Selective Area Epitaxial Growth Research Articles

Leakage Mechanisms of sub-pA InGaAs/GaAs Nano-Ridge Waveguide Photodetectors Monolithically Integrated on a 300-mm Si Wafer

Abstract We report on a comprehensive temperature dependent dark current study of high-quality InGaAs/GaAs multi quantum well waveguide photodetectors monolithically integrated on silicon. They are integrated through metalorganic vapor-phase selective-area epitaxial growth in a 300-mm CMOS pilot line. Defects resulting from the metamorphic growth of III-V devices on Si make these devices susceptible to different leakage mechanisms at higher operating temperatures. For the high-temperature operation of complex photonics-electronics integrations, understanding the leakage mechanisms of the devices has critical significance. This will help to optimize designs promptly and ensure the reliability and longevity of such devices under extreme operating conditions. The photodetector devices exhibit dark currents below 1 pA, at room temperature and –1 V bias voltage, limited by the noise floor of the measurement setup. To resolve the different leakage mechanisms contributing to the dark current, the devices were measured at elevated temperatures and the results were cross-validated with device simulations. The devices exhibited very low dark currents, with a median below 0.1 nA at 195 °C, suggesting very high-quality material growth. Through device models, leakage mechanisms related to Shockley-Read-Hall (SRH) recombination at bulk volume defects are found to be the main factor contributing to the dark current. The surface SRH recombination is found to be limited, yet affecting the forward bias dark current due to the shortening of the diffusion paths of the majority carriers. Also, the device model shows that the actual dark currents at room temperature can be as low as 0.01 pA, more than 1-order lower than the measured levels. This study emphasizes the high quality of the III-V nano-ridge waveguide devices grown on Si, which can potentially expand the capabilities of silicon photonics platforms further.

Selective area growth of in-plane InAs nanowires and nanowire networks on Si substrates by molecular-beam epitaxy

In-plane InAs nanowires and nanowire networks show great potential to be used as building blocks for electronic, optoelectronic and topological quantum devices, and all these applications are keen to grow the InAs materials directly on Si substrates since it may enable nanowire electronic and quantum devices with seamless integration with Si platform. However, almost all the in-plane InAs nanowires and nanowire networks have been realized on substrates of III–V semiconductors. Here, we demonstrate the selective area epitaxial growth of in-plane InAs nanowires and nanowire networks on Si substrates. We find that the selectivity of InAs growth on Si substrates is mainly dependent on the growth temperature, while the morphology of InAs nanowires is closely related to the V/III flux ratio. We examine the cross-sectional shapes and facets of the InAs nanowires grown along the 〈110〉, 〈100〉 and 〈112〉 orientations. Thanks to the non-polar characteristics of Si substrates, the InAs nanowires and nanowire networks exhibit superior symmetry compared to that grown on III–V substrates. The InAs nanowires and nanowire networks are zinc-blende (ZB) crystals, but there are many defects in the nanowires, such as stacking faults, twins and grain boundaries. The crystal quality of InAs nanowires and nanowire networks can be improved by increasing the growth temperature within the growth temperature window. Our work demonstrates the feasibility of selective area epitaxial growth of in-plane InAs nanowires and nanowire networks on Si substrates.

Laser-assisted local metal-organic vapor phase epitaxy.

Selective area epitaxial growth is an important technique, both for monolithic device integration as well as for defect reduction in heteroepitaxy of crystalline materials on foreign substrates. While surface engineering with masking materials or by surface structuring is an effective means for controlling the location of material growth, as well as for improving crystalline properties of epitaxial layers, the commonly involved integral substrate heating presents a limitation, e.g., due to constraints ofr the thermal budget applicable to existing device structures. As a solution, an epitaxial growth approach using a laser source only locally heating the selected growth area, in combination with metal-organic precursors to feed a pyrolithic chemical reaction (also known as metal-organic vapor phase epitaxy, MOVPE), is presented. Without masking or surface structuring, local epitaxial growth of III-V compound semiconductor layers on a 50-1500 µm length-scale, with high structural and optical quality, is demonstrated. We discuss general design rules for reactor chamber, laser heating, temperature measurement, sample manipulation, gas mixing, and distinguish laser-assisted local MOVPE from conventional planar growth for the important compound semiconductor GaAs. Surface de-oxidation prior to growth is mandatory to realize smooth island surfaces. Linear growth rates in the range 0.5-9 µm/h are demonstrated. With increasing island diameter, the probability for plastic deformation within the island increases, depending on reactor pressure. A step-flow mode on the island surface can be achieved by establishing a sufficiently small temperature gradient across the island.

