Gas-source Molecular Beam Epitaxy System Research Articles

Dependence of InGaP nanowire morphology and structure on molecular beam epitaxygrowth conditions

InGaP nanowires (NWs) were grown by the Au-assisted method in a gas source molecularbeam epitaxy system. The dependence of InGaP composition, morphology and stackingfault density was studied with respect to group III and V impingement rate and size of theAu particle. Compositional analysis showed that the NWs had an In-rich core and aGa-rich shell structure. The In incorporation within the NW became limited as the Au seedparticle size diminished or the group III and V flux decreased. The NWs had wurtzite (WZ)crystal structure with zinc blende (ZB) segments (stacking faults). The density of thestacking faults decreased as the group III flux decreased and the group V flux increased.

Accurate tuning of emission of GaInAsP/InP heterostructures in multiwafer gas-source molecular-beam epitaxy

Photoluminescence wavelength emission of Ga x In 1− x As y P 1− y /InP heterostructures grown in multiwafer gas-source molecular-beam epitaxy (GSMBE) is studied in detail for both bulk and multiple quantum well (MQWs) heterostructures. Excellent photoluminescence wavelength uniformity is reported in 4×2-in. configuration, demonstrating the compatibility of GSMBE process with large-scale 1.55 μm telecom laser production. A strong dependence of wavelength uniformity on group-V/group-III flux ratio is reported and analyzed quantitatively. An empirical model based on the interplay between group-V elements incorporation and gas distribution is proposed to predict the influence of AsH 3 and PH 3 fluxes on As content in the solid. This understanding opens the way to an accurate tuning of wavelength dispersion of Ga x In 1− x As y P 1− y /InP MQWs grown in multiwafer GSMBE system.

Homoepitaxial growth and device characteristics of SiC on Si-face (0 0 0 1) 6H–SiC

Homoepitaxial growth of SiC on a Si-face (0 0 0 1) 6H-SiC substrate has been performed in a modified gas-source molecular beam epitaxy system with Si 2H 6 and C 2H 4 at temperatures ranging 1000–1450°C while keeping a constant Si/C ratio (0.7) in the gas phase. X-ray diffraction patterns, Raman scattering measurements, and low-temperature photoluminescence spectra showed single-crystalline SiC. Mesa-type SiC p–n junctions were obtained on these epitaxial layers, and their I– V characteristics are presented.

Gd 2 O 3 / GaN metal-oxide-semiconductor field-effect transistor

Gd 2 O 3 has been deposited epitaxially on GaN using elemental Gd and an electron cyclotron resonance oxygen plasma in a gas-source molecular beam epitaxy system. Cross-sectional transmission electron microscopy shows a high concentration of dislocations which arise from the large lattice mismatch between the two materials. GaN metal-oxide-semiconductor field-effect transistors (MOSFETs) fabricated using a dielectric stack of single crystal Gd2O3 and amorphous SiO2 show modulation at gate voltages up to 7 V and are operational at source drain voltages up to 80 V. This work represents demonstrations of single crystal growth of Gd2O3 on GaN and of a GaN MOSFET using Gd2O3 in the gate dielectric.

Growth of Si whiskers on Au/Si(1 1 1) substrate by gas source molecular beam epitaxy (MBE)

The vapor–liquid–solid growth of Si whiskers from disilane has been studied in a gas source MBE system. The wire-like Si crystals are grown on Si(1 1 1) substrates in a temperature range of 600–800°C, a disilane pressure between 1×10 −4 and 1×10 −7 Torr, and using Au as a growth-promoting agent. The morphology of the Si whiskers is investigated. It is found that the growth rate of the vertical wires is independent of the wire diameter (i.e. whiskers with different diameters have the same growth rate). The growth rate of the wires in the vertical direction increases with increasing substrate temperature and disilane pressure, and is about 8–10 times larger than the growth rate of the planar film on the substrate and the width of the whiskers.

GSMBE growth and PL investigation of lattice-matched [formula omitted] quantum wells

Using a home-made gas-source molecular beam epitaxy system, high quality InGaAs quantum wells with different well widths lattice-matched to a (001) InP substrate have been obtained. Sharp and intense peaks for each well can be well resolved in the PL spectra for the sample. For well widths larger than ∼ 60 A ̊ , the exciton energies are in good agreement with those of calculation. For wells narrower than 40 Å, our line widths are below the theoretical values of line width broadening due to one monolayer interface fluctuation, showing that the interface fluctuation of our sample is within one monolayer.

Study on improving InxGa1−xAs/InyGa1−yP heterointerfaces in gas-source molecular beam expitaxy

The As/P exchange behavior on a GaAs and an InxGa1−xAs surface exposed to a P2 flux and on an InyGa1−yP surface exposed to an As2 flux has been studied by reflection high-energy electron diffraction (RHEED) in a gas-source molecular beam epitaxy system. We found the exposure of InxGa1−xAs to a P2 flux results in a severe substitution of As atoms by P atoms at the normal growth temperature (520 °C), forming a strained transition layer and causing a rough surface within 10 s, which is indicated by a spotty RHEED pattern. The InyGa1−yP surfaces, however, remained relatively stable under an As2 flux. Two methods (a thin protective layer and low-temperature growth) for eliminating the As/P exchange have been developed, and both result in abrupt interfaces.

