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High peak power, room-temperature operation in the long wave infrared spectral region is reported for double-channel, ridge waveguide quantum cascade lasers (QCLs) monolithically integrated onto a silicon substrate. The 55-stage laser structure with an AlInAs/InGaAs core and InP cladding was grown by molecular beam epitaxy directly onto an 8-in. diameter germanium-coated silicon substrate template via a III–V alloy metamorphic buffer. Atomic force microscope imaging demonstrated a good quality surface for the full QCL structure grown on silicon, with improved roughness over wider areas compared to the previous work. Fabricated 3 mm × 26 μm lasers operate at room temperature, deliver more than 3 W of peak (6 mW of average) optical power, and show approximately 3% wall plug efficiency and 4.3 kA/cm2 threshold current density with emission wavelength centered at 11.5 μm. The lasers had a high yield with only around 15% max power deviation and no signs of performance degradation were observed over a 10 h burn in period at maximum power. Singled-lobed high quality output beam with M2 = 1.36 was measured for 3 mm × 22 μm devices, demonstrating that it is possible to produce high-brightness quantum cascade lasers on silicon with standard ridge waveguide processing paving the way for low-cost production of integrated mid-infrared platforms.

After years of progress, GaSb based mid-wave infrared (MWIR) devices have moved from development into manufacturing. To accommodate this maturation, the Molecular Beam Epitaxy (MBE) growth of the MWIR photodetector structures has progressed to a production mode. By necessitating many repetitions of a given growth structure, the increase in volume has enabled the use of Statistical Process Control (SPC) techniques to improve command over critical parameters, and thereby improve the yield and throughput. These products have been grown on GaSb substrates using large format, multi-wafer platens for 100 mm and 125 mm diameter substrates in a Veeco Gen2000 MBE system. The material properties were measured by Atomic Force Microscopy (AFM), High-Resolution X-Ray Diffraction (HRXRD), Photoluminescence (PL), and diode performance (turn-on voltage, dark current (JD), Quantum Efficiency (QE), and cutoff wavelength). Analysis of the run-to-run data will be presented to exhibit the manufacturability of these structures.

As GaSb based LWIR nBn detector structures have progressed from development into production, the standard substrates have been 76.2 and 100 mm in diameter. Additionally, production growths on 125 mm substrates are gaining popularity. To meet demands for larger focal plane arrays (FPA), improve throughput, volume, and yield, IQE has made the next step in this progression. Our first demonstration of multi-wafer growth of 150 mm GaSb exhibited uniform, high quality MWIR epitaxy. In this work, we will share our results for the more challenging GaSb-based LWIR nBn detector structures. These growths were carried out on a large format platen (7 × 150 mm) by Molecular Beam Epitaxy (MBE). The material properties as measured by AFM, HRXRD, Nomarski microscope, and PL, along with diode performance (turn-on, QE, cutoff wavelength), will be presented. Using this data, we will analyze the wafer-to-wafer cross-platen uniformity. Additionally, we will compare the characterization and device results to similar structures grown on smaller diameter substrates, and consider the viability of utilizing 150 mm GaSb substrates for LWIR nBn detector structures.

Effects of GaSb substrate orientation and surface polarity on performance of MWIR photodetectors (PD) were evaluated by comparing devices fabricated on (1 0 0), (2 1 1)A and B, and (3 1 1)A and B oriented substrates. Two types of PDs were evaluated: bulk InAsSb barrier PD with wavelength ∼4 µm, and type-II strained layer superlattice (T2SL) PD with wavelength 5.5 µm. Epitaxial structures were grown by solid source molecular beam epitaxy (MBE) on substrates with various orientations side-by-side in the same growth run. Material performance was evaluated by AFM, Nomarski microscopy, x-ray diffraction, 77 K photoluminescence (PL), and PD current-voltage and spectral testing. All wafers demonstrated reasonable surface morphology, with some variability in roughness from wafer to wafer. Bulk nBn devices fabricated on the high-index substrates show a blue shift up to 0.15 µm for both 77 K PL and for spectral cutoff wavelength compared to the same structure on the (1 0 0) substrate. Growth on high-index substrates also showed moderate reduction of quantum efficiency (QE) and variations in dark current (Jd). The (3 1 1)A and (2 1 1)A oriented structures exhibited the most significant Jd reduction, by a factor of ∼3 and ∼6, respectively. Substrate orientation induces more variation in the T2SL PD parameters, especially in Jd and QE. Here, the (2 1 1)B orientation demonstrates a red shift of the PL and cutoff wavelength by about 1 µm. These results suggest that high-index substrates can be explored to fine-tune and manipulate unique PD characteristic properties for specific applications.

The 6.1 A family of Sb-based III-V materials and heterostructures is a promising candidate for infrared (IR) detector applications. For the realization of low-cost, large-format IR photodetector arrays these materials must be grown on larger diameter substrates. For this purpose, GaAs substrates, with appropriate metamorphic buffer structures, have shown to be a promising alternative. Moreover, other platforms, such as Ge-on-Si (Ge/Si) and Ge-on-insulator-on-Si (GeOI/Si) virtual substrates, enable direct integration of the III-V devices with Si microelectronics read-out and processing architectures. In this paper, we investigate the structural and optoelectronic quality of mid-wavelength infrared InAsSb nBn photodetectors with a room temperature 50% cut-off wavelength of 4.5 μm grown on multiple substrates, including GaSb, GaAs, and Ge/Si. Material quality was examined using non-contact, non-destructive electron channeling contrast imaging (ECCI) in a scanning electron microscope for high-accuracy threading dislocation density (TDD) measurement and time-resolved microwave reflectance (TMR) spectroscopy for minority carrier lifetime (τmc) measurement. The combination of these two techniques enables a direct correlation between TDD and τmc. Our preliminary data indicate that higher TDD results in a reduced lifetime, similar to observations in III-V materials and HgCdTe IR materials. Here we present our analysis of equivalent nBn structures grown on GaSb, GaAs, and Ge/Si. The results of τmc indicate that the sample on GaSb and GaAs have the longest and the shortest lifetime, respectively, for temperatures above 70 K. Combining lifetime characterization with the TDD analysis from ECCI enables the assessment of metamorphic detectors on alternate substrates as a platform for large-format focal plane arrays.

