P. D. Moran

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.

Fabrication of InAs/AlSb/GaSb heterojunction bipolar transistors on Al2O3 substrates by wafer bonding

High-frequency integrated circuit applications of GaSb-based materials are hampered by the lack of a suitable lattice-matched insulating substrate. Wafer bonding was used to fabricate InAs/AlSb/GaSb-based heterojunction bipolar transistors (HBTs) on an insulating sapphire substrate through a low temperature bonding process that results in a high bond strength and permitted the mechanical and chemomechanical removal of the initial GaSb substrate. The use of selective etches allows for the retention of the epitaxial device layers over virtually the entire wafer area. Minimal degradation of the transferred layers occurred in the bonding and substrate removal process. The resulting transferred structures were fabricated into functional HBTs exhibiting a dc current gain of ∼5.

Growth of oriented lithium niobate on silicon by alternating gas flow chemical beam epitaxy with metalorganic precursors

We present the results of investigations of LiNbO3 film growth on Si by conventional chemical beam epitaxy (CBE) and by alternating gas flow deposition with alkoxide precursors. Both growth methods produced films with an intervening interface amorphous layer, whose thickness depends strongly on growth and annealing temperatures. While films grown by chemical beam epitaxy were always polycrystalline, the LiNbO3 films grown by alternating gas flow deposition were oriented materials. Based on our studies, we hypothesize that the alternating layer deposition technique enhances bulk interdiffusion efficiency of metal ions leading to a more controlled epitaxy of LiNbO3 on Si relative to conventional CBE growth.

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...

Oriented crystallization of GaSb on a patterned, amorphous Si substrate

Oriented crystallization of GaSb on patterned, oxidized Si substrates was achieved by metalorganic chemical vapor deposition. The Si substrate was formed by patterning an array of inverted square pyramids having {111} sidewall facets, using lithography and anisotropic etching in KOH. The orientation and structure of GaSb crystals, at various stages of the growth, were examined by scanning electron microscopy and x-ray diffraction. X-ray diffraction pole figure analysis shows that {111} planes of GaSb are predominantly parallel to the {111} planes of the inverted pyramids. Extra (111) spots observed in the x-ray diffraction pole figure are interpreted in terms of multiple twinning of GaSb.

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.

Near-field scanning optical microscopy investigation of immiscibility effects in In1−xGaxP films grown by liquid phase epitaxy

Near-field scanning optical microscopy (NSOM) and electron probe microanalysis (EPMA) were used to study the topographic and microscopic optical properties of indium–gallium–phosphide (In1−xGaxP) samples grown by liquid phase epitaxy on gallium–arsenide substrates. NSOM imaging found strong and highly localized variations in the photoluminescence (PL) intensity for samples that were highly lattice mismatched with the substrate. The topography and optical features were roughly spatially correlated for these samples. Shifts in the PL peak energy position (by as much as 27 meV) were found during scans across highly mismatched samples, whereas no shifts were seen for In1−xGaxP films with a nearly lattice matched composition. Compositional fluctuations were determined to be the cause of these PL peak energy shifts. EPMA provided corroborating evidence that compositional fluctuations are spatially correlated with the topography. These composition fluctuations arise from the known solid–solid miscibility gap in ...

The heterogeneous integration of InAlAs/InGaAs heterojunction diodes on GaAs: impact of wafer bonding on structural and electrical characteristics

We have investigated the influence of low temperature wafer bonding on the electrical and structural characteristics of InAlAs/InGaAs n-p heterojunction structures with similar structure to an emitter-base junction of InAlAs/InGaAs HBTs. Those n-p junction heterostructures were grown on an InP [100] substrate by solid source MBE. The effect of the wafer bonding process on the structural properties of the epitaxial layers was studied by comparing triple crystal X-ray diffraction measurements and simulations before and after bonding. In addition, the influence of the bonding process on the electrical properties of the heterojunction structures was assessed through SIMS analysis of both the bonded and nonbonded samples and an analysis of the I-V characteristics of diodes fabricated on both the bonded and non-bonded sample. These analyses show that the structural and electrical properties of the as-grown epitaxial layers were negligibly changed by the low temperature wafer transfer process.