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We present a technique which permits a quantitative spectroscopy of discrete quantum levels in semiconductor microstructures. The method involves monitoring the capacitance signal resulting from single-electron tunneling. In a microscopic capacitor fabricated in GaAs we study the confined states of a single 1 μm disk to which electrons can tunnel from a nearby metallic layer. Charge transfer occurs only for bias voltages at which a quantum level is resonant with the Fermi energy of the metallic layer. This creates a sequence of distinct capacitance peaks whose bias positions can be directly converted to an energy scale to determine the electronic spectrum of the confined structure. The evolution of the spectrum in magnetic fields allows deduction of the nature of the bound states.

Recent advances in probe design have led to enhanced resolution (currently as significant as ~ 12 nm) in optical microscopes based on near-field imaging. We demonstrate that the polarization of emitted and detected light in such microscopes can be manipulated sensitively to generate contrast. We show that the contrast on certain patterns is consistent with a simple interpretation of the requisite boundary conditions, whereas in other cases a more complicated interaction between the probe and the sample is involved. Finally application of the technique to near-filed magneto-optic imaging is demonstrated.

The resolution of optical microscopy can be extended beyond the diffraction limit by placing a source or detector of visible light having dimensions much smaller than the wavelength, λ, in the near‐field of the sample (

The optical properties of a one-dimensional (1D) electron gas with only one or two occupied subbands have been studied in semiconductor quantum wires, obtained by electron beam lithography and subsequent low-energy ion bombardment of modulation-doped GaAs quantum wells. Large optical singularities have been observed at the Fermi level, both in optical absorption and emission. They disappear at temperatures comparable to the Fermi energy. The 1D singularities are much larger and sharper than in 2D systems due to the lack of certain hole recoil effects in 1D. The experimental data are in qualitative agreement with theoretical results based on the exact diagonalization of finite chains.

We demonstrate that ballistic electrons in ultra-high mobility two-dimensional electron systems can be controlled in ways analogous to the manipulation of photons in optical systems. Among the electron-optical structures we demonstrate are emitters, detectors, absorbers, and refractors. These advances may enable the design of new types of electronic circuits.

Modulation-doped quantum wire structures have been fabricated in the extreme quantum limit in which only the lowest one-dimensional (1D) subband is occupied by electrons. A pronounced Fermi edge singularity is observed for the first time in the absorption and emission spectra of the 1D electron gas. It has a strong temperature dependence determined by the Fermi energy and is much sharper than in two dimensions. The experimental results agree qualitatively with exact diagonalization studies of finite Hubbard chains.

A hybrid near‐field/fiber laser probe has been developed for high flux, reflection mode optical imaging of surfaces on a subwavelength scale. Spatial resolution of ∼100 nm (i.e., ∼λ/10 at λ=1060 nm) has been achieved simultaneously with signals of ∼1014–1015 photons/s, an improvement of ∼103–104 over earlier designs. The probe thus represents an important step in the development of advanced near‐field transducers for high bandwidth applications such as high density data storage.

Modulation‐doped GaAs/AlGaAs quantum wires have been fabricated using electron‐beam lithography followed by electron‐cyclotron resonance reactive ion etching to selectively deplete the electron gas. This technique has the advantages of low damage to the quantum well, strongly anisotropic etching, and reproducible control over the etch depth. The quantum wires exhibit high photoluminescence efficiencies when etched as close as 200 A to the electron gas. The fundamental gaps show the large optical red shifts associated with strongly spatially indirect transitions. The spacings between one‐dimensional subbands determined from inelastic light scattering measurements are larger than 2 meV.

We demonstrate the use of an ultrathin (≊5 nm) Si layer deposited on InP substrates as a mask in selective area epitaxy of InGaAs by metalorganic molecular beam epitaxy. Patterns of varying shapes and sizes, from 5 to 0.5 μm, were written on the mask by focused Ga ion beam and etched by Cl2. The growth rate of InGaAs was studied by scanning force microscopy using stripes with guard rings spaced as close as 0.5 μm from the stripes. A small increase in the growth rate was detected only when the feature size was lower than 5 μm, and the growth rate was not affected by the presence of the guard rings. This shows that precursor material is being transferred from the slow growing {111}‐planes to the (100)‐plane, and that migration of species from the Si mask to the growing areas is negligible.

