| 1. |
- Ahvenniemi, Esko, et al.
(författare)
-
Recommended reading list of early publications on atomic layer deposition-Outcome of the "Virtual Project on the History of ALD"
- 2017
-
Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Vacuum Society. - 0734-2101 .- 1520-8559. ; 35:1
-
Forskningsöversikt (refereegranskat)abstract
- Atomic layer deposition (ALD), a gas-phase thin film deposition technique based on repeated, self-terminating gas-solid reactions, has become the method of choice in semiconductor manufacturing and many other technological areas for depositing thin conformal inorganic material layers for various applications. ALD has been discovered and developed independently, at least twice, under different names: atomic layer epitaxy (ALE) and molecular layering. ALE, dating back to 1974 in Finland, has been commonly known as the origin of ALD, while work done since the 1960s in the Soviet Union under the name "molecular layering" (and sometimes other names) has remained much less known. The virtual project on the history of ALD (VPHA) is a volunteer-based effort with open participation, set up to make the early days of ALD more transparent. In VPHA, started in July 2013, the target is to list, read and comment on all early ALD academic and patent literature up to 1986. VPHA has resulted in two essays and several presentations at international conferences. This paper, based on a poster presentation at the 16th International Conference on Atomic Layer Deposition in Dublin, Ireland, 2016, presents a recommended reading list of early ALD publications, created collectively by the VPHA participants through voting. The list contains 22 publications from Finland, Japan, Soviet Union, United Kingdom, and United States. Up to now, a balanced overview regarding the early history of ALD has been missing; the current list is an attempt to remedy this deficiency.
|
|
| 2. |
- Backes, Claudia, et al.
(författare)
-
Production and processing of graphene and related materials
- 2020
-
Ingår i: 2D Materials. - : IOP Publishing. - 2053-1583. ; 7:2
-
Tidskriftsartikel (refereegranskat)abstract
- We present an overview of the main techniques for production and processing of graphene and related materials (GRMs), as well as the key characterization procedures. We adopt a 'hands-on' approach, providing practical details and procedures as derived from literature as well as from the authors' experience, in order to enable the reader to reproduce the results. Section I is devoted to 'bottom up' approaches, whereby individual constituents are pieced together into more complex structures. We consider graphene nanoribbons (GNRs) produced either by solution processing or by on-surface synthesis in ultra high vacuum (UHV), as well carbon nanomembranes (CNM). Production of a variety of GNRs with tailored band gaps and edge shapes is now possible. CNMs can be tuned in terms of porosity, crystallinity and electronic behaviour. Section II covers 'top down' techniques. These rely on breaking down of a layered precursor, in the graphene case usually natural crystals like graphite or artificially synthesized materials, such as highly oriented pyrolythic graphite, monolayers or few layers (FL) flakes. The main focus of this section is on various exfoliation techniques in a liquid media, either intercalation or liquid phase exfoliation (LPE). The choice of precursor, exfoliation method, medium as well as the control of parameters such as time or temperature are crucial. A definite choice of parameters and conditions yields a particular material with specific properties that makes it more suitable for a targeted application. We cover protocols for the graphitic precursors to graphene oxide (GO). This is an important material for a range of applications in biomedicine, energy storage, nanocomposites, etc. Hummers' and modified Hummers' methods are used to make GO that subsequently can be reduced to obtain reduced graphene oxide (RGO) with a variety of strategies. GO flakes are also employed to prepare three-dimensional (3d) low density structures, such as sponges, foams, hydro- or aerogels. The assembly of flakes into 3d structures can provide improved mechanical properties. Aerogels with a highly open structure, with interconnected hierarchical pores, can enhance the accessibility to the whole surface area, as relevant for a number of applications, such as energy storage. The main recipes to yield graphite intercalation compounds (GICs) are also discussed. GICs are suitable precursors for covalent functionalization of graphene, but can also be used for the synthesis of uncharged graphene in solution. Degradation of the molecules intercalated in GICs can be triggered by high temperature treatment or microwave irradiation, creating a gas pressure surge in graphite and exfoliation. Electrochemical exfoliation by applying a voltage in an electrolyte to a graphite electrode can be tuned by varying precursors, electrolytes and potential. Graphite electrodes can be either negatively or positively intercalated to obtain GICs that are subsequently exfoliated. We also discuss the materials that can be amenable to exfoliation, by employing a theoretical data-mining approach. The exfoliation of LMs usually results in a heterogeneous dispersion of flakes with different lateral size and thickness. This is a critical bottleneck for applications, and hinders the full exploitation of GRMs produced by solution processing. The establishment of procedures to control the morphological properties of exfoliated GRMs, which also need to be industrially scalable, is one of the key needs. Section III deals with the processing of flakes. (Ultra)centrifugation techniques have thus far been the most investigated to sort GRMs following ultrasonication, shear mixing, ball milling, microfluidization, and wet-jet milling. It allows sorting by size and thickness. Inks formulated from GRM dispersions can be printed using a number of processes, from inkjet to screen printing. Each technique has specific rheological