InAlAs Buffer Research Articles

Elucidating the Role of InGaAs and InAlAs Buffers on Carrier Dynamics of Tensile-Strained Ge Double Heterostructures.

Extensive research efforts of strained germanium (Ge) are currently underway due to its unique properties, namely, (i) possibility of band gap and strain engineering to achieve a direct band gap, thus exhibiting superior radiative properties, and (ii) higher electron and hole mobilities than Si for upcoming technology nodes. Realizing lasing structures is vital to leveraging the benefits of tensile-strained Ge (ε-Ge). Here, we use a combination of different analytical tools to elucidate the effect of the underlying InGaAs/InAlAs and InGaAs overlaying heterostructures on the material quality and strain state of ε-Ge grown by molecular beam epitaxy. Using X-ray analysis, we show the constancy of tensile strain in sub-50 nm ε-Ge in a quantum-well (QW) heterostructure. Further, effective carrier lifetime using photoconductive decay as a function of buffer type exhibited a high (low) defect-limited carrier lifetime of ∼68 ns (∼13 ns) in 0.61% (0.66%) ε-Ge grown on an InGaAs (InAlAs) buffer. These results correspond well with the measured surface roughness of 1.289 nm (6.303 nm), consistent with the surface effect of the ε-Ge/III-V heterointerface. Furthermore, a reasonably high effective lifetime of ∼78 ns is demonstrated in a QW of ∼30 nm 1.6% ε-Ge, a moderate reduction from ∼99 ns in uncapped ε-Ge, alluding to the surface effect of the overlying heterointerface. Thus, the above results highlight the prime quality of ε-Ge that can be achieved via III-V heteroepitaxy and paves a path for integrated Ge photonics.

Study of single event effect for the InP-based HEMT with In0.53Ga0.47As/In0.3Ga0.7As/In0.7Ga0.3As composite channel

In this study, the single event effects in In0.53Ga0.47As/In0.3Ga0.7As/In0.7Ga0.3As composite channel InP-based HEMT are investigated using TCAD simulation for the first time. Due to the higher conduction band difference between bottom In0.7Ga0.3As channel and InAlAs buffer, the electrons in the buffer layer induced by ions strike cannot enter the channel, led to reduce the peak concentration in the composite channel and significantly weakened the drain current for composite channel device. Meanwhile, higher barrier height under the gate for composite channel InP-based HEMT is formed after particle strike, and further attenuate the drain current. Therefore, the single event effects can be effectively reduced by designing channel structure. In addition, drain voltage and incident position also show significant impact drain current. With the increase in the drain voltage, the drain current increase and the most sensitive incident position is the gate electrode for the device.

Flat metamorphic InAlAs buffer layer on GaAs(111)A misoriented substrates by growth kinetics control

We have successfully grown, through the detailed control of the growth kinetics, flat InAlAs metamorphic buffer layers on 2∘-off GaAs(111)A substrates using molecular beam epitaxy. Almost full plastic relaxation is obtained for a layer thickness > 40 nm. The control of an adatom diffusion length and a step ejection probability from the bunches permits a reduction of the InAlAs epilayer root-mean-square surface roughness to 0.55 nm.

Effect of InxAl1-xAs graded buffer materials on pseudomorphic InP HEMT

In this paper, The InxAl1-xAs graded buffer was inserted between the InAlAs buffer layer and the pseudomorphic In0.66Ga0.34As channel layer to improve material quality in channel. The results show that the InxAl1-xAs graded buffer layer with 50 nm thickness can obtain a good heterojunction interface and the root mean square (RMS) of 0.154 nm. The two dimensional electron gas (2-deg) mobility and concentration were 8570 cm2/Vs. and 2.7 cm−2 × 1012 cm−2 at 300K, respectively. InxAl1-xAs graded buffer layer can enhance the interface quality and the electrical performance through releasing the interface strain caused by pseudomorphic In0.52Al0.48As/In0.66Ga0.34As HEMT. This study shows great potentials by incorporating InxAl1-xAs graded buffer layer in pseudomorphic InP HEMT materials to improve the properties of devices.

Metamorphic InAs/InGaAs QWs with electron mobilities exceeding 7 × 105 cm2/Vs

We present a study on the influence of strain-relieving InAlAs buffer layers on metamorphic InAs/InGaAs quantum wells grown by molecular beam epitaxy on GaAs. Residual strain in the buffer layer, the InGaAs barrier and the InAs wells were assessed by X-ray diffraction and high-resolution transmission electron microscopy. By carefully choosing the composition profile and thicknesses of the buffer layer, virtually unstrained InGaAs barriers embedding an InAs quantum well with thickness up to 7 nm can be grown. This allows reaching low-temperature electron mobilities much higher than previously reported for samples obtained by metamorphic growth on GaAs, and comparable to the values achieved for samples grown on InP substrates.