A distance regulation method has been developed to enhance the reliability, versatility, and ease of use of near‐field scanning optical microscopy (NSOM). The method relies on the detection of shear forces between the end of a near‐field probe and the sample of interest. The system can be used solely for distance regulation in NSOM, for simultaneous shear force and near‐field imaging, or for shear force microscopy alone. In the latter case, uncoated optical fiber probes are found to yield images with consistently high resolution.

We report the fabrication of strong Bragg reflectors embedded into fiber matched silica on silicon waveguides. First order gratings are dry etched into the waveguide core and are covered with a thin Si3N4 layer prior to cladding deposition. Reflection bands 225 A wide for TE and 193 A wide for TM polarizations are obtained with 200 A Si3N4 cover layers. The TE and TM spectra are overlapping, resulting in nearly polarization independent Bragg reflectors.

Heterostructures of InGaAs/InP have been grown selectively through windows in SiO2‐masked InP substrates using metalorganic molecular beam epitaxy. The structures show high cathodoluminescence efficiency for window sizes down to 5 μm. A significant red shift, consistent with compressive lattice strain, and reduced intensity are observed for smaller features. Anomalous growth is observed near the edges of the windows. Selectively grown InGaAs/InP p‐n junctions and bipolar transistors exhibit excellent electrical characteristics after removal of 1–2 μm of edge material.

We demonstrate the novel application of the scanning tunneling microscope to find and probe the electronic transport properties of single semiconductor nanostructures at temperatures from room temperature to as low as 1.5 K. The current‐voltage characteristics of InGaAs/InAlAs resonant tunneling nanostructures clearly show negative differential resistance. From the dependence of the current on cross‐sectional area the lateral depletion is estimated to be 300 A.

In near-field scanning optical microscopy, a light source or detector with dimensions less than the wavelength (lambda) is placed in close proximity (lambda/50) to a sample to generate images with resolution better than the diffraction limit. A near-field probe has been developed that yields a resolution of approximately 12 nm ( approximately lambda/43) and signals approximately 10(4)- to 10(6)-fold larger than those reported previously. In addition, image contrast is demonstrated to be highly polarization dependent. With these probes, near-field microscopy appears poised to fulfill its promise by combining the power of optical characterization methods with nanometric spatial resolution.

In this article, we review the recent progress on GaAs MOSFET's using in-situ MBE-grown Ga2O3(Gd2O3) as the gate dielectric. Both depletion-mode (D-mode) and inversion-mode (I-mode) GaAs MOSFET's with negligible drain current drift and hysteresis are demostrated. The absence of drain current drift and hysteresis indicates that the excellent stability of the oxide and low oxide/GaAs interface state density have been achieved. The drain current density and transconductance are about one order of magnitude higher than the best previous reported data in the literature for an inversion-mode GaAs MOSFET. Excellent high frequency and power performances were also measured from the depletion-mode devices. These improvements are attributed to the excellent Ga2O3(Ga2O3) oxide properties and novel processing techniques.

We have developed a complete lithographic process combining focused ion beam writing, dry etching, and molecular beam epitaxy for in situ preparation of buried InP‐based microstructures. A focused ion beam is used to locally remove an ultrathin oxide imaging layer grown in situ on the surface of InP. The pattern is transferred into the underlying semiconductor by free Cl2 etching with the patterned oxide layer acting as an etch mask. After removal of the oxide mask, GaInAs/InP heterostructures with excellent morphology and high luminescence efficiency can be grown on the patterned substrate. The entire process of mask formation, lithography, and regrowth can be carried out in situ repeatedly, and used for creating fully buried microstructures.

We have fabricated single quantum wires and quantum wire arrays of nanometer scale lateral dimensions. The wires are produced by two steps of epitaxial growth in orthogonal directions. We utilize the concept of pseudomorphic growth of lattice mismatched epitaxial layers to generate strain modulation within the plane of a conventional quantum well. The strain modulation, as large as 2%, modulates the electronic band structure for carrier motion parallel to the quantum well plane. These potential modulations which are of order 0.1 eV, confine carriers laterally to regions comparable in size to the size of a quantum well. We present in this work optical studies of these one dimensional systems by means of low temperature cathodoluminescence, photoluminescence, photoluminescence excitation and time resolved spectroscopies. We analyse our observations using a new multi-band effective mass and deformation potential model. The measured optical transitions and polarization selection rules agree well with the model. In particular, we find that electrons and light holes are laterally confined to the same region while heavy holes are spatially separate from them. Finally, we demonstrate a novel p-i-n linear junction which provides a means to electrically contact these one-dimensional quantum structures.

