Area Selective Epitaxy Research Articles

Structural properties of InAs‐based nanostructures grown on GaAs(001) and GaAs(111)A by area selective epitaxy

AbstractArea selective epitaxy (ASE) of InAs on patterned SiO2/GaAs(001) and SiO2/GaAs(111)A substrates has been investigated for various In flux intensities and substrate temperatures TS by using migration enhanced epitaxy (MEE). Transmission electron microscopy (TEM) indicates a different behaviour in the strain relaxation mechanism for ASE grown InAs structures on GaAs(001) and those grown on GaAs(111)A. In case of InAs/GaAs(001) Moiré‐like fringes due to strain relaxation are visible up to at least 35 nm in the InAs dot structure, while for InAs/GaAs(111)A the Moiré‐like fringes are confined at the interface. Furthermore, electron dispersion spectroscopy (EDS) showed a relatively high In concentration below the interface for InAs/GaAs(001) indicating the formation of a reaction layer even for structures grown at a low TS of 460 °C. For InAs on GaAs(111)A grown under the same conditions, almost no In was detected below the interface (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Area selective epitaxy of InAs on GaAs(0 0 1) and GaAs(1 1 1)A by migration enhanced epitaxy

Area selective epitaxy of InAs on semi-insulating GaAs(001) and GaAs(111)A substrates masked by SiO2 has been investigated by using migration enhanced epitaxy (MEE). Successful area selective epitaxy has been achieved in an optimized substrate temperature range 460°C<TS<500°C. Scanning electron microscopy and atomic force microscopy measurements indicated a competing behavior between an etching and a growth process in dependence of the substrate temperature and the annealing time ta after In deposition in the MEE sequence. The etching process is most likely connected to Ga dangling bonds along the {n11}A plane. Deposited In atoms react with Ga atoms in the open window area and are re-evaporated and/or incorporated into the InAs islands. In case of InAs growth on GaAs(001) no profound difference was found between structures grown by the MEE sequence and structures grown by simultaneous deposition of In and As. In contrast, for InAs/GaAs(111)A the growth mode changes drastically with the applied growth method.

Area-selective epitaxy of GaAs by migration-enhanced epitaxy with As 2 and As 4 arsenic sources

We demonstrate area-selective epitaxy by migration-enhanced epitaxy with As 2 and As 4 as arsenic sources. The distinct whisker structure growing in [1 1 1]B direction is obtained when employing As 2 as an arsenic source, while (1 1 1)B facet is formed with As 4. The difference in the facet formation can be explained by the formation of As-trimer, which significantly reduces the growth rate of the (1 1 1)B surface. With As 2, area-selective epitaxy can be achieved at lower arsenic pressure condition, where less As-trimers are formed. Therefore, growth in the [1 1 1]B direction is enhanced.

Selective epitaxy of InP on Si(1 0 0) substrates prepared by liquid-phase epitaxy

Selective liquid-phase (LPE) epitaxial growth of InP was performed on patterned Si(1 0 0) substrates. The growth temperature was rapidly cooled, then the crystal growth proceeded at constant temperature. As a result, area-selective epitaxy (ASE) and slight epitaxial lateral overgrowth (ELO) layers were achieved in narrow openings and small nuclei were observed in the wide openings. X-ray diffraction results show that the lattice strain in the InP nuclei on the Si substrate was fully relaxed. Huber etching revealed the dislocation-related etch pits in ASE layers, and it is shown that the etch pit density (EPD) is dependent on the length of open seed area.

Growth Mechanism of GaAs Microdisk Structures by Area-Selective Epitaxy Using Migration-Enhanced Epitaxy

We have carried out area-selective epitaxy of GaAs microdisk structures on a SiO2-masked GaAs substrate by migration-enhanced epitaxy. We have successfully grown “damage-free” disks at 590 °C. It is found that, for the structures grown on (111)B substrates, the facets surrounding the disks are controlled by the V/III beam equivalent pressure ratio. This characteristic is caused by the reduced growth rate in the [111]B direction under high V/III ratios. Using an optimized growth condition, uniform hexagonal GaAs disks surrounded by six vertical {110} facets and a flat (111)B top are grown. The microdisks grown on (001) substrates, however, show no flat-top structures, regardless of the V/III ratio, probably due to the fact that the growth rate in the (001) direction is not sensitive to the V/III ratio. In the latter case, square-pyramidal structures surrounded by four inclined {011} facets are obtained.

