Selective growth and other applications of hydrogen-assisted molecular beam epitaxy

The usefulness of atomic hydrogen in molecular beam epitaxy has been demonstrated, centering around selective growth. Atomic hydrogen is effective for low-temperature cleaning of substrates, surfactant effects such as restrain of island growth and suppression of the surface migration of the adatoms and selective growth on masked or V-grooved substrates. These effects are dependent on substrate temperatures. The selective growth of GaAs has been successfully demonstrated at the conventional growth temperature and growth rate with the aid of atomic hydrogen. The main mechanism of the selective growth is the re-evaporation of Ga and As from mask materials such as SiN_x or SiO₂. Selective growth has also been observed on low-index crystal facets. On (111)A and (110) facets, no GaAs was deposited in the presence of atomic hydrogen, the flux of which is approximately the same as that of Ga. GaAs quantum wire structures have been fabricated on the substrates with V-shaped grooves. The efficient capture and confinement of carriers into wire regions have been observed by photolumenescence.     

Deposition of InP on GaAs Substrates in the InP/PCl3/H2 System

Vapour phase epitaxial layers of InP were deposited onto (111)A-, (111)B-, (001)-, and (110)-oriented GaAs substrates in the InP/PCl₃/H₂ system using a close-space technique. It is shown that the dependence of the layer quality on the substrate orientation is due to differences in the initial growth stages. Results on the growth rates and the electrical properties of the layers are reported.     

Current status of selective area epitaxy by OMCVD

In this paper we review the current status of the achievements and understanding of selective area epitaxy using organometallic chemical vapor deposition (OMCVD) in the conventional mode, atomic layer epitaxy mode, and photon assisted growth mode. The selective epitaxy of GaAs, AlGaAs, and InP can be readily achieved. However, the selective epitaxy of compounds such as GaInAs has proven to be difficult due to a large compositional deviation. In addition, the control of the lateral thickness profile and facets at the edges has proven to be difficult for both binaries and their alloys. Selective epitaxy has been used to fabricate a variety of electronic and optoelectronic devices and low-dimensional structures. While considerable progress has been made, a better understanding of the processes is necessary before they can be applied to large scale optoelectronic integration.     

Transmission electron microscopy observation of GaAs/Al0.3Ga0.7As T-shaped quantum well structure fabricated by glancing angle molecular beam epitaxy on GaAs(100) reverse-mesa etched substrates

GaAs/Al_0.3Ga_0.7As multi-layer structures were grown on GaAs (100) reverse-mesa etched substrates by glancing angle molecular beam epitaxy (GA-MBE). A(111)B facet was formed as a side-facet. Surface migration of Ga and Al atoms from the (100) flat region to the (111)B side-facet region has been investigated to fabricate T-shaped GaAs/AlGaAs quantum wells (QWs) under the condition that Ga and Al atoms impinge only an the (100) flat region and do not impinge on the (111)B side-facet. Observation of T-shaped GaAs/AlGaAs quantum wires (QWRs) by cross-sectional transmission electron microscopy (TEM) revealed that there is no migration of Al atoms from the (100) to the (111)B facet region at a substrate temperature (T_s) as high as 630°C, under a V/III ratio of 28 (in pressure ratio). On the other hand, very thin GaAs epitaxial layers grown on the (111)B side-facet region owing to the Ga migration were observed for substrate temperatures of 600 and 630°C. It was found that the mass flow of Ga atoms from the (100) region to the (111)B side-facet region increases, with the thermal activation energy of 2.0 eV, as the substrate temperature increases from 570 to 630°C. The GA-MBE growth on a reverse-mesa etched GaAs substrate at a low temperature 570°C or lower is desirable to fabricate a nm-scale GaAs/AlGaAs QWR structure with nm-scale precision.     

Effect of atomic hydrogen in highly lattice-mismatched molecular beam epitaxy

Effects of atomic hydrogen on the growth of lattice-mismatched InAs/GaAs and GaAs/InP systems have been investigated. The irradiation of atomic H has resulted in a delay of the onset of formation of three-dimensional islands maintaining flat surface morphology and increase of the critical layer thickness (CLT) from 4 to 10 å in the case of the InAs/GaAs system. The effect of atomic H was shown to be dependent on the growth conditions such as the growth temperature and V/III flux ratio. The increase of CLT with atomic H irradiation may be explained by the uniform distribution of the total misfit stress in the plane of the surface as a result of enhanced two-dimensional growth by atomic H acting as a surfactant.     

