The control and characterisation of wafer defect and strain distributions is of crucial importance for the development of advanced Ultra Large Scale Integration (ULSI) circuits. Within the IC manufacturing sector 0.35 μm linewidth-based advanced Complementary Metal Oxide Semiconductor (CMOS) logic has recently emerged at a high level of maturity, to be closely followed by an even more demanding 0.25 μm process. One very important issue is the need to ensure a uniform, high quality Si substrate, i.e. minimise defect densities and eliminate strain distributions in the starting wafer material. Synchrotron section and back-reflection topographic techniques were applied to 200 mm diameter p-Si wafers, upon which, boron and arsenic doped epitaxial silicon layers had been deposited. These wafers were supplied from manufacturers around the globe and revealed substantial differences in the overall quality of the epilayers and substrates. In all wafers the substrate quality varied significantly with position across the wafer, as measured by the presence of oxygen-related defects and dopant strain homogeneity. The strain field uniformity, induced by the growth of lightly doped Si epilayers, was also observed to vary qualitatively with location on a wafer. Back-reflection topographs verify that the quality of the epilayer-substrate interface improved as the thickness of the epilayer, or the gradient of dopant density across the interface, is reduced. Cellular strain-related structures, of the order of a few hundred μm in circumference, have been observed in the more stressed p on p+ samples. Topographic results are in agreement with those obtained from X-ray diffraction measurements. Finally, an examination was carried out into the quality of commercially supplied 200 mm diameter Si wafers, revealing differences in the overall quality of the wafers.

High quality quantum dots have been fabricated by using self-organized InP islands as stressors. The tensile strain due the islands creates local potential minima in an InGaAs/GaAs quantum well under the islands, and confines both electrons and holes into these minima. The ground state emission from the dots is redshifted by up to 105 meV from the quantum well emission due to this lateral confinement potential, and clearly resolved emission peaks are observed from the excited states. From the time-resolved photoluminescence measurements an interlevel relaxation time of 0.6 ns between the first excited state and the ground state and a radiative lifetime of 0.9 ns for the quantum dot ground state are obtained. Photoluminescence up-conversion measurements show subpicosecond onset of the dot luminescence at high excitation densities, suggesting that Coulomb scattering is responsible for the fast capture process. A large Zeeman splitting of the higher angular momentum states is observed in a magnetic field perpendicular to the sample surface.

Large area transmission and section topographs of semi-insulating gallium arsenide wafers grown by the gradient freeze technique are made with synchrotron radiation at HASYLAB in Hamburg and at ESRF in Grenoble. Several high-resolution images including stereo pairs are obtained on the same film at a time. A typical dislocation line is an arc of a circle which starts from one surface and ends at the same surface. From the disappearance of the dislocation image and using the g · b = 0 criterion it is concluded that the Burgers vector b of the most common dislocations is parallel to ‹110›. Rather large volumes of the wafer are dislocation-free. Section topographs of epitaxial wafers show defects and strain fields at the interface between an n-type substrate and the epitaxial layers grown by chemical vapor deposition. The results are compared with those obtained from detector performance measurements.

The effects of growth temperature, InAs deposition thickness and deposition rate on the areal density, size, uniformity and spatial distribution of self-organized InAs nanoscale islands grown on exact and vicinal (100) InP substrates by metalorganic vapor-phase epitaxy are investigated in detail by AFM. At 500°C, the island density is found to increase as the InAs deposition thickness is increased, while the average island size decreases slightly. At growth temperatures above 500°C, larger inhomogenous islands also appear. Decreasing the deposition rate increases the island density and substrate coverage. The unintentional As/P exchange is found to have a significant influence on island formation by producing excess material for the islands. Low-temperature photoluminescence from the recombination of carriers in the buried InAs islands is observed in the 1.4 – 1.8 μm spectral region.