We recently evaluated the optical and electric characteristics of mid-wave photodetector (PD) diodes grown on high-index substrates. Preliminary results indicate that substrate orientation and surface polarity can modify PD parameters such as photoluminescence (PL), dark current (Jd), quantum efficiency, and spectral characteristics. In this work, we focused on growth parameter optimization for long-wave type-II strained layer superlattice (T2SL) PD structures grown on (211)B and (311)A GaSb substrates. Material and PD diode characteristics were compared with reference data obtained on (100)-oriented substrates. Material quality was evaluated by HRXRD, AFM, Nomarski microscopy, 77 K PL, and PD J-V and spectral testing. Photoluminescence and cutoff wavelength measurements for diode structures fabricated on (211)B and (311)A substrates demonstrate a significant redshift due to a reduction of the optical bandgap in the SL. The extent of redshift increases with superlattice period and Sb mole fraction in the InAsSb layers in the absorber. All wafers demonstrated reasonable surface morphology without surface corrugation, with minor variability in roughness. Redshift in 77 K PL and cutoff wavelength, in combination with high QE and low Jd, obtained from growths on these high-index substrates offer a potential path to achieve enhanced PD characteristics with reduced SL period for a given wavelength by comparison to (100) substrates.

GaSb-based infrared (IR) photodetector technology progression is toward larger-format focal plane arrays (FPAs). This requires a performance-based and cost-based manufacturing process on larger diameter substrates for improved throughput, volume, and yield. IQE has demonstrated molecular beam epitaxy (MBE) growth processes for barrier-design detectors (nBn) in multi-wafer configurations on 4-inch and 5-inch diameter GaSb substrates, and via a metamorphic process on 4-inch and 6-inch GaAs substrates. Recently we took the next step in this progression, growing nBn detectors on 6-inch Si substrates coated with CVD-grown Ge, opening the door for potential integration with Si-based electronic circuitry. Here, we compare the epiwafer characteristics (morphology, x-ray, PL) and diode performance (turn-on, QE, cutoff wavelength) of this M-nBn on Ge-Si with the same M-nBn on GaAs and the corresponding nBn structure grown on native GaSb substrate. Similar performance was obtained on all three types of substrates. We also present FPA data based on a 640×512 pixel, 15 μm pitch process without substrate removal, where QE ~ 80%, NEuT < 20 mK, and operability

Monolithic integration of III–V-based optoelectronic devices onto Si wafers provides enormous benefits to many device manufacturing technologies. Therefore, it is essential to understand the effect of limiting factors such as dislocations on the material properties. In this paper, we study the minority carrier lifetimes in mid-wave infrared InAsSb alloys grown on lattice-matched GaSb and lattice-mismatched semi-insulating GaAs and Ge/Si substrates. Time-resolved microwave reflection measurement has been performed to study the carrier dynamics and different recombination mechanisms over the temperature range of 20–300 K at various optical injection levels. The sample on GaAs is found to have a lower lifetime over the entire temperature region than the sample on the Ge/Si substrate. The threading dislocation density values estimated from the lifetime analysis were found to be 2.9 ± 0.2 times larger in the sample on GaAs when averaged over the temperature range of 70–200 K. Furthermore, we studied the contribution of various recombination mechanisms, and it was shown that the lifetime in the sample on GaAs is dominated by the Shockley–Read–Hall recombination up to 140 K, above which the Auger recombination is the limiting factor. This transition temperature is 80 K and 100 K for the samples on GaSb and Ge/Si, respectively. We have also investigated the effect of the surface recombination on the total lifetime. The extracted bulk lifetime was found to be up to 2 × higher when the surface effect was excluded.

The Sb concentration profile in an nBn photodetector containing an InAs/InAsSb type-II superlattice is collected and analyzed using atom probe tomography. A 3D reconstruction comprises the full composition of 31 periods. The Sb concentration profile is evaluated for the entire 31 period stack, as well as each individual period using segregation models from Muraki and Wood. Trends in the asymmetric Sb profile show a consistent non-negligible Sb concentration in the InAs layers and a lower Sb concentration in the InAsSb with respect to the target concentration.

Lasing is reported for ridge-waveguide devices processed from a 40-stage InP-based quantum cascade laser structure grown on a 6-inch silicon substrate with a metamorphic buffer. The structure used in the proof-of-concept experiment had a typical design, including an Al0.78In0.22As/In0.73Ga0.27As strain-balanced composition, with high strain both in quantum wells and barriers relative to InP, and an all-InP waveguide with a total thickness of 8 µm. Devices of size 3 mm x 40 µm, with a high-reflection back facet coating, emitted at 4.35 µm and had a threshold current of approximately 2.2 A at 78 K. Lasing was observed up to 170 K. Compared to earlier demonstrated InP-based quantum cascade lasers monolithically integrated onto GaAs, the same laser structure integrated on silicon had a lower yield and reliability. Surface morphology analysis suggests that both can be significantly improved by reducing strain for the active region layers relative to InP bulk waveguide layers surrounding the laser core.