Se-doped AlGaAs grown on GaAs(111)A by molecular beam epitaxy

The electrical properties of Se-doped Al_0.3Ga_0.7As layers grown by molecular beam epitaxy (MBE) on GaAs(111)A substrates have been investigated by Hall-effect and deep level transient spectroscopy (DLTS) measurements. In Se-doped GaAs layers, the carrier concentration depends on the misorientation angle of the substrates; it decreases drastically on the exact (111)A surface due to the re-evaporation of Se atoms. By contrast, in Se-doped AlGaAs layers, the decrease is not observed even on exact oriented (111)A. This is caused by the suppression of the re-evaporation of Se atoms, by Se---Al bonds formed during the Se-doped AlGaAs growth. An AlGaAs/GaAs high electron mobility transistor (HEMT) structure has been grown. The Hall mobility of the sample on a (111)A 5° off substrate is 5.9×10⁴ cm²/V·s at 77 K. This result shows that using Se as the n-type dopant is effective in fabricating devices on GaAs(111)A.     

Benefits of chemical beam epitaxy for micro and optoelectronic applications

This paper reviews the benefits that Chemical Beam Epitaxy (CBE) growth technique can bring to micro and optoelectronic devices. The characteristics of the technique are first underlined for a better understanding of the specific advantages it offers compared to other growth techniques. The first one is the low growth temperature, which pushed the thickness limit in strained InGaAsP multi-quantum well structures. Carbon doping of GaAs and In_0.53Ga_0.47As, and its application to GaAs and InP based npn heterojunction bipolar transistors is another important contribution of CBE which has resulted in successful device development. The last developments in surface cleaning and in situ etching with new amine and chloride sources are presented. The capabilities of CBE for selective and uniform growth on partially masked substrates are illustrated through examples of device planarization and integration. Finally, the most recent improvements in the technology of CBE equipment and their impact on CBE production capabilities are presented.     

Liquid-phase epitaxy of AlGaAs heterostructures on profiled substrates

A method of fabrication of planar local structures using the selective epitaxial growth of GaAs and AIGaAs layers from liquid phase on profiled GaAs substrates was developed. The planar regrowth of the recesses formed in GaAs substrates by local etching was performed using the anisotropy of epitaxial growth rates and also by providing the uniformity of mass flow to the surface of local epilayer. The developed method of localized structures fabrication was used for improving the characteristics of discrete light emitting diodes — LED and for fabrication of DLE monolithic arrays.     

Surfactant-mediated molecular-beam epitaxy of III-V strained-layer heterostructures

In this review we first present the two classes of non-reactive and reactive surfactants effective during homoepitaxy and heteroepitaxy, respectively. We then describe and analyse the results obtained by "true" surfactant-mediated molecular-beam epitaxy (SM-MBE) of Ga_1−xIn_xAs layers on GaAs substrates. Then, the data obtained by using In as a "virtual" surfactant during SM-MBE of InAs layers on Al_xGa_0.48−xIn_0.52As/InP and GaAs substrates are presented. We finally provide evidence that the growth mode influences the resulting defect microstructure in (partially) relaxed layers.     

Large area lateral overgrowth of mismatched InGaP on GaAs(111)B substrates

Application of InGaAs/InGaP double‐heterostructure (DH) lasers increases the band offset between the cladding layer and the active layer more than the use of conventional 1.3 µm InGaAsP/InP lasers. As a first step in realizing 1.3 µm InGaP/InGaAs/InGaP DH lasers, we proposed InGaP lattice‐mismatched epitaxial lateral overgrowth (ELO) technique and successfully carried out the InGaP growth on both GaAs (100), (111)B and InP (100) substrates by liquid phase epitaxy. In this work, we grew the InGaP crystal on GaAs (111)B substrate by adjusting Ga and P composition in In solution, to obtain In_0.79Ga_0.21P (λ = 820 nm) virtual substrate for 1.3 µm InGaAs/InGaP DH lasers. To grow the InGaP all over the lateral surface of the substrate, the growth time was extended to 6 hours. The amount of InGaP lateral growth up to 2 hours was gradually increased, but the lateral growth was saturated. The InGaP lateral width was about 250 µm at the growth time of 6 hours. We report the result that optical microscope observation, CL and X‐ray rocking curve measurements and reciprocal lattice space mapping were carried out to evaluate the crystal quality of the grown InGaP layers. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Diffusion of Si-acceptor in δ-doped GaAs grown on GaAs(111)A by molecular beam epitaxy

