InGaAs Films Research Articles

High-quality InGaAs films bonded on Si substrate with a thin polycrystalline Si intermediate layer

We report the fabrication of high-quality InGaAs films on Si by wafer bonding at low temperatures (300 ℃). A thin polycrystalline Si (poly-Si) interlayer is introduced between InGaAs and Si to block the lattice mismatch and absorb the bubble by-products produced at the bonded interface using its disordered crystal orientation and gain boundaries. To achieve a high bonding strength, argon plasma treatment was employed on InGaAs and poly-Si surfaces before the pre-bonding process. By using post-wet etching, a defect-rich region near the surface of exfoliated InGaAs film that was initially caused by the thermal mismatch between InGaAs and InP during epitaxy growth can be removed. As a result, a Si-based InGaAs film with a 1.05 MPa bonding strength and bubble-free bonding interface was produced. The defective region is 1.2 μm-thick. After etching the defective area, a high-quality, 1.8 μm-thick Si-based InGaAs film was obtained with an XRD FWHM of 94 arcsec. The results reveal that this method is prospective for the fabrication of high-quality III-V materials on Si, proving that a prospective approach for the fabrication of low-noise InGaAs/Si PIN photodiodes and InGaAs/Si avalanche photodiodes with ultralow dark currents.

Effect of the bonding layer and multigrading layers on the performance of a wafer-bonded InGaAs/Si single-photon detector.

A wafer-bonded InGaAs/Si avalanche photodiode (APD) at a wavelength of 1550nm was theoretically simulated. We focused on the effect of the I n 1-x G a x A s multigrading layers and bonding layers on the electric fields, electron and hole concentrations, recombination rates, and energy bands. In this work, I n 1-x G a x A s multigrading layers inserted between Si and InGaAs were adopted to reduce the discontinuity of the conduction band between Si and InGaAs. A bonding layer was introduced at the InGaAs/Si interface to isolate the mismatched lattices to achieve a high-quality InGaAs film. In addition, the bonding layer can further regulate the electric field distribution in the absorption and multiplication layers. The wafer-bonded InGaAs/Si APD, structured by a polycrystalline silicon (poly-Si) bonding layer and I n 1-x G a x A s multigrading layers (x changes from 0.5 to 0.85), displayed the highest gain-bandwidth product (GBP). When the APD operates in Geiger mode, the single-photon detection efficiency (SPDE) of the photodiode is 20%, and the dark count rate (DCR) is 1MHz at 300K. Moreover, one finds that the DCR is lower than 1kHz at 200K. These results indicate that high-performance InGaAs/Si SPAD can be achieved through a wafer-bonded platform.

Ultrafast photocarrier dynamics in Fe-implanted InGaAs polycrystalline photoconductive materials

We investigate the ultrafast photoconductivity and charge-carrier transport in thermally annealed Fe-implanted InGaAs/InP films using time-resolved terahertz spectroscopy. The samples were fabricated from crystalline InGaAs films amorphized with Fe ions implantation. The rapid thermal annealing of the InGaAs layer induces solid recrystallization through the formation of polycrystalline grains whose sizes are shown to increase with increasing annealing temperature within the 300–700 °C range. Based on the influence of the laser fluence, the temporal profile of the time-resolved photoconductivity was reproduced using a system of rate equations that describe the photocarrier dynamics in terms of a capture/recombination mechanism. For annealing temperatures below 500 °C, the capture time is found to be less than 1 ps while the recombination time from the charged states did not exceed 5 ps. However, for higher annealing temperatures, the capture and the recombination times show a continuous increase, reaching 7.1 ps and 1 ns respectively, for the film annealed at 700 °C. Frequency-dependent photoconductivity curves are analyzed via a modified Drude–Smith model that considers a diffusive restoring current and the confining particles’ sizes. Our results demonstrate that the localization parameter of the photocarrier transport model is correlated to the polycrystalline grain size. We also show that a relatively high effective mobility of about 2570 cm2 V−1 s−1 is preserved in all these Fe-implanted InGaAs films.

