InAs Mole Fraction Research Articles

Design and implementation of 83-nm low noise InP-based InAlAs/InGaAs PHEMTs**Project supported by the National Natural Science Foundation of China (No. 61275107).

83-nm T-shaped gate InP-based In0.52Al0.48As/In0.65Ga0.35As pseudomorphic high electron mobility transistors (PHEMTs) with excellent DC and RF performance as well as low noise characteristics are reported, including a maximum saturation current density Idss of 894 mA/mm, a maximum extrinsic transconductance gm; max of 1640 mS/mm, an extrapolated cutoff frequency ft of 247 GHz and a maximum oscillation frequency fmax of 392 GHz which were based on the measured S-parameters from 1 to 110 GHz. The minimum noise figure (NFmin) measured by the cold-source method is 1 dB at 30 GHz associated with a gain of 14.5 dB at Vds of 0.8 V and Ids of 17 mA. These results were obtained by the combination of increased InAs mole fraction in the channel, gate size scaling, parasitic reduction and the quantization channel. These excellent results make it one of the most suitable devices for millimeter wave (MMW) low noise applications.

Effect of arsenic cracking on In incorporation into MBE‐grown InGaAs layer

AbstractThe effect of arsenic cracking on In incorporation in MBE‐grown InGaAs selective growth was systematically studied with changing the cracking cell temperature. Incorporation of In was greatly enhanced by the use of As2 molecular beam during the selective growth at 600 °C. On the other hand, almost no In was incorporated into the grown layer by the use of a conventional As4 molecular beam. The relation between InAs mole fraction and the cracking cell temperature was found to monotonously increase with the cracking cell temperature. It is probably because the ratio of As2 molecules increases with the cracking cell temperature. Not only at 600 °C but also at 580 °C, a selective growth was also successfully performed using As2 molecular beam by the formation of the “denuded zone”, with the InAs mole fraction of 10%. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Convection Effects on Crystallinity in the Growth of In0.3Ga0.7 as Crystals by the Traveling Liquidus Zone Method

The influence of convection in a melt on the crystallinity of the TLZ-grown In(0.3)Ga(0.7)As crystals has been investigated by growing crystals with various shapes and dimensions on the ground. No single crystals have been grown when the crystal diameter was 10 mm, but we were successful in growing single crystals by reducing crystal diameter to 2 mm. These results suggested the importance of suppressing convection in the melt during alloy crystal growth because constitutional supercooling tends to occur at the freezing interface or ahead of the interface by the segregation effect. Large area is required for substrate use in various applications. This requirement can be fulfilled by the crystal growth in microgravity because density difference-induced convection is suppressed in microgravity. Another means for suppressing convection without deteriorating area is plate-shape crystal growth with reduced thickness. The latter can be applied on the ground and we succeeded in growing single crystals of plate-shaped In(0.3)Ga(0.7)As by the traveling liquidus zone (TLZ) method. Dimensions of obtained single crystals were 10 mm in width and 2 mm in thickness and lengths ranged from 20 to 40 mm. Compositional uniformity was good and 0.3 +/- 0.02 in InAs mole fraction was achieved.

Excellent compositional homogeneity in In0.3Ga0.7As crystals grown by the traveling liquiduszone (TLZ) method

The influence of convection in a melt on the compositional homogeneity of the TLZ-grown In0.3Ga0.7As crystals has been investigated by growing crystals with various dimensions on the ground. Excellent compositional homogeneity such as 0.3 plus or minus 0.01 in InAs mole fraction for a distance of 25 mm was obtained when the melt diameter was limited to 2 mm and convective flow in the melt was suppressed. On the other hand, when the crystal diameter was increased to 10 mm, both axial and radial compositional homogeneity was deteriorated due to convection in the melt. Comparing with the numerical simulation, convective flow velocity less than 1.4 mm/h may be sufficient for growing homogeneous crystals and it is not so difficult to suppress convective flow velocity below 1.4 mm/h for 10 mm diameter crystals in microgravity. Therefore, larger homogeneous In0.3Ga0.7As crystals are expected to be grown by the TLZ method on board the International Space Station.

