Growth Of GaSb Research Articles

Growth and characterization of GaAs‐GaSb III‐V pseudo‐binary nanoparticles

AbstractThe GaAs‐GaSb pseudo‐binary materials system presents an interesting challenge for growth because of 1) the existence of a miscibility gap in the solid‐solid portion of the equilibrium phase diagram, and 2) the large differences in vapor pressure between the column III element, Ga, and the column V elements, As and Sb. To overcome these challenges in the growth of GaAs, GaSb, and Ga50AsxSb50–x alloy nanoparticles, single‐ and dual‐target pulsed laser deposition (PLD) techniques were implemented using an Nd:YAG laser operated with a harmonic generator to utilize the second harmonic wavelength (532 nm) and a combination of the fundamental and the second harmonic wavelengths (1064 nm + 532 nm). The nanoparticles were collected on amorphous carbon films for subsequent characterization by transmission electron microscopy. The analysis shows that single phase GaAs‐rich Ga50AsxSb50–x (28 > x > 50) nanoparticles and nanocrystalline films have been formed through dual‐target, single‐wavelength (532 nm) pulsed laser ablation. Interestingly, through the ablation of the single component targets, two‐phase particles were also found to form. These two phase particles resemble “nano‐ice cream cones” with solid cones of either GaAs or GaSb with a spherical “ice cream” ball of Ga located at the wide portion of the cone, which is either an amorphous phase or liquid phase. Through an analysis by STEM‐EDX spectroscopy, these particles are found to be consistant with this model. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Room-Temperature Operation of Buffer-Free GaSb–AlGaSb Quantum-Well Diode Lasers Grown on a GaAs Platform Emitting at 1.65 $\mu$m

Buffer-free growth of GaSb on GaAs using interfacial misfit (IMF) layers may significantly improve the performance of antimonide-based emitters operating between 1.6 and 3 mum by integrating III-As and III-Sb materials. Using the IMF, we are able to demonstrate a GaSb-AlGaSb quantum-well laser grown on a GaAs substrate and emitting at 1.65 mum, the longest known operating wavelength for this type of device. The device operates in the pulsed mode at room temperature and shows 15-mW peak power at -10degC and shows high characteristic temperature (To) for an Sb-based active region. Further improvements to IMF formation can lead to high-performance lasers operating up to 3 mum.

GaSb/InGaAsSb/GaSb SINGLE AND MULTIPLE QUANTUM WELLS: OPTICAL PROPERTIES ENGINEERING AND APPLICATION

MBE growth of GaSb / InGaAsSb / GaSb heterostructures of high crystal quality is performed under continual RHEED control. Transmission spectra of the films forming multiple quantum wells in λ ≈ 2–3 μm region confirm possibility to control optical properties of the structures through quantum confinement and through the content of semiconductor elements. New design of saturable absorption semiconductor mirror (SESAM) for Cr 2+: ZnSe laser is proposed and manufactured on the base of the single quantum well GaSb / InGaAsSb / GaSb placed between dielectric antireflection and broadband high reflection coatings.

Growth behavior of GaSb by metal–organic vapor-phase epitaxy

The growth mechanisms of GaSb in a metal–organic vapor-phase epitaxy (MOVPE) system were studied for both trimethyl gallium (TMG)/trimethyl antimony (TMSb) and triethyl gallium (TEG)/TMSb growth chemistries. The effect of growth temperature and precursor mole fractions on GaSb growth rate was determined experimentally. Numerical analysis of the reactor and growth process was described in a combined chemical–thermal–fluid flow model. A Langmuir–Hinshelwood-type mechanism involving a surface reaction between adsorbed monomethyl gallium (MMG) and adsorbed monomethyl antimony (MMSb) or adsorbed Ga and adsorbed MMSb was proposed for the growth of GaSb by MOVPE using TMG or TEG and TMSb chemistries, respectively. The chemical model for TMG/TMSb chemistry included bounds on the surface chemistry derived for the range of V/III precursor ratio which were observed to lead to a second phase, i.e., elemental Ga or Sb, formation. Two growth regimes were observed for TMG/TMSb chemistry: above 575 °C the growth rate was mass transfer controlled whereas for lower temperatures it is kinetically limited. No such temperature dependence has been found for the TEG/TMSb chemistry over all experimental employed ranges of growth parameters.