Low-Temperature epitaxial growth of InGaAs films on InP(100) and InP(411)A substrates

The structural and electrical characteristics of In0.53Ga0.47As epitaxial films, grown in the low-temperature mode on InP substrates with (100) and (411)A crystallographic orientations at flow ratios of As4 molecules and In and Ga atoms of γ = 29 and 90, have been comprehensively studied. The use of InP(411)A substrates is shown to increase the probability of forming two-dimensional defects (twins, stacking faults, dislocations, and grain boundaries), thus reducing the mobility of free electrons, and AsGa point defects, which act as donors and increase the free-electron concentration. An increase in γ from 29 to 90 leads to transformation of single-crystal InGaAs films grown on (100) and (411)A substrates into polycrystalline ones.

Strain relaxation and compositional separation during growth of InGaAs/GaAs(001)

Strain relaxation of InxGa1−xAs/GaAs(001) with systematically changed In content between x=0.23 and x=0.80 has been studied using in situ synchrotron X-ray diffraction during molecular beam epitaxy growth. Correlation between the In composition and the degree of relaxation in the InGaAs films was derived from the reciprocal space maps. While InGaAs with a uniform composition was grown in the regime of the two-dimensional growth, a separation of the In composition was observed for the InGaAs films grown in the Stranski-Krastanov mode.

Magnesium doping in InAlAs and InGaAs/Mg films lattice-matched to InP grown by MOVPE

Mg-doped InAlAs and InGaAs films were grown at 560 °C lattice matched to InP semi-insulting substrate by metalorganic vapor phase epitaxy (MOVPE) under various Cp2Mg flow conditions. Hall effect, photoluminescence (PL), high-resolution X-ray diffraction (HR-XRD), and secondary ion mass (SIMS) were the tools used in this work. The crystalline quality and the n-p conversion of the InAlAs and InGaAs/Mg films are described and discussed in relation to the Cp2Mg flow. Distinguishing triple emission peaks in PL spectra is observed and seems to be strongly dependent on the Cp2Mg flow. SIMS is employed to analyze the elements in the epitaxial layers. The variation of indium and magnesium components indicates a decrease of magnesium incorporation during the growth of InAlAs layers leading to a contracted lattice. In addition, the magnesium incorporation in the InGaAs lattice during growth has been confirmed by SIMS.

InGaAs-OI Substrate Fabrication on a 300 mm Wafer

In this work, we demonstrate for the first time a 300-mm indium–gallium–arsenic (InGaAs) wafer on insulator (InGaAs-OI) substrates by splitting in an InP sacrificial layer. A 30-nm-thick InGaAs layer was successfully transferred using low temperature direct wafer bonding (DWB) and Smart CutTM technology. Three key process steps of the integration were therefore specifically developed and optimized. The first one was the epitaxial growing process, designed to reduce the surface roughness of the InGaAs film. Second, direct wafer bonding conditions were investigated and optimized to achieve non-defective bonding up to 600 °C. Finally, we adapted the splitting condition to detach the InGaAs layer according to epitaxial stack specifications. The paper presents the overall process flow that achieved InGaAs-OI, the required optimization, and the associated characterizations, namely atomic force microscopy (AFM), scanning acoustic microscopy (SAM), and HR-XRD, to insure the crystalline quality of the post transferred layer.