requirements, as well as geometrical constraints. The solvent choice is critical, not only for the GRM stability, but also in terms of optimizing printing on different substrates, such as glass, Si, plastic, paper, etc, all with different surface energies. Chemical modifications of such substrates is also a key step. Sections IV-VII are devoted to the growth of GRMs on various substrates and their processing after growth to place them on the surface of choice for specific applications. The substrate for graphene growth is a key determinant of the nature and quality of the resultant film. The lattice mismatch between graphene and substrate influences the resulting crystallinity. Growth on insulators, such as SiO2, typically results in films with small crystallites, whereas growth on the close-packed surfaces of metals yields highly crystalline films. Section IV outlines the growth of graphene on SiC substrates. This satisfies the requirements for electronic applications, with well-defined graphene-substrate interface, low trapped impurities and no need for transfer. It also allows graphene structures and devices to be measured directly on the growth substrate. The flatness of the substrate results in graphene with minimal strain and ripples on large areas, allowing spectroscopies and surface science to be performed. We also discuss the surface engineering by intercalation of the resulting graphene, its integration with Si-wafers and the production of nanostructures with the desired shape, with no need for patterning. Section V deals with chemical vapour deposition (CVD) onto various transition metals and on insulators. Growth on Ni results in graphitized polycrystalline films. While the thickness of these films can be optimized by controlling the deposition parameters, such as the type of hydrocarbon precursor and temperature, it is difficult to attain single layer graphene (SLG) across large areas, owing to the simultaneous nucleation/growth and solution/precipitation mechanisms. The differing characteristics of polycrystalline Ni films facilitate the growth of graphitic layers at different rates, resulting in regions with differing numbers of graphitic layers. High-quality films can be grown on Cu. Cu is available in a variety of shapes and forms, such as foils, bulks, foams, thin films on other materials and powders, making it attractive for industrial production of large area graphene films. The push to use CVD graphene in applications has also triggered a research line for the direct growth on insulators. The quality of the resulting films is lower than possible to date on metals, but enough, in terms of transmittance and resistivity, for many applications as described in section V. Transfer technologies are the focus of section VI. CVD synthesis of graphene on metals and bottom up molecular approaches require SLG to be transferred to the final target substrates. To have technological impact, the advances in production of high-quality large-area CVD graphene must be commensurate with those on transfer and placement on the final substrates. This is a prerequisite for most applications, such as touch panels, anticorrosion coatings, transparent electrodes and gas sensors etc. New strategies have improved the transferred graphene quality, making CVD graphene a feasible option for CMOS foundries. Methods based on complete etching of the metal substrate in suitable etchants, typically iron chloride, ammonium persulfate, or hydrogen chloride although reliable, are time- and resource-consuming, with damage to graphene and production of metal and etchant residues. Electrochemical delamination in a low-concentration aqueous solution is an alternative. In this case metallic substrates can be reused. Dry transfer is less detrimental for the SLG quality, enabling a deterministic transfer. There is a large range of layered materials (LMs) beyond graphite. Only few of them have been already exfoliated and fully characterized. Section VII deals with the growth of some of these materials. Amongst them, h-BN, transition metal tri- and di-chalcogenides are of paramount importance. The growth of h-BN is at present considered essential for the development of graphene in (opto) electronic applications, as h-BN is ideal as capping layer or substrate. The interesting optical and electronic properties of TMDs also require the development of scalable methods for their production. Large scale growth using chemical/physical vapour deposition or thermal assisted conversion has been thus far limited to a small set, such as h-BN or some TMDs. Heterostructures could also be directly grown. Section VIII discusses advances in GRM functionalization. A broad range of organic molecules can be anchored to the sp(2) basal plane by reductive functionalization. Negatively charged graphene can be prepared in liquid phase (e.g. via intercalation chemistry or electrochemically) and can react with electrophiles. This can be achieved both in dispersion or on substrate. The functional groups of GO can be further derivatized. Graphene can also be noncovalently functionalized, in particular with polycyclic aromatic hydrocarbons that assemble on the sp(2) carbon network by pi-pi stacking. In the liquid phase, this can enhance the colloidal stability of SLG/FLG. Approaches to achieve noncovalent on-substrate functionalization are also discussed, which can chemically dope graphene. Research efforts to derivatize CNMs are also summarized, as well as novel routes to selectively address defect sites. In dispersion, edges are the most dominant defects and can be covalently modified. This enhances colloidal stability without modifying the graphene basal plane. Basal plane point defects can also be modified, passivated and healed in ultra-high vacuum. The decoration of graphene with metal nanoparticles (NPs) has also received considerable attention, as it allows to exploit synergistic effects between NPs and graphene. Decoration can be either achieved chemically or in the gas phase. All LMs,
|
|
| 3. |
- Dhaka, Veer, et al.