Recent improvements in the fabrication technology of InGaAs/InP heterobipolar transistors have enabled highly scaled transistors with power gain bandwidths above 1 THz. Limitations of the conventional fabrication process that reduce RF bandwidth have been identified and mitigated, among which are high resistivity base ohmic contacts, resistive base electrodes, excessive emitter end undercut, and insufficient undercut of large-diameter base posts. A novel two-step deposition process for self-aligned metallization of sub-20-nm bases has been developed and demonstrated. In the first step, a metal stack is directly evaporated onto the base semiconductor without any lithographic processing so as to minimize contamination from resist/developer chemistry. The composite metal stack exploits an ultrathin layer of platinum that controllably reacts with base, yielding low contact resistance, as well as a thick refractory diffusion barrier, which permits stable operation at high current densities and elevated temperatures. Further reduction of overall base access resistance is achieved by passivating base and emitter semiconductor surfaces in a combined atomic layer deposition Al2O3 and plasma-enchanced chemical vapor depositon SiNx sidewall process. This technology enables the deposition of low-sheet-resistivity base electrodes, further improving overall base access resistance and $f_{\textrm {max}}$ bandwidth. Additional process enhancements include the significant reduction of device parasitics by scaling base posts and controlling emitter end and base postundercut.

We report an InP/InGaAs/InP double heterojunction bipolar transistor fabricated in a triple-mesa structure, exhibiting simultaneous 404 GHz fτ and 901 GHz fmax. The emitter and base contacts were defined by electron beam lithography with better than 10 nm resolution and smaller than 20 nm alignment error. The base-collector junction has been passivated by depositing a SiNx layer prior to benzocyclobutene planarization, improving the open-base breakdown voltage BVCEO from 3.7 to 4.3 V.

This work develops an enhanced Monte Carlo (MC) simulation methodology to predict the impacts of layout-dependent correlated manufacturing variations on the performance of photonics integrated circuits (PICs). First, to enable such performance prediction, we demonstrate a simple method with sub-nanometer accuracy to characterize photonics manufacturing variations, where the width and height for a fabricated waveguide can be extracted from the spectral response of a racetrack resonator. By measuring the spectral responses for a large number of identical resonators spread over a wafer, statistical results for the variations of waveguide width and height can be obtained. Second, we develop models for the layout-dependent enhanced MC simulation. Our models use netlist extraction to transfer physical layouts into circuit simulators. Spatially correlated physical variations across the PICs are simulated on a discrete grid and are mapped to each circuit component, so that the performance for each component can be updated according to its obtained variations, and therefore, circuit simulations take the correlated variations between components into account. The simulation flow and theoretical models for our layout-dependent enhanced MC simulation are detailed in this paper. As examples, several ring-resonator filter circuits are studied using the developed enhanced MC simulation, and statistical results from the simulations can predict both common-mode and differential-mode variations of the circuit performance.

GaSb-based infrared (IR) photodetector structures were grown on large diameter, 150 mm, Si substrates using a multistep metamorphic buffer architecture process. A standard bulk InAsSb/AlAsSb barrier detector design with a cutoff wavelength of ∼4 μm was used as a test vehicle for this growth process. First, a Ge layer was deposited by chemical vapor deposition, creating a Ge-Si substrate for the subsequent molecular beam epitaxy growth of the remaining III–V buffer and device layers. X-ray diffraction and photoluminescence measurements demonstrated high crystal quality and excellent cross-wafer uniformity of the device epiwafer characteristics. Microscopy evaluation revealed a moundlike surface morphology with a low root-mean-square roughness value below 2 nm, suitable for focal plane array (FPA) fabrication. Large-area mesa diode test devices measured dark currents of 5 × 10−5 A/cm2 and a quantum efficiency of 60% for the Sb-detector grown on Ge–Si. The same structure was fully fabricated into a standard FPA and produced good imagery resolution with high operability. These excellent results for this first FPA manufactured from an Sb-photodetector grown on Si using this Ge-Si architecture demonstrate a promising path in the progression of Sb-IR technology as it transitions from development to next-generation, large-format IR manufacturing with an eye toward potential heterogeneous integration with silicon.GaSb-based infrared (IR) photodetector structures were grown on large diameter, 150 mm, Si substrates using a multistep metamorphic buffer architecture process. A standard bulk InAsSb/AlAsSb barrier detector design with a cutoff wavelength of ∼4 μm was used as a test vehicle for this growth process. First, a Ge layer was deposited by chemical vapor deposition, creating a Ge-Si substrate for the subsequent molecular beam epitaxy growth of the remaining III–V buffer and device layers. X-ray diffraction and photoluminescence measurements demonstrated high crystal quality and excellent cross-wafer uniformity of the device epiwafer characteristics. Microscopy evaluation revealed a moundlike surface morphology with a low root-mean-square roughness value below 2 nm, suitable for focal plane array (FPA) fabrication. Large-area mesa diode test devices measured dark currents of 5 × 10−5 A/cm2 and a quantum efficiency of 60% for the Sb-detector grown on Ge–Si. The same structure was fully fabricated into a standard ...