Spectroscopic ellipsometry and electrical characterizations of InGaAs:Mg thin films lattice matched to InP

Mg-doped InGaAs films were grown at 560 degrees C lattice matched to InP semi-insulating substrate by metalorganic vapor phase epitaxy (MOVPE) under various Cp2Mg flow conditions. Hall effect, photoluminescence (PL), high-resolution X-ray diffraction (HR-XRD) and spectroscopic ellipsometry (SE) are the tools used in this work. The crystalline quality and the n-p conversion of the InGaAs:Mg films are described and discussed in relation to the Cp2Mg flow. Distinguishing triple emissions peaks in PL spectra are observed and seem to be strongly dependent on the Cp2Mg flow. SE was used to investigate the interband transitions in InGaAs:Mg/InP heterointerfaces and the different critical point energies were identified

Composition analysis of III–V materials grown in nanostructures: The self-focusing-SIMS approach

One of the important growth drivers for the semiconductor industry is the shrinking of transistors to smaller dimensions. System performance and functionality increase as the density of transistors, which can be integrated onto a single chip, increases. To maintain the device performances for very small dimensions, additional improvements are needed such as the implementation of new materials (high-k's, metal gate, III–V or group IV alloys) and the introduction of new three-dimensional device architectures, e.g., field-effect transistor's. In this context, the metrology needs (determination of the exact composition and thickness of deposited/grown thin films) are more and more shifting from the analysis of blanket samples to more real devices where thin films are grown in very confined volumes (with dimensions below 20 nm). Their confined shape suggests that metrology with the standard analysis methods like x-ray photoelectron spectroscopy, secondary ion mass spectrometry (SIMS), and Rutherford backscattering spectroscopy should no longer be applicable due to a lack of spatial resolution. Moreover, even if one could obtain such a very fine focused beam (<10 nm spot size), the resulting signal intensity will be so low that the accuracy when determining layer composition or dopant concentration becomes questionable due to the low counting statistics. The concept of self-focusing-SIMS (SF-SIMS) is a novel concept which overcomes not only the spatial resolution limitations of SIMS for these applications but also eliminates the sensitivity (and thus accuracy) problem. The concept is based on determining the composition of a compound film using a broad beam bombarding an array of identical features. The required spatial resolution is created through the use of cluster ions which contain only the constituents of the compound film and thus limit the information content to the confined volume. Indeed, the cluster formation mechanism implies that all cluster constituents must originate from the same collision cascade and thus are emitted in close proximity (<0.5 nm) and cannot be formed by a recombination process from two very distant regions. As such, the composition information becomes confined (i.e., self-focused) to the areas where all constituents are simultaneously present. Recently, the authors demonstrated the use of SF-SIMS to quantify the Ge content of SiGe films grown in narrow trenches. In the present paper, the SF-SIMS approach is applied on III–V materials. Both InGaAs films grown on InP/Si in shallow trench isolation (STI) and more complex stacks, i.e., InGaAs/InAlAs/InP/Si grown in STI, are analyzed. The authors will show that the SF-SIMS method can accurately determine the In content in each of the layer, even for very confined volumes (width of the III–V structures around 40 nm). The obtained results will be compared to analyses performed with other complementary methods such as Auger electron spectroscopy, transmission electron microscopy/energy dispersive x-ray spectroscopy, and atom probe tomography.

Evaluation of InGaAs and InP Compatibility with Alkaline Photoresist Stripping Formulations

III-V semiconductors, such as InGaAs, are leading contenders to replace Si as high-mobility channel materials for sub-10 nm finFETs.(1,2) Implementation of these high-mobility materials into FEOL processes faces many challenges because of the chemical sensitivity and complex nature of these materials relative to the conventional Si channel. In particular, damage from wet cleaning solutions is a major concern that needs to be understood and controlled when designing new cleaning formulations for use in the manufacture of III-V based devices. Herein, we will describe our work at understanding InGaAs and InP compatibility with formulated alkaline photoresist strippers with a focus on the impact of solvent and alkaline component selection. Initial studies focused on etch rates of InGaAs and InP in a series of proprietary cleaning chemistries. InGaAs films (500 Å) on InP – as well as bulk InP – wafers were used for this study. Etch rates were determined by energy-dispersive X-ray spectroscopy (EDX) as well as by gallium and arsenic leaching via ICP-MS. While acidic chemistries in general showed excellent compatibility, alkaline- and amine-based chemistries displayed varying levels of compatibility with InGaAs. Because of the range of compatibilities observed in alkaline chemistries, we explored the impact of solvent and alkali selection as well as water content on selectivity. Specifically, we evaluated a series of non-proprietary solutions using a selection of solvent types, alkaline components, and water content (semi-aqueous vs. non-aqueous). The impacts of these components will be discussed and compared to results previously presented for GaAs etched in these same chemistries.(3) For the strippers that are reported to be highly compatible with InGaAs and InP, a more thorough analysis of surface changes will be reported including changes in roughness (AFM) and composition (XPS). The results and key learnings from this study will be discussed in relation to how InGaAs and InP may be cleaned with limited surface damage. 1) International Technology Roadmap for Semiconductors, see www.itrs.net2) J. A. del Alomo, Nature, 479, 317 (2011). 3) G. Westwood, SEMATECH Surface Preparation and Cleaning Conference, Austin, TX, 2012.