Latent heat effect on growth rate in the traveling liquidus-zone method

In order to obtain a homogeneous crystal by using the traveling liquidus-zone (TLZ) method, a conventional one-dimensional model is used to determine an appropriate sample translation rate. Although the conventional model predicts the appropriate translation rate, the latent heat effect is unknown since the conventional model is based on pure solution growth. Therefore, a new model including the latent heat is introduced to investigate the latent heat effect. By considering the new model, the maximum latent heat effect αmax is obtained. The αmax is negligibly small under the condition that the InAs mole fraction is far enough from 0 or 1 in the case of an InGaAs crystal. In order to estimate the actual latent heat effect α, one-dimensional numerical simulations with and without the latent heat are carried out. From the numerical results, the applicable limit of the TLZ method is discussed in the case of In0.3Ga0.7As crystals. The growth rate, which is regarded as a pure melt growth, is also discussed by extrapolating the α dependency.

Influence of Lattice Mismatch and Growth Rate on the Decay of RHEED Oscillation in the Case of InGaAs/GaAs Growth

The intensity decay of the oscillation of the reflection high-energy electron diffraction pattern's specular beam is analysed during the molecular beam epitaxy of strained InGaAs/GaAs heteroepitaxial structures. The oscillations' amplitude was found to decrease exponentially with time during the InGaAs growth. Further, the decay time constant decreases with InAs mole fraction, indicating that the lattice strain increases islanding during growth. A simple semi-quantitative model based on the growth front roughening is formulated to explain the results. Assuming that the oscillation decay is related partly to the strain and partly due to kinetic effects during growth, a decay component that is solely due to strain can be separated; we find that the onset of increased roughening due to the misfit strain component roughly corresponds to the equilibrium critical layer thickness for misfit dislocation generation.

Chemical composition of In xGa 1− xAs epilayers grown simultaneously on differently oriented GaAs substrates

We investigate the In-composition of In x Ga 1− x As ternary layers epitaxially grown by molecular beam epitaxy. The epilayers of different indium content (mole fraction 0.2< x<1) are grown simultaneously onto GaAs substrates of different crystallographic orientation, namely (0 0 1), (1 1 1)B and (1 1 3)A surfaces. High-resolution X-ray diffraction, electron probe microanalysis, energy-dispersive X-ray spectroscopy and scanning electron microscopy measurements show that for a suitable set of parameters high-quality In x Ga 1− x As layers can be simultaneously grown by MBE on differently oriented GaAs substrates. Secondary ion mass spectrometry measurements show that the In-incorporation is constant over the whole layer thickness and for all surface orientations. In addition, the epilayers grown during the same run have the same chemical composition independent from the substrate surface orientation. Moreover, a comparison of the InAs mole fractions obtained by X-ray diffraction and electron probe microanalysis confirms the validity of Vegard's rule for the In x Ga 1− x As lattice parameter and the Poisson's ratio within 0.5% of the experimental accuracy.

Effect of Lattice Mismatch on the Decay of Rheed Oscillations During Growth of Strained InGaAs/GaAs Heterostructures

ABSTRACTThe decay of the oscillation of the intensity of the specular beam of the reflection high-energy electron diffraction pattern is analyzed during the molecular beam epitaxial growth of strained InGaAs/GaAs heteroepitaxial structures. The oscillations' amplitude was found to decrease exponentially versustime during the InGaAs growth. Further, the decay time constant decreases with InAs mole fraction, indicating that the lattice strain increases islanding during growth. A simple semi-quantitative model based on the growth front roughening is formulated to explain the results. Assuming that the oscillation decay is related partly to the strain and partly due to kinetic effects during growth, a decay component that is solely due to strain can be separated; we find that the onset of increased roughening due to misfit strain component roughly corresponds to the equilibrium critical layer thickness

