Growth of InP/InGaAs multiple quantum well structures by chemical beam epitaxy

InP/InGaAs multiple quantum well structures with up to 200 periods have been grown by CBE. These structures exhibit exceptional lateral uniformity, measured as ±1 Å in period, ±13 ppm in lattice mismatch and ±0.5 nm in wavelength across a 2 inch wafer. Good surface morphology, sharp interfaces and excellent growth control have all been demonstrated.     

Laser-assisted chemical beam epitaxy for selective growth

A recent exciting development in the growth of compound semiconductors is the use of light to modify the film growth rate in the irradiation area. We report Ar⁺-laser-assisted CBE of GaAs, InP, GaP and InGaAs to generate various patterned films without lithography. A linked-circle pattern is formed by laser beam scanning and a 0.85 μm pitch corrugation pattern formed by a holographic interference technique. Relationships between the growth rate and substrate temperature for the materials are compared. The mechanism of the growth rate enhancement is revealed to be photolytic decomposition of metalorganic molecules. In the case of InGaAs, laser irradiation above 500°C results in new phenomena of growth rate suppression and composition variation.     

Optimized InAs quantum effect device structures grown by molecular beam epitaxy

We have investigated InAs quantum effect devices based on both antimonides and arsenides. In an InAs quantum point contact device based on antimonides (InAs/AlGaSb), we have successfully reduced the leakage currents and observed quantum effects at around 77 K by optimizing the heterostructure growth and mesa-etched split-gate approach. Strained InAs quantum dots based on arsenides (AlInAs/AlAs/InAs/InGaAs/AlInAs) were successfully fabricated by MBE growth and mesa-etching. Blue-shifted photoluminescence was obtained from millions of quantum dots with an average lateral size of approximately 2000 å square.     

Dependence of InP and GaAs chemical beam epitaxy growth rate on substrate orientations; applications to selective area epitaxy

In order to optimize the shape of chemical beam epitaxy (CBE) selective area growth, growth rates on (100), (111)B, (111)A and (110) substrate orientations have been examined for GaAs and InP materials. (111)B GaAs growth rate appears to be drastically enhanced at low V/III ratio, which has been applied to grow selective GaAs patterns limited by vertical sidewalls. Concerning InP, high growth rates were obtained on all orientations. This was used to perfectly fill a rectangular groove by selective embedded InP growth.     

Fabrication of InGaAs ridge quantum wires by selective molecular beam epitaxy and their characterization

InGaAs/InAlAs ridge quantum wires were successfully fabricated by selective molecular beam epitaxy (MBE) for the first time. Prior to wire fabrication, detailed data on selective growth characteristics were taken by using test structures. Then, triangular shaped InGaAs ridge quantum wires with a width of 300 å were fabricated, using the selectivity data. Photoluminescence (PL) measurements detected a strong and narrow peak from the wires which showed a blue shift of 159 meV with respect to the InGaAs band-gap. This value agrees excellently with the calculation.     

Symmetric InP mirror facets fabricated by selective chemical beam epitaxy on reactive-ion-etched sidewalls

Vertical (0 1)-oriented parallel minor facets as smooth as cleaved ones were obtained by selective chemical beam epitaxy (CBE) on both sidewalls of [011]-direction ridges formed by reactive ion etching (RIE) on a (100) InP substrate. The obtained vertical facets often had a symmetric shape on the both sidewalls of the ridge, which was required to use as Fabry-Perot mirrors in a semiconductor laser, although an asymmetric shape had been often obtained before optimizing the growth conditions. We clarified the cause of asymmetry using simulation of the flux distribution on the sidewalls of the ridge during growth, and found the optimum growth conditions to obtain symmetric and parallel mirror facets.     

High-quality InP grown by chemical beam epitaxy

InP films were grown by chemical beam epitaxy using trimethylindium (TMI) and pure phosphine (PH₃) in a flow control mode with hydrogen as the carrier gas, with the TMI flow rate fixed at 3 SCCM. Substrate temperatures were varied between 505 and 580°C and V/III ratios from 3 to 9. InP layers with high optical quality (intense and narrow excitonic transition lines) and high crystalline quality (narrow and symmetric X-ray diffraction peaks) could be grown only within a narrow parameter window around a substrate temperature of 545°C (δT_s ≤ 25°C) and a V/III ratio of 5.5 (δ(V/III) ≤ 2). Carrier densities of 8 × 10¹⁴ cm^-3 with mobilities of 70000 cm²/V.s measured at 77 K were obtained for growth conditions close to the edge of this parameter window towards low V/III ratios. The growth rate of inP was also clearly at its maximum in the given parameter window. Leaving the window, by changing either the growth temperature or the V/III ratio, significantly decreased the growth rate. This reduced growth rate was accompanied by a degradation in the crystalline quality. We also demonstrate that for higher TMI flow the parameter window shifts to higher growth temperatures. The InP could be doped effectively with Si in the range from 9 × 10¹⁵ to 3 × 10¹⁸ cm^-3.     

