Long wavelength ͑ϳ1.55 m͒ Ga x In 1Ϫx As multiple-quantum-wire ͑MQWR͒ lasers have been grown by a single-step molecular beam epitaxy technique. The MQWR heterostructure was fabricated in situ using the strain-induced lateral-layer ordering process. The wire formation was confirmed by cross-sectional transmission electron microscopy and polarized photoluminescence spectroscopy. The 77 K threshold current densities for the MQWR laser diodes with laser cavities along ͓110͔ and ͓110͔ directions show an anisotropy ratio of ϳ10. Lasers with contact stripes aligned perpendicular to the quantum wire direction consistently show a lower threshold current density than those with stripes aligned parallel. The typical threshold current density for the MQWR laser with a stripe perpendicular to the quantum wires is ϳ1 kA/cm 2 at 300 K.

Growth of the first few layers of an oxide mixture Ga 2 O 3 ͑Gd 2 O 3 ͒ on GaAs ͑100͒ substrate, electron-beam evaporated from a Ga 5 Go 3 O 12 source, was found to be a single crystal. Reflection high-energy electron diffraction and x-ray diffraction studies show that the thin oxide film is epitaxially grown on GaAs with the surface normal ͑110͒ and in-plane axis ͓001͔ parallel to ͑100͒ and ͓011͔ of GaAs, respectively, and has a structure isomorphic to Mn 2 O 3. Studies using high-resolution transmission electron microscopy on the oxide-GaAs interface indicate some atomic registry between the oxide and GaAs during the initial growth. The chemical composition of the oxide film was determined by x-ray photoelectron spectroscopy to be unequivocally pure Gd 2 O 3 .

Ga,Inr -,As quantum wire (QWR) arrays were grown on (100) on-axis InP substrates by single-step molecular-beam epitaxy. The QWRs were formed ia situ in (GaASj&nASj,, short-period-superlattice (SPS) layers by the strain-induced lateral-layer ordering (SILO) process. An analysis of the cross-sectional and plan-view transmission electron microscopy images, photoluminescence peak energies, and polarization anisotropy has confirmed the QWR nature of these heterostructures. The SILO process occurs over a wide growth temperature range near 500 "C. However, both high and low growth temperatures result in a weaker lateral composition modulation. The strength of the lateral composition modulation is proportional to the total thickness of the SPS quantum-well layers, regardless of the thickness of the individual quantum well. In other words, the magnitude of composition modulation accumulates when growth proceeds. A strain-driven bulk solid-state diffusion model has been proven to be part of the driving force of the SILO process, in addition to a dynamic surface diffusion during growth. 0 1995 American Institute of Physics.

We report the effects of misoriented GaAs substrates and varied substrate temperatures on the formation of GaxIn1−xP lateral quantum wells (LQWs) by the strain-induced lateral-layer ordering (SILO) process. Nominally [001] GaAs on-axis substrates, [001] substrates cut 2° off toward the [110] direction, and [001] substrates cut 2° off toward the [1̄10] direction were used to simultaneously grow LQWs. The samples were characterized using plan-view and cross-sectional transmission electron microscopy and polarized photoluminescence spectroscopy. We found that regardless of the substrate misorientation or substrate growth temperature, the SILO process induced LQWs always formed along the [1̄10] direction; primarily determined by the direction of the group-V dimer bonds on the surface during growth.

Growth and physical properties of Ga 2 O 3 thin films on GaAs(001) substrate by molecular-beam epitaxy Ga 2 O 3 ͑Gd 2 O 3 ͒-GaAs heterostructures in situ fabricated using a multichamber ultrahigh vacuum ͑molecular beam epitaxy͒ system were studied by x-ray reflectivity measurement and high-resolution transmission electron microscopy. The oxide-GaAs interfaces were found to be very smooth with the roughness no more than 1 nm. Moreover, an interfacial roughness as small as one atomic layer of GaAs ͑0.33 nm͒ was observed using x-ray reflectivity.