Characterizing composition modulations in InAs/AlAs short-period superlattices

The formation of quantum wires has much interest due to their novel electronic properties which may lead to enhanced optoelectronic device performance and greater photovoltaic efficiencies. One method of forming these structures is through spontaneous lateral modulation found during the epitaxial growth of III/V alloys. In this paper, we report and summarize our investigations on the formation of lateral modulation in the molecular-beam epitaxy grown InAlAs/InP(001) system. This system was grown as a short-period superlattice where n monolayers of InAs are deposited followed by m monolayers of AlAs (with n and $m\ensuremath{\sim}2)$ and this sequence is repeated to grow a low strain InAlAs ternary alloy on InP(001) that exhibits lateral modulation. Films were grown under a variety of conditions (growth temperature, effective alloy composition, superlattice period, and growth rate). These films have been extensively analyzed using x-ray diffraction, atomic force microscopy, and transmission electron microscopy (TEM) and microcharacterization, in addition to photon-based spectroscopes. Here we present results of several microstructural characterizations using a wide range of TEM-based techniques, and compare them to results from the other methods to obtain a unified understanding of composition modulation. Two strong points consistently emerge: (1) The lateral modulation wavelength is insensitive to growth temperature and effective alloy composition, but the strength of the lateral modulation is greatest near an effective alloy composition of ${\mathrm{In}}_{0.46}{\mathrm{Al}}_{0.54}\mathrm{As},$ which corresponds to a slightly tensile global strain with respect to InP. (2) The composition variation for the strongly modulated films is as much as 0.38 InAs mole fraction. In addition, for these strongly modulated films, the modulation wave is asymmetric showing strongly peaked, narrower InAs-rich regions separated by flat AlAs-rich regions. We discuss these results and their possible implications in addition to detailing the techniques used to obtain them.

Selective electrochemical profiling of threading defects in mismatched heteroepitaxial systems

The defect structure of molecular beam epitaxy grown InGaAs/GaAs(001) heteroepitaxial systems is studied by using selective electrochemical etching. The InAs mole fraction varied between 0.03 and 0.3 whilst the layer thickness changed between 0.02 and 0.5 μm (above the critical layer thickness). Different aqueous electrolytes and bias voltages were applied to achieve optimum etching conditions. By incremental layer removal, the depth profile of the dislocation density was mapped. The density of defects is inversely proportional to the layer thickness and increases with misfit. The experimental results are compared to theoretical models.

Influence of growth conditions on the formation and luminescence properties of InGaAs quantum dots in a Si matrix

The influence of the growth conditions during molecular-beam epitaxy and of the degree of lattice mismatch between the epilayer and the substrate on the formation of InGaAs islands on a Si(100) surface is studied. An increase in lattice mismatch (the InAs mole fraction) leads to an increase in the critical thickness corresponding to the onset of island growth, in contrast to the formation of InGaAs islands on GaAs(100). An increase in the deposition temperature also increases the critical thickness, whereas an increase in the arsenic pressure has the opposite effect. Structures containing an array of InGaAs islands in a Si matrix display a luminescence line in the range 1.2–1.3 µm, depending on the mole fraction of InAs.

Reciprocal-Space and Real-Space Analyses of Compositional Modulation in InAs/AlAs Short-Period Superlattices

AbstractThe microstructure of lateral composition modulation in InAs/AlAs superlattices grown by MBE on InP is examined. The use of x-ray diffraction, TEM, AFM, and STEM to characterize the modulations is discussed. Combining the information from these techniques gives increased insight into the phenomenon and how to manipulate it. Diffraction measures the intensity of modulation and its wavelength, and is used to identify growth conditions giving strong modulation. The TEM and STEM analyses indicate that local compositions are modulated by as much as 0.38 InAs mole fraction. Plan-view images show that modulated structures consists of short (≳0.2 μm) In-rich wires with a 2D organization in a (001) growth plane. However, growth on miscut substrates can produce a single modulation along the miscut direction with much longer wires (≲0.4 μm), as desired for potential applications. Photoluminescence studies demonstrate that the modulation has large effects on the bandgap energy of the superlattice.