Modulation doped quantum well wires have been fabricated in the one-dimensional (ID) quantum limit, where only the first ID band is occupied. Novel properties have been found in the optical spectra. Strong Fermi edge singularities are present which markedly differ from the 2D case due to the hole recoil and phase space filling properties unique to ID. The elementary excitations of the ID electron gas have also been investigated, and the ID intraband plasmon dispersion relation has been measured. Very good quantitative agreement is found with the linear dispersion expected for ID systems.

Selective area growth is used in the fabrication of Si epitaxial devices such as bipolar transistors. This growth technique facilitates the preparation of very complex self-aligned and buried transistor structures. Selective growth has been investigated in the III-V materials, without, however, any significant results pertaining to the optical or electrical quality of the material grown, or device results. In this work, we investigate selective growth of InP and GaInAs on S'02-masked InP substrates using metalorganic molecular beam epitaxy (MOMBE). Group Ill and V elements are derived from triethylgallium and trimethylindium, and AsH3 and PH3 respectively. Excellent selectivity is achieved in the temperature range from 5 10 to 540 deg C.

Spatial light modulators (SLMs) designed to replace photomasks for optical lithography have been designed, fabricated, and tested. These microelectromechanical devices are fabricated with alternating polycrystalline Si and sacrificial SiO2 layers that are patterned by a 193nm wavelength scanner to dimensions as small as 150nm. Aerial image simulations were used to define the mechanical requirements of the devices. Piston motion of electrically actuated devices was measured with an optical profilometer. The measurements were fit to a simple equation to within 1nm precision, which is adequate for defining 50nm features lithographically. Transient response measurements show that one version of the SLM responds to actuation as quickly as 20μs, fast enough for current 193nm wavelength excimer laser sources.

We have studied the optical properties of buried InGaAs/InP nanostructures fabricated by in situ focused gallium ion beam writing, dry etching, and overgrowth by gas source molecular beam epitaxy. Due to the small size and buried nature of these structures, cathodoluminescence imaging and spectroscopy are the most suitable techniques for studying them. We have determined the dose dependence of their optical properties and have fabricated fully buried quantum wires. We find high quantum efficiency of optical emission from structures as small as 2000 A in lateral extent. With improvements in the in situ processing it should be possible to fabricate fully buried nanostructures as small as a few hundred angstroms in laterial dimensions.

The biaxial tensile stress of 2.65 kbar in as‐grown GaAs/Si is reduced by post‐growth patterning of the GaAs and the reduction in stress is dependent on the pattern size and shape. For stripe patterns less than 15 μm wide the stress becomes largely uniaxial with stress relief normal to the stripe direction. Rectangular patterns exhibited stress relief in orthogonal directions, and have the lowest stress in the narrow direction of the rectangle. A 9×12 μm2 rectangle exhibited an average stress of 0.5 kbar.

Recent progress of GaAs-on-Si technology is reviewed and the importance of initial nucleation is emphasized. Growth initiation with a gallium prelayer at a suitable low temperature combined with migration enhanced epitaxy and in-situ thermal annealing may be able to give substantially improved material quality. During the initial growth, use of the minimum necessary As4:Ga flux ration is found to be critical. Patterned growth or post-growth patterning releases tensile stress only if the growth edges are free. GaAs-on-Si was almost completely relaxed from stress by post-growth patterning to 5 μm × 5 μm size patterns. Steps on the surface owing to substrate misorientation do not affect the two-dimensional electron gas (2DEG) transport properties in AlGaAs/GaAs selectively doped heterojunction transistor (SDHT) structures. For a sheet density of 1012 cm−2, a 2DEG mobility greater than 50 000 cm2 V−1 s−1 at 77 K was obtained on silicon substrates, which was found to be adequate for the fabrication of the state-of-the-art devices. For 1 μm-gate-length SDHTs, maximum transconductances of 220 and 365 mS mm−1 were measured at 300 K and 77 K, respectively. A minimum propagation delay time of 28 ps stage−1 was measured at 300 K for direct coupled field effect transistor logic (DCFL) ring oscillators with a power dissipation of 1.1 mW stage−1. The propagation delay time reduced to 17.6 ps stage−1 at 77 K. These results are comparable to the SDHT technology on GaAs substrates.