(författare)
-
Aluminum-Induced Photoluminescence Red Shifts in Core-Shell GaAs/AlxGa1-xAs Nanowires
- 2013
-
Ingår i: Nano letters (Print). - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 13:8, s. 3581-3588
-
Tidskriftsartikel (refereegranskat)abstract
- We report a new phenomenon related to Al-induced carrier confinement at the interface in core-shell GaAs/AlxGa1-xAs nanowires grown using metal-organic vapor phase epitaxy with Au as catalyst. All AlxGa1-xAs shells strongly passivated the GaAs nanowires, but surprisingly the peak photoluminescence (PL) position and the intensity from the core were found to be a strong function of Al composition in the shell at low temperatures. Large and systematic red shifts of up to similar to 66 nm and broadening in the PL emission from the GaAs core were observed when the Al composition in the shell exceeded 3%. On the contrary, the phenomenon was observed to be considerably weaker at the room temperature. Cross-sectional transmission electron microscopy reveals Al segregation in the shell along six Al-rich radial bands displaying a 3-fold symmetry. Time-resolved PL measurements suggest the presence of indirect electron-hole transitions at the interface at higher Al composition. We discuss all possibilities including a simple shell-core-shell model using simulations where the density of interface traps increases with the Al content, thus creating a strong local electron confinement. The carrier confinement at the interface is most likely related to Al inhomogeneity and/or Al-induced traps. Our results suggest that a low Al composition in the shell is desirable in order to achieve ideal passivation in GaAs nanowires.
|
|
| 4. |
- Dhaka, Veer, et al.
(författare)
-
Protective capping and surface passivation of III-V nanowires by atomic layer deposition
- 2016
-
Ingår i: AIP Advances. - : American Institute of Physics (AIP). - 2158-3226. ; 6:1
-
Tidskriftsartikel (refereegranskat)abstract
- Low temperature (similar to 200 degrees C) grown atomic layer deposition (ALD) films of AlN, TiN, Al2O3, GaN, and TiO2 were tested for protective capping and surface passivation of bottom-up grown III-V (GaAs and InP) nanowires (NWs), and top-down fabricated InP nanopillars. For as-grown GaAs NWs, only the AlN material passivated the GaAs surface as measured by photoluminescence (PL) at low temperatures (15K), and the best passivation was achieved with a few monolayer thick (2 angstrom) film. For InP NWs, the best passivation (similar to 2x enhancement in room-temperature PL) was achieved with a capping of 2nm thick Al2O3. All other ALD capping layers resulted in a de-passivation effect and possible damage to the InP surface. Top-down fabricated InP nanopillars show similar passivation effects as InP NWs. In particular, capping with a 2 nm thick Al2O3 layer increased the carrier decay time from 251 ps (as-etched nanopillars) to about 525 ps. Tests after six months ageing reveal that the capped nanostructures retain their optical properties. Overall, capping of GaAs and InP NWs with high-k dielectrics AlN and Al2O3 provides moderate surface passivation as well as long term protection from oxidation and environmental attack.
|
|
| 5. |
- Kostamo, Pasi, et al.