Real‐time diagnostics for metalorganic vapor phase epitaxy

AbstractMetalorganic vapor phase epitaxy is a complicated process whereby constituents of incoming reactant species are incorporated into the growing crystal through a number of stages. A range of optical probes has been developed to provide detailed information about these stages and the sample as growth proceeds. While many of these probes are mature, spectroscopic ellipsometry (SE) and polarimetry (SP) are both undergoing rapid improvements as a result of applications in integrated‐circuits technology. Here, I review some of these advances and the motivation behind them, and illustrate capabilities with an application regarding the heteroepitaxial growth of GaSb on GaAs. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Initial growth stage of GaSb on Si(0 0 1) substrates with AlSb initiation layers

Although we recently found that a high-quality GaSb film can be grown on Si substrate by using an AlSb initiation layer, the growth mechanism, especially the effects of AlSb initiation layer, was not clear. Therefore, we investigated the initial growth stage of GaSb on Si(0 0 1) substrates with AlSb initiation layers by atomic force microscopy. When small AlSb islands were formed on the Si substrate before the growth of GaSb, two-dimensional GaSb growth occurred. In contrast, without the growth of AlSb small islands, large GaSb islands were formed on the Si substrate. Therefore, the AlSb islands played an important role in preventing excessive surface diffusion of Ga atoms on the Si surface and promoting two-dimensional growth of GaSb.

GaSb single-crystal growth by vertical gradient freeze

GaSb 2-inch-diameter ingots doped with Tellurium have been grown by vertical gradient freeze (VGF) in quartz crucibles using an encapsulant. Twinning in the seed or in the cone of the crucible occurred in all growths when crucibles with a 6 mm diameter seed on (1 0 0) orientation and a cone angle to the vertical of 90° or 32.5° were used and in most cases the twins induced nucleation of polycrystalline growth. The amount of twinning could not be reduced by increasing the thermal gradient thereby suppressing the formation of facets. However, the use of full-diameter seeds with a carefully controlled diameter resulted in single-crystal growth of GaSb. First results on the quality of the VGF-grown GaSb:Te are promising. The dislocation density of the GaSb grown from a full-diameter seed is low; around 65 cm −2 at the seeding area and diminishing towards the end of the crystal and the dislocation density of GaSb grown from a 6-mm seed is even lower, around 4 cm −2 near the seed.

The growth of n-type GaSb by metal-organic chemical vapour deposition: effects of two-band conduction on carrier concentrations and donor activation

n-type GaSb has been prepared by metal-organic chemical vapour deposition with tellurium donors using diethyltelluride as the dopant precursor. The maximum carrier concentration achieved was 1.7 × 1018 cm−3, as measured by van der Pauw–Hall effect measurements, for an atomic tellurium concentration of 1.8 × 1019 cm−3. The apparent low activation of tellurium donors is explained by a model that considers the effect of electrons occupying both the Γ and L bands in GaSb due to the small energy difference between the Γ and L conduction band minima. The model also accounts for the apparent increase in the carrier concentration determined by van der Pauw–Hall effect measurements at cryogenic temperatures.

Investigation of the phase diagram of the Pb–Ga–Sb system

The growth of GaSb and its solid solutions from ‘neutral’ solvents could be useful to improve the characteristics of these materials. Pb can be used as such a ‘neutral’ solvent. The phase diagram of the system Pb–Ga–Sb was determined experimentally in a region where it could be used for liquid phase epitaxy. The results are compared with the calculated phase diagram. Photoluminescence characteristics and secondary ion mass spectroscopy analysis of samples grown from Pb containing liquid phases are discussed.

Integrated rotating-compensator polarimeter for real-time measurements and analysis of organometallic chemical vapor deposition

We describe a single-beam rotating-compensator rotating-sample spectroscopic polarimeter (RCSSP) integrated with an organometallic chemical vapor deposition (OMCVD) reactor for in-situ diagnostics and control of epitaxial growth, and report representative results. The rotating compensator generates Fourier coefficients that provide information about layer thicknesses and compositions, while sample rotation provides information about optical anisotropy and therefore surface chemistry. We illustrate capabilities with various examples, including the simultaneous determination of 〈 ε〉 and α 10 during exposure of (001)GaAs to TMG, the heteroepitaxial growth of GaP on GaAs, and the growth of (001)GaSb with TMG and TMSb. Using a recently developed approach for quantitatively determining thickness and dielectric function of depositing layers, we find the presence of metallic Ga on TMG-exposed (001)GaAs. The (001)GaSb data show that Sb deposition is self-limiting, in contrast to expectations.