G-factor modification in a bulk InGaAs epilayer by an in-plane electric field

We report on the modification of the g-factor by an in-plane electric field in an In$_{0.031}$Ga$_{0.969}$As epilayer. We performed external magnetic field scans of the Kerr rotation of the InGaAs film in order to independently determine the g-factor and the spin-orbit fields. The g-factor increases from $-0.4473\pm0.0001$ at 0 V/cm to $-0.4419\pm0.0001$ at 25 V/cm applied along the [1$\overline{1}$0] crystal axis. In addition, spatially-resolved spin measurements show a g-factor dependence on diffusive velocity. The change in g-factor with electric field can have a large effect on the determination of the internal spin-orbit and nuclear fields from Larmor precession frequency measurements.

Effect of epitaxial strain on phase separation in thin films

In epitaxially grown alloy thin films, spinodal decomposition may be promoted or suppressed depending on the sign of the epitaxial strain. We study this asymmetry by extending Cahn’s linear theory of spinodal decomposition to systems with a composition dependent lattice parameter and modulus (represented by Vegard’s law coefficients, and y, respectively), and an imposed (epitaxial) strain (e). We show analytically (and confirm using simulations) that the asymmetric effect of epitaxial strains arises only in elastically inhomogeneous systems. Specifically, we find good agreement between analytical and simulation results for the wave number of the fastest growing composition fluctuation. The asymmetric effect due to epitaxial strain also extends to microstructure formation: our simulations show islands of elastically softer (harder) phase with (without) a favourable imposed strain. We discuss the implications of these results to GeSi thin films on Si and Ge substrates, as well as InGaAs films on GaAs substrates.

Kinetics and Structure of Nickelide Contact Formation to Ingaas Fin Channels

The InGaAs high mobility channels are vowed as serious candidates for alternative channel materials for sub-10 nm technology nodes urging studies for analogous contacts to the dominant silicide contacts in the Si technology mainstream. The Ni-InGaAs (nickelide) contact technology has been demonstrated as a suitable self-aligned contact technology for InGaAs channels with record small specific contact resistivity. However, the majority studies on nickelide contact formation were conducted on planar InGaAs films and little studies focused on the contact metallurgy specific in nanoscale InGaAs nanowire or Fin channels. Here, we utilized a novel wafer bonding technique to transfer thin (50 nm) In0.53Ga0.47As layers onto SiO2/Si substrates and Si transmission electron microscopy (TEM) frames. InGaAs Fins with variable widths, lengths, and orientations were fabricated through a combination of electron-beam lithography and top-down dry etching steps, followed by Ni contact deposition. Rapid thermal annealing and in-situ TEM thermal heating cycles were conducted to react Ni with the InGaAs channel and deduce the reaction kinetics, dynamics, and resultant nickelide and interface structures. We observed sharp and abrupt nickelide-InGaAs interfaces for Fin channels narrower than 250 nm whereas for wider Fins, multiple interfaces evolve due to multiple nickelide layer nucleation event per interface. A faster reaction rate for [100] oriented Fins was observed when compared with [110] oriented ones. When a simple analytical treatment is applied to the Fin geometry, the nickelide length was found to have a square root dependence of inverse channel width and inverse channel height, in excellent agreement with experimental data. From this dependency, we extracted a surface diffusion coefficient of 1.2x10-15 ~ 2.6x10-15 m2/s at a reaction temperature of 250 °C, which is 4-5 times larger than the extracted Fin ‘body’ diffusion coefficient. These results will be contrasted with those obtained for silicide reaction with Si nanowires, and the detailed structure, interface and reaction dynamics will be discussed.