(författare)
-
GaAs Medipix2 hybrid pixel detector
- 2008
-
Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier. - 0168-9002 .- 1872-9576. ; 591:1, s. 174-177
-
Tidskriftsartikel (refereegranskat)abstract
- A GaAs Medipix2 hybrid pixel detector based on high purity epitaxial GaAs material was successfully fabricated. The mesa type GaAs sensor with 256×256 pixels and total area of 1.4×1.4 cm2 was made of a 140-μm-thick epitaxial p–i–n structure utilizing reactive ion etching. A final thickness of approximately 110 μm for the all-epitaxial sensor element is achieved by back-thinning procedure. The sensor element is bump bonded to a Medipix2 read-out ASIC. The detector is capable of room temperature spectroscopic operation and it demonstrates the potential of GaAs for high resolution X-ray imaging systems operating at room temperature. This work describes the manufacturing process and electrical properties of the GaAs Medipix2 hybrid detector.
|
|
| 6. |
- Omanakuttan, Giriprasanth, 1989-
(författare)
-
Epitaxial III-V/Si heterojunctions for photonic devices.
- 2019
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Monolithic integration of III-V materials on silicon is of great interest for efficient electronic-photonic integrated devices and multijunction solar cells on silicon. However, defect formation in the heteroepitaxial layers due to lattice mismatch, thermal mismatch, and polarity mismatch makes it a great challenge. In this work, high quality III/V epitaxial layers are realised on Si by epitaxial lateral overgrowth (ELOG) and corrugated epitaxial lateral overgrowth (CELOG) techniques using a hydride vapour phase epitaxy (HVPE) reactor. We demonstrate electroluminescence of multi quantum well structure grown on InP/Si by ELOG and photodiode behaviour of CELOG n-InP/p-Si. Extensive characterization of CELOG InP/Si and CELOG GaxIn1-xP/Si is also the main subject of this thesis. This includes X-ray diffraction, (time resolved) photoluminescence, Raman spectroscopy, cathodoluminescence and scanning and transmission electron microscopies.A wafer-scale InP layer is obtained on a 3” Si wafer via ELOG. The ELOG InP/Si is then used as a substrate to fabricate a multi quantum well LED emitting at 1530 nm. Although the MQWs were grown on InP covering ELOG InP layer and InP layer on the defective seed, rather strong luminescence is observed from the electrically injected MQW on InP/Si. We identify that unsatisfactory surface morphology after MQW growth as the main factor yielding broad emission without leading to stimulated emission. However transparency condition measurements reveal that there is gain in the material indicating the potential of this technique for fabricating lasers on silicon. We need to address also the warping of ELOG/Si due to thermal strain in the device processing.CELOG of InP/Si revealed a highly crystalline InP layer on Si with an abrupt interface free of dislocations despite an 8% lattice mismatch. That misfit dislocations are confined to the interface and do not lead to threading dislocations in the layer is characteristic of the wafer bonded interface. We find the same behaviour in our CELOG InP/Si suggesting that our method acts as epitaxial wafer bonding at growth temperatures. As a proof of concept demonstration, an n-InP/p-Si heterojunction photodiode has been fabricated by CELOG technique with an open circuit voltage of 180 mV, a short circuit current density of 1.89 mA/cm2, internal quantum efficiency of 6% and external quantum efficiency of 4%. Despite low performance, this demonstrates the potential of CELOG method for III-V/Si for solar cell application.The CELOG technique is also used to demonstrate a dislocation free GaxIn1-xP/Si interface. As a pre-study GaInP growth optimization was done on ELOG patterns on GaAs substrate. CELOG GaxIn1-xP/Si exhibits orientation dependent growth and composition anisotropy. Stacking faults are observed in the CELOG GaxIn1-xP/Si interface region but no threading dislocations were observed in the interface. An atomic disorder layer of ~1nm thickness is present at the interface. The CELOG GaxIn1-xP layers are fully relaxed and no strain is observed despite a ~4% lattice mismatch.We conclude that there is room for improvement with ELOG and CELOG processes to obtain device quality III-V layers on Si. We have demonstrated that the CELOG technique is a generic technology that can be extended to realize high quality heterojunctions with mismatched material systems. Thus optimized ELOG and CELOG techniques can facilitate monolithic integration of III-V on Si for silicon photonics and high-efficiency low-cost multijunction solar cells.