Heteroepitaxial growth of GaSb on Si(0 0 1) substrates

We investigated the heteroepitaxial growth of GaSb on Si(0 0 1) substrate. We found that high-quality GaSb films can be grown on Si substrate by introducing an AlSb initiation layer. We obtained a narrow X-ray diffraction rocking curve and over-1400-nm emission from GaSb/AlGaSb quantum wells by optimizing the growth temperature and thickness of the AlSb initiation layer. During the growth of GaSb, the AlSb initiation layer played two important roles for improving crystal quality; i.e., it acted as a surfactant and as a buffer layer preventing generation and propagation of dislocations.

In situ monitored MOVPE growth of undoped and p-doped GaSb(1 0 0)

MOVPE-grown GaSb(1 0 0) surfaces were investigated with in situ RAS, LEED, and UPS. The in situ signals turned out to be very useful in determining suitable growth parameters and in monitoring the critical deoxidation procedure. Undoped GaSb(1 0 0) films were grown with triethylantimony and triethylgallium as precursors. Characteristic differences in the in situ signals were correlated with surface sensitive measurements after having transferred the samples with a patented procedure from the MOVPE reactor into ultrahigh vacuum chambers. p-type doping was accomplished with the precursors ditertiarybutylsilane and carbon tetrabromide, that are sustainable alternatives compared to silane and carbon tetrachloride. LEED images of the surfaces displayed a c(2×6) surface reconstruction. Doping levels in the range from 10 17 to 10 20 cm −3 were observed with SIMS and Hall measurements. Characteristic RAS peaks at the E 1 and E 1+ Δ 1 interband transitions were attributed to the linear electro-optic effect and were found to increase linearly with the dopant concentration.

Preparation of GaSb substrates for GaSb and GaInAsSb growth by organometallic vapor phase epitaxy

The preparation of GaSb substrates for epitaxial growth of GaSb and GaInAsSb is reported. The effects of several wet chemical etchants and ambient atmosphere during substrate heating on surface morphology and interfacial impurities were investigated. Based on surface roughness and interfacial contamination, which were determined by atomic force microscopy and by secondary ion mass spectroscopy, respectively, the most suitable etchant is one that does not attack GaSb and preferentially removes only the oxide layer. Characterization of metastable GaInAsSb epilayers shows that the starting surface roughness can impact the extent of phase separation, and higher material quality is achieved for a smoother GaSb substrate surface. These results indicate that morphological undulations associated with surface roughness can enhance alloy decomposition, and are detrimental for growth of metastable alloys.

Indium surface segregation in AlSb and GaSb

The effect of indium surface segregation during the molecular beam epitaxial growth of AlSb and GaSb on In(As,Sb) is investigated using various techniques including reflection high-energy electron diffraction (RHEED), high-resolution transmission electron microscopy (HRTEM), and high-resolution X-ray diffraction (HRXRD). The peculiar RHEED intensity variation observed during the growth of AlSb and GaSb on In(As,Sb) is interpreted as the consequence of indium surface segregation. This is confirmed by HRTEM investigation. The interface width associated with In segregation is found to increase with the growth temperature, as expected for a kinetically limited surface segregation phenomenon. In the investigated growth temperature range (400–540°C), the In segregation length is always higher for GaSb than for AlSb. Finally, a very good agreement between simulated and experimental HRXRD data corresponding to a GaSb/InAs superlattice is obtained by taking into account the In segregation profile deduced from the RHEED data.

Low-resistance p-type polycrystalline GaSb grown by molecular beam epitaxy

We report the growth and electrical properties of low resistance carbon-doped polycrystalline GaSb (poly-GaSb) by molecular beam epitaxy using CBr 4. The resistivity of poly-GaSb is found to have strong dependence on film thickness and grain size of the polycrystalline film, particularly when the film thickness is comparable with the grain size. It is observed that grain size is mainly determined by growth temperature, while hole concentration is significantly affected by antimony to gallium beam flux ratio. With same doping level, grain size, and similar film thickness, the resistivity of carbon-doped poly-GaSb is more than one order of magnitude lower than that of carbon-doped poly-GaAs. This result is attributed to GaSb's favorable surface Fermi-level pinning in the valence band and higher hole mobility. It is proposed that carbon-doped poly-GaSb be used as extrinsic base material in InP heterojunction bipolar transistor to improve the device's high-frequency performance.

