Source Molecular Beam Epitaxy Growth Research Articles

Reflectance anisotropy and reflection high-energy electron diffraction intensity oscillations during gas source molecular beam epitaxy growth of Si and SiGe on Si(001)

Dynamic reflectance anisotropy (RA) and reflection high-energy electron diffraction (RHEED) intensity measurements were used to study the epitaxial growth of Si and SiGe on Si(001) using gas source molecular beam epitaxy (GSMBE). Oscillatory behaviour in the RA response was observed using a HeNe laser at 1.96 eV during growth of Si and SiGe over a wide range of temperatures. Whilst the surface retains a two domain (1 × 2) + (2 × 1) reconstruction during growth, the period of the RA oscillations corresponds to the time required for the growth of two monolayers (ML). Simultaneous RHEED intensity oscillations observed along the [110] azimuth indicate that the growth proceeds in a ML mode and that the frequency observed is twice that of the RA oscillations. This oscillatory behaviour of the RA response is explained in terms of the varying dimer concentrations along the two orthogonal 〈110〉 directions and hence the relative coverages of the two domains. Comparisons are made between the RHEED and RA oscillations to explain the significance of the RA response.

Solid source molecular-beam epitaxial growth of Ga0.5In0.5P using a valved, three-zone phosphorus source

Ga0.5In0.5P/GaAs heterojunction films were grown using a valved, three-zone phosphorus source and valved arsenic source. The design of the phosphorus source eliminates the flux bursts experienced upon valve opening with two-zone furnaces. Narrow x-ray linewidths with Pendellosung interference oscillations were observed in double crystal measurements. Chemically abrupt As/P and P/As interfaces were obtained using both valved sources. The optical band gap determined from photoluminescence was consistent with minimal ordering in the films. GaInP films were doped with silicon in the 1017 cm−3 range with good mobilities and negligible carrier freeze-out upon cooling. A GaInP(emitter)/GaAs(5×1019 cm−3 carbon doped base) heterojunction bipolar transistor exhibited a current gain of 30.

Metal Semiconductor Metal Photodetectors and Modulators for Long Wavelength Applications: Optimization of Solid Source Molecular Beam Epitaxy of AlInAs/(Al)GaInAs-Heterostructures

Solid source molecular beam epitaxial (MBE) growth of AlInAs/(Al)GaInAs heterostructures for applications in metal-semiconductor-metal (MSM) photodetectors and electrooptic MSM modulators has been optimized with regard to high frequency performance. The influence of the thickness of an AlInAs barrier enhancement layer on the dynamical characteristics is also investigated. In contrast to the commonly chosen thickness of about 10 nm we show that an increase to 100 nm AlInAs results in bandwidth enhancement and noise reduction. Using these improved structures with breakdown voltages exceeding V B=100 V for electrooptic switching we attain an on-off-ratio of 19:1.

Synchrotron Radiation‐Assisted Si Epitaxial Growth Using Si2 H 6 and SiH2Cl2 Gases: Properties in the Low Temperature Region

Synchrotron radiation excited gas source molecular beam epitaxial growth was examined using reaction gases and . In , good crystallinity was obtained only at high temperature regions, where the growth rate is limited by the supply rate to the substrate surface of gas molecules or by the desorption rate of the surface‐terminating hydrogen. The growth rate significantly depends on the temperature at the region of the rate limited by the hydrogen desorption. In, the growth rate was almost independent of the temperature and the crystallinity was good at all temperatures examined (400 to 550°C). Desorption of H and Cl in the form of is considered.

