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ABSTRACT: The strain relaxation mechanism and defect properties of compositionally step-graded InAs <sub>y</sub> P <sub>1-y</sub> buffers grown by molecular beam epitaxy on InP have been investigated. InAsP layers having lattice misfits ranging from 1% to 1.4% with respect to InP, as well as subsequently grown lattice matched In <sub>0.69</sub> Ga <sub>0.31</sub> As overlayers on the metamorphic buffers were explored on both (100) and 2° offcut (100) InP substrates. The metamorphic graded buffers revealed very efficient relaxation coupled with low threading dislocation densities on the order of (1–2)×10<sup>6</sup> cm <sup>-2</sup> for the range of misfit values explored here. A detailed analysis via high resolution x-ray diffraction revealed that the strain relaxed symmetrically, with equivalent numbers of α and β dislocations, and to greater than 90% for all cases, regardless of substrate offcut. Further analysis showed the relaxation to always be glide limited in these materials when grown on a graded buffer compared to a single step layer. The threading dislocation density was observed by plan-view transmission electron microscopy to be constant for the range of misfit values studied here in the top layer of the graded structures, which is attributed to the very efficient use of residual dislocations and the dominance of dislocation glide over nucleation in these graded anion metamorphic buffers, suggesting great promise for metamorphic devices with lattice constants greater than that of InP to be enabled by InAsP metamorphic structures on InP.
Journal of Applied Physics 04/2009; · 2.17 Impact Factor
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ABSTRACT: Electron transport in low dislocation density, strain-relaxed InAs layers grown on metamorphic In As <sub>y</sub> P <sub>1-y</sub>/ In P substrates by molecular beam epitaxy was characterized using quantitative mobility spectrum analysis (QMSA) of Hall effect measurements. QMSA applied to systematically varied metamorphic InAs samples reveals high bulk electron mobilities of ∼20 000 cm <sup>2</sup>/ V s at 300 K at a Si doping concentration of 1×10<sup>17</sup> cm <sup>-3</sup> , simultaneously with a separate population of much slower electrons having an average mobility of ∼2400 cm <sup>2</sup>/ V s due to parallel conduction within the InAs surface electron accumulation layer. Measurements made on higher doped samples reveal only a single electron population participating in transport due to lowered surface band bending that reduces surface accumulation of electrons in conjunction with the high conductivity of the high mobility metamorphic InAs bulk that overwhelms any remaining surface conductivity in the Hall effect measurements.
Applied Physics Letters 09/2008; · 3.84 Impact Factor
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ABSTRACT: We have demonstrated a high performance 80nm gate In<sub>0.52</sub>Al<sub>0.48</sub>As/In<sub>0.53</sub>Ga<sub>0.47</sub>As/InAs<sub>0.3</sub>P<sub>0.7</sub> composite channel HEMT. The device has a g<sub>m</sub> as high as 1 S/mm and an f<sub>T</sub> 280 GHz. To complete this study, the noise and power performance of such device will be further studied and compared with conventional InGaAs channel devices in near future.
Semiconductor Device Research Symposium, 2007 International; 01/2008
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ABSTRACT: In <sub>0.8</sub> Al <sub>0.2</sub> As / In As heterostructures were grown on virtual InAs substrates consisting of a relaxed In As <sub>y</sub> P <sub>1-y</sub> step-graded buffer grown on InP by molecular-beam epitaxy. Hall measurements revealed the presence of a high-mobility two-dimensional electron gas within the relaxed InAs layer, with a peak electron mobility of 133 000 cm <sup>2</sup>/ V s at 25 K . In contrast, identical In Al As / In As heterostructures grown directly on InAs buffers on InP showed only bulk transport characteristics. A combination of transport modeling and electron microscopy demonstrates that reduced dislocation scattering in the channel region is responsible for observing the two-dimensional transport within the relaxed InAs on graded InAsP. These results demonstrate the potential of achieving ultrahigh-speed InAs based high electron mobility transistors using relaxed, virtual InAs substrates on InP.
