The physics of the growth mechanisms, characterization of epitaxial structures and device properties of GaAs and other compound semiconductors on Si are reviewed in this paper. The nontrivial problems associated with the heteroepitaxial growth schemes and methods that are generally applied in the growth of lattice mismatched and polar on nonpolar material systems are described in detail. The properties of devices fabricated in GaAs and other compound semiconductors grown on Si substrates are discussed in comparison with those grown on GaAs substrates. The advantages of GaAs and other compound semiconductors on Si, namely, the low cost, superior mechanical strength, and thermal conductivity, increased wafer area, and the possibility of monolithic integration of electronic and optical devices are also discussed.

Gallium arsenide and other compound semiconductors on silicon

The technology of high‐resolution focused ion beams has advanced dramatically in the past 15 years as focusing systems have evolved from laboratory instruments producing minuscule current densities to high current density tools which have sparked an important new process: direct micromachining at the micrometer level. This development has been due primarily to the exploitation of field emission ion sources and in particular the liquid‐metal ion source. Originally developed in the early 1960’s as a byproduct of the development of electrostatic rocket engines, the liquid‐metal ion source was adapted for focused beam work in the late 1970’s, when it was demonstrated that submicrometer focused ion beams could be produced with current densities greater than 1 A cm−2. Ions can be produced with liquid‐metal ion sources from elements including Al, As, Au, B, Be, Bi, Cs, Cu, Ga, Ge, Fe, In, Li, P, Pb, Pd, Si, Sn, and Zn. In the past decade, focused ion beam systems with liquid‐metal ion sources have had a signific...

High‐resolution focused ion beams

A direct, accurate and convenient procedure for calibrating the spring constants of probes used for force microscopy/spectroscopy is described. It amounts to deflecting an 'unknown' cantilever with a 'standard' lever, where the standard lever has been precalibrated. The absolute and relative accuracies of the procedure are ±20-30% and ±10-20%, respectively; the former is limited by uncertainties in the determination of the spring constant for the 'standard' lever, as well as that for the 'unknown'. The method differs from others of the static deflection variety by its exploitation of the routine features of current instruments. The technique is compared with other static and dynamic methods currently being used.

https://iopscience.iop.org/article/10.1088/0957-4484/7/3/014/pdf

Determination of the spring constants of probes for force microscopy/spectroscopy

We discuss recent advances made in the theory and measurements of stresses and strains in Si‐based heterostructures containing submicron‐ and micron‐size features Several reports on theoretical as well as experimental studies of stresses in the substrates with local oxidation of silicon structures on the surface have been published recently With the advent of GeXSi1−X strained layers and stripes extensive studies of both the stripe and the substrate stresses have also been made Unlike the previous calculations and analytical models, recent finite element (FE) calculations take into account the coupling between the film–substrate stresses without making the approximation that the interface is rigid or that there is no variation of stresses in the stripes in a direction perpendicular to the interface The results of these calculations have been compared with the analytical models and limitations of the analytical models have been pointed out Micro‐Raman measurements of the stresses in the stripes, quant

Stresses and strains in lattice‐mismatched stripes, quantum wires, quantum dots, and substrates in Si technology

We report a new method for the natural reduction of threading dislocations in GaAs on Si by growing on patterned Si substrates. We also explore other effects of patterning on dislocation formation during growth: stress relief near the mesa edges at high aspect ratios, and limited dislocation nucleation and propagation. Prior to growth, the Si substrates were processed to produce a plurality of mesas varying in width (5-170 μm) and geometry (circular, rectangular, and square mesas). After growth of the GaAs, the material was characterized with cathodoluminescence (CL) and secondary electron microscopy. For a GaAs growth temperature of 570° C and a thickness of 10 μm, the GaAs grown on the 40μ-wide Si mesas show a factor of 1.6 increase in luminescence intensity over the luminescence intensity from the unpatterned control area. Also, the emission wavelength from the smaller mesas is shifted to shorter wavelengths as compared to GaAs/GaAs and the unpatterned control area. The emission wavelength and CL intensity varies across the mesas; for 40 μm wide mesas, the emission wavelength is fairly constant across the mesa and the CL intensity decreases near the edges, whereas for larger mesas the emission wavelength decreases and the CL intensity increases at the mesa edges. For the 40 μm wide mesas, the integrated CL intensity is equal to that of a control GaAs/GaAs grown with the same doping level. No cracks were observed in the GaAs grown on the Si mesas, even though the thickness of the GaAs was 10 μ,m.

Epitaxial necking in GaAs grown on pre-patterned Si substrates

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.

In situ pattern formation and high quality overgrowth by gas source molecular beam epitaxy

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.

Optical and electrical properties of InP/InGaAs grown selectively on SiO2‐masked InP

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.

Vacuum lithography for in situ fabrication of buried semiconductor microstructures

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 ...

Warpage of GaAs‐on‐Si wafers and its reduction by selective growth of GaAs through a silicon shadow mask by molecular beam epitaxy

We demonstrate a direct‐write lithography process for InP wafers in which a finely focused Ga+ ion beam is used to form the pattern which is then transferred into the substrate by dry etching. The result is a patterned substrate which is suitable for epitaxial growth. We have combined the ion beam writing and dry etching in a common vacuum chamber with a gas source molecular beam epitaxy (GSMBE) system. GaInAs/InP heterostructures grown on the in situ patterned substrates show excellent morphology and high luminescence efficiency. Surface relief on the order of 1000–2000 A has been produced with this process using a 20 keV Ga+ ion beam. Lateral resolution is limited by the ion beam diameter, 2000 A.

J. S. Weiner

Papers

In situ pattern formation and high quality overgrowth by gas source molecular beam epitaxy

Optical and electrical properties of InP/InGaAs grown selectively on SiO2‐masked InP

Vacuum lithography for in situ fabrication of buried semiconductor microstructures

Warpage of GaAs‐on‐Si wafers and its reduction by selective growth of GaAs through a silicon shadow mask by molecular beam epitaxy

A focused ion beam vacuum lithography process compatible with gas source molecular beam epitaxy