The Nature and Origin of Lateral Composition Modulations in Short-Period Strained-Layer Superlattices

AbstractThe nature and origin of lateral composition modulations in (AlAs)m(InAs)nshort-period strained-layer superlattices grown by molecular beam epitaxy on InP substrates have been investigated by x-ray diffraction, atomic force microscopy, and transmission electron microscopy. Strong modulations were observed for growth temperatures between ≈ 540 and 560° C. The maximum strength of modulations was found for SPS samples with InAs mole fraction x (= n/(n+m)) close to ≈ 0.50 and when n≈m≈2. The modulations were suppressed at both high and low values of x. For x &gt; 0.52 (global compression), the modulations were along the &lt;100&gt; directions in the (001) growth plane. For x &lt; 0.52 (global tension), the modulations were along the two &lt;310&gt; directions rotated ≈ ±27° from [110] in the growth plane. The remarkably constant wavelength of the modulations, between ≈ 20–30 nm, and the different modulation directions observed, suggest that the origin of the modulations is due to surface roughening associated with the high misfit between the individual SPS layers and the InP substrate. Highly uniform unidirectional modulations have been grown by control of the InAs mole fraction and growth on suitably offcut substrates, which show great promise for application in device structures.

Local Structural Changes of Ion Damaged InGaAs

AbstractIon damage and amorphization behavior in InGaAs with InAs mole fractions in the range of 0 to 50%are studied. We found that the degree of dynamic annealing increases as the InAs mole fraction increases in the InGaAs when the implantation is carried out at room temperature (RIT). Extended x-ray absorption fine structure measurements reveal that in the amorphous state the InAs nearest neighbor distance, RIn-As is very different from that in the crystalline InGaAs and is ∼0.01 Å longer than that in pure crystalline InAs. For RT implanted materials, before a complete amorphous layer is formed, the RIn-As remains close to its crystalline value even when the layer is heavily damaged. A sudden increase of the RIn-As is observed when a complete amorphous layer is formed. The behavior of the measured values of RIn-As for InGaAs implanted with various doses, indicates that at RT the formation of amorphous InGaAs occurs by the simultaneous nucleation of the amorphous phase when the critical free energy in the damage layer is exceeded. At liquid nitrogen temperature, when dynamic annealing is negligible, the RIn-As value increases as the damage in the layer increases, suggesting that the amorphous InGaAs is formed by the accumulation and overlapping of amorphous zones created along the individual ion tracks.

Numerical analysis of device performance of metamorphic In/sub y/Al/sub 1-y/As/In/sub x/Ga/sub 1-x/As (0.3≤x≤0.6) HEMTs on GaAs substrate

A numerical model describing the influence of InAs mole fraction on metamorphic HEMT structures (MM-HEMT) is proposed. The material properties are calculated using the Monte Carlo method, while the charge control law is calculated using a self-consistent solution of Poisson's and Schrodinger's equations. The modeling of the dc, ac, noise and high frequency performance of a device with 0.25-/spl mu/m gate length is performed using the quasi-two-dimensional (Q2D) approach. This analysis shows that an InAs mole fraction of about 0.40 is an optimum composition for manufacturing high gain, low noise amplifiers. In this range of composition, the performance of MM-HEMT structures is similar to that obtained for lattice-matched HEMTs on InP substrates.

Optical properties of InAlAs quantum dots in an AlGaAs matrix

Structural and optical properties of InxAl1−xAs quantum dots (QD) embedded in an Al0.30Ga0.70As matrix are studied as a function of InAs mole fraction (x). Decreasing of x results in a sequential disappearance of bound electron and hole states in the QDs. There is a range of indium compositions were photoluminescence is determined by type-II optical transitions between electrons localized in a Al0.3Ga0.7As layer and holes localized in the QDs.