Gas source molecular beam epitaxy growth of ZnSe on novel buffer layers

Thin films of ZnSe on pseudomorphic and partially relaxed (In,Ga)P buffer layers (on GaAs) have been examined; both epilayers were grown by gas source molecular beam epitaxy. The ZnSe layers were grown using elemental Zn and thermally decomposed H2Se. The II–VI nucleation occurred following an ex situ transfer in air of the As-passivated (In,Ga)P buffer layers, grown using In, Ga, and cracked PH3. Microstructural characterization of the II–VI/III–V heterostructures was performed with high-resolution x-ray diffraction and transmission electron microscopy. The (511) reflection of the x-ray rocking curves was used to measure the residual strain in the ZnSe/(In,Ga)P/GaAs structures, and to determine the alloy composition of the (In,Ga)P. The (400) reflection of the x-ray diffraction rocking curves indicated peaks having full width at half-maximum of 130 and 18 arcsec for the relaxed ZnSe on thin (1 μm) pseudomorphic (In,Ga)P buffer layers, respectively. Transmission electron microscopy confirmed the relaxed or pseudomorphic nature of each heterolayer. Thicker (≳4 μm) In0.52Ga0.48P buffer layers were still not completely relaxed, and exhibited a residual lattice mismatch of approximately 0.11% between the ZnSe layer and the In0.52Ga0.48P buffer layer. Relatively thick (1–2 μm) ZnSe films had surface morphologies that were featureless when examined by Nomarski microscopy and scanning electron microscopy. Low-temperature photoluminescence spectra originating from the ZnSe films on the partially relaxed (In,Ga)P buffer layers were dominated by donor-bound and free-excitonic features with each exhibiting nearly the same intensity. Luminescence from extended defects (the Y0 and Iv transitions) within the ZnSe layer, and luminescence originating from the (In,Ga)P buffer layers, were also observed.

Gas source molecular beam epitaxy growth of GaP/AlP short period superlattices

GaP/AlP short period superlattices (SLs) are grown on GaP substrates by gas source molecular beam epitaxy (MBE). Strong photoluminescence is observed in the green-to-yellow wavelength range at 4.2 K. Photoluminescence and electroreflectance spectra are in good agreement with the theoretical predictions for the formation of the zone-folded direct band gap. The refractive indices of the SLs are larger than those of bulk GaP, AlP and AlGaP, indicating the possibility of formation of laser diode structures using GaP/AlP SL as an active layer. By using Be as a p-type dopant source, a hole concentration of as high as 1.5 × 10 19 cm −3 is easily obtained in GaP. It is also shown that the interface and optical properties of SLs are improved by gas source migration enhanced epitaxy.

Effects of Phosphorus Pressure on Growth Rate and Layer Quality of InP Grown by Gas Source Molecular Beam Epitaxy

Effects of phosphorus pressure on the growth mechanism and the quality of the grown layers in gas source molecular beam epitaxial (MBE) growth of InP on (001) substrate are investigated. It is found that the normal growth process with the growth rate limited by indium flux intensity takes place only in a very narrow range of phosphorus supply. Outside this range, the growth rate depends also on phosphorus pressure. A significant decrease in growth rate under high phosphorus pressure is demonstrated to be due to oversaturation of the substrate surface by excess phosphorus. High phosphorus pressure deteriorates both the electrical and optical properties as well as the crystalline quality of the epitaxial layers. Incorporation of excessive phosphorus is shown to be responsible for deterioration, indicating that control of phosphorus pressure is very important for successful MBE growth of InP.

Gas source molecular beam epitaxial growth and device applications in In 0.5Ga 0.5P and In 0.5Al 0.5P heterostructures

This article reviews briefly the recent progress in the In 0.5Ga 0.5P and In 0.5Al 0.5P epilayers lattice-matched to GaAs grown by gas source molecular beam rpitaxy (GSMBE). It covers the growth conditions, and the structural, electrical, and optical properties. Important research results on the electronic and photonic device applications of these materials grown by GSMBE are also reviewed and discussed. We focus on the InGaP/InGaAs and InAlP/InGaAs pseudomorphic modulation-doped field-effect transistors, InGaP/GaAs and InAlP/GaAs heterojunction bipolar transistors, short wavelength visible laser diodes, and 0.98 μm lasers using In 0.5Ga 0.5P as the cladding layers. The results clearly demonstrate that high quality In 0.5Ga 0.5P and In 0.5Al 0.5P heterostructures prepared by GSMBE are suitable for state-of-the-art device applications.

