D. J. Arent

Franz–Keldysh oscillations originating from a well‐controlled electric field in the GaAs depletion region

The Franz–Keldysh oscillations induced by the electric field in the depleted zone below the GaAs surface are studied by photoreflectance spectroscopy. The electric field is precisely controlled by a molecular beam epitaxy grown buried highly doped layer and the pinned position of the Fermi level at the surface. It is shown that the electric field value as derived from theory is in disagreement with the value derived from electrostatic calculations. Consequently a determination of the Fermi level pinning is only possible from a measurement of both n‐ and p‐doped samples.

Strain effects and band offsets in GaAs/InGaAs strained layered quantum structures

Strained single quantum wells composed of GaAs/InGaAs/GaAs were grown by molecular beam epitaxy and characterized at room temperature by photoreflectance and at 6 and 77 K by photoluminescence spectroscopy. For the InGaAs/GaAs heterojunction, utilizing a band offset ratio of 85:15 (conduction band:valence band) for the intrinsic (nonstrained) interface and a contribution of the hydrostatic compression to the valence band movement corresponding to the pressure sensitivity of the spin orbit band, excellent agreement is found between calculated excitonic transition energies and those found by experiment at all temperatures studied. Our analysis indicates that material parameters and the combined strain components used to calculate band structure are not temperature dependent to our degree of sensitivity. An empirical equation, which differs slightly from that for bulk InGaAs crystals, describing the nonstrained band‐gap energy as a function of In fraction at 77 K is presented. The difference between band off...

Optical characterization of stress in narrow GaAs stripes on patterned Si substrates

Photoluminescence (PL) and spatially resolved cathodoluminescence (CL) techniques are used to characterize the stress in narrow GaAs stripes grown on Si platforms. Since no overgrowth occurs over the recess edges, the GaAs stripes are grown unconstrained along one dimension. A duplication of the optical transitions is found in the PL spectrum from a region containing embedded GaAs and stripes. The peaks in the high‐energy shoulders of the PL spectrum are identified by CL measurements with high spatial resolution as the luminescence contribution of the GaAs stripes. They are submitted to lower internal stress values. A study on the geometrical dependence of the strain regime shows that a nonuniform biaxial strain field with a dominant longitudinal component is present in the stripes. The uniform biaxial strain, found in GaAs on Si (001), is present at stripe intersections.

Miniband dispersion in gaas/alxga1-xas superlattices with wide wells and very thin barriers

Photoreflectance spectra have been used to characterize miniband formation in GaAs/ Alx Ga1−x As superlattices with wide wells (275–255 A) and withb arriers as thin as 17 A. Thirty‐two optical transitions are resolved in the photoreflectance spectra of the 17 A barrier sample. These experimental transitions match all those theoretically predicted from the selection rule Δn=0, including Γ‐ and Π‐type transitions arising from miniband dispersion; these results imply sample perfection. A sample with a 40 A barrier exhibits forbidden transitions with Δn≠0; these additional transitions, together with the narrow width of the minibands for 40 A barriers, create difficulty in resolving the miniband structure.

Miniband dispersion in GaAs/Al/sub x/Ga/sub 1-//sub x/As superlattices with wide wells and very thin barriers

Photoreflectance spectra have been used to characterize miniband formation in GaAs/ Alx Ga1−x As superlattices with wide wells (275–255 A) and withb arriers as thin as 17 A. Thirty‐two optical transitions are resolved in the photoreflectance spectra of the 17 A barrier sample. These experimental transitions match all those theoretically predicted from the selection rule Δn=0, including Γ‐ and Π‐type transitions arising from miniband dispersion; these results imply sample perfection. A sample with a 40 A barrier exhibits forbidden transitions with Δn≠0; these additional transitions, together with the narrow width of the minibands for 40 A barriers, create difficulty in resolving the miniband structure.

Structural characterization of embedded gallium arsenide on silicon by molecular beam epitaxy

A gallium arsenide film is grown embedded in masked pre‐etched wells in silicon vicinal (001) substrates by molecular beam epitaxy. The morphology and crystallinity of the embedded GaAs on Si layers are identical to those of large area GaAs on Si grown on the same wafer, as indicated by the comparison of Nomarski contrast photomicrographs and electron channeling patterns. High‐resolution electron microscope images reveal the epitaxial relation of the GaAs/Si interface on the bottom and the sidewall of the wells. On the slope most of the dislocations are restricted to a narrow region near the interface. The same photoluminescent behavior is found for the GaAs deposit in the different silicon environments. This embedded growth technique is suitable for realization of a coplanar GaAs on Si surface.

Embedded growth of gallium arsenide in silicon recesses for a coplanar GaAs on Si technology

A GaAs on Si coplanar technology by molecular‐beam epitaxy, that is suitable to combine GaAs and Si circuits on chip is reported. Coplanarity is obtained after the GaAs is grown embedded in masked wells in the Si substrate, which were formed by wet chemical etching with a controlled solution of HF:HNO3. Scanning electron microscope and profiling studies show the extreme flatness and the intentional misorientation of several degrees of the recessed surfaces. A possible process is proposed to realize a coplanar surface by lifting off polycrystalline GaAs with the masking dielectric. The GaAs surface step height remaining after liftoff is <0.6 μm for a 2‐μm‐thick deposit. Metallization without loss of continuity is performed over the GaAs to Si border with evaporated metal lines, 150 nm thick and 1.25 μm wide, indicating the feasibility of interconnecting side by side integrated devices in both semiconductor materials.

Photomodulated absorption spectroscopy on AlGaAs-GaAs heterostructures

Optical transitions in quantum‐well heterostructures are very well revealed by photomodulated absorption spectroscopy. With respect to nonmodulated absorption spectroscopy, a strong increase in both room‐temperature resolution and signal‐to‐noise ratio is observed. This new technique is most attractive for the investigation of multilayers grown on transparent substrates. The evolution of the spectral lineshapes of bulk and excitonic transitions as a function of temperature is shown.

Heterojunction Band Discontinuities for Pseudomorphically Strained InxGa1 - xAs/AlyGa1 - yAs Heterointerfaces

A general description is presented for calculating the strain-induced variations in the band edge discontinuities for pseudomorphically strained III–V heterointerfaces grown in the (100) direction. InxGal-xAs/AlyGal-yAs ternary/ternary heterointerfaces are specifically treated within the virtual crystal approximation, accounting for band parabolicity and composition dependent material parameters. In conjunction with the development of an equation describing the strained InxGal-xAs band gap as a function of In concentration, the conduction band offset ratios, calculated as a function of both In and Al content, are shown to be nonconstant and are in very good agreement with experimental data derived from strained single quantum well samples grown by molecular beam epitaxy and analyzed using room temperature photoreflectance spectroscopy and data from the literature.

Photoreflectance and Photoluminescence of Strained InxGal−xAs/GaAs Single Quantum Wells

Molecular Beam Epitaxy (MBE) grown single strained layer quantum wells composed of GaAs/InxGa1−x As/GaAs have been characterized at room temperature by photoreflectance and at 6K and 77K by photoluminescence. Excellent agreement between experimentally determined quantum transitions and theory is achieved utilizing a band offset ratio of 85:15 (conduction band:valence band) and a contribution of the hydrostatic compression to the valence band movement corresponding to the pressure sensitivity of the spin orbit band. Analysis of low temperature data indicate that strain induced band changes are not temperature dependent and data obtained at 77K leads to an empirical equation describing the non-strained band gap energy as a function of In fraction, and which differs slightly from that for bulk InGaAs crystals.