D. M. Hansen

Photoluminescence of erbium-implanted GaN and in situ-doped GaN:Er

The photoluminescence of in situ-doped GaN:Er during hydride vapor phase epitaxy was compared to an Er-implanted GaN sample. At 11 K, the main emission wavelength of the in situ-doped sample is shifted to shorter wavelengths by 2.5 nm and the lifetime is 2.1±0.1 ms as compared to 2.9±0.1 ms obtained for the implanted sample. The 295 K band edge luminescence of the in situ-doped sample was free of the broad band luminescence centered at 500 nm which dominated the spectrum of the implanted sample. Reversible changes in the emission intensity of the in situ-doped sample upon annealing in a N 2 versus a NH 3 / H 2 ambient indicate the probable role of hydrogen in determining the luminescence efficiency of these samples.

Flux growth and luminescence of Ho : YAl3(BO3)4 and PrAl3(BO3)4 crystals

Abstract HoxY1−xAl3(BO3)4 and PrAl3(BO3)4 crystals have been grown from high-temperature solutions. Holmium segregation coefficients ranged from 1.08 to 1.40. Strong visible and near-infrared luminescence from Ho3+ and Pr3+ was obtained in the crystals with only weak-concentration quenching. Spectral evidence of energy transfer among Ho3+ ions was also observed. The simultaneous observations of low-concentration quenching and Ho3+–Ho3+ energy transfer suggest that YAl3(BO3)4 is a suitable host lattice for high-efficiency rare-earth energy transfer and sensitization schemes.

INGAAS HETEROEPITAXY ON GAAS COMPLIANT SUBSTRATES : X-RAY DIFFRACTION EVIDENCE OF ENHANCED RELAXATION AND IMPROVED STRUCTURAL QUALITY

In0.44Ga0.56As (3% mismatch) films 3 μm thick were grown simultaneously on a conventional GaAs substrate, glass-bonded GaAs compliant substrates employing glasses of different viscosity, and a twist-bonded GaAs compliant substrate. High-resolution triple-crystal x-ray diffraction measurements of the breadth of the strain distribution in the films and atomic force microscopy measurements of the film’s surface morphology were performed. The films grown on the glass-bonded compliant substrates exhibited a strain distribution whose breadth was narrowed by almost a factor of 2 and a surface roughness that decreased by a factor of 4 compared to the film simultaneously grown on the conventional substrate. These improvements in the film’s structural quality were observed to be independent of the viscosity of the glass-bonding media over the range of viscosity investigated and were not observed to occur for the film grown on the twist-bonded substrate.

Experimental test for elastic compliance during growth on glass-bonded compliant substrates

Highly mismatched films (In0.44Ga0.56As, 3% mismatch) grown well beyond their critical thickness (to 3 μm) on GaAs glass-bonded compliant substrates exhibit surfaces four times smoother and strain distributions twice as narrow as films grown simultaneously on conventional GaAs substrates. The compliant substrates consist of a thin (∼10 nm) GaAs template layer bonded via a borosilicate glass to a mechanical handle wafer. The improvement of highly mismatched films grown well beyond their critical thickness on compliant substrate structures is commonly modeled in terms of an elastic partitioning of strain from the film to the thin (∼10 nm) single-crystal template layer. The present study is a direct test for this mechanism of elastic compliance. A comparison is reported of the strain in 92 nm In0.09Ga0.91As films and 76 nm In0.03Ga0.97As films grown simultaneously on conventional GaAs substrates and the compliant substrates responsible for the improved structural quality of In0.44Ga0.56As films. Elastic part...

Lateral epitaxial overgrowth of GaSb on GaSb and GaAs substrates by metalorganic chemical vapor deposition

Lateral epitaxial overgrowth of GaSb on GaSb and GaAs substrates patterned with SiO2 or Si3N4 films by metalorganic chemical vapor deposition was accomplished using trimethylgallium and trimethylantimony. Transmission electron microscopy measurements show that coalesced films grown on GaSb substrates exhibit defect-free materials, while those on GaAs substrates show regular, small-angle crystal tilting originating from large lattice mismatch.