Antimony-based materials continue to provide great interest for infrared photodetector and focal plane array imaging applications. Detector architectures include InAs/Ga(In)Sb strained-layer superlattices, which create a type-II band alignment that can be tailored to cover a wide range of the mid- and long-wavelength bands by varying the thickness and composition of the constituent materials, and bulk InAsSb-based XBn barrier designs. These materials can provide desirable detector features such as wider wavelength range, suppression of tunneling currents, improved quantum efficiency, and higher operating temperatures. In order to bring these advantages to market, a reliable manufacturing process must be established on large diameter substrates. We report our latest work on the molecular beam epitaxy growth of Sb-detector epiwafers on 100 mm diameter GaSb substrates in a multi-wafer production format. The growth process has been established to address the challenges of these demanding structures, including the large numbers of alternating thin layers and mixed group-V elements. Various characterization techniques demonstrate excellent surface morphology, crystalline structure quality, and optical properties of the epiwafers. The measured wafer-to-wafer consistency and cross-wafer uniformity demonstrate the potential for volume manufacturing.

GaSb and its heterostructures grown by molecular beam epitaxy (MBE) have received much attention given their application in a wide range of mid-wave and long-wave IR photodetector applications. With the maturation of the MBE growth process, focus is now turned to improving manufacturing readiness and the transition to the production of large-format wafers. We will discuss the transition from the development of early detector layer structures on 2” diameter GaSb substrates, through today’s 3”/4” production standard, and to the onset of 5” pilot production from the perspective of volume compound semiconductor manufacturing. We will report on the growth of 5” GaSb-based MWIR nBn detector structures using a large format 5×5” production MBE platform. Structural and optical properties, as well as electrical data from large-area mesa diodes will be presented and compared with results achieved with smaller batch size MBE reactor platform.

Gallium Antimonide (GaSb) is an important Group III-V compound semiconductor which is suitable for use in the manufacture of a wide variety of optoelectronic devices such as infra-red (IR) focal plane detectors. A significant issue for the commercialisation of these products is the production of epitaxy ready GaSb, which remains a challenge for the substrate manufacturer, as the stringent demands of the MBE process, requires a high quality starting wafer. In this work large diameter GaSb crystals were grown by the Czochralski (Cz) method and wafers prepared for chemo-mechanical polishing (CMP). Innovative epi-ready treatments and novel post polish cleaning methodologies were applied. The effect of these modified finishing chemistries on substrate surface quality and the performance of epitaxially grown MBE GaSb IR detector structures were investigated. Improvements in the lowering of surface defectivity, maintaining of the surface roughness and optimisation of all flatness parameters is confirmed both pre and post MBE growth. In this paper we also discuss the influence of bulk GaSb quality on substrate surface performance through the characterisation of epitaxial structures grown on near zero etch pit density (EPD) crystals. In summary progression and development of current substrate polishing techniques has been demonstrated to deliver a consistent improved surface on GaSb wafers with a readily desorbed oxide for epitaxial growth.

Electronic circuit designers commonly start their design process with a schematic, namely an abstract representation of the physical circuit. In integrated photonics on the other hand, it is common for the design to begin at the physical component level, and create a layout by connecting components with interconnects. In this paper, we discuss how to create a schematic from the physical layout via netlist extraction, which enables circuit simulations. Post-layout extraction can also be used to predict how fabrication variability and non-uniformity will impact circuit performance. This is based on the component position information, compact models that are parameterized for dimensional variations, and manufacturing variability models such as a simulated wafer thickness map. This final step is critical in understanding how real-world silicon photonic circuits will behave. We present an example based on treating the ring resonator as a circuit. A silicon photonics design kit, as described here, is available for download at http://github.com/lukasc-ubc/SiEPIC_EBeam_PDK.

Silicon photonics is a scalable, cost-effective technology for the production of photonic integrated circuits (PICs). The emergence of silicon photonics as a dominant technology for PICs is largely because it leverages decades of investment in design and fabrication technologies for electronic integrated circuits. However, the lithography requirements for photonic and electronic components are importantly different: geometries are generally curved; sidewall roughness is critically important; and, while the feature sizes are generally much larger, photonic device performance can be extraordinarily sensitive to the precise final geometry. For example, rounding of 90 degree corners in y-branches or multimode interferometers can have a dramatic impact on performance. The use of optical proximity correction (OPC) can greatly reduce these problems but does not eliminate them altogether. The designer is therefore faced with the problem of potentially optimizing a component using highly accurate numerical simulations that cannot be manufactured to the desired geometry, leading to a discrepancy between desired and actual performance. To solve this problem, we present a method for designing and optimizing photonic components that are lithography friendly so that the simulated geometry can be readily manufactured. As an example, we consider the case of waveguide Bragg gratings which are particularly challenging to manufacture by lithography.

GaSb-based infrared (IR) photodetectors are moving from a developmental phase into manufacturing, requiring among other things a shift to larger wafer diameters and volumes. We report on the multi-wafer molecular beam epitaxy (MBE) growth of mid-wave IR nBn photodetector structures on 5-inch GaSb and 6-inch GaAs substrates. The 5 × 5-inch and 4 × 6-inch multi-wafer configurations exhibited excellent cross-wafer uniformity of standard epiwafer characteristics, including morphology, and structural and optical properties. Large-area mesa diode characteristics from these epiwafers are comparable to those grown on smaller diameter substrates. The results represent an important technological path toward next-generation large-format IR detector array applications.