Phase Control Growth of InAs Nanowires by Using Bi Surfactant

To realize practical applications of nanowire-based devices, it is critical, yet challenging, to control crystal structure growth of III-V semiconductor nanowires. Here, we demonstrate that controlled wurtzite and zincblende phases of InAs nanowires can be fabricated using bismuth (Bi) as a surfactant. For this purpose, catalyst free selective area epitaxial growth of InAs nanowires was performed using molecular beam epitaxy (MBE). During the growth, Bi was used which may act as a wetting agent influencing the surface energy at growth plane ends, promoting wurtzite crystal phase growth. For a demonstration, wurtzite and zincblende InAs nanowires were obtained with and without using Bi-flux. Photoluminescence spectroscopy (PL) analysis of the nanowires indicates a strong correlation between wurtzite phase and the Bi-flux. It is observed that the bandgap energy of wurtzite and zincblende nanowires are ∼0.50 eV and ∼0.42 eV, respectively, and agree well with theoretical estimated bandgap of corresponding InAs crystal phases. A blue shift in PL emission peak energy was found with decreasing nanowire diameter. The controlled wurtzite and zincblende crystal phase and its associated heterostructure growth of InAs nanowires on Si may open up new opportunities in bandgap engineering and related device applications integrated on Si. Furthermore, this work also illustrates that Bi as a surfactant could play a dynamic role in the growth mechanism of III-V compound semiconductors.

(Invited) Selective Epitaxy of Submicron Ge Wire Structures for Photodetectors and Optical Modulators in Si Photonics

A selective-area epitaxial growth of Ge on the submicron scale is studied using chemical vapor deposition (CVD) on Si in terms of the fabrication of integrated photonic devices operating at the optical communication wavelengths of around 1.55 μm. A mesa structure of Ge on the micron scale, having a vertical pin junction, is effective for fabricating a waveguide-integrated photodetector in the optical receiver. A 3-dB cutoff frequency is obtained up to approximately 50 GHz. For a higher frequency operation, a narrower structure of submicron-wide Ge wire, having a lateral pin junction, is required. Such a wire structure is also important for the application to an electro-absorption optical intensity modulator in the optical transmitter. Structural and optical properties are investigated for a submicron-wide Ge wire on Si selectively grown by CVD.

Low Dark Current and High Responsivity 1020nm InGaAs/GaAs Nano-Ridge Waveguide Photodetector Monolithically Integrated on a 300-mm Si Wafer

We report on high-quality InGaAs/GaAs multi-quantum well waveguide photodetectors, monolithically integrated through metalorganic vapor-phase selective-area epitaxial growth and contact metallization in a 300-mm CMOS pilot line. The photodetectors are implemented using the nano-ridge engineering concept, leveraging aspect-ratio trapping in combination with precise control of the nano-ridge cross section dimensions and composition. The InGaAs/GaAs p-i-n nano-ridge photodetectors are shown to achieve high internal responsivities of up to 0.65 A/W at -1 V bias and 1020 nm wavelength. A clear correlation is observed between measured responsivity and contact-plug design, correlating well with simulation models. In addition, a record-low dark current density of 1.98 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-8</sup> A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and low absolute dark currents of <; 1 pA are demonstrated, illustrating the high quality of the III-V materials and effective in-situ InGaP surface passivation layers. Initial RF measurements suggest RC-limited photodetection bandwidths in the GHz range. These results illustrate the strong potential of the III-V/Si nano-ridge epitaxy and waveguide device concept, to complement the Silicon Photonics toolbox with high-quality, high-throughput III-V functionality.

Surface Diffusion of Gallium as the Origin of Inhomogeneity in Selective Area Growth of GaN Nanowires on AlxOy Nucleation Stripes

Selective area epitaxial growth of III–V and III–N nanostructures and nanowires was proven efficient for synthesis of scalable and highly ordered electronic and optoelectronic nanomaterials on diss...