Flat Metamorphic Inalas Buffer Layer on Gaas(111)A Misoriented Substrates by Growth Kinetics Control

Flat Metamorphic Inalas Buffer Layer on Gaas(111)A Misoriented Substrates by Growth Kinetics Control

High performance InGaAs channel MOSFETs on highly resistive InAlAs buffer layers

We investigated the effect of growth temperature on the structural and electrical properties of InAlAs layers grown on InP (100) substrates by metalorganic chemical vapor deposition (MOCVD) method. Flat surface morphology of InAlAs layers with root mean square (RMS) surface roughness values below 0.4 nm were obtained at 500 °C and 660 °C, while RMS surface roughness values of InAlAs layers grown in the region of intermediate temperature increase from 0.7 nm at 540 °C to 3.9 nm at 620 °C with increasing growth temperature. This increase in surface roughness is caused by the phase separation of the InAlAs layer, which is divided into In-rich and Al-rich column regions. The resistivity values of the InAlAs layers grown at 500 °C and 660 °C, in which the phase separation was not observed, were analyzed by the transmission line method (TLM) and those values were ~1 × 104 Ω·cm and 0.06 Ω·cm, respectively. We propose that oxygen atoms being incorporated into InAlAs layers during growth were the cause effect explaining the change in resistivity depending on the growth temperature. In order to evaluate high-resistivity InAlAs layers grown at 500 °C for a buffer layer of devices, we fabricated InGaAs-channel metal oxide field effect transistors (MOSFETs). The on/off current ratio values obtained from ID-VG transfer measurement was a value of 6.10 × 105, indicating a high-performance characteristic.

Comparative study of metamorphic InAs layers grown on GaAs and Si for mid-infrared photodetectors

We report a comparative study of metamorphic InAs p-i-n photodetectors epitaxially grown on GaAs and Si by molecular beam epitaxy. Linearly graded InAlAs buffers were employed to bridge the high lattice mismatch between InAs and Si. Quantitative measurement for threading dislocation density (TDD) in the InAs layers grown on GaAs and Si has been performed using transmission electron microscopy and electron channeling contrast imaging, both of which revealed that the TDD of InAs/Si sample is ~35% higher than that of GaAs sample. Comparison of fabricated InAs p-i-n photodetectors indicated that reduction of threading dislocation density is crucial for low dark current and high responsivity mid-infrared photodetectors on Si.

Effects of buffer doping on the strain relaxation of metamorphic InGaAs photodetector structures

The strain relaxation behaviors of metamorphic In0.83Ga0.17As photodetector structures on Si-doped, Be-doped and undoped InxAl1-xAs graded buffers are investigated. The cross-hatch period and surface roughness are increased by doping in buffer layers. X-ray diffraction reciprocal space mapping measurements reveal that the doping of Si and Be induces the increase of misfit dislocation density along [1−10] and [110] directions, respectively. The photoluminescence intensity of In0.83Ga0.17As photodetector structures is deteriorated by the doping in InxAl1-xAs buffers. The dark currents of fabricated photodetector chips are characterized and the In0.83Ga0.17As photodetector on undoped InAlAs buffer shows the lowest dark currents. The Si doping shows more detrimental effects on photoluminescence and dark current performances than Be doping due to the enhanced growth roughness. These results indicate that the doping of buffer layers is critical for the design and fabrication of metamorphic optoelectronic devices.

Effect of Strongly Mismatched GaAs and InAs Inserts in a InAlAs Buffer Layer on the Structural and Optical Properties of Metamorphic InAs(Sb)/InGaAs/InAlAs/GaAs Quantum-Confined Heterostructures

Metamorphic InAs(Sb)/InGaAs/InAlAs quantum-confined heterostructures with thin (1–5 nm) strongly mismatched GaAs and InAs inserts in a gradient metamorphic InxAl1−xAs buffer layer have been grown on GaAs (001) substrates by molecular beam epitaxy. It has been shown that the use of a 5-nm GaAs insert in the region of a metamorphic buffer layer at x ~ 0.37 almost doubles the photoluminescence intensity at 300 K (λ ~ 3.5 μm) from an InAs/InGaAs quantum well with a monolayer InSb insert. This is explained by an increase in the hole localization energy in InSb measured by photomodulation reflection Fourier transform infrared spectroscopy. This increase is due to increased elastic stresses in the quantum well because of a decreased density of threading dislocations in this structure caused by the introduction of an additional inverse step into the metamorphic buffer layer in the form of a 5-nm GaAs layer. The introduction of a 5-nm InAs layer into the metamorphic buffer layer violates its functions as a dislocation filter, leading to a higher density of dislocations in the quantum well region and to an order of magnitude decrease in the luminescence intensity.