Selective area growth of III–V compound semiconductors by chemical beam epitaxy

The reactions of triethylgallium (TEG) on a silicon nitride surface have been investigated to determine the underlying causes for selective area epitaxy. Using the techniques of X-ray photo electron spectroscopy and temperature programmed desorption, TEG is found to weakly adsorb on defect sites at room temperature. Desorption is favoured over further decomposition at higher substrate temperatures. The results are compared with the interaction of TEG on GaAs(100) surface and the implications for the influence of surface arsenic on selective area growth are discussed.     

Growth of InP in chemical beam epitaxy with high purity tertiarybutylphosphine

InP layers were grown by chemical beam epitaxy (CBE) using high purity thermally precracked tertiarybutylphosphine (TBP) and trimethylindium (TMI) as the source of the group III element. For optimized substrate temperature and V/III ratio, InP films of good electrical and optical quality have been obtained; the n-type background carrier concentration is (1–2) × 10¹⁵ cm^-3, with a Hall mobility at 77 K being μ₇₇ = 45,000 cm² V^-1 s^-1. Given the low value of the V/III ratio, and according to mass spectrosc measurements, the phosphorus species giving rise to epitaxy is expected to be the dimer P₂. The TBP consumption in CBE is very low when compared to organometallic vapour phase epitaxy (OMVPE), typicaly below 0.25 g/μm of InP layer.     

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.     

Growth reactions and mechanisms in chemical beam epitaxy (CBE)

The rapidly increasing interest in chemical beam epitaxy (CBE) and related ultra-high vacuum (UHV)-based epitaxial growth techniques has arisen primarily as a result of their expected technological advantages compared to either the conventional molecular beam epitaxy (MBE) or metalorganic vapour phase epitaxy (MOVPE) processes. The CBE-related techniques do, however, provide the additional important advantage, compared to MOVPE, that the UHV environmental allows in-vacuo analytical techniques to be used to provide in-situ characterization regarding the composition and crystallography of the growing layers, and also vital information regarding the growth mechanisms involved. The present paper reviews the current understanding relating to III–V CBE reaction mechanisms, and highlights specific topics which require further investigation.     

Effect of growth interruptions on ultra-thin InAs/InP quantum wells grown by chemical beam epitaxy

We have studied the effect of growth interruptions on 2 monolayer thick InAs/InP strained quantum wells (QWs) grown by chemical beam epitaxy. The main feature is the formation of up to 8 monolayer thick InAs islands during As₂ annealing of the QW. Their formation is characterized by a two- to three-dimensional transition of the reflection high energy electron diffraction (RHEED) pattern and by multiple-line photoluminescence spectra. This interpretation of the data is confirmed by transmission electron microscopy (TEM).     

Difference of anisotropic structures of InAs/GaAs quantum dots between organometallic vapor-phase epitaxy and molecular beam epitaxy

The anisotropies of the baseline in and [1 1 0] of InAs quantum dots (QDs) fabricated by molecular beam epitaxy (MBE) and organometallic vapor-phase epitaxy (OMVPE) are investigated. The structural and optical difference between QDs by MBE and OMVPE are investigated through an atomic force microscopy, a transmission electron microscopy, and a photoluminescence polarization measurement. It is found that the InAs QD structural anisotropy in MBE agrees with the individual growth rate anisotropy. Moreover, it is found that the mixture of the different structural anisotropies is unique in OMVPE at low growth temperature (440°C) and the growth mode is complex. From the photoluminescence polarization measurement, the InAs QD structures which mainly contribute to the optical property are decided by the plus and minus of the polarization degree of the ground state, and it is shown that the baseline anisotropy of the QDs mainly agrees with the growth rate anisotropy.     