High current gain InGaP/GaAs heterojunction bipolar transistors grown by multi-wafer gas-source molecular beam epitaxy system

We report for the first time on the high quality and highly uniform InGaP/GaAs heterojunction bipolar transistors with a carbon-doped base grown by a multi-wafer gas-source molecular beam epitaxy (GSMBE) system, which was developed by ourselves. A large-area uniform growth of p-type GaAs and InGaP has been realized. The variation in layer thickness of these layers was less than ± 1.8% across three 3-inch wafers. A large-area (200 × 200 μm 2) heterojunction bipolar transistor (HBT) with a base-sheet resistance of 350 Ω showed a high current gain of 190. This is effectively the highest value considering the base sheet resistance, and is comparable to the best data of AlGaAs/GaAs HBTs reported so far. The small signal current gains showed an excellent uniformity of 3% across one of five 2-inch wafers. The wafer-to-wafer variation of current gains for the two 2-inch wafers, in the same growth run, was less than 3%. The base sheet resistances also showed an excellent uniformity of 0.86%. In addition the average base sheet resistances of the two 2-inch wafers was the same. The device also showed an excellent high-frequency characteristics. The cut-off frequency ( f t ) of 61 GHz, and the maximum-oscillation frequency ( f max ) of 94 GHz were obtained for the transistor having a base dopant concentration of 4 × 10 19 cm −3. These promising results demonstrate the high potential capability of multi-wafer GSMBE for the production of InGaP/GaAs HBTs.

Heteroepitaxial growth of InP/In0.52Ga0.48As structures on GaAs (100) by gas-source molecular beam epitaxy

High quality In0.52Ga0.48As, InP, and In0.52Ga0.48As/InP single quantum wells were grown on GaAs (100) by gas-source molecular beam epitaxy (GSMBE) with a 2-μm thick InxGa1−xAs buffer layer where x was linearly graded from 0 to 0.52. Reflection high-energy electron diffraction patterns and specular beam intensity oscillations showed that the growth mode of In0.52Ga0.48As and InP were layer by layer despite the lattice mismatch (Δa/a=3.8%) between InP and GaAs. Photoluminescence line widths at 10 K of a 1-μm thick InP and a 5-nm wide In0.52Ga0.48As/InP single quantum well are 4.9 and 10 meV, respectively, which are comparable to the values measured from similar structures grown lattice matched on an InP substrate (3.5 and 7 meV, respectively) by the same GSMBE system. The quantum-well luminescence intensity is also comparable to lattice-matched samples.

Reflection high-energy electron diffraction intensity oscillations and surface reconstructions measured during epitaxial growth of Si(001) from Si2H6 molecular beams

The growth of Si(001) from a gas source molecular-beam epitaxy system using disilane (Si2H6) was investigated using reflection high-energy electron diffraction (RHEED). Surface reconstructions which occurred during growth were studied as a function of both substrate temperature and surface coverage. Growth below 600 °C was found to be initiated by the formation of three-dimensional (3D) islands. Near 645 °C, (2×2) and c(4×4) reconstructions occurred on the growing Si(001) surface. At higher temperatures, above 680 °C, growth was found to proceed two dimensionally. The Si(001) surface was found to have undergone a series of reconstructions which have been attributed to the number of hydrogen adatoms and Si dimers covering the surface. RHEED intensity oscillations have been used to monitor Si(001) during growth. Oscillations are easily obtained on well prepared surfaces on which a buffer layer has been grown. Oscillations of the specular beam in both the [010] and [110] azimuths have been measured as a function of temperature and disilane flow rate. Strong and damped oscillations are observed between 610 and 680 °C in the two-dimensional growth regime. At higher temperatures growth by step propagation dominated, while at lower temperatures growth became three dimensional (3D) and consequently oscillations were weak or absent. Oscillations of the fractional order and specular beams in the [110] azimuths indicate that growth occurs in a monolayer rather than a bilayer fashion, and the alternating intensity of sequential oscillations in the specularly reflected beam in the [110] azimuth may be indicative of the relative step density in the two orthogonal directions. Growth rates, as determined from the oscillations, are found to be independent of incident beam flux at substrate temperatures below 600 °C. Above this temperature the growth rate increases proportionally to the incident flux. An Ahrrenius plot indicates an activation energy (EA) of 40.7 kcal/mol in the low temperature regime (T<600 °C) and an apparent EA dependence on disilane flux in the high temperature regime.