The continued decrease in critical dimensions and increasing integration levels in Si CMOS technology is imposing ever tighter constraints on quality control parameters for the IC manufacturing industry. One very important issue is the need to ensure a uniform, high quality Si substrate, i.e. minimise defect/dislocation densities and eliminate strain distributions in the starting wafer material. A comprehensive Synchrotron X-Ray Topography (SXRT) study was applied to commercially supplied 200mm diameter Si wafers. These wafers, which all included a surface Si epilayer growth were supplied from manufacturers from around the globe. The study revealed not only differences in the overall quality of the wafers, but also differences in the quality of the individual Silicon epilayers and substrates. In all wafers the substrate quality varied dramatically with position across the wafer, as measured by the distribution of oxygen precipitates and stacking faults in the wafer. This distribution also varied significantly from manufacturer to manufacturer. The strain fields induced by the growth of lightly doped Si epilayers were also observed to qualitatively vary with location on a wafer, together with (as expected) thickness of the epilayers. The results clearly indicate that optimal quality control for such commercial wafers has not yet been achieved.

Section topographs made with synchrotron radiation show the strain field below the surface of silicon wafers which have gone through a process for integrated circuits. The contrast observed is a series of curved lines starting at one edge of an oxide layer and ending at its other edge. The strain is also calculated using the finite-element method. Electrical measurements such as the threshold voltage of a transistor are made in order to find the influence of the strain on the device performance and yield.

The strain of self-organized InP islands is used to induced quantum dots in near-surface GaInP/AlGaInP quantum wells. To obtain quantum dot luminescence in a widely tunable wavelength range of 630–700 nm, the composition and thickness of the GaInP quantum well is varied. The effect of different cap layer materials, i.e., GaAs, AlGaAs, GaInP, and AlGaInP on the InP island formation and quantum dot luminescence properties is investigated. The luminescence intensity ratio of the quantum dot peak to the quantum well peak is found to be highest when a GaAs cap is used.

An epitaxial method for in situ passivation of epitaxial AlxGa1−xAs/GaAs surfaces is reported. The deposition of an ultrathin InP layer (about one monolayer) on the surface of AlxGa1−xAs/GaAs structures by metalorganic vapor phase epitaxy results in drastically reduced surface recombination. The effect is studied by low-temperature photoluminescence of near-surface Al0.22Ga0.78As/GaAs quantum wells where the top barrier thickness is varied from 0 to 50 nm. At the thicknesses of ≤5 nm, the intensity from passivated samples is more than four orders of magnitude larger than that obtained from unpassivated structures. For a passivated surface quantum well where InP is deposited directly onto the GaAs quantum well, we observe a blueshift of 15 meV and an intensity reduction of only a factor of 10 as compared to the luminescence from a quantum well placed at a depth of 50 nm from the surface.

We have fabricated InGaAsP/InP separate confinement heterostructure multiple quantum-well lasers emitting at 1.43 mu m, which corresponds to a local absorption maximum of liquid water. We have carried out the modeling of the laser, including the calculation of gain, optical confinement factor, and threshold current, The laser structure was grown by atmospheric-pressure all-organometallic vapor-phase epitaxy. The study of the laser structure growth indicates that tertbutylphosphine partial pressure of 2.0 Torr or larger is necessary for the growth of layers with mirrorlike surface morphology, Photoluminescence measurements show that the optimum purge time between the growth of quaternary quantum-well and barrier layers is from 0.5 to 2.5 s, Lattice-matched 500-mu m-long devices with three quantum wells lased at a threshold current density of 1.35 kA/cm(2) with external quantum efficiency of about 25% per facet. These results are comparable with the results reported for lattice-matched 1.3- and 1.55-mu m devices, and are in agreement with the values obtained with laser modeling.

The authors report optical properties of in situ passivated AlGaAs and GaAs surfaces. The deposition of an ultra thin InP layer (about one monolayer) on the surface of AlGaAs/GaAs structures by metalorganic vapor phase epitaxy (MOVPE) results in drastically reduced surface recombination. The effect is studied by low-temperature photoluminescence (PL) of near-surface AlGaAs/GaAs quantum wells (QW) where the top barrier thickness is varied from 0 to 50 nm. At the thickness of 15 nm the intensity from passivated samples is more than four orders of magnitude larger than obtained from unpassivated structures. Photoreflectance (PR) measurements are used to determine the Fermi level pinning at the surface. The InP passivation is shown to reduce the surface pinning by about 0.3 eV