Effects of pressure and temperature on RD detected growth oscillations

We report on the vacuum chemical epitaxy (VCE) growth of GaAs from triethylgallium and arsine at varying partial pressures of arsine and hydrogen. In situ, monolayer growth oscillations were, for the first time, detected in a hydrogen environment using reflectance difference (RD). These results offer the possibility to link surface mechanisms occuring during chemical beam epitaxy (CBE) with those taking place in metalorganic vapour phase epitaxy (MOVPE) and may lead to the observation of growth oscillations also during MOVPE. Finally, the behaviour of the RD signal as a function of substrate temperature is studied over a wider temperature interval than has previously been reported, giving further information about surface processes.     

Kinetics and mechanisms of surface reactions in epitaxial growth of Si from SiH4 and Si2H6

Surface science and kinetic modelling studies of the surface chemical mechanisms active during low pressure chemical vapor deposition (CVD) and chemical beam epitaxy (CBE) growth of Si from mono- and disilane are summarized. Time-of-flight direct recoiling (DR) is discussed as an in situ method to analyze the composition of the growth interface. Steady state measurements of surface hydrogen coverage (θ_H) are made by DR in situ during CBE Si growth from Si₂H₆ and SiH₄, and are illustrated here. Key results using other experimental methods are briefly discussed.     

Growth of InN films and nanostructures by MOVPE

Since a few years, a lot of research efforts have been devoted to InN, the least known of the semiconducting group-III nitrides. Most of the samples available today have been grown using the molecular beam epitaxy technique, and fewer using the metal organic vapor phase epitaxy (MOVPE) method. Whatever the method, the growth of InN is extremely challenging, in particular due to the fact that no lattice matched substrate is available.     

In situ processing of III–V semiconductors: Mile stones and future prospects

In situ processing combined with metalorganic vapor phase epitaxy (MOVPE), molecular beam epitaxy, or chemical beam epitaxy appears to be an attractive method for fabricating sophisticated optoelectronic devices such as buried heterostructure lasers, vertical cavity surface emitting lasers, and photonic integrated circuits. Successful reduction of residual contaminants at the regrowth interface and improvement in the optical and electrical quality of the regrown layer has been achieved by using in situ processing techniques. Device fabrication is alrady taking advantage of this kind of technology. Nevertheless, interface quality between an in situ etched layer and a regrown layer has not yet reached the status of continuously grown interfaces. In this paper, progress of in situ processing is reviewed mainly focusing on our recent studies on in situ HCl gas etching in MOVPE. The approach of two-step HCI gas etching has proven superior to obtain clean regrowth interfaces, leading to the conclusion that the in situ processing can be widely used for advanced optoelectronic device fabrication.     

Selectively embedded growth by chemical beam epitaxy for the fabrication of InGaAs/InP double-heterostructure lasers

In order to fabricate InGaAs/InP double-heterostructure (DH) lasers, a novel selectively embedded one-step growth by chemical beam epitaxy (CBE) was adopted. Before the selective CBE growth, 6–8 μm wide channels on an n-InP substrate were undercut by wet chemical etching through a 170 nm thick SiO₂ film mask. A 6 μm wide stripe-geometry DH laser structure with an active layer of 0.14 μm thickness was grown selectively with good planarity into the channels and operated by a pulse.     

New frontiers of molecular beam epitaxy with in-situ processing

The in-situ process combines film growth and device fabrication steps which take place under an ultra-high vacuum (UHV) or a controlled ambient environment. Processing, materials, and devices produced using this technique with molecular beam epitaxy (MBE) are reviewed.     

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.     

Ga and In incorporation rates in Ga1−xInxAs growth by chemical beam epitaxy

GaAs, InAs and Ga_1?xIn_xAs layers were grown by chemical beam epitaxy (CBE) using triethylgallium, trimethylindium and tertiarybutylarsine as precursors for Ga, In and As, respectively. The growth rate during the homoepitaxial growth of GaAs and InAs, deduced from the frequency of reflection high-energy electron diffraction intensity oscillations, was used to calibrate the incorporation rates for the III elements. The In content of the Ga_1?xIn_xAs layers was measured by Rutherford backscattering spectrometry and compared with the value predicted from the above calibration data; while the measured In mole fraction is close to the predicted value for the samples grown for low In to Ga flux ratios (x<0.2), the In incorporation is enhanced for larger values of this ratio. The results obtained on layers grown at different substrate temperatures show that In mole fraction is almost constant at growth temperatures in the range 400–500 °C, but a strong dependence on the substrate temperature has been found outside this range. The above results, not observed for samples grown by solid source molecular beam epitaxy, indicate that some interaction between Ga and In precursors at the sample surface could take place during the growth by CBE.     