Diffusion of Si-acceptors (Si occupying As sites) in δ-doped GaAs grown on GaAs(111)A has been investigated by secondary ion mass spectrometry (SIMS). We have measured the diffusion parameters in GaAs(111)A and found that they differ from those in GaAs(001). The diffusion coefficient in GaAs(111)A is smaller than that in GaAs(001) and the activation energy in GaAs(111)A is larger than that in GaAs(001). Furthermore, the diffusion mechanism of Si in GaAs(111)A has been investigated by photoluminescence; we have found that in p-type layers Si-donors (Si occupying Ga sites) diffuse easily to As sites. The activation energy of Si-acceptor diffusion is 2.74±0.11 eV. These results indicate that Si-acceptors are more stable than Si-donors.     

Surface diffusion length of Ga adatoms in molecular-beam epitaxy on GaAs(100)-(110) facet structures

By the molecular-beam epitaxial (MBE) growth of GaAs on [001]-mesa stripes patterned on GaAs(100) substrates, (110) facets were formed on the mesa edges defining (100)-(110) facet structures. The surface diffusion length of Ga adatoms along the [010] direction on the mesa stripes was obtained for a variety of growth conditions by in-situ scanning microprobe reflection high-energy electron diffraction (μ-RHEED). Using these values and the corresponding growth rate on the GaAs(110) facets, the diffusion length on the (110) plane was estimated. We found that the Ga diffusion length on the (110) plane is longer than that on the (100) and (111)B planes. The long diffusion length on the (110) plane is discussed in terms of the particular surface reconstruction on this plane.     

Selective area growth of GaAs using a Ga beam with a step-function lateral intensity profile

Selective area growth of GaAs has been carried out in order to investigate the surface diffusion of Ga atoms using molecular beam epitaxy (MBE) with the aid of a Ga beam with a lateral step-function intensity profile. This step-function profile was obtained using a closely fitted GaAs shadow mask. When the mask edge was parallel to [01 ], a (311)A facet was typically observed near the edge of the Ga beam, while in the case of the mask edge parallel to [011], a (111)B facet was formed. MBE growth simulation based on the diffusion model was carried out in order to understand the mechanism of this selective area growth. The calculated results were in good agreement with the experimental results, and the diffusion lengths of Ga atoms were determined to be 0.10 μm along [011] direction on the (100) GaAs surface, 0.37 μm along [233] direction on the (311)A GaAs surface and 0.17 μm along [21 ] direction on the (111)B GaAs surface during MBE growth. These diffusion lengths seem to be smaller than those previously observed, which is probably due to a large V/III ratio in the region of the substrate close to the mask edge.     

Oriented growth of whiskers of AIIIBV compounds by VLS-mechanism

The oriented growth of GaAs, GaP, InAs and GaInAs whiskers on the same (GaAs, GaP) or different (InAs/GaAs, GaInAs/GaAs) substrates was studied. A detailed morphological study of GaAs whiskers on polar A(III), B(111 ) and non-polar (001), (011) substrates was performed. The growth conditions for ordered (perpendicular to substrate) growth on the A(111) and B(111 ) faces were determined. There were found discrete spectra of whisker systems on all substrates with the preferential growth of “arsenic” B{111 } faces. The dependence of the growth rate on the whisker diameter is typical for the vapour-liquid-solid (VLS) mechanism and is used for the determination of kinetic coefficients for polar faces. There was observed a periodic instability in growth of InAs and GaInAs whiskers.     

固态源MBE系统生长高质量的调制掺杂GaAs结构材料和InP/InP外延材料的兼容性研究

通过固态源的分子束外延系统生长了调制掺杂AlGaAs/GaAs结构材料和InP/InP外延材料.在生长含磷材料之后,生长条件(真空状态)变差;我们通过采取合理的工艺方法和生长工艺条件的优化,获得了电子迁移率为1.86×105cm2/Vs(77K)调制掺杂AlGaAs/GaAs结构材料和电子迁移率为2.09×105cm2/Vs(77K)δ-Si掺杂AlGaAs/GaAs结构材料.InP/InP材料的电子迁移率为4.57×104 cm2/Vs(77K),该数值是目前国际报道最高迁移率值和最低的电子浓度的InP外延材料.成功地实现了在一个固态源分子束外延设备交替生长高质量的调制掺杂AlGaAs/GaAs结构材料和含磷材料.     