We report on the development of InAs/InGaAlAs quantum-dash-in-well structure on InP substrate for wideband emitter applications. A spectral width as broad as 58 meV observed from both photoluminescence and surface photovoltage spectroscopy on the sample indicating the formation of highly inhomogeneous InAs-dash structure that results from the quasi-continuous interband transition. The two-section superluminescent diodes (SLDs), with integrated photon absorber slab as lasing suppression section, fabricated on the InAs dash-in-well structure exhibits the close-to-Gaussian emission with a bandwidth (full-width at half-maximum) of up to 140 nm at ~ 1.6 mum peak wavelength. The SLD produces a low spectrum ripple of 0.3 dB and an integrated power of ~ 2 mW measured at 20degC under 8 kA/cm2. The oxide stripe laser exhibits wide lasing wavelength coverage of up to 76 nm at ~ 1.64 mum center wavelength and an output optical power of ~ 400 mW from simultaneous multiple confined states lasing at room temperature. This rule changing broadband lasing signature, different from the conventional interband diode laser, is achieved from the quasi-continuous interband transition formed by the inhomogeneous quantum-dash nanostructure.

We investigate the intermixing effect in InAs/InAlGaAs quantum-dash-in-well structures grown on InP substrate. Both impurity-free vacancy disordering (IFVD) via dielectric cap annealing, and impurity-induced disordering (IID) using nitrogen ion-implantation techniques have been employed to spatially control the group-III intermixing in the quantum-dash (Qdash) system. Differential bandgap shifts of up to 80 nm and 112 nm have been observed from the IFVD and IID processes, respectively. Compared to the control (nonintermixed) lasers, the light-current characteristics for the 125 nm wavelength shifted Qdash lasers are not significantly changed, suggesting that the quality of the intermixed material is well preserved. The intermixed lasers exhibit a narrower linewidth as compared to the as-grown laser due to the improved dash homogeneity. The integrity of the material is retained after intermixing, suggesting the potential application for the planar integration of multiple active/passive Qdash-based devices on a single InP chip.

The effect of thermal crosstalk in a thermo-optically tuned silicon optical router is assessed using a combination of component level physical simulations and circuit level simulations. By restricting the physical simulation volume to only a small number of components and using fast compact models for circuit-scale simulations, this methodology can be scaled effectively to large switch matrices.

We present a vision for photonic circuit simulation within sophisticated EDA-style design flows and the tool development roadmap to achieve it. Our approach aims to deliver highly-usable, predictive capabilities for a variety of use cases, that seamlessly interoperates with 3rd-party, best-in-class design tools.

The GaSb-based 6.1 A lattice constant family of materials and heterostructures provides rich bandgap engineering possibilities and have received considerable attention for their potential and demonstrated performance in infrared (IR) detection and imaging applications. Mid-wave and long-wave IR photodetectors are progressing toward commercial manufacturing applications. To succeed, they must move from research laboratory settings to general semiconductor production, and high-quality GaSb-based epitaxial wafers with diameter larger than the current standard 3-inch are highly desirable. 4-inch GaSb substrates have been in production for a couple of years and are now commercially available. Recently, epi-ready GaSb substrates with diameter in excess of 6-inch were successfully produced. In this work, we report on the MBE (Molecular Beam Epitaxy) growth of generic MWIR bulk nBn photodetectors on 6-inch diameter GaSb substrates. The surface morphology, optical and structural quality of the epiwafers as evaluated by atomic force microscopy (AFM), Nomarski microscopy, low temperature photoluminescence (PL) spectroscopy, and high-resolution x-ray diffraction (XRD) will be discussed. Current density versus voltage (J-V) and photoresponsivity measurements from large-area mesa diode fabricated will also be reported. Material and device properties of these 6-inch epiwafers will be compared to similar structures grown on commercially available 4-inch diameter GaSb substrates.

We demonstrate an InAsSb nBn detector monolithically integrated with a microlens fabricated on the back side of the detector. The increase in the optical collection area of the detector resulted in a five-fold enhancement of the responsivity to Rp = 5.5 A/W. The responsivity increases further to Rp = 8.5 A/W with an antireflection coating. These 4.5 μm cut-off wavelength antireflection coated detectors with microlenses exhibited a detectivity of D* (λ) = 2.7 × 1010 cmHz0.5/W at T = 250 K, which can be reached easily with a single-stage thermoelectric cooler or with a passive radiator in the space environment. This represents a 25 K increase in the operating temperature of these devices compared to the uncoated detectors without an integrated microlens.

We present recent studies on a set of three different long wave IR interband cascade infrared photodetectors with Type-II InAs/GaSb absorbers. Two of these detectors were two- and three-stage structures with regular-illumination configuration and the other was a two-stage structure with reverse-illumination configuration. The 100% cutoff wavelength for these detectors was 6.2 μm at 78 K and extended to 8 μm at 300 K. At T=125 K and higher temperatures we were able to observe the benefits of the three-stage detector over the two-stage device in terms of lower dark current and higher detectivity. We conjecture that the imperfections from the device growth and fabrication had a substantial effect on the low-temperature device performance and were responsible for unexpected behavior at these temperatures. We also found that the zero-bias photo-response increased for temperatures up to 200 K, which was indicative of efficient collection of photo-generated carriers at relatively high temperatures. Electroluminescence and X-ray diffraction measurements suggest that all three grown structures had comparable material qualities. However, the twostage detectors with the reverse-illumination had significantly lower performance than the other two detectors. The activation energy for the two-stage detectors with the reverse-illumination was 37 meV for T=78-100 K, which was much lower than the activation energies of the other two detectors (~140 meV). This low activation energy was attributed to shunt leakage observed in detectors with the reverse-illumination configuration.

Silicon photonics has become a promising technology for photonic integrated circuits. During the past few years, there has been a dramatic increase in the scale and complexity of silicon photonic circuits, which introduces many new design challenges and creates a need for efficient and standardized design flows. We have developed a complete design flow that combines mature electronic design automation (EDA) software with optical simulation software. This flow makes it possible to reliably design, simulate, layout and manufacture large-scale silicon photonic circuits in a unified environment.

