Regrown Samples Research Articles

Strain mapping of GaN substrates and epitaxial layers used for power electronic devices by synchrotron X-ray rocking curve topography

Strain and tilt maps of gallium nitride (GaN) materials including substrates, ion-implanted and annealed epilayers, and etched and regrown epilayers by different etching methods have been generated from synchrotron X-ray rocking curve topography. The strain map of the ammonothermal grown GaN substrate shows uniform low strain values, while that of the patterned hydride vapor phase epitaxy (HVPE) grown substrate shows high strain centers as well as uniformly distributed low strain between them. Strain variations within the as-implanted wafers and the annealed wafers are similar, while the tilt levels are significantly decreased for the annealed wafers. The inductively coupled plasma (ICP) etched and then regrown sample gives rise to the significant variations in strain values within the imaged region, while using tertiary butyl chloride (TBCl) to etch the sample does not affect the strain distribution compared to the continuously grown sample without etching and can remove some damage from a preceding ICP etching process.

Human ß-defensin 2 is up-regulated during re-epithelialization of the cornea

Purpose. Human ß-defensins 1 and 2 (hBD-1, -2) are antimicrobial peptides found in several epithelia including corneal epithelium. Breach of the epithelium leaves the cornea vulnerable to infection so we sought to determine if there is an increase in defensin expression after injury. Methods. The epithelium from human cadaver corneas was collected by scraping (original samples). The corneas were then placed into organ culture to permit regeneration of the epithelium. Samples of re-grown epithelium were collected when healing was partially and 100% complete as determined by fluorescein staining. Total RNA was extracted from original and re-grown samples and used in RT-PCR reactions using primers specific for hBD-1 and hBD-2 and the constitutively expressed gene glyceraldehyde-3-phosphate dehydrogenase. Immunoblotting was performed to detect defensin peptide in original and re-grown samples. Results. hBD-1 mRNA was detected in all original epithelial tissue samples (n = 10) examined suggesting that it is constitutively expressed. hBD-2 mRNA was detectable in only two of the ten samples. Of six corneas placed in to organ culture, hBD-1 mRNA expression was unchanged in the re-grown epithelial samples compared to the original epithelium samples, however the expression of hBD-2 mRNA was markedly increased. hBD-1 and hBD-2 peptides showed the same pattern of expression as their respective transcripts. Conclusions. These data show that hBD-2 mRNA and peptide is up-regulated in the corneal epithelium during re-epithelialization which is in keeping with the role of this defensin as an antimicrobial peptide.

On the interface resistance of regrown GaInAs on InP

The contact resistance of regrown ohmic contacts on n-InP are characterized. Ga 0.47In 0.53As doped by Si in excess of 10 18 cm −3 is used as the regrowth material. TLM measurements are carried out between 80 and 300 K. It is found that at low temperatures, non-annealed contacts made on regrown samples still preserve their linear ohmic behavior, whereas standard non-annealed metal contacts on n-InP show Schottky diode like characteristics. Contact resistance measurements made on annealed contacts are compared with theoretical calculations based on thermionic emission and thermionic field emission theories as applied to the electron transport across the heterostructure interface and good agreement is reported.

Dopant Activation And Epitaxial Regrowth in P-Implanted Pseudomorphic Ge0.12Si0.88 Layers on Si (100)

AbstractA pseudomorphic Ge0.12Si0.88 film 265 nm thick grown on a Si (100) substrate by molecular beam epitaxy was implanted at room temperature with a dose of 1.5 × 1015 cm2 of 100 keV P ions. The projected range of the ions is about 125 nm, which is well within the film thickness. Only the top portion of the Ge0.12Si0.88 layer was amorphized by the implantation. Both implanted and non-implanted samples were subsequently annealed in vacuum for 30 Minutes from 400 °C to 800 °C. Values of electron Hall sheet mobility and concentration in the implanted Ge0.12Si0.88 epilayer were measured after annealing. The solid phase epitaxial regrowth is complete at 550 °C, where the implanted phosphorus reaches - 100 % activation. The regrown Ge0.12Si0.88 layer exhibits inferior crystalline quality to that of the virgin sample and is relaxed, but the non-implanted portion of the film remains pseudomorphic at 550 °C. When annealed at 800 °C, the strain in the whole epilayer relaxes. The sheet electron mobility values measured at room temperature in the regrown samples (Tann ≥ 550 °C) are about 20% less than those of pure Si.

Homoepitaxial Alignment of SrTiO3 Thin Films Prepared by Metallo-Organic Decomposition.

ABSTRACTWe demonstrate the homoepitaxial growth of SrTiO3 prepared by the method of metallo-organic decomposition (MOD). Thin films of SrTiO3 are prepared by spin-coating and thermal decomposition of a solution of metallo-organic compounds, on single crystal, <100> oriented, SrTiO3 substrates and subsequently heat treated at temperatures ranging from 650°C to 1100°C for 30 minutes. Heat treatment at 1100°C results in the formation of single-crystal SrTiO3, perfectly aligned with respect to the underlying substrate.Ion-channeling analysis shows that the transformation to singlecrystal material proceeds epitaxially from the coating-substrate interface towards the surface of the sample. Transmission electron microscopy (TEM) studies of partially regrown samples reveal two distinct phases: an epitaxially aligned single-crystal phase, adjacent to the substrate, and a polycrystalline phase on top. On the basis of these observations, it is proposed that the crystallization of the MOD films involves the competition between two processes: layer-by-layer solid phase epitaxy and random nucleation and growth of crystallites. Layerby- layer epitaxy is the predominant crystallization mechanism unless it is inhibited by extrinsic factors like the contamination of the interface between the MOD film and the single-crystal substrate.

Low Temperature Epitaxial Growth of NiSi2 on BF2+-Implanted (001)Si

Epitaxial growth of NiSi 2 on BF 2 + -implanted (O0l)Si at low temperatures has been studied by both cross-sectional and planview transmission electron microscopy. In implanted regrown samples with a 30-nm-thick Ni layer, epilaxial NiSi 2 was found to form at a temperature as low as 250 °C. The dominant phase was observed to be NiSi in samples annealed at 400-700 °C. The final structure of the silicide layer was found to depend critically on the thickness of tile starting Ni overlayer and the annealing temperature. The presence of B and/or F atoms in silicon was found to be essential for the tormation of epitaxial NiSi 2 on crystalline silicon at 220-300 °C. In addition, tile amorphicity of the substrate was also found to play an important role in promoting the formation of polycrystalline NiSi 2 at low temperatures.

Solid Phase Epitaxy of GexSi1-x Alloys on [100] Si

AbstractSolid phase epitaxy was studied in the GexSi1-x/[100] Si system in the composition range of 4% to 10% Ge. For strained samples regrowth rates decreased with increasing Ge concentrations, with an activation energy of 2.8 and 3.0 eV for the Ge4Si96 and Ge8Si92 alloys respectively. In contrast, the rates of the strain-relaxed samples increased compared with that of pure Si. The minimum yield of fully regrown samples with Ge concentrations lower than 8% recovered to that of the as-deposited samples. However, the minimum yield of a 3500 Å-thick Ge10Si90 alloy increased to 12 % after recrystallization.