B. E. Hammons

InGaAsN solar cells with 1.0 eV band gap, lattice matched to GaAs

The design, growth by metal-organic chemical vapor deposition, and processing of an In{sub 0.07}Ga{sub 0.93}As{sub 0.98}N{sub 0.02} solar Al, with 1.0 ev bandgap, lattice matched to GaAs is described. The hole diffusion length in annealed, n-type InGaAsN is 0.6-0.8 pm, and solar cell internal quantum efficiencies > 70% arc obwined. Optical studies indicate that defects or impurities, from InGAsN doping and nitrogen incorporation, limit solar cell performance.

Lattice engineered compliant substrate for defect-free heteroepitaxial growth

Presented here is proof-of-principle that a thin single crystal semiconductor film—when twist-wafer bonded to a bulk single crystal substrate (of the same material)—will comply to the lattice constant of a different single crystal semiconductor thick film grown on its surface. In our experiment, a 100 A film of GaAs was wafer bonded to a GaAs bulk substrate, with a large twist angle between their 〈110〉 directions. The resultant twist boundary ensures high flexibility in the thin film. Dislocation-free films of In0.35Ga0.65P(∼1% strain) were grown with thicknesses of 3000 A, thirty times the Matthews–Blakeslee critical thickness, on twist-wafer-bonded films of GaAs.

Dislocation-free InSb grown on GaAs compliant universal substrates

An innovative compliant GaAs substrate was formed by wafer bonding a 30 A GaAs layer to a bulk GaAs crystal with a large angular misalignment inserted about their common normals. InSb epitaxial layers, which is about 15% lattice mismatched to GaAs, have been grown on both compliant substrates and conventional GaAs substrates. Transmission electron microscopy studies showed that the InSb films grown on the compliant substrates have no measurable threading dislocations, whereas the InSb films on the conventional GaAs substrates exhibited dislocation densities as high as 1011u2009cm−2. The observations made here suggest that the defect-free heteroepitaxial growth of exceedingly large lattice-mismatched crystals can be achieved with compliant universal substrates.

Wet oxidation of AlxGa1−xAs: Temporal evolution of composition and microstructure and the implications for metal-insulator-semiconductor applications

Three important processes dominate the wet thermal oxidation of AlxGa1−xAs on GaAs: (1) oxidation of Al and Ga in the AlxGa1−xAs alloy to form an amorphous oxide, (2) formation and elimination of crystalline and amorphous elemental As and of amorphous As2O3, and (3) crystallization of the amorphous oxide film. Residual As can lead to strong Fermi-level pinning at the oxidized AlGaAs/GaAs interface, up to a 100-fold increase in leakage current, and a 30% increase in the dielectric constant of the oxide layer. Thermodynamically favored interfacial As may impose a fundamental limitation on the use of AlGaAs wet oxidation in metal-insulatorsemiconductor devices in the GaAs material system.

Long wavelength (1.3 μm) vertical-cavity surface-emitting lasers with a wafer-bonded mirror and an oxygen-implanted confinement region

We proposed and demonstrated a novel design for long wavelength (1.3 μm) vertical-cavity surface-emitting lasers (VCSELs). In this design, oxygen-implanted current-confinement regions were formed in a GaAs/AlGaAs Bragg reflector which is the bottom mirror wafer bonded to an AlGaInAs/InP cavity consisting of nine strain-compensated quantum wells. Room- temperature continuous-wave (cw) operation of 1.3 μm-VCSELs with a record low cw threshold current density of 1.57u2009kA/cm2 and a record low cw threshold current of 1 mA have been realized.

Growth of InGaAs multi-quantum wells at 1.3 μm wavelength on GaAs compliant substrates

InGaAs multiple quantum wells at 1.3 μm wavelength have been grown on a twist-bonded GaAs compliant substrate. The GaAs compliant substrate contains a 30 A GaAs thin layer bonded to a GaAs bulk substrate with a 22-degree angle. Nomarski phase contrast microscopy, transmission electron microscopy (TEM), and photoluminescence were used to characterize the heteroepitaxial layers. The smooth and crosshatch-free surface morphology, dislocation-free cross-sectional TEM, and strong luminescence intensity all provide convincing evidences for substantial improvement of the quality of heteroepitaxial material using the compliant substrate technique. Research is underway to apply the concept and technique of compliant substrate to Si and other materials.

Origin of the Time-Dependence of Wet Oxidation of AlGaAs

The time dependence of the wet oxidation of high-Al-content AlGaAs can be either linear, indicating reaction-rate limitation, or parabolic, indicating diffusion-limited rates. The transition from linear to parabolic time dependence can be explained by the increased rate of the formation of intermediate As2O3 versus its reduction to elemental As. A steadily increasing thickness of the As2O3-containing region at the oxidation front will shift the process from the linear to the parabolic regime. This shift from reaction-rate limited (linear) to diffusion-limited (parabolic) time dependence is favored by increasing temperature or increasing Al mole fraction.

Low-threshold proton-implanted 1.3-μm vertical-cavity top-surface-emitting lasers with dielectric and wafer-bonded GaAs-AlAs Bragg mirrors

We demonstrate a new structure for long-wavelength (1.3-/spl mu/m) vertical-cavity top-surface-emitting lasers using proton implantation for current confinement. Wafer bonded GaAs-AlAs Bragg mirrors and dielectric mirrors are used for bottom and top mirrors, respectively. The gain medium of the lasers consists of nine strain-compensated AlGaInAs quantum wells. A record low room temperature pulsed threshold current density of 1.13 kA/cm/sup 2/ has been achieved for 15-/spl mu/m diameter devices with a threshold current of 2 mA. The side-mode-suppression-ratio is greater than 35 dB.

2×106 cm2/V s electron mobility by metalorganic chemical vapor deposition with tertiarybutylarsine

We demonstrate the metalorganic chemical vapor deposition (MOCVD) growth of two‐dimensional electron gases (2DEGs) with electron mobilities up to 2.0×106 cm2/Vu2009s at 0.3 K. These are the highest mobilities to date for MOCVD materials, and were achieved using a safer replacement precursor for arsine, tertiarybutylarsine (TBA). For structures grown using arsine, we obtained a maximum mobility of 1.0×106 cm2/Vu2009s, which although comparable to the best by MOCVD to date, is half that obtained using TBA. Our studies on thick GaAs and AlGaAs layers indicate that the use of TBA in place of arsine reduces both the carbon and donor impurity concentrations. Thus, TBA is not only a safe alternative to arsine, but also produces significantly purer films.

Intracavity spectroscopy in vertical cavity surface‐emitting lasers for micro‐optical‐mechanical systems

We demonstrate lasing action in a novel microcavity laser device based on vertical cavity surface‐emitting laser technology. This laser can be used for intracavity spectroscopy, high contrast imaging of small (10 μm) structures, and is well suited for use in micro‐optical mechanical systems for analysis of particles or fluids. Here, we investigate spectra of intracavity polystyrene spheres. Lasing threshold, single‐mode operation, and multimode operation are all studied. Transverse mode separation in the multimode regime is found to be effective for sizing of the spheres.