A highly mismatched In xGa 1−xAs/AlGaAs (0 ≦ x ≦ 0.5) pseudomorphic HEMT on GaAs substrate using an In x/2 Ga 1− x/2 As buffer layer

A pseudomorphic HEMT with a large InAs mole fraction (x) for the channel is fabricated successfully on a GaAs substrate by employing a thick In x/2 Ga 1− x/2 As buffer layer. The transconductance increases with increasing InAs mole fraction, and shows a peak value at x = 0.4. The maximum transconductance and the cutoff frequency for a 1.7 μm gate HEMT with x = 0.4 were 500 mS mm −1 and 13.3 GHz, respectively. The effective saturation velocity evaluated using the cutoff frequency increased with increasing x.

Properties of carbon-doped InGaAs grown by atmospheric pressure metalorganic chemical vapor deposition using CCl 4

This paper shows the results of a van der Pauw-Hall analysis of carbon-doped InGaAs epilayers grown by atmospheric pressure metalorganic chemical vapor deposition using CCl 4 gas. Heavily C-doped In x Ga 1 − x As ( x = 0 to 0.52) epilayers were obtained by varying the V III ratio from 1.3 to 32 and at a low growth temperature of 550°C, while keeping the flow rate of CCl 4 constant. For up to an InAs mole fraction of 0.43, a hole concentration of about 1.1 × 10 19 cm −3 was obtained. In the case of as-grown samples, a type conversion from p-type to n-type to n-type occurred at an InAs mole fraction of 0.48. This work also describes the effects of a rapid thermal annealing (RTA) on the electrical properties, particularly on a type conversion of InGaAs. After the RTA process at an annealing temperature of 750°C for 5 s, as-grown In 0.44Ga 0.56As with the p-type of 5.6 × 10 17 cm −3 was converted into the n-type of 3.9 × 10 17 cm −3. This can be attributed to the breaking of the CH or CH x bonds after the RTA process. The broken carbon atoms could enter into arsenic sites or indium (or gallium) sites in the epilayers. With increasing InAs mole fraction, more carbon atoms were supposed to enter into indium sites rather than arsenic sites, due to a lower binding energy of InC than that of AsC.

Effects of rapid thermal annealing on the electrical properties of heavily carbon-doped InGaAs

The effects of rapid thermal annealing (RTA) on the electrical properties of carbon-doped InGaAs epilayers have been analyzed by the Van der Pauw-Hall measurement. After RTA, the highest hole concentration of 3.3 × 10 20 cm −3 at In 0.09Ga 0.91As epilayer was obtained. RTA processes cause the inactivated carbon atoms to be active by breaking CH or CH x bonds in the epilayers. This leads to the increase of the hole concentration. Below the InAs mole fraction of 0.35, we have obtained the maximum activation efficiency of the carbon atoms at the RTA temperature of 650°C. The activation efficiency decreased with increasing InAs mole fraction. The type conversion from p-type to n-type took place after RTA at the InAs mole fraction of 0.44, while it occurred at that of 0.48 in the as-grown. The reason for the shift of the type conversion to the lower value after RTA would be due to the outdiffusion of In atoms in the InGaAs epilayer, and the activated carbon atoms would more effectively enter into In sites than As sites due to the outdiffusion of In atoms.

Molecular-beam epitaxy of high quality lattice matched In1−x−yGaxAlyAs epitaxial layers on InP substrates

The InGaAlAs epilayer is lattice matched to the InP substrate at an InAs mole fraction of 0.53. Experiments were conducted systematically to establish growth parameters for InGaAlAs epilayers with good crystalline and optical quality suitable for laser device applications. Quaternary alloy epilayers of InGaAlAs were grown on InP substrates by the conventional solid source molecular-beam epitaxy technique. The normalized In flux was varied in the range 0.25–0.47 resulting in compressive, matched, and tensile epilayers with respect to the InP substrate. Rocking curves obtained from a double crystal x-ray diffractometer showed the best half-width of 15 arcsec for the epilayer matched to the InP substrate with a mismatch of only 0.03%. Photoluminescence peaks obtained at room and 4 K temperatures indicate half-widths of 70 and 12 meV, respectively. These results are comparable with the best values reported on this material.