Electronic structure of epitaxial half-Heusler Co1-xNixTiSb across the semiconductor to metal transition

Here, we report on the growth, electronic, and surface properties of the electron-doped half-Heusler series Co1-xNixTiSb (001) grown by molecular beam epitaxy. High-quality epitaxial growth of thin films is achieved on InP (001) substrates using an InAlAs buffer layer for all nickel concentrations. The semiconductor to metal transition as a function of substitutional alloying was examined using electrical transport, Seebeck measurements, and angle-resolved photoemission spectroscopy (ARPES). Temperature-dependent electrical transport measurements of films with composition x ≤ 0.1 exhibit thermally activated behavior while x > 0.1 exhibit metallic behavior. Smooth, highly ordered film surfaces can be achieved following ex-situ transfer of the films and subsequent desorption of a sacrificial, protective antimony capping layer. Using this transfer technique, ARPES experiments were performed to investigate the effects of nickel alloying on the electronic band structure. An electron pocket is observed below the Fermi level at the bulk X point for compositions x > 0.1, in accordance with the crossover from semiconducting to metallic behavior observed in the transport measurements.

Growth temperature optimization of GaAs-based In0.83Ga0.17As on InxAl1−xAs buffers

Improved quality of gas source molecular beam epitaxy grown In0.83Ga0.17As layer on GaAs substrate was achieved by adopting a two-step InxAl1−xAs metamorphic buffer at different temperatures. With a high-temperature In0.83Al0.17As template following a low-temperature composition continuously graded InxAl1−xAs (x = 0.05–0.86) buffer, better structural, optical and electrical properties of succeeding In0.83Ga0.17As were confirmed by atomic force microscopy, photoluminescence and Hall-effect measurements. Cross-sectional transmission electron microscopy revealed significant effect of the two-step temperature grown InAlAs buffer layers on the inhibition of threading dislocations due to the deposition of high density nuclei on GaAs substrate at the low growth temperature. The limited reduction for the dark current of GaAs-based In0.83Ga0.17As photodetectors on the two-step temperature grown InxAl1−xAs buffer layers was ascribed to the contribution of impurities caused by the low growth temperature of InAlAs buffers.

Growth mode of tensile-strained Ge quantum dots grown by molecular beam epitaxy

Growth mode of tensile-strained Ge quantum dots on different III–V buffers by molecular beam epitaxy is studied by a combination of reflection high-energy electron diffraction, atomic force microscopy and transmission electron microscopy. The Ge-QDs growth on the InAlAs buffer lattice matched to InP and on InAs buffer on GaSb follows the Volmer–Weber growth mode with round Ge QDs and no Ge wetting layer, while it obeys the Stranski–Krastanov growth mode on GaSb, AlSb and AlGaSb on GaSb substrates, showing rectangular shaped platelets and a clear Ge wetting layer. The discovery of the Volmer–Weber growth mode is essential to avoid forming a wetting layer and the subsequent antiphase-domain defects when capping III–Vs on Ge-QDs, important for potential optoelectronic applications.

Anisotropic strain relaxation of Si-doped metamorphic InAlAs graded buffers on InP

The effects of Si doping on the strain relaxation of InP-based metamorphic InxAl1−xAs graded buffers have been investigated. The highly Si-doped sample shows an increased ridge period along the [1 1 0] direction in the cross-hatch morphology measured by atomic force microscope. X-ray diffraction reciprocal space mapping measurements reveal that the high Si-doping induced incomplete relaxation as well as inhomogeneous residual strain along the [1 −1 0] direction, which was also observed in micro-Raman measurements. The anisotropic strain relaxation is attributed to the Si-doping enhanced anisotropy of misfit dislocations along the orthogonal directions. The α-misfit dislocations along the [1 −1 0] direction are further delayed to generate in highly Si-doped InAlAs buffer, while the β-misfit dislocations along the [1 1 0] direction are not. These results supply useful suggestions on the design and demonstration of semiconductor metamorphic devices.

Preventing phase separation in MOCVD-grown InAlAs compositionally graded buffer on silicon substrate using InGaAs interlayers

Compositionally graded InAlAs buffers grown by metal–organic chemical vapor deposition are impaired by phase separation occurring at In content higher than 35%. Phase separation results in rough epilayers with poor crystalline material quality. By introducing low temperature grown InGaAs interlayers in the compositionally graded InAlAs buffer, the surface roughness decreases, allowing a grading of up to In0.60Al0.40As without any phase separation occurring. This composite buffer is applied to fabricate a 200mm diameter InP-on-Si virtual substrate with a threading dislocation density around 1×108cm−2.

