Gas-source Molecular Beam Epitaxy Growth Research Articles

Effects of B doping on hydrogen desorption from Si(001) during gas-source molecular-beam epitaxy from Si2H6 and B2H6

Boron doping concentrations ≳6×1019 cm−3 were found to increase Si(001) growth rates RSi at low temperatures while decreasing RSi at higher temperatures during gas-source molecular beam epitaxy (GS-MBE) from Si2H6 and B2H6. In order to probe the mechanisms governing these effects, Si(001) samples with B coverages θB ranging from <0.05 to ≂0.5 ML were prepared by exposing clean Si(001)2×1 wafers to B2H6 doses between 2×1017 and 4×1020 cm−2 at 200–400 °C. The samples were then heated to 700 °C to desorb the hydrogen, cooled to 200 °C, and exposed to atomic deuterium until saturation coverage. D2 temperature programmed desorption spectra exhibit β2 and β1 peaks due to dideuteride and monodeuteride desorption at 405 and 515 °C as well as new B-induced peaks, β2* and β1*, at 330 and 470 °C. Increasing θB increases the area under β2* and β1* at the expense of β2 and β1. Moreover, the total D coverage continuously decreases from ≂1.23 ML in the absence of B to ≂0.74 ML at θB=0.5 ML. We propose that the observed B-induced decrease in the Si*-D bond strength, where Si* represents surface Si atoms bonded to second-layer B atoms, is due to charge transfer and increased Si* dimer strain. The Si* to B charge transfer also deactivates Si surface dangling bonds causing the decrease in θD. These results are used to explain the GS-MBE growth kinetics.

Highly strained [formula omitted] quantum wells grown on GaP and on an [formula omitted] buffer layer by gas-source molecular beam epitaxy

We report gas-source molecular beam epitaxial growth of highly strained In x Ga 1−x P GaP quantum wells on GaP and on an In x 2 Ga 1−x 2 P buffer layer. High-resolution X-ray diffraction and photoluminescence (PL) have been used to characterize the material quality. Satellite peaks up to ±2nd order are observed from a 50 period In x Ga 1−x P(50 A ̊ ) GaP(50 A ̊ ) multiple quantum well (MQW) grown on an In x 2 Ga 1−x 2 P buffer layer, whereas only the 1st-order satellite peak is observed for the same structure grown directly on GaP under the same growth condition, which indicates better-quality In x Ga 1−x P GaP MQWs can be achieved by using an In x 2 Ga 1−x 2 P buffer layer. Furthermore, an increase in the X-ray satellite peak intensity of the In x Ga 1−x P GaP MQWs grown on the In x 2 Ga 1−x 2 P buffer layer has been observed as the period of the MQW increases, suggesting no structural degradation and an increase of the critical layer thickness of the MQWs. PL measurements also show that an In x 2 Ga 1−x 2 P buffer layer is effective in improving the optical quality of the In x Ga 1−x P GaP MQWs .

P 2-induced [formula omitted] exchange on GaAs during gas-source molecular beam epitaxy growth interruptions

P As exchange behavior on GaAs under a P 2 flux in a gas-source molecular beam epitaxy (GSMBE) system has been studied by reflection high-energy electron diffraction (RHEED), high-resolution double-crystal X-ray rocking curves (DCXRC) and cross-sectional scanning tunneling microscopy (STM). We found that the exposure of GaAs to a P 2 flux results in severe substitution of As atoms by P atoms at the normal temperature for growing GaAs ( T s = 570°C). When T s < 500°C, a streaky RHEED pattern can be maintained even during P 2 flux exposure of over 10 min. DCXRC of a 25-period P 2-exposed GaAs structure grown at 550°C show a set of satellite peaks, indicating formation of a periodic structure. Approximately an average of 0.45 monolayer of phosphorus is incorporated at each interface via As P exchange. High-resolution cross-sectional STM images reveal non-uniform (both laterally and vertically) interfacial layers of width as large as 10 monolayers. For the sample grown at 450°C, no clear satellite peaks are present. STM images of the sample exhibit much thinner interlayers, consistent with a lower level of phosphorus substitution.