Applied Physics Letters 02/2007; · 3.84 Impact Factor
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ABSTRACT: Electronic transport properties of strain-relaxed Si-doped In As <sub>y</sub> P <sub>1-y</sub> layers with arsenic mole fractions between y=0.05 and y=0.50 were studied. All layers were grown on semi-insulating InP substrates by solid source molecular beam epitaxy using intermediate In As <sub>y</sub> P <sub>1-y</sub> step-graded buffers to reduce dislocation density. Variable magnetic field (0–8.5 T ) Hall effect measurements in conjunction with quantitative mobility spectrum analysis in the temperature range of 25–300 K were used to extract individual carrier mobilities, densities, and donor ionization energy as a function of temperature and alloy composition. The low field mobility is calculated by taking into account various scattering mechanisms, and these results are compared with the experimental results. At a constant electron carrier concentration of ∼2×10<sup>16</sup> cm <sup>-3</sup> , the 300 K carrier mobility increases from 2856 to 5507 cm <sup>2</sup>/ V s with increasing arsenic mole fraction from 0.05 to 0.50. The experimental mobilities are in close agreement with the theoretical results using various scattering mechanisms. Both optical polar phonon scattering and ionized impurity scattering are important at 300 K while at 100 K , ionized impurity scattering is the limiting process. Alloy scattering is found to be only of second order importance. The Si donor ionization energy was determined to be ȣ-
c;2–4 meV for all alloy compositions.
Journal of Applied Physics 10/2006; · 2.17 Impact Factor
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ABSTRACT: An In<sub>0.53</sub>Ga<sub>0.47</sub>As/InAs<sub>0.3</sub>P<sub>0.7</sub> composite channel high electron mobility transistor (HEMT) structure was grown by molecular beam epitaxy. Room-temperature Hall measurement showed that the device wafer had an electron mobility of 7300 cm<sup>2</sup>/V s and a sheet electron density of 3×10<sup>12</sup> cm<sup>-2</sup>. The fabricated HEMT devices with a gate length of 0.25 μm exhibited excellent DC and microwave performance with a peak extrinsic transconductance of 888.3 mS/mm, a cutoff frequency (f<sub>T</sub>) of 115 GHz, and a maximum frequency of oscillation of 137 GHz. This is believed to be the first report of InGaAs/InAsP composite channel HEMTs. The f<sub>T</sub> is the highest ever reported for any composite channel HEMTs with the same gate length.
Electronics Letters 04/2006; · 0.96 Impact Factor
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ABSTRACT: In this paper we report growth, fabrication and characterization of In<sub>0.52</sub>Al<sub>0.4</sub>sAs/In<sub>0.53</sub>Ga<sub>0.47</sub>As/InAs<sub>0.3</sub>P<sub>0.7</sub> composite channel HEMTs with a gate length of 0.25 μm. In comparison with InAlAs/InGaAs/InP composite channel HEMTs, these devices have better band structure for transferring electrons to the composite channel under high electric field, thus exhibit excellent DC and microwave performance with a peak extrinsic transconductance of 888.3 mS/mm, an f<sub>T</sub> of 115 GHz, and an f<sub>max</sub> of 137 GHz. To our knowledge, this is the first report of InAlAs/InGaAs/InAsP composite channel HEMTs. The f<sub>T</sub> is the highest ever reported for any composite channel HEMTs with the same gate length.
Microwave Conference Proceedings, 2005. APMC 2005. Asia-Pacific Conference Proceedings; 01/2006
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ABSTRACT: Lattice-mismatched InAs0.32P0.68/In0.68Ga0.32As/InAs0.32P0.68 double heterostructures (DH) were grown on compositionally graded InAsyP1−y/InP substrates by solid-source molecular-beam epitaxy (MBE) out to a misfit of ∼ 1%. The kinetics of carrier recombination were investigated in the nearly totally relaxed MBE-grown DH structures using photoconductivity decay (PCD) measurements. High minority carrier lifetimes of 4–5 μs close to the radiation limit were measured, indicating the ability of MBE-grown InAsyP1−y buffers in achieving high-electronic-quality, low-band-gap mismatched InGaAs layers. Analysis suggests that very low interface recombination velocities are achieved. A photogenerated carrier diffusion model is presented to explain the initial nonlinear decays observed in PCD data for these heterostructures.