Broad adoption of silicon photonics technology for photonic integrated circuits requires standardized design flows that are similar to what is available for analog and mixed signal electrical circuit design. We have developed a design flow that combines mature electronic design automation (EDA) software with optical simulation software. An essential component of any design flow, whether electrical or photonic, is the ability to accurately simulate largescale circuits. This is particularly important when the behavior of the circuit is not trivially related to the individual component performance. While this is clearly the case for electronic circuits consisting of hundreds to billions of transistors, it is already becoming important in photonic circuits such as WDM transmitters, where signal cross talk needs to be considered, as well as optical cross-connect switches. In addition, optical routing to connect different components requires the introduction of additional waveguide sections, waveguide bends, and waveguide crossings, which affect the overall circuit performance. Manufacturing variability can also have dramatic circuit-level consequences that need to be simulated. Circuit simulations must rely on compact models that can accurately represent the behavior of each component, and the compact model parameters must be extracted from physical level simulation and experimental results. We show how large scale circuits can be simulated in both the time and frequency domains, including the effects of bidirectional and, where appropriate, multimode and multichannel photonic waveguides. We also show how active, passive and nonlinear individual components such as grating couplers, waveguides, splitters, filters, electro-optical modulators and detectors can be simulated using a combination of electrical and optical algorithms, and good agreement with experimental results can be obtained. We then show how parameters, with inclusion of fabrication process variations, can be extracted for use in the circuit level simulations. Ultimately, we show how a multi-channel WDM transceiver can be created, from schematic design to tapeout, using key features of EDA design flows such as schematic driven layout, design rule checking and layout versus schematic.

We demonstrate 1.3 μm InAs quantum dot lasers on silicon by molecular beam epitaxial growth with low thresholds (16 mA), high output power (>50 mW), high T0 (>200 K), and high temperature lasing (115 °C).

The GaSb-based family of materials and heterostructures provides rich bandgap engineering possibilities for a variety of infrared (IR) applications. Mid-wave and long-wave IR photodetectors are progressing toward commercial manufacturing applications, but to succeed they must move from research laboratory settings to general semiconductor production and they require larger diameter substrates than the current standard 2-inch and 3-inch GaSb. Substrate vendors are beginning production of 4-inch GaSb, but another alternative is growth on 6-inch GaAs substrates with appropriate metamorphic buffer layers. We have grown generic MWIR nBn photodetectors on large diameter, 6-inch GaAs substrates by molecular beam epitaxy. Multiple metamorphic buffer architectures, including bulk GaSb nucleation, AlAsSb superlattices, and graded GaAsSb and InAlSb ternary alloys, were employed to bridge the 7.8% mismatch gap from the GaAs substrates to the GaSb-based epilayers at 6.1 A lattice-constant and beyond. Reaching ~6.2 A extends the nBn cutoff wavelength from 4.2 to

Bulk 4" GaSb crystal growth methods based on the Czochralski technique are detailed which deliver highly mono-crystalline substrates that are characterized by low dislocation densities. The latest developments in epitaxy-ready surface finishing will be described and results presented for 4” GaSb substrates processed on a large format, commercial multiwafer polishing platform. Bulk material quality assessments will be made and the surface condition of bare substrates and epitaxial material grown on top of 4" GaSb substrates will be assessed by various surface analytical techniques. We will comment on the available production capacity for 4" GaSb and remark on the scaling challenges that will be required to support the anticipated increase in demand for large diameter GaSb substrates.

Characterizations of electro-optic modulators in a variety of configurations were determined from physics-based simulation of the electrical and optical behaviour. Ultimately, the complete transmission response was determined as a function of bias.

Mid-wavelength infrared nBn photodetectors based on bulk InAsxSb1-x absorbers with a greater than 5 μm cutoff grown on GaSb substrates are demonstrated. The extended cutoff was achieved by increasing the lattice constant of the substrate from 6.09 to 6.13 A using a 1.5 μm thick AlSb buffer layer to enable the growth of bulk InAs0.81Sb0.19 absorber material. Transitioning the lattice to 6.13 A also enables the use of a simple binary AlSb layer as a unipolar barrier to block majority carrier electrons and reduce dark current noise. Individual test devices with 4 μm thick absorbers displayed 150 K dark current density, cutoff wavelength, and quantum efficiency of 3 × 10−5 A/cm2, 5.31 μm, and 44% at 3.4 μm, respectively. The instantaneous dark current activation energy at a given bias and temperature is determined via Arrhenius analysis from the Dark current vs. temperature and bias data, and a discussion of valence band alignment between the InAsxSb1-x absorber and AlSb barrier layers is presented.

In this work, we report the demonstration of quaternary GaInAsSb-based mid-wavelength infrared photodetectors with cutoff wavelengths longer than 4 μm at 300 K. Both interband cascade infrared photodetector (ICIP) with a three-stage discrete absorber architecture and conventional one-stage detector structures have been grown by molecular beam epitaxy and investigated in experiments for their electrical and optical properties. High absorption coefficient and gain were observed in both detector structures. The three-stage ICIPs had superior carrier transport over the one-stage detectors. A detectivity as high as 1.0 × 109 cm Hz1/2 W−1 was achieved at 3.3 μm for both one- and three-stage detectors under zero bias at 300 K. The implications of these results are discussed along with potential of GaInAsSb-based ICIPs for high-speed applications.