Monolithic integration of InP on Si by molten alloy driven selective area epitaxial growth.

We report a new approach for monolithic integration of III-V materials into silicon, based on selective area growth and driven by a molten alloy in metal-organic vapor epitaxy. Our method includes elements of both selective area and droplet-mediated growths and combines the advantages of the two techniques. Using this approach, we obtain organized arrays of high crystalline quality InP insertions into (100) oriented Si substrates. Our detailed structural, morphological and optical studies reveal the conditions leading to defect formation. These conditions are then eliminated to optimize the process for obtaining dislocation-free InP nanostructures grown directly on Si and buried below the top surface. The PL signal from these structures exhibits a narrow peak at the InP bandgap energy. The fundamental aspects of the growth are studied by modeling the InP nucleation process. The model is fitted by our X-ray diffraction measurements and correlates well with the results of our transmission electron microscopy and optical investigations. Our method constitutes a new approach for the monolithic integration of active III-V materials into Si platforms and opens up new opportunities in active Si photonics.

Epitaxy of GaN in high aspect ratio nanoscale holes over silicon substrate

Dislocation filtering in gallium nitride (GaN) by epitaxial growth through patterned nanoscale holes is studied. GaN grown from extremely high aspect ratio holes by metalorganic chemical vapor deposition is examined by transmission electron microscopy and high-resolution transmission electron microscopy. This selective area epitaxial growth method with a reduced epitaxy area and an increased depth to width ratio of holes leads to effective filtering of dislocations within the hole and improves the quality of GaN significantly.

Semi-polar {1 0 1} blue and green InGaN/GaN light-emitting diodes on micro-stripe patterned Si (1 0 0)

A novel III-nitride-based light emitting diode (LED) fabrication process which is based on selective-area epitaxial growth on Si {1 1 1} facets etched into Si (1 0 0) substrates is presented. A micro-stripe pattern is formed with semi-polar {1 0 1} crystallographic planes of GaN evolving from an epitaxial lateral overgrowth (ELOG)-like process. The {1 0 1} planes of GaN serve as a template for the growth of semi-polar blue and green LED structures with InGaN/GaN multiple quantum wells (MQW). A complete fabrication chain encompassing substrate etching, metalorganic vapor phase epitaxy (MOVPE), characterization, LED processing and device manufacture has been developed.The semi-polar LED stacks are of high crystalline quality, which is manifested by homogeneous InGaN layers in the {1 0 1} MQW structure and smooth {1 0 1} LED surface planes. Although threading dislocations intersect with the semi-polar {1 0 1} MQW, V-shaped defects typically observed in polar c-plane MQW structures are not detected.The blue and green semi-polar LED show only a weak polarization-related wavelength shift at large current densities consistent with the lower built-in electric fields in the semi-polar MQW. At low current densities, the green LED exhibit a strong wavelength shift due to In clustering effects. The blue LED reveal a stable emission color, which indicates a homogeneous In distribution in the wells.

(Invited) Heterogeneous Nano- to Wide-Scale Co-Integration of Beyond-Si and Si CMOS Devices to Enhance Future Electronics

This paper overviews possibilities of heterogeneous material and device integrations base on selective area epitaxial growth. The options applicable at various scale from that of individual devices like FinFETs and Nanowires to wide areas of IIIV-Ge materials are described. Finally, multi-level integration of new 2-D crystals will be discussed as well.

Patterned buffer layer promotes maskless lateral epitaxial overgrowth of low-dislocation-density ZnO films in aqueous solution at low temperature

In this article, we describe a facile approach, with the assistance of a stripe-patterned ZnAl2O4 buffer layer, for the maskless lateral epitaxial growth (LEO) of low-dislocation-density ZnO films. During hydrothermal processing, the selective-area epitaxial growth of ZnO mesas occurred preferentially on ZnAl2O4 stripes. The ZnO growth subsequently occurred in the lateral direction; eventually, adjacent stripe-patterned ZnO mesas coalesced to form a continuous film. The dislocation density at the coalesced LEO ZnO was 108 cm−2. The photoluminescence of LEO-grown ZnO films featured a strong near-band-edge ultraviolet emission, but other defect-related visible emissions were suppressed almost entirely, indicating a significant improvement in crystalline quality.