Applied Physics Letters 02/2005; 86(7):071908-071908-3. · 3.84 Impact Factor
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ABSTRACT: The structural, morphological, and defect properties of mixed anion, InAs <sub>y</sub> P <sub>1-y</sub> and mixed cation, In <sub>x</sub> Al <sub>1-x</sub> As metamorphic step-graded buffers grown on InP substrates are investigated and compared. Two types of buffers were grown to span the identical range of lattice constants and lattice mismatch (∼1.1–1.2%) on (100) InP substrates by solid source molecular beam epitaxy. Symmetric relaxation of ∼90% in the two orthogonal <110> directions with minimal lattice tilt was observed for the terminal InAs <sub>0.4</sub> P <sub>0.6</sub> and In <sub>0.7</sub> Al <sub>0.3</sub> As overlayers of each graded buffer type, indicating nearly equal numbers of α and β dislocations were formed during the relaxation process and that the relaxation is near equilibrium and hence insensitive to asymmetric dislocation kinetics. Atomic force microscopy reveals extremely ordered crosshatch morphology and very low root mean square (rms) roughness of ∼2.2 nm for the InAsP relaxed buffers compared to the InAlAs relaxed buffers (∼7.3 nm) at the same degree of lattice mismatch with respect to the InP substrates. Moreover, phase decomposition is observed for the InAlAs buffers, whereas InAsP buffers displayed ideal, step-graded buffer characteristics. The impact of the structural differences between the two buffer types on metamorphic devices was demonstrated by comparing identical 0.6 eV band gap lattice-mismatched In <sub>0.69</sub> Ga <sub>0.31</sub> As thermophotovoltaic (TPV) devices that were grown on these buffers. Clearly superior device performance was achieved on InAs <sub>y P <sub>1-y</sub> buffers, which is attributed primarily to the impact of layer roughness on the carrier recombination rates near the front window/emitter interface of the TPV devices. © 2004 American Institute of Physics.
Journal of Applied Physics 05/2004; · 2.17 Impact Factor
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ABSTRACT: Single-junction, lattice-mismatched (LMM) In/sub 0.69/Ga/sub 0.31/As thermophotovoltaic (TPV) devices with bandgaps of 0.60 eV were grown on InP substrates by solid-source molecular beam epitaxy (MBE). Step-graded InAs/sub y/P/sub 1-y/ buffer layers with a total thickness of 1.6 /spl mu/m were used to mitigate the effects of 1.1% lattice mismatch between the device layer and the InP substrate. High-performance single-junction devices were achieved, with an open-circuit voltage of 0.357 V and a fill factor of 68.1% measured at a short-circuit current density of 1.18 A/cm/sup 2/ under high-intensity, low emissivity white light illumination. Device performance uniformity was outstanding, measuring to better than 1.0% across a 2-in diameter InP wafer indicating the promise of MBE growth for large area TPV device arrays.
IEEE Electron Device Letters 10/2003; · 2.85 Impact Factor
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ABSTRACT: Relaxed, high-quality, compositionally step-graded InAsyP1−y layers with an As composition of y = 0.4, corresponding to a lattice mismatch of ∼1.3% were grown on InP substrates using solid-source molecular-beam epitaxy. Each layer was found to be nearly fully relaxed observed by triple axis x-ray diffraction, and plan-view transmission electron microscopy revealed an average threading dislocations of 4×106 cm−2 within the InAs0.4P0.6 cap layer. Extremely ordered crosshatch morphology was observed with very low surface roughness (3.16 nm) compared to cation-based In0.7Al0.3As/InxAl1−xAs/InP graded buffers (10.53 nm) with similar mismatch and span of lattice constants on InP. The results show that InAsyP1−y graded buffers on InP are promising candidates as virtual substrates for infrared and high-speed metamorphic III–V devices. © 2003 American Institute of Physics.
Applied Physics Letters 05/2003; 82(19):3212-3214. · 3.84 Impact Factor
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ABSTRACT: Single-junction, lattice-mismatched (LMM) In0.69Ga0.31As thermophotovoltaic (TPV) devices with bandgaps of 0.60 eV were grown on InP substrates by solid-source molecular beam epitaxy (MBE). Step-graded InAsyP1-y buffer layers with a total thickness of 1.6 μm were used to mitigate the effects of 1.1% lattice mismatch between the device layer and the InP substrate. High-performance single-junction devices were achieved, with an open-circuit voltage of 0.357 V and a fill factor of 68.1% measured at a short-circuit current density of 1.18 A/cm2 under high-intensity, low emissivity white light illumination. Device performance uniformity was outstanding, measuring to better than 1.0% across a 2-in diameter InP wafer indicating the promise of MBE growth for large area TPV device arrays.
IEEE Electron Device Letters - IEEE ELECTRON DEV LETT. 01/2003; 24(9):538-540.
