[en] The strain relaxation in In_0.25Ga_0.75As and In_0.4Ga_0.6As grown on GaAs substrates at low temperature has been studied before and after laterally oxidizing an underlying Al_0.98Ga_0.02As layer. The relaxation as a function of layer thickness has been measured by cross-sectional transmission electron microscopy and x-ray analysis. It is found that oxidation of the Al_0.98Ga_0.02As layer improves the relaxation of the strained In_xGa_1-xAs layer. Moreover, the interfacial misfit dislocations have been removed, and the threading dislocation density has decreased approximately by one order of magnitude after oxidation

[en] Molecular beam epitaxy (MBE) is a versatile ultrahigh vacuum technique for growing multiple epitaxial layers of semiconductor crystals with high precision. The extreme control of the MBE technique over composition variation, interface sharpness, impurity doping profiles, and epitaxial layer thickness to the atomic level makes it possible to demonstrate a wide variety of novel semiconductor structures. Since its invention nearly 40 years ago, the MBE technique has evolved from a laboratory apparatus for exploring new materials and novel devices to a favored tool for the mass production of III–V high-speed devices. This paper will review some of the past developments in this technology and propose an outlook of future developments

[en] Amorphous and polycrystalline compounds of (Ga,As) and (Al,As) grown at very low temperatures by molecular-beam epitaxy are characterized. The ultimate microstructure and the amount of excess arsenic incorporated in the (Ga,As) or (Al,As) layers are found to depend on the arsenic overpressure during the low-temperature growth. With lower arsenic overpressure, a polycrystalline structure prevails and less excess arsenic is observed inside the layer. In contrast, a high incorporation of excess arsenic achieved by high-arsenic overpressures leads to the formation of amorphous films. Upon wet oxidation, the lateral oxidation rate of (Al,As) is found to depend on the crystallinity of the (Al,As) layer and the amount of excess arsenic. During the same process, recrystallization proceeds in the (Ga,As) layer

[en] High quality InAsSb grown on semi-insulating InP substrates by molecular beam epitaxy was achieved using AlSb/AlAsSb structure as the buffer layer. A 1000 A InAsSb layer grown on top of 1 μm AlSb/AlAsSb buffer layer showed a room temperature electron mobility of ∼12 000 cm²/V s. High structural quality and low misfit defect density were also demonstrated in the InAsSb layer. This novel AlSb/AlAsSb buffer layer structure with the AlAsSb layer lattice matched to InP substrates could enhance the performance of optoelectronic devices utilizing 6.1 A family of compound semiconductor alloys

[en] The results of the growth of thin (∼3 nm) InGaN/GaN single quantum wells (SQWs) with emission wavelengths in the green region by plasma-assisted molecular beam epitaxy are present. An improved two-step growth method using a high growth temperature up to 650 °C is developed to increase the In content of the InGaN SQW to 30% while maintaining a strong luminescence intensity near a wavelength of 506 nm. The indium composition in InGaN/GaN SQW grown under group-III-rich condition increases with increasing growth temperature following the growth model of liquid phase epitaxy. Further increase in the growth temperature to 670 °C does not improve the photoluminescence property of the material due to rapid loss of indium from the surface and, under certain growth conditions, the onset of phase separation

[en] GaN-based Schottky barrier diodes (SBDs) with single-crystal Al barriers grown by plasma-assisted molecular beam epitaxy are fabricated. Examined using in-situ reflection high-energy electron diffractions, ex-situ high-resolution x-ray diffractions, and high-resolution transmission electron microscopy, it is determined that epitaxial Al grows with its [111] axis coincident with the [0001] axis of the GaN substrate without rotation. In fabricated SBDs, a 0.2 V barrier height enhancement and 2 orders of magnitude reduction in leakage current are observed in single crystal Al/GaN SBDs compared to conventional thermal deposited Al/GaN SBDs. The strain induced piezoelectric field is determined to be the major source of the observed device performance enhancements.

[en] The spontaneous surface luminescence properties of InGaN/GaN quantum structure lattice (QSL) are reported. The QSL consists of a two-dimensional array of InGaN/GaN quantum boxes (QBs) arranged in a rectangular pattern of 200 nm periodicity. The measured angular dependent photoluminescence (PL) spectra show a strong dependence on the in-plane Bragg diffractions between QBs. The maximum PL intensity of the InGaN/GaN QSL array that fulfill the Bragg condition points in the normal direction of the sample surface with a narrow radiation angle of ∼ ±12°. In addition, a small side lobe is also shown at ±40°. For the QSL sample that does not fulfill the Bragg diffraction condition, the radiation pattern shows a conventional cosine distribution. The finite-difference time-domain numerical analysis confirms that the lowest order and higher order Bragg diffractions between QBs determine the main and the small side lobe of the radiation pattern measured in QSLs, respectively

[en] Thermal wet oxidations of GaP and Al_0.4Ga_0.6P at 650 degree sign C for various times have been performed. Comparisons are made on oxidation rates and post oxidation morphology. Transmission electron microscopy shows that when oxidizing GaP, polycrystalline monoclinic GaPO₄·2H₂O forms without noticeable loss of phosphorus. Oxidation for 6 h or more leads to poor morphology resulting in cracks and detachment. A thickness expansion of about 2.5-3 times is noticed as a result of oxidation. In contrast, oxidized Al_0.4Ga_0.6P exhibits much better morphology without cracks or detachment from the substrate. The oxide has an almost amorphous-like microstructure. The oxidation process shows typical diffusion-limited reaction at long anneals. Preliminary work on the oxidation of AlP indicates that the reaction leads to formation of Al₂O₃ and possible volatile P₂O₅ diffusing out of the specimen. Thus, from the structural viewpoint, AlGaP forms a better oxide suitable for device needs. (c) 2000 American Institute of Physics

[en] A comparison of the water vapor oxidation characteristics of AlAs, Al_0.98Ga_0.02As, and an Al_xGa_1-xAs digital alloy was performed. The Al_xGa_1-xAs digital alloy consists of periods of 49 monolayers of AlAs and 1 monolayer of GaAs and has an equivalent composition of x=0.98. Oxidation rates and the structural integrity of the three layers were compared. When oxidized in water vapor, the Al_xGa_1-xAs digital alloy and the AlAs have similar oxidation rates, both of which are twice as fast as the Al_0.98Ga_0.02As layer. Post-oxidation annealing of these samples at 450 degree sign C showed severe delamination at the oxide/GaAs interface in the AlAs sample while the Al_xGa_1-xAs digital alloy sample was not damaged. (c) 2000 American Institute of Physics

[en] The interface when switching from AlAs to GaAs during solid source molecular-beam epitaxial growth is investigated. The growth conditions for the AlAs layers were kept constant except for the As overpressure. Using a valved As cracker cell, we varied the V/III flux ratio from ∼5.0 to ∼25.0. Cross-sectional transmission electron microscopy, photoluminescence spectroscopy, and reflectivity measurements from distributed Bragg reflectors indicate that the material quality tends to improve with increasing dimeric As overpressure. Using secondary ion mass spectroscopy, it is shown that the rough interfaces are due to oxygen accumulation at the AlAs growth front. It is believed that arsenic forms an oxide with the oxygen on the AlAs surface, which is subsequently desorbed away at typical growth temperatures. For samples grown at higher overpressures, there is more arsenic present to remove the oxygen thereby resulting in a smoother interface (c) 2000 American Vacuum Society