We summarize the electric-field dependence of absorption and luminescence in quantum wells for fields perpendicular to the layers, present extended discussion of electroabsorption spectra and devices in waveguide samples, and derive sum rules for electroabsorption. Optical bistability, self-linearized modulation, and optical level shifting are demonstrated in self-electrooptic effect device configurations, with good modulation contrast and polarization-dependent properties. The electroabsorption spectra enable quantitative comparison of theory and experiment for absorption strengths in quantum wells with field. The sum rules enable excitonic effects to be included in the comparison, and good agreement is seen. One sum rule is also more generally applicable to electroabsorption in semiconductors.

The necessity for an adequate salt intake for people working in hot climates has been recognized for a long time (Moss, 1923). Salt deficiency is with some certainty known to cause heat cramps (Talbott, 1935 ; McCance, 1936 ; Ladell, 1949) and is very likely the cause of lesser degrees of ill health and inefficiency (Taylor, Henschel, Mickelsen, and Keys, 1943 ; Ladell, Waterlow, and Hudson, 1944). To understand how such ill-effects arise, it is obviously necessary to establish the changes in salt metabolism associated with sweating at high temperatures. In reviews of this matter Ladell (1945) and Robinson (1949) have pointed to the confusion in the literature regarding the exact effects of dietary chloride and acclimatization on the chloride content of the sweat. The recent experi ments of Conn and Johnston (1944; Conn, Johnston, and Louis, 1946) have thrown much light on this problem. This work indicates that when the salt loss during exposure to heat is greater than the dietary supply, the " negative " balance may only be temporary ; a restriction in both sweat and urine chloride output takes place so that after some days the salt deficit is made good and the total salt output is readjusted to the level of intake. Conn's work is important in showing that balance is possible at levels of salt intake even as low as 6 g. per day for men sweating 5-6 kg. a day. Unfortunately, this, as well as earlier work, may give the impression that this restriction in salt loss is necessarily or invariably a part of the process of acclimatization to heat, whereas in logical extension of Conn's findings one would expect no decrease in sweat chloride on a sufficiently high salt intake. The sweat chloride content on higher salt diets during the acclimatization period seems not as yet to have been investigated in experiments like those of Conn in which the subjects lived continuously in the heat. In the earlier work of Black, McCance, and Young (1944), h wever, in which recumbent individuals were exposed daily for short periods in a radiant heat bath, a decrease in sweat chloride output did not, in fact, occur on a high salt diet whereas on a low level of intake a decrease took place. Th experiments reported in this paper are similar to those of McCance (1936) and Black, McCance, and Young (1944), in that they involve short periods of exposure to heat. They were carried out on working subjects exposed to strictly standardized condi ions of work. When this investigation was nearly completed, papers by Robinson, Kincaid> an Rhamy (1950) appeared in which they reported results with which those of the present experiments are in substantial accord. It seems useful to ecord our results, for in addition to confirmation of an important physiological response to hot climates, they are concerned also with ano her aspect of this problem. In our experiments chlorid analysis was made not only of the body swe t from the general body surface but also on sweat collected in arm bags. The difference in the composition between the sweat from these two collections helps to explain some of the confusion referred to by Robinson (1949) and Ladel (1945). Finally, a separate series of ex periments on unacclimatized persons is presented because of its bearing on the " salt conserving " responses of the body at high temperatures.

SUMMARY The output of urinary adrenocorticoids has been studied in man before, during and immediately after exposure to high environmental temperatures. The results indicate that while there was no significant change in the excretion of 17-hydroxycorticoids, cortisone and cortisol or of tetrahydrocortisone and tetrahydrocortisol there was a significant increase in the output of aldosterone.

Time‐resolved band‐to‐band photoluminescence offers a quick and contactless technique for determining the photoexcited free carrier lifetime in GaAs samples with deep traps.

We report the first measurements of perpendicular field electroabsorption (quantum confined Stark effect) in GaAs/AlGaAs quantum wells for light propagating parallel to the plane of the layers. This geometry is well suited for integrated optics. The absorption edge shifts to longer wavelengths with increasing field by as much as 40 meV, giving a modulation depth>10 dB. The strong dichroism present in this geometry is retained even at high fields, making polarization‐sensitive electro‐optical devices possible. We also demonstrate in the waveguide geometry optical bistability due to the self‐electro‐optic effect with 20:1 on/off ratio.

