer, RuxCo1−x, Co63Cr37 underlayers, and a Co68Cr18Pt8B6 hard magnetic layer. One of the layers in the stack on a wafer has been deposited so that both a thickness variation and composition variation occurred. The method allows cross terms between thickness and the individual compositional terms to be investigated. Coercivity and squareness of the samples was measured by magneto-optical Kerr rotation. The results showed that for the range of thickness under investigation, the highest coercivity and squareness does not occur for the same set of conditions. Maximum squareness is reached without a radio frequency (rf) bias, while the coercivity increases fur...

Texture of Al thin films deposited by magnetron sputtering onto epitaxial W(001)

Highly textured epitaxial metallizations will be required for the next generation of devices with the main driving force being a reduction in electromigration. Herein a model system of 190 nm of Al on a 140 nm layer of W grown on MgO 〈00l〉 substrates was studied. The W layer was 〈00l〉 oriented and rotated 45° with respect to the MgO substrate to minimize the misfit; the remaining strain was accommodated by dislocations, evident in transmission electron microscopy images. From high-resolution x-ray diffraction (XRD) measurements, the out-of-plane lattice parameter was determined to be 3.175 A, and the in-plane parameter was 3.153 A, i.e., the W film sustained a strain resulting in a tetragonal distortion of the lattice. XRD pole figures showed that the Al had four fold symmetry and two dominant orientations, 〈016〉 and 〈3 9 11〉, which were twinned with multiple placements on the epitaxial W layer. The driving force for the tilted 〈001〉 and 〈011〉 orientations of Al on W is due to strain minimization through ...