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.     

p-Type GaAs doped by diiodomethane (CI2H2) in molecular beam epitaxy, metalorganic molecular beam epitaxy, and chemical beam epitaxy

Highly p-type carbon-doped GaAs epitaxial layers were obtained using diiodomethane (CI₂H₂) as a carbon source. In the low 10¹⁹ cm⁻³ range, almost all carbon atoms are electrically activated and at 9×10¹⁹ cm⁻³, 91% are activated. The carbon incorporation efficiency in GaAs layers grown by metalorganic molecular beam epitaxy (MBE) and chemical beam epitaxy (CBE) is lower than that by MBE due to the site-blocking effect of the triethylgallium molecules. In addition, in CBE of GaAs using tris-dimethylaminoarsenic (TDMAAs), the carbon incorporation is further reduced, but it can be increased by cracking TDMAAs. Annealing studies indicate no hydrogenation effect.     

Anisotropy in InGaAs/GaAs heterostructures grown by low-pressure MOVPE and CBE

InGaAs/GaAs heterostructures grown on (001) substrates by low-pressure MOVPE exhibit a measurable anisotropy in their structural, optical and electrical properties. This anisotropy occurs in structures which have undergone partial or complete strain relaxation and it can be strongly reduced by using slightly misoriented substrates. A comparison with similar structures grown by CBE indicates that this anisotropy is less important. This study suggests that strain relaxation is achieved by a combination of several mechanisms whose relative importance depends on the orientation of the substrate and on growth temperature which varies with the growth technique.     

In situ surface passivation of III–V semiconductors in MOVPE by amorphous As and P layers

A new process for chemical passivation of III–V semiconductor surfaces in metalorganic vapour phase epitaxy (MOVPE) is developed. A passivation layer is deposited directly after growth in the reactor. It consists of amorphous arsenic or a double-layer package of amorphous phosphorus and arsenic, which are grown by photo-decomposition of the group-V hydrides. These layers (caps) serve to protect the surfaces against contamination in air after removing the samples from the MOVPE growth reactor. Such passivation is applicable e.g. for a two-step epitaxy or for further surface characterizations.     

CBE growth of GaAs/GaAlAs HBTs using the new DEAlH-NMe3 precursor and all-gaseous dopants

This paper describes the first reported use of diethylaluminium hydride-trimethylamine adduct (DEAlH-NMe₃) for the growth of GaAs/GaAlAs power heterojunction bipolar transistors (HBTs) by chemical beam epitaxy (CBE). This precursor possesses a significantly higher vapour pressure than the more conventionally used triethylaluminium (TEA), and leads to much less stringent requirements for bubbler and gas-line heating, and also much-improved GaAs/GaAlAs heterojunction definition when no carrier gas is employed. The use of all-gaseous n- and p-type dopants offers significant technological advantages in CBE, and the current paper also provides the first report of the use of hydrogen sulphide for n-type doping of CBE-grown GaAlAs HBT emitter regions. In conclusion, DC and RF data obtained from the heterojunction bipolar transistors fabricated to date are described. A DC gain of 40 has already been measured and encouraging early data obtained from RF-probed devices are also presented.     

Characterization of p-type ZnSe grown by MOVPE; excitonic emission lifetime measurements

Time-resolved photoluminescence (TRPL) measurements are made on p-type nitrogen-doped ZnSe grown by photoassisted metalorganic vapor phase epitaxy (MOVPE) together with post-growth thermal annealing, in order to investigate optical quality of the layers. It is suggested that the annealing degrades the layer quality and the MOVPE samples have more non-radiative recombination centers compared with MBE samples. A key issue for high quality p-ZnSe by MOVPE seems to be optimization of annealing conditions.     

Metalorganic vapor phase epitaxy of III–V-on-silicon: Experiment and theory

The integration of III–V semiconductors with Si has been pursued for more than 25 years since it is strongly desired in various high-efficiency applications ranging from microelectronics to energy conversion. In the last decade, there have been tremendous advances in Si preparation in hydrogen-based metalorganic vapor phase epitaxy (MOVPE) environment, III–V nucleation and subsequent heteroepitaxial layer growth. Simultaneously, MOVPE itself took off in its triumphal course in solid state lighting production demonstrating its power as industrially relevant growth technique. Here, we review the recent progress in MOVPE growth of III–V-on-silicon heterostructures, preparation of the involved interfaces and fabrication of devices structures. We focus on a broad range of in situ, in system and ex situ characterization techniques. We highlight important contributions of density functional theory and kinetic growth simulations to a deeper understanding of growth phenomena and support of the experimental analysis. Besides new device concepts for planar heterostructures and the specific challenges of (001) interfaces, we also cover nano-dimensioned III–V structures, which are preferentially prepared on (111) surfaces and which emerged as veritable candidates for future optoelectronic devices.     

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.     