Indium surface segregation in InGaAs-based structures prepared by molecular beam epitaxy and atomic layer molecular beam epitaxy

We present a comparative study on In surface segregation in InGaAs/GaAs structures prepared by molecular beam epitaxy (MBE) and atomic layer MBE (ALMBE) at different growth temperatures. The effect of segregation is evaluated by the energy position of exciton transitions in pseudomorphic 10 ML thick In_xGa_1−xAs/GaAs (0.15≤x≤0.30) and in 1 ML thick InAs/GaAs quantum wells. We show that: (i) In segregation decreases with the growth temperatures and is minimized at ALMBE and MBE growth temperatures lower than 260 and 340°C, respectively, and (ii) the segregation is more effective in ALMBE structures than in the MBE counterparts. The growth conditions that have been singled out allow the preparation of structures with high photoluminescence efficiencies even at the low growth temperatures required to minimize In segregation.     

Growth of EuTe islands on SnTe by molecular beam epitaxy

Semiconductor magnetic quantum dots are very promising structures, with novel properties that find multiple applications in spintronic devices. EuTe is a wide gap semiconductor with NaCl structure, and strong magnetic moments S=7/2 at the half filled 4f⁷ electronic levels. On the other hand, SnTe is a narrow gap semiconductor with the same crystal structure and 4% lattice mismatch with EuTe. In this work, we investigate the molecular beam epitaxial growth of EuTe on SnTe after the critical thickness for island formation is surpassed, as a previous step to the growth of organized magnetic quantum dots. The topology and strain state of EuTe islands were studied as a function of growth temperature and EuTe nominal layer thickness. Reflection high energy electron diffraction (RHEED) was used in-situ to monitor surface morphology and strain state. RHEED results were complemented and enriched with atomic force microscopy and grazing incidence X-ray diffraction measurements made at the XRD2 beamline of the Brazilian Synchrotron. EuTe islands of increasing height and diameter are obtained when the EuTe nominal thickness increases, with higher aspect ratio for the islands grown at lower temperatures. As the islands grow, a relaxation toward the EuTe bulk lattice parameter was observed. The relaxation process was partially reverted by the growth of the SnTe cap layer, vital to protect the EuTe islands from oxidation. A simple model is outlined to describe the distortions caused by the EuTe islands on the SnTe buffer and cap layers. The SnTe cap layers formed interesting plateau structures with easily controlled wall height, that could find applications as a template for future nanostructures growth.     

InGaAsP/InP multiple quantum wells grown by gas-source molecular beam epitaxy

We have grown In₁-_xGa_xAs_yP₁-_y/InP multiple quantum well structures with 1.3 μm excitonic absorption at room temperature by gas-source molecular beam epitaxy. In-situ composition determination in GaAs₁-_xP_x and InAs_xP₁-_x was carried out by measuring group-V-induced intensity oscillations of reflection high-energy electron diffraction. Based on the in-situ composition calibration for these ternary end members, Ga and As compositions in the quaternary compound, In₁-_xGa_xAs_yP₁-_y, were controlled successfully. Measurements by X-ray rocking curve, low-temperature photoluminescence and absorption spectroscopy indicate that high-quality In₁-_xGa_xAs_yP₁-_y/InP multiple quantum well samples were obtained.     

Growth mechanisms of GaAs nanowires by gas source molecular beam epitaxy

GaAs nanowires were grown on GaAs (1 1 1)B substrates in a gas source molecular beam epitaxy system, using self-assembled Au particles with diameters between 20 and 800 nm as catalytic agents. The growth kinetics of the wires was investigated for substrate temperatures between 500 and 600 °C, and V/III flux ratios of 1.5 and 2.3. The broad distribution of Au particles enabled the first observation of two distinct growth regimes related to the size of the catalyst. The origins of this transition are discussed in terms of the various mass transport mechanisms that drive the wire growth. Diffusion of the growth species on the 2-D surface and up the wire sidewalls dominates for catalyst diameters smaller than ∼130 nm on average, while direct impingement on the catalyst followed by bulk diffusion through the Au particle appears to sustain the wire growth for larger catalyst diameters. A change in wire sidewall facets, indicating a probable transition in the crystal structure, is found to be primarily dependent on the V/III flux ratio.     

Growth of quaternary AlInGaN/GaN heterostructures by plasma-induced molecular beam epitaxy

Epitaxial growth of AlInGaN/GaN heterostructures on sapphire substrates was achieved by plasma-induced molecular beam epitaxy. Different alloy compositions were obtained by varying the growth temperature with constant Al, In, Ga and N fluxes. The In content in the alloy, measured by Rutherford backscattering spectroscopy, increased from 0.4% to 14.5% when the substrate temperature was decreased from 775°C to 665°C. X-ray reciprocal space maps of asymmetric AlInGaN (2.05) reflexes were used to measure the lattice constants and to verify the lattice match between the quaternary alloy and the GaN buffer layers.