The warpage of GaAs‐on‐Si wafers, caused by the different thermal expansion coefficients of GaAs and Si, has been studied as a function of the GaAs thickness on 3‐in.‐diam Si wafers. The warpage increases from 7 to 52 μm as the GaAs layer thickness increases from 1.2 to 4.2 μm. Under vacuum clamping conditions the GaAs/Si wafers can be forced to the original flatness. By growing GaAs selectively through a Si shadow mask as islands of 1 mm×1 mm size with a periodicity of 2 mm in a 5 cm×5 cm central area of the wafer, the warpage is reduced considerably. Spatially resolved cathodoluminescence (CL) spectra indicated that the tensile strain is reduced significantly within 10 μm from the edge of the growth. Near the edge, the CL intensity is also increased indicating a reduction in nonradiative recombination at defects. The use of the Si shadow mask to obtain patterned growth is relatively simple, requiring no processing step before or after the growth, and has a great potential in the integration of GaAs and ...

We demonstrate a combination of focused Ga beam writing and dry etching techniques to pattern InP wafers in a common vacuum chamber. Surface steps on the order of 1000 A can be efficiently prepared using moderate Ga ion fluences. The implanted areas exhibit a faster etch rate, even for Ga doses below ∼1014 cm−2. The implantation damage is removed by the low‐energy Cl‐assisted ion beam etching as shown by the high quality of p‐n junctions grown on etched surfaces. GaInAs/InP heterostructures grown on in situ patterned substrates show excellent morphology and high luminescence efficiency.

The first investigation of nonlinear absorption in InGaAs/InAlAs multiple quantum wells using picosecond and cw infrared lasers is presented. The nonlinearity is demonstrated to be due to plasma‐induced excitonic bleaching. The measured saturation densities agree with those predicted by theory.

We propose a new two‐coupled‐waveguide structure for second harmonic generation. An input TEω0 mode is phase matched to a harmonic TM2ω1 mode by varying the separation between the guides. Calculation of conversion efficiency in an AlGaAs structure gives 12% for 10 mW of input power at 1.3 μ over a 2‐mm phase‐matched length.

We demonstrate a vacuum lithography process which uses a finely focused Ga ion beam to write the pattern which is then transferred to the InP pattern by low energy dry etching. Surface steps on the order of 1000-2000A in height, and lateral resolution limited only by size of the ion beam, can be efficiently prepared using moderate Ga ion fluences. The surfaces prepared by this process are damage free and suitable for epitaxial overgrowth. GaInAs/InP heterostructures grown on in-situ patterned substrates show excellent morphology and high luminescence efficiency.

There is considerable interest in external modulators for optical fiber data transmission systems. In contrast to direct laser modulation, this should allow higher transmitter power injected into the fiber, provide signals that have a transform-limited optical spectrum under high-speed modulation, and produce a better on/off ratio. We have previously demonstrated a high-speed electroabsorption modulator made from multiple quantum wells(MQWs) of GaAs/AIGaAs.1 In this device, the light propagated perpendicular to the MQW layers, so there was less than 1 μm of optical interaction length. Nevertheless, this device demonstrated a 131 ps impulse response speed, with an on/off ratio of 1.7:1.2

Recent progress of GaAs-on-Si technology is reviewed and the importance of initial nucleation is emphasized. Growth initiation with a Ga prelayer at a suitable low temperature combined with migration enhanced epitaxy and in-situ thermal annealing has a prospect of giving substantially improved material quality. During the initial growth, use of the minimum necessary As4/Ga flux ratio is found to be critical. The random alignment of the major axis of the oval defects is suggested to be an alternative simple technique to detect the presence of antiphase domains. Patterned growth or post growth patterning releases tensile stress only if the growth edges are free. GaAs-on-Si was completely relaxed from stress by post-growth patterning to 5 μm × 5 μm size patterns. Steps on the surface due to substrate misorientation do not affect the two dimensional electron gas (2DEG) transport properties in AlGaAs/GaAs selectively doped heterojunction transistor (SDHT) structures. For a sheet density of 1012 cm−2, the 2DEG mobility >50,000 cm2V−1s−1 at 77 K was obtained on Si substrates, which is sufficient for fabrication of high performance SDHTs. The study shows that GaAs-on-Si has a great potential for SDHT technology.