The compositional dependence of effective tunneling barrier height (E-beff) and defect assisted band alignment transition from staggered gap to broken gap in GaAsSb/InGaAs n-channel tunnel field effect transistor (TFET) structures were demonstrated by x-ray photoelectron spectroscopy (XPS). High-resolution x-ray diffraction measurements revealed that the active layers are internally lattice matched. The evolution of defect properties was evaluated using cross-sectional transmission electron microscopy. The defect density at the source/channel heterointerface was controlled by changing the interface properties during growth. By increasing indium (In) and antimony (Sb) alloy compositions from 65% to 70% in InxGa1-xAs and 60% to 65% in GaAs1-ySby layers, the E-beff was reduced from 0.30 eV to 0.21 eV, respectively, with the low defect density at the source/channel heterointerface. The transfer characteristics of the fabricated TFET device with an E-beff of 0.21eV show 2x improvement in ON-state current compared to the device with E-beff of 0.30 eV. On contrary, the value of E-beff was decreased from 0.21 eV to -0.03 eV due to the presence of high defect density at the GaAs0.35Sb0.65/In0.7Ga0.3As heterointerface. As a result, the band alignment was converted from staggered gap to broken gap, which leads to 4 orders of magnitude increase in OFF-state leakage current. Therefore, a high quality source/channel interface with a properly selected E-beff and well maintained low defect density is necessary to obtain both high ON-state current and low OFF-state leakage in a mixed As/Sb TFET structure for high-performance and lower-power logic applications. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4764880]

Mega-pixel FPAs in both MWIR and LWIR spectral bands based on Sb strained layer superlattices and nBn epitaxial structures grown on GaSb substrates have recently demonstrated impressive performances at high operating temperatures. An essential component of SLS epitaxial growth initiation is the starting wafer flatness, smoothness and haze. Large diameter GaSb wafers must be manufactured meeting these stringent demands and current state-of-the-art GaSb substrate manufacturing is focused on 100mm wafer diameters. Using a newly developed polishing process, 100mm GaSb substrate manufacturing has resulted in consistent starting wafer peak-to-valley flatness well below 5mm and surface roughness below Rms of 0.2nm. Final substrate and epitaxial wafer Surfscan mapping (l1000/cm2 surface defects) and surface roughness (Rms~0.2nm) are presented and compared with measurements of the starting substrates. This paper evaluates the manufacturing and epitaxial growth on 100mm GaSb substrates that have been processed to achieve an MBE grown InAsSb-based nBn MWIR photodetector structure.© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

InAs/InAs1-xSbx strain-balanced superlattices (SLs) on GaSb are a viable alternative to the well-studied InAs/Ga1-xInxSb SLs for mid- and long-wavelength infrared (MWIR and LWIR) laser and photodetector applications, but the InAs/InAs1-xSbx SLs are not as thoroughly investigated. Therefore, the valence band offset between InAs and InAs/InAs1-xSbx, a critical parameter necessary to predict the SL bandgap, must be further examined to produce InAs/InAs1-xSbx SLs for devices operational at MWIR and LWIR wavelengths. The effective bandgap energies of InAs/InAs1-xSbx SLs with x = 0.28 - 0.40 are designed using a three-band envelope function approximation model. Multiple 0.5 μm-thick SL samples are grown by molecular beam epitaxy on GaSb substrates. Structural characterization using x-ray diffraction and atomic force microscopy reveals excellent crystalline properties with SL zero-order peak full-width-half-maximums between 30 and 40 arcsec and 20 x 20 μm2 area root-mean-square roughnesses of 1.6 - 2.7 A. Photoluminescence (PL) spectra of these samples cover 5 to 8 μm, and the band offset between InAs and InAs/InAs1-xSbx is obtained by fitting the PL peaks to the calculated values. The bowing in the valence band is found to depend on the initial InAs/InSb valence band offset and changes linearly with x as CEv_bowing = 1.58x - 0.62 eV when an InAs/InAs1-xSbx bandgap bowing parameter of 0.67 eV is assumed. A fractional valence band offset, Qv = ΔEv/ΔEg, of 1.75 ± 0.03 is determined and is practically constant in the composition range studied.

Antimony-based photodetector materials have attracted considerable interest for their potential and demonstrated performance in infrared detection and imaging applications. Mid-wavelength infrared detector has been demonstrated using bulk InAsSb/AlAsSb-based nBn structures. Heterostructures based on InAs/Ga(In)Sb strained layer superlattices create a type-II band alignment that can be tailored to cover a wide range of the mid- and long-wavelength infrared absorption bands by varying the thickness and composition of the constituent materials. Through careful design, these Sb-based detectors can realize desirable features such as higher operating temperature, better uniformity, suppression of Auger recombination, reduction of tunneling currents, and higher quantum efficiency. The manufacturing challenge of these structures is the reproducible growth of high-quality Sb-based epiwafers due to their complex designs including large numbers of alternating thin layers and mixed group-V elements. In this paper, we discuss the manufacturability of such epiwafers on 3" and 4" diameter GaSb substrates by molecular beam epitaxy using multi-wafer production tools. Various techniques were used to characterize the material properties of these wafers, including high-resolution x-ray diffraction, low-temperature photoluminescence, Nomarski optical microscopy, and atomic force microscopy.