Growth and MBMS studies of reaction mechanisms for InxGa1−xAs CBE

The reaction mechanism involved in the growth of In_xGa_1−xAs lattice matched to InP by chemical beam epitaxy (CBE) was investigated using growth and modulated beam mass spectrometry studies. Emphasis was placed on elucidating how variations in substrate temperature, indium composition and arsenic overpressure influence growth kinetics and how sensitive changes in experimental conditions bring about deviations in the ideal stoichiometry (In_0.53Ga_0.47As) required for lattice matching to InP. Our observations indicate that the compositional variations in the InGaAs stoichiometry at high temperatures (> 485°C) arise because of the changes in the DEG decomposition: desorption branching ratio which is controlled by a temperature- and arsenic pressure-dependent surface population of indium atoms. The low temperature behaviour is governed by the availability of metal surface sites for triethylgallium decomposition which is increased by the presence of surface indium atoms.     

Progress in Modeling of III-Nitride MOVPE

This review provides an introduction to III-Nitrides MOVPE process modeling and its application to the design and optimization of MOVPE processes. Fundamentals of the MOVPE process with emphasis on transport phenomena are covered. Numerical techniques to obtain solutions for the underlying governing equations are discussed, as well as approaches to describe multi-component diffusion for typical regimes during MOVPE. Properties of common industrial MOVPE reactor types like close spaced showerhead reactors, rotating disk reactors and Planetary Reactors are compared in terms of underlying working principles and generic process parameter dependencies.The main part of the paper is devoted to reviewing gas phase and surface reaction mechanisms during MOVPE. The process design in particular for MOVPE of III-Nitrides is determined by complex gas phase reaction kinetics. Advances in the modeling and predicting of these processes have contributed to understanding and controlling these phenomena in industrial scale MOVPE reactors. Detailed kinetics and simplified surface kinetic approaches describing the incorporation of constituents into multinary solid alloys are compared and a few application cases are presented. Differences in thermodynamic and kinetic properties of multi-layered structures of different compositions such as InGaN, AlGaN can cause enrichment of the adsorbed layer by certain group III atoms (indium in case of InGaN and gallium in case of AlGaN) that translate into specific features of composition profiles along the growth direction.An intrinsic feature of III-nitride materials is epitaxial strain that shows up in different forms during growth and affects both deposition kinetics and material quality. In case of InGaN MOVPE there is a strong interplay between indium content and strain that has direct influence on distribution of material composition in the epitaxial layers and multi-layered structures. Epitaxial strain can relax via different routes such as nucleation and evolution of the extended defects (dislocations), layer cracking and roughening of the surface morphology. Simulation approaches that address coupling of growth kinetics with strain and defect dynamics are discussed and exemplified.     

MOMBE growth characteristics of antimonide compounds

This paper describes the MOMBE (metalorganic molecular beam epitaxy) growth characteristics of antimonide compounds using TMIn (trimethylindium), TEGa (triethylgallium) and TIBAl (triisobutylaluminium) as group III sources, and As₄, Sb₄, TEAs (triethylarsine) and TESb (triethylstibine) as group V sources. Large differences in the growth characteristics of GaAs and GaSb MOMBE are observed. These are explained, using a theoretical consideration of the growth mechanism, by the difference in the effective surface coverage of excess As and Sb atoms during the growth. The use of TEAs and TESb instead of As₄ and Sb₄ alters the growth rate variation of both GaAs and GaSb with substrate temperature (T_sub), which results from the interaction of alkyl Ga species with the alkyl radicals coming from the thermally cracked TEAs and TESb. The alkyl exchange reaction process is observed in the growth of AlGaSb using TIBAl and TEGa, where the incorporation rate of Al is suppressed by the coexistence of TEGa on the growth surface, in the low T_sub region. This is caused by the formation of an ethyl-Al bond which is stronger than the isobutyl-Al bond. The composition and the growth rate variations of InGaSb with T_sub are similar to those of InGaAs, which are closely related to the MOMBE growth process and are quite different from those of MBE (molecular beam epitaxy) and MOVPE (metalorganic vapor phase epitaxy) growth. In the MOMBE growth of InAsSb and GaAsSb using TEAs and TESb, the composition variation with T_sub is weaker than that of MBE. This is a superior point of MOMBE growth for the composition control. The electrical and optical properties of MOMBE grown films as well as the quantum well structures are also described.     

Aerosol particles from bubblers in metalorganic vapor phase epitaxy

We report on aerosol particles generated by bubblers in metalorganic vapour phase epitaxy (MOVPE). A triethylgallium bubbler was investigated in a MOVPE set-up regarding the generation of aerosol. Our measurements show that aerosol particles are produced, and the production depends on the carrier gas flow bubbling through. The distribution of the particle diameters was measured and was found to range from 10 to 600 nm, with the maximum at about 200 nm. While the number of particles is not negligible the precursor is almost only transported as gas molecules. However, particles could possibly reach the substrate and create defects on the surface.