Epitaxial Lateral Overgrowth of GaN with Chloride-Based Growth Chemistries in Both Hydride and Metalorganic Vapor Phase Epitaxy

Epitaxial lateral overgrowth (ELO) of GaN on SiO 2 -masked (0001) GaN substrates has been investigated by using chloride-based growth chemistries via hydride vapor phase epitaxy (HVPE) and metal organic vapor phase epitaxy (MOVPE). Diethyl gallium chloride, (C 2 H 5 ) 2 GaCl, was used in as the MOVPE Ga precursor. The lateral and vertical growth rates as well as the overgrowth morphology of ELO GaN structures are dependent on growth temperature, V/III ratio and the in-plane orientation of the mask opening. A high growth temperature and low V/III ratio increase the lateral growth rate and produce ELO structures with a planar surface to the GaN prisms. High-quality coalesced and planar ELO GaN has been fabricated by both growth chemistries. The use of the diethyl gallium chloride source allows for the benefits of HVPE growth to be realized within the MOVPE growth environment.

Lateral epitaxial overgrowth of GaN using diethyl gallium chloride in metal organic vapor phase epitaxy

Abstract Diethyl gallium chloride (DEGaCl) was studied as an alternative gallium source for the lateral epitaxial overgrowth (LEO) of GaN by metal organic vapor phase epitaxy. The decomposition of DEGaCl to GaCl produces growth conditions similar to those found in the hydride vapor phase epitaxy technique near the growth front producing increased lateral growth rates. Controlled vertical and sloped facets were produced through the choice of the reactor operating conditions. X-ray diffraction was used to determine the LEO tilting angles that were found to decrease with decreasing lateral-to-vertical growth rate ratio. LEO GaN using DEGaCl source has shown a smaller kink density along the growing facets under the conditions required for rapid and smooth coalescence. The increased lateral growth rates and smoother sidewall facets within DEGaCl based growth were attributed to the ‘nearer-to-equilibrium’ conditions at the growth front that can result from the presence of HCl-related etching reactions.

Chemical role of oxygen plasma in wafer bonding using borosilicate glasses

Plasma-treated oxide layers are commonly used in wafer bonding applications. Borosilicate glass (BSG) layers deposited by low-pressure chemical vapor deposition treated with an O2 plasma in reactive ion etching mode for 5 min at 0.6 W/cm2 and rinsed with DI H2O readily bond to GaAs and Si. The chemical role of this prebonding treatment was investigated using attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. The peak intensities for both the Si–O and B–O absorbance bands decreased in intensity as a result of the plasma treatment is consistent with the uniform sputtering of 9.8 nm±0.8 nm of BSG. Polarization dependent ATR-FTIR revealed that the H2O/OH absorbance bands decreased in peak intensity with the OH groups being preferentially oriented perpendicular to the sample surface after the plasma treatment. The subsequent DI H2O rinse restores the water to the surface while removing B2O3 from the BSG layer. This prebonding treatment, therefore, results in a hydrophilic bond, but...

Chemical investigations of GaAs wafer bonded interfaces

The bonding chemistry of various GaAs-to-oxide/GaAs bonded samples was investigated using multiple internal transmission Fourier transform infrared spectroscopy for thermally annealed and thermocompression annealed samples. The oxides used in these investigations included a native GaAs oxide as well as two compositions of borosilicate glass (BSG) deposited by low-pressure chemical vapor deposition (LPCVD). For the thermally annealed samples, the hydrogen-bonded H2O/OH groups on the hydrophilic surface form a room temperature bond without the application of pressure. Chemical changes at the wafer-bonded interface occur in two temperature regions. For anneals between 200 and 400 °C for 1 h in N2, the H2O/OH groups react and evolve H that becomes absorbed within the oxide. The LPCVD BSG oxide was chemically unaltered during anneals in this temperature range, however, the GaAs native oxide underwent chemical modification. Initially, the GaAs oxide consisted of As(III)–O and Ga–O related oxides. The As(III)–O ...

Realization and Characterization of Ultrathin GaAs‐on‐Insulator Structures

The fabrication of a GaAs‐on‐insulator structure for which the GaAs layer is 10 nm is reported. The bonding and thinning methods employed to obtain the structure are described. The materials and dimensions of the structure are chosen so as to be relevant to fabrication of a compliant substrate. Spectrally resolved ellipsometry and high resolution X‐ray reflectivity measurements were performed and compared to model calculations to assess the accuracy of the structure determination. The surface morphology of the 10 nm GaAs layer, determined by atomic force microscopy (AFM), shows the GaAs‐on‐insulator structures to initially have a surface morphology that is unsuitable for subsequent epitaxial growth. A method for improving the surface morphology is reported and assessed by AFM.