Growth of high quality InP layers in STI trenches on miscut Si (0 0 1) substrates

In this work, we report the selective area epitaxial growth of high quality InP in shallow trench isolation (STI) structures on Si (0 0 1) substrates 6° miscut toward (1 1 1) using a thin Ge buffer layer. We studied the impact of growth rates and steric hindrance effects on the nano-twin formation at the STI side walls. It was found that a too high growth rate induces more nano-twins in the layer and results in InP crystal distortion. The STI side wall tapering angle and the substrate miscut angle induced streric hindrance between the InP facets and the STI side walls also contribute to defect formation. In the [1̄ 1 0] orientated trenches, when the STI side wall tapering angle is larger than 10°, crystal distortion was observed while the substrate miscut angle has no significant impact on the InP defect formation. In the [1̄ 1 0] trenches, both the increased STI tapering angle and the substrate miscut angle induce high density of defects. With a small STI tapering angle and a thin Ge layer, we obtained extended defect free InP in the top region of the [1 1 0] trenches with aspect ratio larger than 2.

Effect of As preadsorption on InAs nanowire heteroepitaxy on Si(111): A first-principles study

Arsenic preadsorption has recently been found to be crucial for selective-area epitaxial growth of oriented III-V semiconductor nanowires on Si(111). To understand the effect of preadsorption on the heteroepitaxy, this first-principles study examines the structure of As-adsorbed Si(111) surfaces. Reconstruction models such as adatom, trimer, and dimer-adatom-stacking fault structures are found to be metastable. The stability of unreconstructed arsenide structure $(1\ifmmode\times\else\texttimes\fi{}1\text{-As})$ is confirmed but the faulted and unfaulted domains of $1\ifmmode\times\else\texttimes\fi{}1\text{-As}$ are found to be practically degenerate in energy. These domains can therefore coexist on a Si(111)-As surface, and then epitaxial growth will be disrupted at domain boundaries where translational symmetry is broken. Indium adsorption on the Si(111)-As surface, however, destabilizes unfaulted domains, thus assisting its transformation into a coherent surface that allows epitaxy. This effect is attributed to the interlayer covalent interactions induced by In $p$ electrons.

Selective area heteroepitaxy of low dimensional a ‐plane and c ‐plane InGaN nanostructures using pulsed MOCVD

AbstractHigh density a ‐plane and c ‐plane InGaN nanostructures have been developed by nanoscale selective area epitaxial growth using pulsed MOCVD. SiO2 was used as a mask with nanopatterning through an anodic aluminum oxide template. The lateral dimensions of the pattern were controlled and varied from 30 nm to 180 nm by changing the anodization voltage and the electrolyte. Different substrates such as a ‐plane GaN on r ‐plane sapphire, r ‐plane sapphire and c ‐plane sapphire were used to develop InGaN nanostructures in a ‐ and c ‐ crystallographic directions respectively. Under identical growth conditions, InGaN nanostructures of various shapes were obtained on different substrates with differences in emission wavelength. The shape of the nanostructures on different substrates is discussed with respect to the stability and growth rates of various planes. However, the difference in emission wavelength is attributed to the In incorporation in the nanostructures. The optical properties of the nanostructures were studied by photoluminescence (PL) spectroscopy. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Chemical vapor deposition of Si on chlorosilane-treated SiO2 surfaces. I. Suppression and enhancement of Si nucleation

We have investigated the nucleation processes in chemical vapor deposition (CVD) of Si on SiO2 surfaces that were treated with different chlorosilane gases SiHnCl4−n, where n=0, 1, or 2. These gases chemisorb on the SiO2 surface in a self-limiting manner. At 493 K, the saturation coverage was reached at 4×108 L exposure for the SiH2Cl2 gas, and at 2×109 L for the SiHCl3 and SiCl4 gases. CVD of Si was carried out on the chlorosilane-saturated SiO2 surfaces using Si2H6 as a source gas at 853 K. It has been found that the SiCl4 and SiHCl3 treatments effectively passivate the nucleation centers on the SiO2 surfaces, while the SiH2Cl2 treatment drastically enhances Si nucleation. The reaction mechanisms causing these differences are discussed, considering the structural changes of the adsorbed chlorosilane fragments at the CVD temperature. Application of the SiCl4 treatment to the patterned SiO2 mask for selective-area epitaxial growth of Si is demonstrated.