Gas source molecular beam epitaxial growth and characterization of 600–660 nm GaInP/AlInP double-heterostructure lasers

Gas source molecular beam epitaxy (GSMBE) is one of the most promising technologies for growing AlGaInP which is an important compound system for realizing high performance 550–700 nm range visible light emitting devices. In this paper we review the investigations carried out for GSMBE-grown AlGaInP crystals and visible lasers, involving several results for AlGaInP systems grown by metal-organic chemical vapour deposition. First of all, we investigated growth conditions of high optical-quality GaInP by GSMBE, followed by the fabrication of 600 nm range GaInP/AlInP double-heterostructure lasers. To improve the lasing performances, various techniques described in this paper have been investigated. (GaInP) 2.5/(AlInP) 2.5 short-period superlattices were utilized to suppress the non-radiative recombination at the interface between the active and AlInP cladding layers. These superlattices were also used as the superlattice barriers in multiple-quantum-well active layers. The effect of misoriented GaAs substrates from the (100) surface toward the [011] direction on material properties and lasing performances was systematically investigated. It was clarified that the spontaneous crystal ordering was suppressed and the Al-related non-radiative recombination was reduced. Also, this substrate misorientation effect was effective in enhancing the electrical activity of Be in AlInP cladding layers with a resultant drastic reduction in threshold current density. The introduction of novel multiple-quantum-barrier structure into lasers was also investigated, for the first time; this was very effective in reducing the carrier overflow from the active layer. As a result, a drastic improvement in lasing performance of 660 nm lasers was obtained. Finally, a new shutter control method to form a strained quantum well layer without growth interruption is presented.

Transient growth rate change during gas source molecular beam epitaxy of Si1−xGex alloys

Reflection high-energy electron diffraction intensity oscillations during gas source molecular beam epitaxy growth of Si1−xGex using disilane and germane are reported. Transient changes of the oscillation period and hence the growth rate are observed during the growth. Their origin is discussed on the basis of hydrogen desorption kinetics on the alloy surface and attributed to Ge surface segregation effects at the growth interface. This observation provides a unique opportunity for in situ investigations with monolayer-scale resolution, of Ge segregation effects in Si/Si1−xGex heterostructures.

Growth of pseudomorphic In xGa 1-xAs⧸GaP yAs 1-y multiple quantum well structures on GaAs by gas source molecular beam epitaxy

We report gas source molecular beam epitaxial growth of strain balanced In xGa 1-xAs⧸GaP yAs 1-y multiple quantum well structures on GaAs that exhibit sharp excitonic absorption features at 1.06 μm. Because these materials also lie at the extreme limit of elastic stability, we examine the mechanism by which strain initially relaxes using RHEED and X-ray diffraction. A structural instability is found for a critical strain layer thickness beyond which a transition from smooth to rough growth occurs. When strain relaxation occurs our measurements indicate that surface energy driven processes cause the layer to form lateral domains. The domains consist of regions containing small misorientation angular tilts. Domain formation has a direct consequence on the field dependent absorption measurements in strain balanced multiple quantum well structures on GaAs.

Gas source molecular-beam epitaxial growth of normal incidence GaAs/AlGaAs quantum well infrared photodetectors

Normal incidence illumination of long wavelength quantum well infrared photodetectors is demonstrated for the first time by using hole intersubband absorption in the GaAs valence band without diffraction gratings. The strong mixing between the heavy and light holes at k≠0 allows the desirable normal incidence illumination geometry to be used. Grown by gas source molecular beam epitaxy, a normal incidence quantum efficiency of η=28% and detectivity of D*λ = 3.1 × 1010 cm√Hz/W at 77 K for a cutoff wavelength λc = 7.9 μm have been achieved.

Gas source molecular beam epitaxy growth of short period GaP/AlP(001) superlattices

Short period GaP/AlP superlattices are grown on GaP and GaAs substrates at 600 °C by gas source molecular beam epitaxy with growth interruption. Alternating monolayer growth of GaP and AlP is confirmed by the observation of the reflection high-energy electron diffraction intensity oscillations during growth. The formation of short period superlattice structures and the zone-folded LO phonons are observed in the x-ray diffraction rocking curves and Raman spectra, respectively.