Influence of growth temperature on growth of InGaAs nanowires in selective-area metal–organic vapor-phase epitaxy

Indium-rich InGaAs nanowires were grown on an InP (111)B substrate by catalyst-free selective-area metal–organic vapor phase epitaxy, and the growth-temperature dependence of growth rate and composition was studied. In particular, nanowire growth rate rapidly decreases as growth temperature increases. This tendency is opposite (for a similar temperature range) to that found in a previous study on selective-area growth of gallium-rich InGaAs nanowires. This difference between indium-rich and gallium-rich nanowires suggests that the influence of growth temperature on the growth of InGaAs nanowires is dependent on the group-III supply ratio. On the basis of previous experimental observations in InAs and GaAs nanowires, temperature dependence of nanowire growth rate and its dependence on group-III supply ratio are predicted. A guideline to determine the optimum growth conditions of InGaAs nanowires is also discussed.     

Epitaxial growth of GaAs and GaN by gas source molecular beam epitaxy using organic group V compounds

GaAs and GaN epilayers were grown on GaAs substrates by gas source molecular beam epitaxy technique using triethylarsine (TEAs) and diethylarsine (DEAsH) as As sources, and dimethylhydrazine (DMHy) as an N source. It was found that GaAs grows layer by layer even when organic arsine molecular sources are used. Cubic GaN was found to grow epitaxially on sufficiently nitrided surfaces of GaAs (001) substrates, in contrast with the growth of hexagonal GaN on GaAs (111) surfaces. It was also found that nitridation of GaAs surfaces does not occur when DEAsH and DMHy beams are supplied onto the GaAs substrates, simultaneously. Thus, GaN/GaAs multilayers were obtained only by intermittent supply of a DEAsH beam.     

Growth of ZnTe layers on (111) GaAs substrates by metalorganic vapor phase epitaxy

ZnTe layers were grown on (111) GaAs substrates by metalorganic vapor phase epitaxy using dimethylzinc and diethyltelluride as the source materials. X-ray diffraction analysis revealed that epitaxial ZnTe layers can be obtained on (111) GaAs substrates. X-ray rocking curves, Raman spectroscopy, and photoluminescence measurements showed that the crystal quality of ZnTe layers depends on the substrate temperature during the growth. A high-crystalline quality (111) ZnTe heteroepitaxial layer with strong near-band-edge emission at 550 nm was obtained at a substrate temperature of 440 °C.     

Transmission electron microscopic evaluation of InGaAs/InAlAs in-plane superlattices grown on slightly misoriented (110)InP substrates by molecular beam epitaxy

InGaAs/InAlAs in-plane superlattices (IPSLs) consisting of InAs/GaAs and InAs/AlAs monolayer superlattices grown on slightly misoriented (110)InP substrates by molecular beam epitaxy have been structurally evaluated by transmission electron microscopy. We used (110)InP 3° tilted toward the [00 ] direction. The ISPLs were fabricated by an alternative growth of half monolayers of AlAs and GaAs and one monolayer of InAs while maintaining regular arrays of one monolayer steps on the growth surface. In electron diffraction patterns from the ( 10) cross-section, two types of superstructure spots double-positioned in the 001 direction are observed, consistent with the existence of the IPSLs. Dark-field imaging from the superstructure spots reveal a periodic diffraction contrast with an average lateral periodicity of about 4 nm, i.e., one terrace width. However, meandering of the vertical interface and partial disordering in the IPSLs are often observed. From high resolution ( 10) cross-sectional TEM images, the presence of IPSLs was also confirmed with an atomic scale resolution, although their vertical interface are meandering. In electron diffraction patterns from the (110) plan-view, extra-spots similar to those observed in the ( 10) cross-section were seen. Dark-field images from the superstructure spots indicated that the IPSLs were formed almost exactly along the 110 direction, suggesting that the steps on the growth surface are very straight along the 110 direction.     

Selective area epitaxy of InP/GaInAsP heterostructures by MOMBE

This study reports on the selective area growth of InP/GaInAsP layers and heterostructures by metaloganic molecular beam epitaxy (MOMBE). It was found that neither the growth rate nor the material composition for GaInAsP depends on the area where material growth takes place. This enables a flexible SiO₂ mask to be designed independent of the aspect ratio. The use of slightly misoriented substrates allows the selective growth of planar structures having nearly perfectly vertical side walls even for 2 μm thick layers or narrow stripes to take place.