|
|
| 7. |
- Reuterskiöld Hedlund, Carl
(författare)
-
Compound semiconductor materials and processing technologies for photonic devices and photonics integration
- 2020
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The advancement of semiconductor optoelectronics relies extensively on materials and processing technologies of ever-increasing sophistication, such as nanometer-range lithography, epitaxial growth methods with monatomic layer control, and anisotropic etching procedures that allows for the precise sculpturing of device features even in the limit of extreme aspect ratios. However, upcoming application needs puts requirements on optimized designs or device performances, e.g. in terms of integration density, power efficiency, modulation bandwidth or spectral response, which call for innovative and refined methodologies. In the present thesis, we investigate a few different device designs or processing schemes that aims for extended performances or manufacturability as compared to presently available technologies. In specific, we study the design and fabrication of transistor-vertical-cavity surface-emitting lasers (T-VCSELs), the regrowth of InP-based driver electronics in the trenches of arrayed spatial light modulators (SLMs), the epitaxial growth and analysis of quantum dot (QD)-based interband photodetectors, the realization of InGaAs/GaAs QD-based single-photon emitters for the 1.55-μm waveband, as well as the fabrication of discrete and silicon-integrated photonic-crystal surface-emitting lasers (PCSELs).The transistor laser, invented at the University of Illinois around 2006, has received considerable interest due to potential major advantages in modulation bandwidth, noise properties and novel functionality as compared to conventional diode lasers. Here we study the design and fabrication of pnp-type 980-nm AlGaAs/InGaAs/GaAs T-VCSELs. Using an epitaxial regrowth process, an intracavity contacting scheme, and an optimized layer design, continuous-wave (CW) result in terms of threshold, output power and temperature performance comparable to conventional VCSELs could be demonstrated. In addition, the collector-current breakdown mechanism was shown to be due to a band-filling effect rather than an intracavity photon absorption process as previously suggested.A subsequent study regards the epitaxial regrowth for the integration of driver electronics with two-dimensional arrays of spatial light modulators (SLMs). The challenge here relies in controlling the regrowth morphology in the restricted areas that limit the SLM array fill factor. It is shown that the orientation of the SLM array with respect to the crystallographic directions is critical for controlling the regrowth7morphology, with mesa alignments along the <001> directions preferable over the <011> directions. Following this scheme, an optimized etch/regrowth process for top-contacted field-effect transistors is demonstrated.Next, we discuss the development of long-wavelength infrared (LWIR; 8-12 μm) detector elements for thermal imaging. Such detectors have traditionally been realized in the mercury-cadmium-telluride system (MCT; high performance but difficult materials properties resulting in high cost) or using AlGaAs/GaAs quantum-well infrared photodetectors (QWIPs; excellent manufacturing properties but compromised performance figures). In this work we consider interband QD photodetectors based on spatially indirect transitions in the In(Ga)Sb QD/InAs type-II system to combine the respective advantages of MCT detectors and QWIPs. An epitaxial growth process is optimized for photo-response in the LWIR regime, and the QD properties were also studied using excitation power-dependent PL and spatially resolved current-voltage spectroscopy using a scanning-tunneling microscope.Quantum dot-based structures were also studied for the development of single-photon telecommunication-wavelength emitters. In this case, InAs QDs were formed in an In-rich InGaAs metamorphic buffer layer grown on GaAs substrate. This resulted in narrow and bright micro-photoluminescence emission lines from isolated QDs around 1.55 μm at low temperature, thereby making the application of such QDs an interesting alternative approach to InAs/InP QDs for the realization of single-photon emitters for telecommunication-wavelength fiber-based quantum networks.Finally, we describe the development of silicon-integrated and discrete photonic-crystal surface-emitting lasers (PCSELs). In the former case, a transfer-print process is used to combine an SOI-based PC structure with an InP-based active region. This results in an ultra-shallow device structure and a buried tunnel-junction configuration is used for current injection. In the latter case, the metal-organic vapor-phase epitaxy (MOVPE) growth conditions are tuned to form perfectly encapsulated cavities in the InP matrix. Low-threshold lasing is thereby obtained from optical pumping.
|
|
| 8. |
- Sanatinia, Reza, et al.