A RHEED study of the surface reconstructions of Si(001) during gas source MBE using disilane

The growth of Si(001) from a gas-source molecular beam epitaxy system (Si-GSMBE) using disilane (Si 2H 6) was investigated using RHEED. Substrates were prepared by two commonly used etching techniques, one producing a surface oxide and the other a hydrogen passivated surface. Comparisons are made with regard to the growth mode and quality of the overlayer. Surface reconstructions which occurred during growth were studied as a function of both substrate temperature and surface coverage. All growth was found to be initiated by the formation of three-dimensional (3D) islands which coalesced at substrate temperatures above 600°C. Near 645°C, (2 × 2) and c(4 × 4) reconstructions occurred on the growing Si(001) surface. At higher temperatures, growth was found to proceed two-dimensionally. The Si(001) surface was found to have undergone a series of reconstructions which may be related to the number of hydrogen adatoms and Si dimers covering the surface.

Surface reconstructions of Si(001) observed using reflection-high- energy-electron diffraction during molecular-beam epitaxial growth from disilane

The growth of Si(001) from a gas source molecular-beam epitaxy system (Si-GSMBE) using disilane (Si2H6) was investigated. The surface reconstructions occurring between 100–775 °C were studied as a function of both substrate temperature and surface coverage. Further, we report the first observation of (2×2) and c(4×4) reconstructions during growth at substrate temperatures near 645 °C using Si2H6. All growth was found to be initiated by the formation of 3D islands which coalesce at substrate temperatures above 600 °C, following which, growth proceeds in a two-dimensional (2D) fashion. The Si surface was found to have undergone a series of reconstructions which were related to the number of hydrogen adatoms and Si dimers covering the surface.

A safety system for gas source molecular beam epitaxy

Gas source molecular beam epitaxy (GSMBE) is one of the newest developments in epitaxial growth technology wherein the group V sources such as arsine and phosphine are gaseous and in the form of hydrides, while the Group III sources such as indium, aluminum, gallium are all solids. However, the gases involved are very hazardous, extremely toxic, highly inflammable and explosive at elevated temperatures. Adequate care must be taken for the safe use of these gases so that this attractive technique can be properly utilized. This paper discusses the salient safety features of one such GSMBE system (installed in the Epicenter at the University of Illinois) consisting of a gas delivery system with its robust piping assembly, gas manifold and a scrubber. The system is integrated with a Multiple Point Toxic Gas Monitor (MPTGM) acting as the central alarm command system based on the concept of fail safe total safety. This alarm system is equipped with audio-visual alarms for a variety of monitored conditions and interlocks for automatic shutdown. A well-designed air flow pattern has been incorporated to provide good air quality in the laboratory and in the gas storage facility. Additionally a set of good laboratory practices ensured by administrative and personal control are instituted to reduce the hazards to an acceptable risk level.

Epitaxial growth of lattice matched metallic ErP 0.6As 0.4 on (001) and (111) GaAs with a GSMBE system

Lattice matched metallic ErP 0.6As 0.4 layers have been grown on GaAs, for the first time, by gas source molecular beam epitaxy (GSMBE). By adjusting the PH 3 and AsH 3 flows, a lattice mismatch below 5×10 −4 has been reproducibly achieved. These epitaxial films exhibit metallic behaviour with resistivities of 80–90 μω cm at room temperature and yield Schottky barrier diodes on GaAs with good characteristics. By cross-section transmission electron microscopy we demonstrated the good crystalline quality of the ErP 0.6As 0.4 films and the overgrown GaAs layers.

Raman spectra of AlxIn1−xAs grown molecular-beam epitaxy

Photoluminescence wavelength emission of GaxIn1−xAsyP1−y/InP heterostructures grown in multiwafer gas-source molecular-beam epitaxy (GSMBE) is studied in detail for both bulk and multiple quantum well (MQWs) heterostructures. Excellent photoluminescence wavelength uniformity is reported in 4×2-in. configuration, demonstrating the compatibility of GSMBE process with large-scale 1.55 μm telecom laser production. A strong dependence of wavelength uniformity on group-V/group-III flux ratio is reported and analyzed quantitatively. An empirical model based on the interplay between group-V elements incorporation and gas distribution is proposed to predict the influence of AsH3 and PH3 fluxes on As content in the solid. This understanding opens the way to an accurate tuning of wavelength dispersion of GaxIn1−xAsyP1−y/InP MQWs grown in multiwafer GSMBE system.

Structural properties of the ZnSe/GaAs system grown by molecular-beam epitaxy

Photoluminescence wavelength emission of GaxIn1−xAsyP1−y/InP heterostructures grown in multiwafer gas-source molecular-beam epitaxy (GSMBE) is studied in detail for both bulk and multiple quantum well (MQWs) heterostructures. Excellent photoluminescence wavelength uniformity is reported in 4×2-in. configuration, demonstrating the compatibility of GSMBE process with large-scale 1.55 μm telecom laser production. A strong dependence of wavelength uniformity on group-V/group-III flux ratio is reported and analyzed quantitatively. An empirical model based on the interplay between group-V elements incorporation and gas distribution is proposed to predict the influence of AsH3 and PH3 fluxes on As content in the solid. This understanding opens the way to an accurate tuning of wavelength dispersion of GaxIn1−xAsyP1−y/InP MQWs grown in multiwafer GSMBE system.