Metamorphic InAs/InGaAs/InAlAs quantum wells with submonolayer InSb insertions emitted in the mid-infrared spectral range

Metamorphic InAs/InGaAs/InAlAs quantum wells with submonolayer InSb insertions have been grown for the first time by molecular beam epitaxy on GaAs (001) substrates using a graded InAlAs buffer layer with increasing In composition. The given nanoheterostructures demonstrate an intense photoluminescence at a wavelength of over of over 3 μm (80 K), which is shifted toward longer wavelengths as compared with that of the structures without InSb insertions.

Erratum to: “Structural and electrical properties of InAlAs/InGaAs/InAlAs HEMT heterostructures on InP substrates with InAs inserts in quantum well”

A complex study of the influence of nanoscale InAs inserts with thicknesses from 1.7 to 3.0 nm introduced into In0.53Ga0.47As quantum wells (QWs) on the structural and electrical properties of In0.52Al0.48As/In0.53Ga0.47As/In0.52Al0.48As heterostructures with one-sided δ-Si-doping has been performed. The structural quality of a combined QW was investigated by transmission electron microscopy. A correlation between the electron mobility in QW with the thickness of InAs insert and the technology of its fabrication is established. Specific features of the InP(substrate)/InAlAs(buffer) interface are investigated by transmission electron microscopy and photoluminescence spectroscopy. A relationship between the energy positions of the peak in the photoluminescence spectra in the range of photon energies 1.24 eV < ħω < 1.38 eV, which is due to the electronic transitions at the InP/InAlAs interface, and the structural features revealed in the interface region is established. It is found that an additional QW is unintentionally formed at the InP/InAlAs interface; the parameters of this QW depend on the heterostructure growth technology.

Effects of continuously graded or step-graded InxAl1−xAs buffer on the performance of InP-based In0.83Ga0.17As photodetectors

InP-based high indium content In0.83Ga0.17As photodetector structures with lattice mismatch up to 2.1% have been grown by gas source molecular beam epitaxy system. The photodetectors using continuously graded and step-graded InxAl1−xAs buffer structures were grown and demonstrated. The effects of the buffer scheme were investigated by the measurements of atomic force microscopy, high-resolution X-ray diffraction, photoluminescence and device performance. Results show that the full relaxation of the photodetector structure has been achieved by using continuously graded InAlAs buffer. Superior optical properties and lower dark currents can be reached for the photodetector structure with continuously graded buffer layer.

Optimization of InAlAs buffers for growth of GaAs-based high indium content InGaAs photodetectors

The impact of buffer schemes on the strain relaxation and structural characteristics of In0.83Ga0.17As photodetector structures with relatively high lattice mismatch (5.9%) grown on GaAs substrate by gas source molecular beam epitaxy has been investigated. Reduction of surface roughness, full widths at half maximum of X-ray diffraction signals and threading dislocations, as well as an enhancement of photoluminescence intensity were observed for the In0.83Ga0.17As photodetector structure with fixed-composition In0.83Al0.17As buffer compared to those with continuously graded InxAl1−xAs buffer. The role of fixed-composition In0.83Al0.17As buffer layer is investigated, and it is believed that a couple monolayers of In0.83Al0.17As at the initial growth stage can provide high density of nucleation site by the formation of quantum dots at the interface and thus to reduce the strain energy caused by the large lattice mismatch between In0.83Al0.17As and GaAs.

Specific features of the photoluminescence of HEMT nanoheterostructures containing a composite InAlAs/InGaAs/InAs/InGaAs/InAlAs quantum well

The specific features of the photoluminescence and the electrical properties of doped nanoheterostructures containing a composite InAlAs/InGaAs/InAlAs quantum well with a thin InAs insert in the middle are studied. The insert thickness is varied in the range from 1.7 to 3.0 nm. It is established that the position of the peaks in the photoluminescence spectra in the photon energy range 0.6–0.8 eV correlates with the InAs insert thickness. Simulation of the band structure shows that the experimentally observed variation in the energy of optical transitions is associated with lowering of the energy of electron and hole states in the quantum well with increasing insert thickness. In the photon energy range 1.24–1.38 eV, optical transitions in the region of the InAlAs buffer-InP substrate interface are observed. The signal photon energy and intensity depend on the features of the formation of this heterointerface and on the conditions of substrate annealing. It is conceived that this is due to the formation of a transition region between the InAlAs buffer and the substrate.