(författare)
-
Wafer-Scale Self-Organized InP Nanopillars with Controlled Orientation for Photovoltaic Devices
- 2015
-
Ingår i: Nanotechnology. - : Institute of Physics Publishing (IOPP). - 0957-4484 .- 1361-6528. ; 26:41
-
Tidskriftsartikel (refereegranskat)abstract
- A unique wafer-scale self-organization process for generation of InP nanopillars is demonstrated, which is based on maskless ion-beam etching (IBE) of InP developed to obtain the nanopillars, where the height, shape, and orientation of the nanopillars can be varied by controlling the processing parameters. The fabricated InP nanopillars exhibit broadband suppression of the reflectance, 'black InP,' a property useful for solar cells. The realization of a conformal p-n junction for carrier collection, in the fabricated solar cells, is achieved by a metalorganic vapor phase epitaxy (MOVPE) overgrowth step on the fabricated pillars. The conformal overgrowth retains the broadband anti-reflection property of the InP nanopillars, indicating the feasibility of this technology for solar cells. Surface passivation of the formed InP nanopillars using sulfur-oleylamine solution resulted in improved solar-cell characteristics. An open-circuit voltage of 0.71 V and an increase of 0.13 V compared to the unpassivated device were achieved.
|
|
| 9. |
- Sundgren, Petrus
(författare)
-
Development of 1.3-μm GaAs-based vertical-cavity surface-emitting lasers
- 2005
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Long-wavelength vertical-cavity surface-emitting lasers (VCSELs) are desirable as low-cost sources for optical metropolitan-area and access networks. In the development of 1.3-µm VCSELs, most attention today is given to monolithic GaAs-based solutions, although no established active material exists in this wavelength region. This thesis investigates the possibility of reaching the 1.3-µm telecom wavelength window using GaInNAs quantum wells (QWs) or 1.2-µm InGaAs QWs in conjunction with negative gain-cavity detuning in VCSELs. The work includes metal-organic vapor-phase epitaxy and characterization of InGaAs and GaInNAs QWs, realization of 1.3-µm InGaAs VCSELs as well as elements of optimization and analysis of such lasers. The evaluation of GaInNAs and InGaAs QWs has been performed using a number of characterization methods such as photoluminescence (PL), high-resolution x-ray diffraction, secondary-ion mass spectroscopy, and atomic-force microscopy as well as fabrication and evaluation of broad-area lasers (BALs). Both performance and growth reproducibility of GaInNAs QWs are considered and could be improved by using high V/III ratios. Nontrivial relations between PL and laser performance are pointed out and the technologically important but problematic combination of AlGaAs and GaInNAs in the same epitaxial structure is studied. Parallel to the work on GaInNAs, the possibility of extending the wavelength of InGaAs QWs towards 1.3 µm has been investigated. Generally better luminescence efficiency and laser performance are obtained for InGaAs than for GaInNAs QWs, but the gain-peak wavelength for InGaAs QWs is presently limited to about 1.24 µm due to strain-induced degradation. In this work the InGaAs QW growth is optimized for long wavelength and high luminescence. It is demonstrated that multiple QW structures can be grown with strain similar to that of single QWs, which is interesting for VCSEL applications. Record BALs with two to five InGaAs/GaAs QWs have low threshold current densities, 70 A/cm2 per QW at 1.24 µm. The main advantage of InGaAs QWs compared to GaInNAs QWs is that they represent a better-known material system with less complex and more stable growth. However, InGaAs QWs > 1.2 µm are on the verge of strain relaxation, and the possible consequences for laser production and reliability have to be considered. Using 1.2-µm InGaAs QWs, high-performance 1.3-µm VCSELs were achieved by negative gain-cavity detuning. Dynamic performance and surface reliefs to improve the single-mode operation have been investigated. The VCSELs have excellent high-temperature performance due to a smaller spectral distance between the gain-peak and the laser mode at elevated temperature. More specifically, a 1.27-µm single-mode device showed maximum output powers of 1.1 and 0.5 mW at 20 and 140ºC, which is state-of-the-art for GaAs-based long-wavelength VCSELs. In all, two methods for 1.3-µm GaAs-based VCSELs, GaInNAs and InGaAs QWs, have been investigated. GaInNAs is a difficult material but is still promising and several companies have predicted a near-future market introduction. However, the growth of GaInNAs is both complex and sensitive to growth fluctuations. On the other hand, gain-cavity detuned InGaAs-QW VCSELs show state-of-the-art performance at 1260-1290 nm with straightforward growth and processing. The devices exhibit good static and dynamic performance, and preliminary reliability tests indicate that there is no intrinsic problem. Both approaches are promising for application in real-world optical networks and deserve further attention.
|
|