Local epitaxy and lateral epitaxial overgrowth of SiC

Selective epitaxial growth and lateral overgrowth of SiC using a graphite mask is reported in this paper. Selective area SiC growth is accomplished using physical vapor transport (PVT) epitaxy. The growth was carried out on 4 H and 6H-SiC wafers on- and 8° off-oriented from the basal plane in the 〈1 1 2 ̄ 0〉 direction. A graphite mask, consisting of rows and columns of uniformly spaced open circles of 75-μm in diameter was used for the selective nucleation of SiC mesa structures. Using PVT epitaxy, selective area hexagonal-shaped structures were successfully grown. There was essentially no direct growth of SiC on the graphite film observed. A lateral/vertical growth rate ratio of 6 was achieved. Optical and scanning microscope images show perfectly formed hexagonal islands, which are located over the open circular windows. The results suggest that the selective area epitaxial growth of SiC is a promising technique for obtaining high quality, locally grown mesa structures for SiC device applications.

Selective-area chemical-vapor deposition of Si using a bilayer dielectric mask patterned by proximal probe oxidation

Silicon nitride (Si3N4) is a very robust material against oxidation and is typically used as an oxidation mask. Here, we report atomic-force microscope (AFM)-based local oxidation of Si3N4 and its applications in selective-area epitaxial growth using chemical-vapor deposition. High growth selectivity is accomplished in this work by employing a SiO2/Si3N4 bilayer mask structure, which is formed by locally oxidizing the Si3N4 surface (for defining the growth windows), depositing a blanket SiO2 layer, and then selectively removing SiO2 in the growth windows. High-resolution transmission electron microscopy images reveal that the selectively deposited Si structures can be grown with a high degree of crystalline perfection, while excellent size uniformity is confirmed by large-area AFM images.

Selective-area epitaxial growth of GaAs in deep dielectric windows using molecular beam epitaxy

An improved selective-area epitaxial growth process for GaAs in deep dielectric windows (DDWs) is reported. The growth was carried out on (100)-oriented semi-insulating (SI) GaAs substrate at ∼520°C by solid source molecular beam epitaxy (SSMBE) using a valved arsenic cracker source. Dielectric stacks with 10 periods of alternating silicon nitride (2000 Å) and silicon dioxide (1000 Å) layers were deposited using plasma-enhanced chemical vapor deposition (PECVD) for the formation of deep (3 μm) dielectric windows. The alternating dielectric layer stack has been shown to be of greater stability than a single dielectric layer for the purpose of forming the DDW. A process of fabricating the DDW structures, which eliminates the possible contamination at the growth area during photoresist patterning and removing, and subsequent etching of the DDW, has resulted in improved epitaxial layer quality. Micro-Raman spectroscopy measurements showed a significant increase in the longitudinal-optic (LO) to transverse-optic (TO) signal intensity ratio ( I LO/TO) from ∼4.0 to ∼16.0 of the first-order Raman line of GaAs. Supporting evidence from low-temperature (4 K) photoluminescence (PL) showed a reduction in intensity of the conduction band to neutral carbon acceptor (e-C°) emission by a factor of 4.5. This suggests lower levels of carbon contamination originating from the improved fabrication process of the DDW. Scanning electron microscopy (SEM) images showed smoother surface morphology of the GaAs inside the DDW area. These results have important implications on the process of MBE regrowth for optoelectronics integration.

Nanoscale selective-area epitaxial growth of Si using an ultrathin SiO2/Si3Ni4 mask patterned by an atomic force microscope

We report selective epitaxial growth of Si using an ultrathin bilayer mask. The key feature of this process is direct writing of nanoscale patterns by means of local anodic oxidation of a Si3N4 layer using an atomic force microscope operated in air. Windows for selective growth are defined by wet etching of the locally oxidized regions. High growth selectivity upon chemical vapor deposition of Si is accomplished by employing the bilayer mask structure which is formed by oxidizing the Si3N4 surface and then selectively desorbing SiO2 in the windows. High-quality homoepitaxial growth is verified by transmission electron microscopy. We also report a simple plasma-treatment technique which solves the problem of retarded SiO2 desorption in the nanoscale windows.