We report the first measurements of excitonic absorption in undoped GaAs single quantum wells for light propagating along the plane of the layers. We also observed for the first time nonlinear absorption for a field polarized normal to the layers. The samples consisted of leaky waveguide structures in which a single GaAs quantum well is embedded in a GaAs/AlGaAs superlattice grown on a GaAs substrate. The quantum wells exhibit two series of excitons formed from the electrons and the predominantly heavy holes (hh) or the predominantly light holes (lh), respectively. When the incident polarization was parallel to the layers (solid curve in Fig. 1) we observed both hh and lh excitons in agreement with previous measurements.1 We have also observed for the first time linear and nonlinear absorption for the perpendicular polarization (dashed curve in Fig. 1).

Physiological responses to physical exercise were measured in 203 Sudanese villagers and cleaners of irrigation canals in order to assess the effect of Schistosoma mansoni infection on work capacity. The investigations were carried out on economically active males (18–45 years old) of Gezira villages, where no mass antischistosomal treatment or molluscicidal applications had been made. Before the physiological tests, all subjects received antimalarial prophylaxis (chloroquine phosphate). There was a statistically significant difference (P 2,000 eggs/g). Age, body weight, stature, lean body mass, leg muscle volume, and nutritional status were similar for canal cleaners and villagers. However, the villagers had a significantly higher (P < 0.001) mean hemoglobin concentration compared to that of canal cleaners which would at least partly explain the difference in O2 max. The results of this study provide quantitative evidence of the adverse effect of high levels of S. mansoni infection on physical working capacity.

In optical experiments with laterally patterned modulation-doped GaAs/AlGaAs quantum wells we observe spatially separate confinement of electrons and holes to one-dimensional quantum wires. We determine the one-dimensional subband spacing and Fermi energy from inelastic light scattering and photoluminescence spectra. From these measurements we directly determine the one-dimensional electron density.

Physiological tests of work performance and measurement of field productivity were made in 194 Sudanese cane cutters in order to study the effect of Schistosoma mansoni infection. The cane cutters were selected from two age ranges (16-24 and 25-45 years) and subdivided into three clinical groups: not infected, infected with, and infected without clinical signs of hepatosplenomegaly. Men infected with Schistosoma haemotobium, malaria (blood film), or with hemoglobin levels less than 10 g/100 ml were excluded. There was a statistically significant (P less than 0.002) higher mean hemoglobin concentration in those not infected but the mean difference was less than 1 g/100 ml. Submaximal responses to exercise on a stationary bicycle ergometer, oxygen intake, ventilation, tidal volume, cardiac frequency and estimated maximal aerobic power output calculated both in absolute terms and relative to lean body mass and leg volume were similar in the six groups of cane cutters. No significant differences were found in physique, body composition or in thermoregulatory function tests. The cane cutters were found to have little natural acclimatization to heat in terms of sweating capacity when compared with a group of fully acclimatized Sudanese soldiers. The mean productivity (mean daily weight of cane cut per man) was significantly correlated with the individual's estimated maximum aerobic capacity determined in the laboratory, but not with the degree of S. mansoni infection. The noninfected group was less "efficient" (mean productivity:oxygen intake) during cutting than the infected groups but a larger proportion of the noninfected were in their first season of cutting. There was a positive correlation between the number of seasons' cutting experience and the individual's age, degree of infection and mean productivity. Cane cutters studied in this investigation were a relatively fit, active population from whom the more seriously ill were excluded. These results do not, therefore necessarily reflect the effects of S. mansoni on physiological work capacity and productivity of more static populations in areas of high endemicity.

The biaxial tensile stress of 2.65 kbar in as-grown GaAs/Si for T < 100K is reduced by post-growth patterning of the GaAs and the reduction in stress, as determined by photoluminescence and cathodoluminescence, is dependent on the pattern size and shape. For stripe patterns less than 15 gm wide the stress is largely uniaxial with stress relief normal to the stripe direction. Rectangular patterns exhibited stress relief in orthogonal directions, and a 9 x 12 µm2 rectangle exhibited an average stress of 0.5 kbar. For as-grown GaAs/Si layers 0.9 to 3.25 µm thick, the stress is weakly dependent on layer thickness. For T > looK the stress in as-grown GaAs/Si is reduced and at 295K a value of 1.51 ± 0.21 kbar is obtained. With patterned growth, using a native SiO2 mask, no reduction in stress was observed irrespective of the pattern size, indicating the importance of free GaAs edges in obtaining stress relief.