In-situ pyrometric interferometry monitoring of [formula omitted] material systems during gas-source molecular beam epitaxy growth

In-situ pyrometric interferometry measurements were characterized for various In 0.5 Ga 0.5 P In 0.5 Al 0.5 P layered structures, including quarter-wavelength ( λ 4 ) distributed Bragg reflectors (DBR) at both 960 and 680 nm lattice matched to GaAs substrates by gas-source molecular beam epitaxy (GSMBE). Sustained quasi-sinusoidal oscillating signals were observed for the 960 nm DBR structures at a monitoring wavelength ( λ m) of 940 nm. Our results showed that pyrometric interferometry can be applied to real-time closed-loop growth of In 0.5 Ga 0.5 P In 0.5 Al 0.5 P DBR structures.

Improved modulation contrast of asymmetric Fabry–Perot field-effect transistor self-electro-optic effect devices by in situ thickness corrections

We present an in situ optical method for thickness correction during the gas-source molecular beam epitaxial growth of asymmetric Fabry–Perot cavities. Separate growth corrections are made to center the spectrum of the mirror reflectivity, and to place the cavity resonance at the desired wavelength, all by measuring the reflectivity spectrum without breaking the vacuum. We choose to use an AlInP/InGaP quarter-wave mirror to demonstrate that the correction can be made after the growth of only three periods. By adding additional GaAs cap layer thickness and thereby adjust the positions of the Fabry–Perot minima of a AlGaAs/GaAs field-effect transistor self-electro-optic effect devices, improvement of modulation contrast from 3:1 to 9:1 is demonstrated.

A New type of Graded Buffer Layer for Gas-Source Molecular Beam Epitaxial Growth of Highly Strained INxGA1−XP/GAP Multiple Quantum Wells on Gap

ABSTRACTA new type of graded buffer layer, called graded short-period superlattice (GSSL) buffer layer, is proposed, and its effect on improving the material quality is investigated by comparing the qualities of 50-period InGaP/GaP multiple quantum wells (MQWs) grown on top of it and on a linearly graded (LG) buffer layer. Unlike the linearly graded buffer layer, in which the In composition is changed 1% per step size with a constant composition InGaP, the new buffer uses InGaP/GaP short-period superlattice within each step, while maintaining the average In composition of the short-period superlattice being changed the same amount per step size. Characterization of these structures by high-resolution X-ray diffraction and low-temperature photoluminescence indicates that, while the MQWs grown on a GSSL buffer show comparable structural properties as compared with those on an LG buffer, they exhibit higher PL intensity and narrower PL line width.

Necessity of Ga prelayers in GaAs/Ge growth using gas-source molecular beam epitaxy

We have investigated the gas-source molecular beam epitaxy growth of GaAs on a (001) Ge surface, off-cut 6° towards the [110]. Initiation of GaAs on Ge with the typical procedure of using a self-terminating As layer invariably produces poor GaAs surface morphology and generates a plethora of antiphase boundaries, despite the large miscut of the (001) surface. However, initiation of GaAs growth with approximately 1 ML (monolayer) of Ga results in single-domain films with excellent surface morphology. We conclude that the Ga monolayer prevents the Ge surface from forming a high step density surface which is established when Ge is exposed to As2.

Electronic and Photonic Device Applications of In0.5Ga0.5P and In0.5Al0.5P Grown by Gas Source Molecular Beam Epitaxy

ABSTRACTAdvances in gas-source molecular beam epitaxial (GSMBE) growth techniques have allowed the successful fabrication of electronic and photonic devices based on In0.5Ga0.5P and In0.5A10.5P heterostructures lattice matched to GaAs. Basically the interest in In0.5Ga0.5P and In0.5A10.5P derives from their unique material properties as well as their band alignment to GaAs. In this paper, we review the growth, fabrication, and performance of In0.5A10.5P/In0.2Ga0.8As pseudomorphic high electron mobility transistors (HEMT's), InO.5A10.5P/GaAs heterojunction bipolar transistors (HBT's), and In0.5Ga0.5P red light emitting diodes (LED's) grown on Ge/graded GexSil-x/Si substrates. The results provide a solid demonstration of the feasibility of using In0.5Ga0.5P and In0.5A10.5P prepared by GSMBE for manufacturing GaAs-based optoelectronic devices.

Gas-source molecular beam epitaxy growth of GaxIn1−xAsyP1−y lattice matched to GaAs

Gas-source molecular beam epitaxy growth of GaxIn1−xAsyP1−y layers lattice matched to GaAs is reported. X-ray diffraction, photoluminescence, and Hall measurements show that the layers are of good quality. High-quality GaAs/GaxIn1−xAsyP1−y heterojunction and (In)GaAs/GaxIn1−xAsyP1−y quantum well structures have also been prepared, as deduced from the device characteristics of heterojunction diodes and quantum well lasers.