High carbon doping efficiency of bromomethanes in gas source molecular beam epitaxial growth of GaAs

Carbon tetrabromide (CBr4) and bromoform (CHBr3) have been studied as carbon doping sources for GaAs grown by gas source molecular beam epitaxy (GSMBE) with elemental Ga and thermally cracked AsH3. Hole concentrations in excess of 1×1020 cm−3 have been measured by Hall effect in both CBr4- and CHBr3-doped GaAs, which agrees closely with the atomic C concentration from secondary-ion mass spectrometry, indicating complete electrical activity of the incorporated carbon. The GaAs growth rate is unaffected by the CBr4 and CHBr3 fluxes over the range of dopant flow investigated. The efficiencies of carbon incorporation from CBr4 and CHBr3 are, respectively, 750 and 25 times that of trimethylgallium (TMG), which is commonly employed as a carbon doping source in metalorganic MBE (MOMBE). The sensitivity of carbon incorporation to varying substrate temperature and V/III ratio has been observed to be significantly reduced with CBr4 and CHBr3 from that obtained under similar growth conditions with TMG in MOMBE.

Diffusion limited δ-doping profiles in GaAs grown by gas source molecular beam epitaxy

We report on results that compare the planar confinement, diffusion and surface segregation of Si and Be δ-doped GaAs grown by gas source molecular beam epitaxy and conventional molecular beam epitaxy. For gas source molecular beam epitaxy growth of †-doped Si and Be we observed diffusion limited doping profile distributions. In molecular beam epitaxy growth the doping profiles further broaden by an impurity surface segregation process.

Atomic diffusion and surface segregation of Si in δ-doped GaAs grown by gas source molecular beam epitaxy

We report on results that compare the planar confinement, diffusion, and surface segregation of Si δ-doped in GaAs for growth by gas source molecular-beam epitaxy and conventional molecular-beam epitaxy. For gas source molecular-beam epitaxy growth, Si diffusion versus inverse anneal temperature shows a unique two component Arrhenius form in which activation energies for diffusion differ by the fundamental GaAs band gap energy, 1.5 eV. Capacitance–voltage profiles of as-grown δ-doped Be and Si layers in GaAs produce record full width at half-maximum, 1.9 and 2.4 nm, respectively, for the gas source molecular-beam epitaxy case.

Very high purity GaAs grown by gas source molecular beam epitaxy

We report gas source molecular beam epitaxy (GSMBE) growth of very high purity GaAs in which a peak mobility near 300,000 cm 2/V·s was observed. We investigate this high purity layer by means of deep level transient spectroscopy (DLTS), photoluminescence and transport measurements. We present evidence that an unintentionally doped donor has binding energy less than 2 meV and the temperature dependence of mobility at low temperature significantly deviates from the expected transport behavior.

Electron beam source molecular beam epitaxial growth of analog graded AlxGa1−xAs ballistic transistors

A new method has been developed for the growth of graded band-gap AlxGa1−xAs alloys by molecular beam epitaxy which is based upon electron beam evaporation of the group III elements. The metal fluxes are measured and feedback controlled using a modulated ion gauge sensor. The system is computer controlled which allows precise programming of the Ga and Al evaporation rates. The large dynamic response of the metal sources enables growth of variable band-gap III-V alloys with arbitrary composition profiles. This new technique is demonstrated by synthesis of analog graded AlxGa1−xAs unipolar ballistic electron transistors.

Silicon doping from disilane in gas source MBE of GaAs

Disilane (Si 2H 6) is used as an n-type dopant in gas source molecular beam epitaxial growth of GaAs using triethylgallium (TEG) and AsH 3. A linear relationship is obtained between the disilane flow rate and the electron concentration in the range from 1.3×10 17 to 1.2×10 18 cm -3. The doping efficiency depends on the substrate temperature varied from 480 to 600°C, but only slightly on the AsH 3 flow rate. Furthermore, the doping efficiency is observed to be enhanced by a factor of 2.5 when UV laser irradiation is directed normal to the substrate surface.