Numerical study of transport phenomena in the THM growth of compound semiconductor crystal

A numerical simulation study was carried out for the crystal growth of GaSb from a Ga-solution by the traveling heater method (THM). The effects of crucible temperature, crucible rotation and crucible material on the crystal/solution interface shape were investigated. It was found that the interface curvature increases with increasing crucible temperature. In such a case, the use of crucible rotation was very beneficial in suppressing the natural convection in the melt, and in obtaining an interface with smaller curvature. When the crucible temperature was lower (while keeping the same temperature gradient), the interface shape was slightly convex towards the crystal. The crucible rotation did not affect the interface shape significantly. The use of a pBN crucible required a higher growth temperature compared with a system of SiO 2 or carbon crucible.

P-type carbon doping of GaSb

The growth of carbon-doped GaSb by MOVPE has never been reported to our knowledge, despite increasing interest in carbon-doped GaAsSb alloys for heterojunction bipolar transistor applications. In this work, we report the use of carbon tetrachloride (CCl4) in conjunction with triethylgallium (TEGa) and trimethylantimony (TMSb) to achieve p-type doping levels in GaSb from 5 1016 cm−3 to greater than 1019 cm−3. High resolution x-ray diffraction measurements confirm that the effect of carbon on the lattice parameter is significant for hole concentrations above 1 1019 cm−3 as in the case of GaAs. By introducing controlled low doping levels of carbon into thick homoepitaxial samples, we have succeeded in identifying a carbon-related low temperature photoluminescence band at 795 meV, which we ascribe to band-to-acceptor transitions of carbon acceptors. Temperature-dependent Hall measurements on lightly carbon-doped samples yield somewhat lower binding energies than the spectroscopic data due to impurity banding in the acceptor excited states.

Heat and Momentum Transfer Numerical Analysis in a Vertical Bridgman Growth System

In this work the momentum and heat transfer on a Bridgman system for the growth of GaSb has been studied. The main objective was to obtain some information about the role of the different processes like conduction, radiation and convective effects both in the melted material and the surrounding environment. These simulations are based on a 2D axi-symmetrical model using a finite element method based code. The simulations have been carried out both in steady and transient states. It has been demonstrated that the consideration of a moving environment is important in the distribution of temperatures. The effects of the variations of thermal conductivities and emissivities on the thermal and velocity fields have been investigated. The results show that the key parameters are the thermal conductivities of the different materials present in the system, which produce significant changes in the convective flows inside the melt.

Transfer of n-type GaSb onto GaAs substrate by hydrogen implantation and wafer bonding

Many GaSb devices would greatly benefit from the availability of a semi-insulating substrate. Since semi-insulating GaSb is not currently available, the formation of thin GaSb layers through wafer bonding and tranfer onto a semi-insulating GaAs substrate was investigated. GaSb-on-insulator structures, formed on GaAs substrates, were realized by the ion-cut process using H+ ions. Blistering, bonding and layer splitting phenomena were studied to optimize the ion dose and the process window. Bonded structures of thin layers of GaSb bonded to GaAs wafers were formed using a borosilicate glass (BSG) layer. The transferred GaSb layers were characterized by atomic force microscopy, MeV helium ion channeling and high-resolution x-ray diffractometry. The transferred film possessed a narrow x-ray linewidth of about 140 arcsec indicating improved crystalline quality over the direct growth of GaSb on GaAs.

Growth of antimony-based materials in a multiwafer planetary MOVPE-reactor

Four-junction photovoltaic solar cells are expected to reach conversion efficiencies around 40%. Mechanical stacking of two monolithic tandem cells is suggested. As a top cell the highly developed GaInP:GaAs tandem cell is considered. Device modelling is presented for the bottom cell. An infrared monolithic tandem solar cell is proposed which is a combination of an (AlGa)(AsSb) top cell (E/sub gap/=1.03 eV) and a GaSb bottom cell based on GaSb as substrate material. The MOVPE growth of GaSb, GaAsSb and AlGaSb in a multiwafer planetary reactor that is suited to large-scale industrial production is reported. Influences of the substrate preparation, orientation of the growth surface, growth temperature and the V-III ratio on material quality are presented. Both hydrogen and nitrogen were employed as the carrier gas in different experiments. The best layers were obtained on [100] substrates oriented 2/spl deg/ toward [111]A, using hydrogen as carrier.