Planarized growth of AlGaAs/GaAs heterostructures on patterned substrates by molecular beam epitaxy

The profiles of AlGaAs/GaAs heterostructures grown by gas-source molecular beam epitaxy (GSMBE) on patterned substrates at different growth temperatures have been studied. It was found that at higher substrate temperature, the GSMBE growth results in Al clustering and the formation of high index planes. With a proper combination of low growth temperature and etched profile, a quasiplanarized surface is obtainable. A process simulation program is found to be capable of simulating the GSMBE growth profile at lower substrate temperature with reasonable accuracy.

Gas-source molecular beam epitaxy growth of GaxIn1-xAsyP1-y on GaAs for photonic and electronic applications

Gas-source molecular beam epitaxy growth of Ga x In 1-x As y P 1-y , layers lattice-matched to GaAs in reported. X-ray diffraction, photoluminescence, and Hall measurements show that the layers are of good quality. High-performance Al-free (In)GaAs(P)/Ga x In 1-x As t P 1-y , quantum well lasers, emitting at 0.8≤λ≤ 1.1 μm, and GaAs/Ga x In 1-x As y P 1-y , heterojunction diodes are also demonstrated. The results are comparable to those obtained for the best AlGaAs based materials and devices. In particular, we report on the first tensile-strained GaAsP/GaInAsP/GaInP quantum well laser

Gas-source molecular beam epitaxial growth, characterization, and light-emitting diode application of InxGa1−xP on GaP(100)

Highly lattice-mismatched InxGa1−xP (x≤0.38) layers were grown on GaP substrates by gas-source molecular beam epitaxy. A relatively thin, compositionally linear-graded buffer layer was used to reduce the number of threading dislocations. Studies by double-crystal x-ray diffraction and transmission electron microscopy show this buffer layer to be 97% strain-relaxed along both 〈110〉 directions with dislocations well confined within the graded buffer and the substrate. Threading dislocation densities in the top layers were less than 1×107 cm−2. Room-temperature photoluminescence, ranging from 560 to 600 nm, is achieved. Heterojunction p-i-n diodes emitting at 560 nm at 300 K exhibit good rectifying and reverse breakdown characteristics.

Generation of fast-switching As2 and P2 beams from AsH3 and PH3 for gas-source molecular-beam epitaxial growth of InGaAs/InP multiple quantum well and superlattice structures

In an attempt to maximize the cracking and dimerization efficiencies with the use of Ta baffling, a severe memory effect was observed which necessitated excessive growth pause durations for group V beam switching. This memory effect was significantly reduced by the implementation of separate Ta-tube catalytic hydride crackers for each group V source. A comparison of W and Ta tubes revealed that the catalytic effect which was observed for the decomposition of AsH3 and PH3 on a Ta surface was not observed for a W surface. The improved high-conductance design yielded cracking and dimerization efficiencies on the order of 99% and 90%, respectively. Switching characteristics have been studied using time-resolved quadrupole mass spectrometry, and switching times of &amp;lt;1 s have been achieved for As2 and P2 with significantly longer switching times observed for As4. Multiple layer heterostructures have been grown with the baffled/common cracker and the separate open-tube crackers for evaluation of the memory effects by secondary ion mass spectrometry. InGaAs/InP quantum well structures have been grown with the fast-switching crackers. Double crystal x-ray diffraction, transmission electron microscopy, and low temperature photoluminescence (PL) characterization suggest that the interfaces obtained with the fast-switching crackers are abrupt to within ∼5 Å when short growth interuptions (∼10 s) are used. However, low temperature (5 K) PL excitation spectra indicate that an interface asymmetry is present. These data suggest that despite verification of fast As2 and P2 switching using time-resolved quadrupole mass spectrometry, growth pause optimization, and group III flux stabilization are still required in order to obtain optimal interface quality for InGaAs/InP heterostructures.