Area selective epitaxy of GaAs with AlGaAs native oxide mask by molecular beam epitaxy

We have carried out area selective epitaxy of GaAs on GaAs substrates using a native oxide film of AlGaAs as a mask material. By optimizing the AlAs fraction and the thickness of AlGaAs mask layer, well-defined area selective epitaxy has been achieved on (0 0 1) and (1 1 1)B GaAs substrates by migration-enhanced epitaxy. No discernible difference is observed in both the shapes and the facets of the grown structures between the growth using AlGaAs native oxide and SiO 2 masks. It is found that the shape of the grown structures can be easily controlled by As 4 pressure during growth. It has been proved that the AlGaAs native oxide film is useful as a mask material in area selective epitaxy instead of the SiO 2 mask.

Area selective epitaxy of indium phosphide on silicon (100) substrates without buffer layers by liquid phase epitaxy

Area selective epitaxy (ASE) of InP was performed by liquid phase epitaxy on Si (100) substrates without the use of buffer layers. At the start of epitaxy, the growth temperature was rapidly lowered to obtain high supersaturation. Epitaxial growth was then carried out at constant temperature. While small InP nuclei were observed in the broader open areas, ASE layers and layers showing slight epitaxial lateral overgrowth were formed in the narrow openings. Etch pit density of the InP ASE layers on Si is dependent on the length of open seed region and X-ray diffraction results indicate that the lattice strain in the InP nuclei on the Si substrate was fully relaxed.

17aB03 液相成長法によるSi(100)基板上のInp選択エピタキシャル成長(半導体エピ(1),第35回結晶成長国内会議)

17aB03 液相成長法によるSi(100)基板上のInp選択エピタキシャル成長(半導体エピ(1),第35回結晶成長国内会議)

Selective growth of C 60 layers on GaAs and their crystalline characteristics

C 60 films are grown uniformly and area selectively on GaAs substrates by molecular beam epitaxy. Their crystalline and optical properties are investigated by reflection high energy electron diffraction, X-ray diffraction, and photoluminescence measurements. The C 60 films are found to be grown epitaxially on the substrates. The epitaxial relationships are [001] GaAs[111] C60, [11̄0] GaAs[11̄0] C60 for GaAs (001) substrates and [111] GaAs[111] C60, [11̄0] GaAs[11̄0] C60 for GaAs (111)B substrates. Area selective epitaxy of C 60 on GaAs (111)B substrates is successfully achieved by using SiO 2 mask. Efficient photoluminescence is observed in both uniformly and area selectively grown layers. The observed spectrum appears in the same spectral region as that observed in bulk cubic C 60.

Growth of GaAs nanostructures by area selective epitaxy by migration-enhanced epitaxy

We have carried out area selective epitaxial growth of GaAs nanostructures using solid source molecular-beam epitaxy (MBE) which makes it possible to achieve ‘damage-free’ structures. However, area selective epitaxy by MBE is very difficult unless the substrate temperature is very high. This problem has been solved by using migration-enhanced epitaxy (MEE) deposition sequence. To achieve well-defined nanostructures, lateral growth beyond the SiO 2 mask boundaries has to be strictly prohibited. By MEE method, uniform two-dimensional lattice structures with vertical sidewalls can be fabricated without shrinking holes, even though the mask diameter is as small as 30 nm with a dot density as high as 5.0×10 9 cm −2 . Also uniform one-dimensional channel structures have been successfully grown.

Selective growth of C60/GaAs and the optical characteristic

Area selective epitaxy of C60/GaAs heterostructures on GaAs substrates masked by SiO2 has been investigated by solid-source molecular beam epitaxy. The crystallinity of the C60/GaAs heterostructures on GaAs planer substrates during growth is evaluated by reflection high-energy electron diffraction. The surface morphology of the mask substrate is then elucidated by scanning electron microscopy. Finally, the optical characteristic and selectivity are evaluated by microphotoluminescence.

Area-selective epitaxy and epitaxial lateral overgrowth of InP by liquid phase epitaxy on three integral axes

The area-selective epitaxy (ASE) and epitaxial lateral overgrowth (ELO) were performed on {0 0 1}-, {1 1 1}A,B- and {1 1 0}-oriented InP by liquid phase epitaxy at constant growth temperature (450–650°C). The as-grown surface and cross section were investigated by Nomarski interference optical microscope, SEM and confocal laser scanning microscope. From the cross sectional structure, area-selective epitaxy and ELO layers have shown {1 0 0} and {1 1 1}A,B facets on these surface. When compared with three integral axes, the vertical growth rate on {1 1 0} plane is the fastest among the three integral axes. According to the observations of cross sectional shape, the orientation dependence of vertical growth rate was determined to be {1 1 0}>{1 1 1}A,B>{1 0 0} under the present experimental conditions.

