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Microstructure and interfacial properties of laterally oxidized Al{sub x}Ga{sub 1{minus}x}As

Description: Oxidation of high Al content Al{sub x}Ga{sub 1-x}As has received much attention due to its use in oxide-aperture, vertical-cavity surface emitting lasers (VCSELs) and for passivating AlAs against environmental degradation. We have recently identified the spinel, gamma phase of Al{sub 2}O{sub 3} in layers laterally oxidized in steam at 450 C for x=0.98 & 0.92 and have seen evidence for an amorphous precursor to the gamma phase. At the interface with the unoxidized Al{sub x}Ga{sub 1-x}As, an {approximately}17nm amorphous phase remains which could account for the excellent electrical properties of oxide-confined VCSELs and help reduce stress concentrations at the oxide terminus.
Date: December 31, 1996
Creator: Twesten, R.D.; Follstaedt, D.M. & Choquette, K.D.
Partner: UNT Libraries Government Documents Department

InAlGaP vertical cavity surface emitting lasers (VCSELs): Processing and performance

Description: (Al{sub y}Ga{sub 1{minus}y}){sup 1{minus}x}In{sub x}P semiconductor alloys lattice-matched to GaAs are widely used in visible optoelectronic devices. One of the most recent developments in this area is the AlGaInP-based red vertical cavity surface emitting laser (VCSEL). These lasers, which employ AlGaInP active regions and AlGaAs distributed Bragg reflectors (DBRs), have demonstrated continuous-wave (CW) lasing over the 630--690 nm region of the spectrum. Applications for these lasers include plastic fiber data communications, laser printing and bar code scanning. In this paper, the authors present an overview of recent developments in the processing and performance of AlGaInP based VCSELs. This overview will include a review of the general heterostructure designs that have been employed, as well as the performance of lasers fabricated by both ion implantation and selective oxidation.
Date: June 1, 1997
Creator: Crawford, M.H.; Choquette, K.D.; Hickman, R.J. & Geib, K.M.
Partner: UNT Libraries Government Documents Department

Fabrication issues of oxide-confined VCSELs

Description: To insert high-performance oxide-confined vertical-cavity surface- emitting lasers (VCSELs) into the manufacturing arena, we have examined the critical parameters that must be controlled to establish a repeatable and uniform wet thermal oxidation process for AlGaAs. These parameters include the AlAs mole fraction, sample temperature, carrier gas flow, and bubbler water temperature. Knowledge of these parameters has enable the compilation of oxidation rate data for AlGaAs which exhibits an Arrhenius rate dependence. The compositionally dependent activation energies for Al{sub x}Ga{sub 1-x}As layers of x=1.00, 0.98, and 0.92 are found to be 1.24, 1.75, and 1.88 eV, respectively. 7 figs, 1 tab, 14 refs.
Date: April 1, 1997
Creator: Geib, K.M.; Choquette, K.D.; Hou, H.Q. & Hammons, B.E.
Partner: UNT Libraries Government Documents Department

Microstructure and interface properties of laterally oxidized Al{sub x}Ga{sub 1{minus}x}As

Description: The selective and passivating nature of the oxidation of high Al content AlGaAs has been used to create high-performance vertical-cavity surface emitting lasers (VCSELs). This is accomplished by using the fact the Ga content of a AlGaAs film will drastically affect its oxidation rate, allowing the strategic placement of high Al content layers in the structure; these are then oxidized to form current-confining and optical-mode-defining apertures. Here, the microstructure and interface properties of Al{sub x}Ga{sub 1{minus}x}As materials that have been laterally oxidized in wet N{sub 2} for several compositions (x = 0.80, 0.82...1.00) and temperatures (360 C to 450 C) have been studied. The microstructure is found to be relatively insensitive to composition and oxidation temperature. The oxidation forms an amorphous solid solution (Al{sub x}Ga{sub 1{minus}x}){sub 2}O{sub 3} that transforms to polycrystalline, {gamma}-(Al{sub x}Ga{sub 1{minus}x}){sub 2}O{sub 3} is formed via post oxidation annealing of the oxide. The level of hydrogen present in the oxidized layers is 1.1 {times} 10{sup 21} cm{sup {minus}3}, which is too low for the amorphous phase observed to be a hydroxide rather than an oxide. The amount of As in the layer is reduced to <2 atm%, and no As precipitates are observed. The (Al{sub x}Ga{sub 1{minus}x}){sub 2}O{sub 3}/GaAs interface is abrupt, but prolonged oxidation will cause the GaAs to oxidize at the internal interfaces. The reaction front between the oxidized and the unoxidized Al{sub x}Ga{sub 1{minus}x}As has a 10 to 20nm-wide amorphous zone that shows a different contrast than the remainder of the amorphous oxide and is stable under electron irradiation.
Date: December 31, 1996
Creator: Twesten, R.D.; Follstaedt, D.M. & Choquette, K.D.
Partner: UNT Libraries Government Documents Department

Fabrication, Packaging, and Performance of VCSELs and Photodetectors for Space Applications