Study of growth temperature in gas-source molecular-beam epitaxy growth of InGaAs/GaAs quantum well lasers

Strained-layer InGaAs/GaAs single quantum well lasers were grown by gas-source molecular-beam epitaxy at temperatures between 430 and 610 °C. The optimum growth temperature for the quantum wells of the lasers was found to be about 520 °C, as deduced from the measurement of threshold current density of the lasers and room-temperature photoluminescence (PL) of the quantum wells. If the growth temperature is lower than 520 °C, the threshold current density dramatically increases due to the formation of nonradiative carrier recombination centers in the quantum well. These recombination centers originate from lattice mismatch defects and alloy disordering. If the growth temperature is higher than 520 °C, indium desorption and segregation become increasingly severe. Thus, at high growth temperature, the InGaAs/GaAs interfaces become rough and the threshold current density increases. In addition, rapid thermal annealing was observed to remove most of the nonradiative recombination centers from the quantum wells and to improve the threshold current density of the lasers and PL intensity of the quantum wells.

GSMBE growth of GaInAsP on GaAs substrates and its application to 0.98 μm lasers

We report on the first gas-source molecular beam epitaxy (GSMBE) growth of GaInAsP on GaAs substrates. The Hall mobility, X-ray diffraction and photoluminescence measurements indicate that high-quality GaInAsP and InGaAs/GaInAsP quantum wells were obtained. High-performance strained-layer InGaAs/GaInAsP/GaInP multiple-quantum-well lasers, emitting at 0.98 μm, have been demonstrated. A low threshold current density of 169 A/cm 2 and a high characteristic temperature of 235 K were obtained for the laser with three quantum wells. A single mode CW room temperature operation was maintained up to 80 mW output power for an HR/AR coated 5.5 μm × 800 μm ridge waveguide laser. This study suggests that GSMBE is suitable for the growth of GaInAsP lattice matched to GaAs, and the GaInAsP is a promising candidate for optoelectronic device applications.

In situ control of As composition in InAsP and InGaAsP grown by gas-source molecular beam epitaxy

Group-III- and group-V-induced intensity oscillations of reflection high-energy electron diffraction are observed for InAsP in gas-source molecular beam epitaxial growth. The As incorporation rate is found to be dominant, independent of the presence of P when the phosphine flow rate is reasonably low. This observation suggests a simple method of controlling the As composition in InAsP by just controlling the incorporation-rate ratio of As to In when this ratio is less than unity. This successful in situ composition control for InAsP, combined with the in situ composition calibration in GaAsP reported previously, provides a general guideline for controlling the compositions in InGaAsP.

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.

In Situ Monitoring of the Smear-Out of the Ge Profile in GAS Source SiGe MBE Using Rheed Intensity Oscillations

ABSTRACTWe have studied the deposition of GexSi1−x layers on (100) Si substrates by gas source molecular beam epitaxy (GSMBE) using disilane and germane.The investigation of RHEED intensity oscillations during growth reveals the well known rate enhancement obtained when adding a small amount of germane to the disilane flux. However, when exposing a previously deposited Ge layer to a pure disilane flux the growth rate during the first few monolayers remains at an enhanced value but returns to its homoepitaxial value after about 10 to 15 monolayers. This behaviour was observed under a variety of growth conditions. It is in marked contrast to the experience obtained in conventional Si/Ge MBE and suggests a catalytic effect of the particular surface present during GSMBE growth. We propose that this effect is caused by the surface segregation of Ge species and leads to a smear-out of the Ge profile in the layer.

Gas-source molecular beam epitaxy growth of highly strained device quality InAsP/InP multiple quantum well structures

InAsxP1−x/InP strained multiple quantum wells with strain as high as 2.5% were grown by gas-source molecular beam epitaxy. Successful control of the arsenic composition over a wide range was achieved by two different growth techniques. Structural and optical studies, such as high-resolution x-ray rocking curve, cross-sectional transmission electron microscopy, photoluminescence, and absorption measurement, indicate that we have obtained high quality multiple quantum wells that are suitable for optoelectronic applications.

Growth of heavily Be-doped AlInP by gas source molecular beam epitaxy

Heavily Be-doped p-type AlInP layers have successfully grown on (001)GaAs by gas source molecular beam epitaxy (GSMBE) using phosphine (PH3). Net hole concentration (Nh) as high as about 3.5×1018 cm−3 is achieved for the first time. The surface morphology is found to be smooth up to a Be concentration of 3×1019 cm−3. The resistivity for Nh=3.5×1018 cm−3 is as low as 0.3 Ω cm. The improvement of the electrical activity and surface morphology may be ascribed to subhidrides of phosphorus decomposed from PH3 during GSMBE growth.