Ga(In)Sb/InAs-based strained-layer superlattices (SLS) have received considerable attention recently for their potential in infrared (IR) applications. These heterostructures create a type-II band alignment such that the conduction band of InAs layer is lower than the valence band of Ga(In)Sb layer. By varying the thickness and composition of the constituent materials, the bandgap of these SLS structures can be tailored to cover a wide range of the mid-wave and long-wave infrared (MWIR and LWIR) absorption bands. Suppression of Auger recombination and reduction of tunneling current can also be realized through careful design of the Type-II band structure. The growth of high-quality Ga(In)Sb/InAs-based SLS epiwafers is challenging due to the complexity of growing a large number of alternating thin layers with mixed group V elements. In this paper, the development of a manufacturable growth process by molecular beam epitaxy (MBE) using a multi-wafer production reactor will be discussed. Various techniques were used to analyze the quality of the epitaxial material. Structural properties were evaluated by high-resolution x-ray diffraction (XRD) and cross-sectional transmission electron microscopy (XTEM). Optical properties were assessed by low-temperature photoluminescence measurements (PL). Surface morphology and roughness data as measured by Nomarski optical microscope and atomic force microscope (AFM) will be presented. Device characteristics such as dynamic impedance, responsivity, quantum efficiency, and J-V characteristics of photodiodes fabricated using our SLS epiwafers will be discussed.

In this work newly developed 4" GaSb substrates are investigated for their suitability in the epitaxial growth of type II InAs/GaInSb superlattice detectors. The Czochralski technique was used to grow 4" GaSb crystals with etch pit densities in the range of 1.5-2.5E3 cm-2. Bulk crystal structure was investigated by X-ray topography and revealed large central areas of zero or low dislocation density. Epitaxy-ready substrate surfaces were characterized by low levels of surface roughness and uniform oxide coverage. The material quality of superlattice detector structures grown on 2" and 4" GaSb substrates has been compared. Surface morphology evaluations of a 4" GaSb epiwafer reveal very low haze surface and defect density level that is similar to a 2" epiwafer. An rms surface roughness of 4.4 A was measured by AFM which is only 1-2 A larger than seen on 2" diameter SLS epiwafers. High resolution X-Ray measurements of the epitaxial layer structure indicate high structural quality and reproducible SL periodicity. Good layer thickness uniformity with a center-to-edge variation just over 2% has been achieved.

Type I InP/InGaAs/InP double heterojunction bipolar transistors were fabricated using a simple mesa structure, where emitter junction widths have been scaled from 250 nm to 200 nm. These devices exhibit ƒ max in excess of 800 GHz, and ƒ τ = 360 GHz. Greater than fifty percent device yield was obtained by employing two 25 nm SiN x sidewalls to protect and anchor the refractory metal emitter contact to the emitter semiconductor. A hybrid dry and wet etch process is used to form a vertical emitter mesa, causing reductions in both the emitter-base gap resistance R gap and the spreading resistance beneath the emitter R b,spread , leading to an expected and observed increase in ƒ max . Peak HBT current gains β ≈ 21–33, BV ceo ∼ 4 V, BV cbo ∼ 5 V, and J e at low V cb is over 10 mA/μm2.

We report on a direct epitaxial growth approach for the heterogeneous integration of high speed III-V devices with Si CMOS logic on a common Si substrate. InP-based heterojunction bipolar transistor (HBTs) structures were successfully grown on patterned Si-on-Lattice-Engineered-Substrate (SOLES) substrates using molecular beam epitaxy. DC and RF performance similar to those grown on lattice-matched InP were achieved in growth windows as small as 15×15μm2. This truly planar approach allows tight device placement with InP-HBTs to Si CMOS transistors separation as small as 2.5 μm, and the use of standard wafer level multilayer interconnects. A high speed, low power dissipation differential amplifier was designed and fabricated, demonstrating the feasibility of using this approach for high performance mixed signal circuits such as ADCs and DACs.

We report InP/InGaAs/InP double heterojunction bipolar transistors (DHBT) fabricated using a simple mesa structure. The devices employ a 30 nm highly doped InGaAs base and a 150 nm InP collector containing an InGaAs/InAlAs superlattice grade. These devices exhibit a maximum fmax = 755 GHz with a 416 GHz /fT. This is the highest fmax reported for a mesa HBT. Through the use of i-line lithography, the emitter junctions have been scaled from 500-600 nm down to 250-300 nm -all while maintaining similar collector to emitter area ratios. Because of the subsequent reduction to the base spreading resistance underneath the emitter Rb,spread and increased radial heat flow from the narrower junction, significant increases to fmax and reductions in device thermal resistance θJA are expected and observed. The HBT current gain β ≈ 24-35, BVceo = 4.60 V, BVcbo = 5.34 V, and the devices operate up to 20 mW / μm2 before self-heating is observed to affect the DC characteristics.

Authors report the demonstration of the emission wavelength tuning of InAs quantum-dashes within InAlGaAs quantum-wells grown on InP substrate, that gives the initial wavelength emission at ~1.65 µm. The impurity-free dielectric cap annealing and the nitrogen ion-implantation induced intermixing techniques have been implemented to spatially control the group-III intermixing in the structure, which produces differential bandgap shift of 80 nm and 112 nm, respectively. Transmission electron microscopy, optical and electrical characterizations have been performed to evaluate the quality of the intermixed QD material and bandgap tuned devices. Compared to the control (non-intermixed) lasers, the light-current characteristics for the over 125 nm wavelength shifted QD lasers are not significantly changed suggesting that the quality of the intermixed material is well-preserved. The intermixed lasers exhibit the narrow linewidth as compared to the as-grown due to the improved QD homogeneity. The integrity of the QD material is retained after intermixing suggesting the potential application for the planar integration of multiple active/passive QD-based devices on a single InP chip. Keywords: InAs/InP, InAs/InAlGaAs, quantum-dots, quantum-dash, quantum-well intermixing, dash-in-well, interdiffusion, disordering, quantum-well intermixing, quantum-dot intermixing, ion implantation, annealing, bandgap tuned laser, photonic integrated circuits