Micro-Raman study on chirped InGaAs-InAlAs superlattices

The folded acoustic phonon and confined optical phonon modes in chirped InGaAs–InAlAs superlattices have been studied by micro-Raman spectroscopy. The folded and confined phonons were probed at the () and (001) faces. Raman scattering measurements for the chirped superlattices and an InGaAs film were performed at different temperatures. The temperature dependence of the longitudinal optical phonon frequencies indicates that a compressive strain existed in the InGaAs layers of the chirped superlattices, which is significant for analyzing the device failure of quantum cascade lasers operating at higher active region temperatures.

Investigation of Pd–InGaAs for the formation of self-aligned source/drain contacts in InGaAs metal–oxide–semiconductor field-effect transistors

The formation of salicide-like source/drain contacts on III–V MOSFETs necessitates a search for suitable metals that can react with III–V materials to form ohmic contacts with low sheet resistance and contact resistivity. To advance this search, the reaction between Pd and In0.53Ga0.47As is explored in this work. Reaction temperatures ranging from 200 to 400°C were investigated, and extensive physical and electrical characterization was performed. Pd completely reacts with In0.53Ga0.47As after annealing at temperatures as low as 200°C for 60 s to form a very smooth and uniform Pd–InGaAs film with good interfacial quality. Pd–InGaAs formed at 250°C was found to have a work function of ∼4.6±0.1eV, sheet resistance of ∼77.3Ω/square for a thickness of 20nm, and contact resistivity of ∼8.35×10−5Ωcm2 on In0.53Ga0.47As with n-type active doping concentration of ∼2×1018cm−3. With further development, Pd–InGaAs could potentially be useful as self-aligned contacts for InGaAs transistors.

Roughening and pre-roughening processes on InGaAs surface

Roughening and pre-roughening processes on InGaAs surface are studied using scanning tunneling microscopy. There are different roughening and pre-roughening processes for InGaAs films at different substrate temperatures and As beam equivalent pressure. Under low temperature and low As beam equivalent pressure, pits is main mechanism in the beginning of InGaAs morphology evolution, with the increase of annealing time, a great number of pits and islands are observed which make the surface rough. Small islands should play a leading role during the InGaAs morphology evolution at high temperature and high As beam equivalent pressure, and the number of islands will increase gradually with the increase of annealing time till it reaches an equilibrium state.

Growth and Characterization of In x Ga1−x As/GaAs1−y P y Strained-Layer Superlattices with High Values of y (~80%)

Strained-layer superlattice (SLS) structures, such as InGaAs/GaAsP lattice matched to GaAs, have shown great potential in absorption devices such as photodetectors and triple-junction photovoltaic cells. However, until recently they have been somewhat hindered by their usage of low-phosphorus GaAsP barriers. High-P-composition GaAsP was developed as the barrier for InGaAs/GaAsP strained-layer superlattice (SLS) structures, and the merits of using such a high composition of phosphorus are discussed. It is believed that these barriers represent the highest phosphorus content to date in such a structure. By using high-composition GaAsP the carriers are collected via tunneling (for barriers ≤30 A) as opposed to thermionic emission. Thus, by utilizing thin, high-content GaAsP barriers one can increase the percentage of the intrinsic in a p-i-n structure that is composed of InGaAs wells in addition to increasing the number of periods that can be grown for given depletion width. However, standard SLSs of this type inherently possess undesirable compressive strain and quantum size effects (QSEs) that cause the optical absorption of the thin InGaAs SLS wells to shift to higher energies relative to that of bulk InGaAs of the same composition. To circumvent these deleterious QSEs, stress-balanced, pseudomorphic InGaAs/GaAsP staggered SLSs were grown. Staggering was achieved by removing a portion of one well and adding it to an adjacent well. The spectral response obtained from device characterization indicated that staggering resulted in thicker InGaAs films with reduced cutoff energy. Additionally, these data confirm that tunneling is a very effective means for carrier transport in the SLS.