Ballistic and tunneling GaAs static induction transistors: nano-devices for THz electronics

GaAs static induction transistors (SIT) with 10-nm scale channel and with a 100-nm channel were fabricated with molecular layer epitaxy (MLE). Area-selective epitaxy of GaAs/AlGaAs/GaAs was used for the gate. Temperature dependence of current-voltage (I-V) characteristics of the 100-nm SIT indicates ballistic injection of electrons. In the 10-nm scale SIT, electrons are transported ballistically in the drain-side electric field. Direct tunneling is responsible for the transport through the potential barrier. It is indicated by the temperature dependence and by the electroluminescence spectrum. Electron transport in the 10-nm scale SIT is nearly scattering-free. The plausible estimation of the electron transit time is 2/spl middot/10/sup -14/ s; the worst case estimation based on saturated drift velocity gives 1/spl middot/10/sup -13/ s. It makes the ISITs suitable for THz applications. Multiple area-selective MLE GaAs regrowth was used as a tool for automatic definition of the channel length.

Growth of GaAs/InAs Antidot Structure by Solid-Source MBE

Area selective epitaxy of antidot structures of GaAs/InAs heterostructures on GaAs substrates masked by SiO2 has been investigated by solid-source molecular beam epitaxy. 100-nanometer-scale antidot structures have successfully been grown by a migration-enhanced deposition sequence. When the diameter of a SiO2-covered hole is larger than 150 nm, the sidewalls exhibit triangular shapes because of the formation of inclined {110} facets. However, when the diameter is reduced below this value, the {110} facets disappear from the sidewall. Instead, facet-free vertical sidewalls appear, implying the importance of surface tension during growth on small-diameter holes. Longitudinal resistance in Hall-bar samples with the antidot structure shows prominent fluctuation in the magnetic field between 0 and 2 T.

Area selective epitaxy of anti-dot structure of GaAs by solid source MBE

Area selective epitaxy of anti-dot structures of GaAs on GaAs substrates masked by SiO 2 has been investigated by using migration-enhanced epitaxy (MEE). By using this method, successful area selective epitaxy of anti-dot structures have been achieved at a substrate temperature of 590°C. The anti-dot area selective epitaxy has proved useful to grow equi-thickness layers regardless of the lateral structure. This characteristic is caused by the fact that, in the anti-dot epitaxy, the growth front always has negative curvature, which prevents the facet formation. As a result, flat layer growth is achieved over the whole network structure.

Determination of the Facet Index in Area Selective Epitaxy of GaAs

Area selective epitaxy of GaAs on GaAs substrates masked by SiO2 has been investigated using migration-enhanced epitaxy (MEE) with 2 s annealing after Ga deposition. By this method, successful area selective epitaxy of GaAs has been achieved at substrate temperatures around 590°C. We have carried out area selective epitaxy of GaAs on GaAs substrates of various surface indices. Side facets are found to be composed of vertical {110} facets when epitaxial growth is carried out on GaAs (n11)A substrates, and composed of inclined {n20} facets when GaAs (n11)B substrates are used. It is determined that the growth rates of A- and B-surfaces are the most important factors in the facet index determination.

Step-flow MOVPE of GaN on SiC substrates

Step-flow MOVPE of GaN on SiC substrates is confirmed by AFM observation. Compared to the growth on sapphire substrates, there are no step terminations and no 2D nuclei within a 10 micron square area, showing step-flow mode is dominant. The surface mostly consists of 190-nm-wide atomic terraces and 0.6-nm-high doubly stacked monolayers (DSM) along [1 1 2 ̄ 0]. This DSM dissolves into a pair of monolayers at the adjacent DSM steps, due to the asymmetry between these two monolayers which have different bond configurations at the step edge. By the homogeneity of step-flow growth, FWHMs of about 100 arcsec in X-ray locking curve and sharp photoluminescence (FWHM: 20 meV) from 1.1-nm-thick GaN/AL 0.15Ga 0.85N quantum well are obtained. We also found, in finite area selective epitaxy (FAE), steps originate from a single 2D nucleus, which shows heterointerface flatness will be significantly improved by using the combination of SiC substrates and FAE.

An X-Ray Sensitive CCD Camera System and Its Application to the X-Ray Diffractometric Investigation on Area Selective Semiconductor Epitaxy

An X-Ray Sensitive CCD Camera System and Its Application to the X-Ray Diffractometric Investigation on Area Selective Semiconductor Epitaxy