Surface segregation of InGaAs films by the evolution of reflection high-energy electron diffraction patterns

Surface segregation is studied via the evolution of reflection high-energy electron diffraction (RHEED) patterns under different values of As4 BEP for InGaAs films. When the As4 BEP is set to be zero, the RHEED pattern keeps a 4×3/(n × 3) structure with increasing temperature, and surface segregation takes place until 470 °C. The RHEED pattern develops into a metal-rich (4 × 2) structure as temperature increases to 495 °C. The reason for this is that surface segregation makes the In inside the InGaAs film climb to its surface. With the temperature increasing up to 515 °C, the RHEED pattern turns into a GaAs(2 × 4) structure due to In desorption. While the As4 BEP comes up to a specific value (1.33 × 10-4 Pa−1.33 × 10-3 Pa), the surface temperature can delay the segregation and desorption. We find that As4 BEP has a big influence on surface desorption, while surface segregation is more strongly dependent on temperature than surface desorption.

Transition from a disordered to a crystalline state in II–VI and III–V films

The initial stages of HgCdTe growth on Al2O3, GaAs, CdTe, and KCl substrates have been studied by electron diffraction. HgCdTe films were produced by pulsed laser deposition and isothermal vapor phase epitaxy. InGaAs films were grown by isothermal chloride epitaxy on GaAs substrates. In the initial stages of the growth process, we observed a transition from an amorphous to a textured polycrystalline phase and then to a mosaic single-crystal structure. We have calculated the critical size of crystalline grains below which amorphization occurs in II-VI and III-V compounds. The critical grain size agrees with the grain size of the disordered (amorphous) phase that forms in the initial stage of epitaxy. We have determined some characteristics of the heterostructures: critical film thickness below which pseudomorphic growth is possible without misfit dislocation generation, elastic stress in the epitaxial system, surface density of dangling bonds at dislocations, and the critical island radius above which no interfacial misfit dislocations are generated.

The effect of helium ion implantation on the relaxation of strained InGaAs thin films

Previous work on pseudomorphic SiGe on Si has shown that a significant reduction in the threading dislocation density can be achieved through appropriate ion beam processing. Helium ion implantation was used in an analogous study to induce strain relaxation within strained pseudomorphic InGaAs layers on GaAs through the intentional introduction of subsurface damage without the introduction of surface nucleated dislocations and their associated threading segments. Wafers of fully-strained 28 nm thick films of In 0.24Ga 0.76As were separately implanted with helium doses of 5 × 10 14, 2 × 10 15, and 1 × 10 16 cm −2 at 25 keV. These wafers became substrates for additional InGaAs film growth. The final InGaAs films always exhibited lower residual strain as compared to films grown directly on a control substrate of non-implanted GaAs. The broadening of the X-ray peaks indicates an increase in dislocation density within the InGaAs films and the strain relaxation was found to occur with a significant increase in surface roughness. This result stands in contrast to related work on SiGe films on Si where a reduction of the threading dislocation density within a SiGe film was observed. The reaction of the InGaAs/GaAs structure and materials to ion irradiation, with local disturbance to the stoichiometry, could preclude the use of ion beam techniques for realizing a reduction in threading dislocation density during strain relaxation.