Description: Optocouplers are used for a variety of applications aboard spacecraft including electrical isolation, switching and power transfer. Commercially available light emitting diode (LED)-based optocouplers have experienced severe degradation of light output due to extensive displacement damage occurring in the semiconductor lattice caused by energetic proton bombardment. A new optocoupler has been designed and fabricated which utilizes vertical cavity surface emitting laser (VCSEL) and resonant cavity photodetector (RCPD) technologies for the optocoupler emitter and detector, respectively. Linear arrays of selectively oxidized GaAs/AlGaAs VCSELS and RCPDS, each designed to operate at a wavelength of 850nm, were fabricated using an airbridge contacting scheme. The airbridged contacts were designed to improve packaging yields and device reliability by eliminating the use of a polyimide planarizing layer which provided poor adhesion to the bond pad metallization. Details of the airbridged optocoupler fabrication process are reported. Discrete VCSEL and RCPD devices were characterized at temperatures between {minus}100 to 100 C. Devices were packaged in a face-to-face configuration to form a single channel optocoupler and its performance was evaluated under conditions of high-energy proton bombardment.
Date: March 9, 1999
Creator: Armendariz, M.G.; Briggs, R.D.; Choquette, K.D.; Geib, K.M. & Serkland, D.K.
Partner: UNT Libraries Government Documents Department

Many-body effects in a semiconductor microcavity laser: Experiment and theory

Description: Many-body effects are observed in the threshold properties of selectively oxidized vertical-cavity surface-emitting lasers. These microcavity lasers represent the state-of-the-art in low threshold semiconductor injection lasers.
Date: July 1996
Creator: Crawford, M. H.; Choquette, K. D.; Chow, W. W. & Schneider, R. P., Jr.
Partner: UNT Libraries Government Documents Department

Properties of small-aperture selectively oxidized VCSELs

Description: We report an analysis of the size dependence of VCSEL threshold which agrees with experimental results. The increasing threshold current density of small area VCSELs arises from both increasing threshold gain and increasing leakage current.
Date: December 31, 1996
Creator: Choquette, K.D.; Chow, W.W.; Hadley, G.R.; Hou, H.Q. & Geib, K.M.
Partner: UNT Libraries Government Documents Department

Engineering high-performance vertical cavity lasers

Description: The cw and high-speed performance of vertical cavity surface emitting laser diodes (VCSELs) are affected by both electrical and optical issues arising from the geometry and fabrication of these devices. Structures with low resistance semiconductor mirrors and Al-oxide confinement layers address these issues and have produced record performance including 50% power conversion efficiency and modulation bandwidths up to 20 GHz at small bias currents.
Date: December 31, 1996
Creator: Lear, K.L.; Hou, H.Q.; Hietala, V.M.; Choquette, K.D. & Schneider, R.P. Jr.
Partner: UNT Libraries Government Documents Department

Growth of vertical-cavity surface emitting lasers by metalorganic vapor phase epitaxy

Description: We present growth and characterization of visible and near-infrared vertical-cavity surface emitting lasers (VCSELs) grown by metalorganic vapor phase epitaxy. Discussions on the growth issue of VCSEL materials include growth rate and composition control using an {ital in}{ital situ} normal-incidence reflectometer, comprehensive p- and n-type doping study in AlGaAs by CCl{sub 4} and Si{sub 2}H{sub 6} over the entire composition range, and optimization of ultra-high material uniformity. We also demonstrate our recent achievements of all-AlGaAs VCSELs which include the first room-temperature continuous- wave demonstration of 700-nm red VCSELs and high-efficiency and low- threshold voltage 850-nm VCSELs.
Date: October 1, 1996
Creator: Hou, H.Q.; Hammons, B.E.; Crawford, M.H.; Lear, K.L. & Choquette, K.D.
Partner: UNT Libraries Government Documents Department

Selectively oxidized vertical-cavity laser performance and technology

Description: The authors discuss revolutionary performance advances in selectively oxidized vertical-cavity surface emitting lasers (VCSELs), which have enabled low operating power laser diodes appropriate for aerospace applications. Incorporating buried oxide layers converted from AIGaAs layers within the laser cavity produces enhanced optical and electrical confinement enabling superior laser performance, such as high efficiency and modulation bandwidth. VCSELs also shown to be viable over varied environmental conditions such as ambient temperature and ionized radiation. The development of novel VCSEL technologies for advanced system applications is also described. Two dimensional individually addressable VCSEL arrays exhibit uniform threshold and operating characteristics. Bottom emitting 850 nm VCSEL arrays fabricated using wafer fusion are also reported.
Date: February 1, 1998
Creator: Choquette, K.D.; Hou, H.Q.; Geib, K.M. & Hammons, B.E.
Partner: UNT Libraries Government Documents Department

Uniformity and performance of selectively oxidized VCSEL arrays

Description: The authors report the uniformity characteristics of low threshold 1,060 nm and high power 850 nm 8 x 8 individually addressable oxide-confined VCSEL arrays. Uniformity of lasing thresholds and operating characteristics are described, as well as thermal issues for 2-dimensional laser arrays.
Date: January 1, 1998
Creator: Geib, K.M.; Choquette, K.D.; Hou, H.Q. & Hammons, B.E.
Partner: UNT Libraries Government Documents Department

Selective oxidation of buried AlGaAs for fabrication of vertical-cavity lasers

Description: The authors discuss the selective conversion of buried layers of AlGaAs to a stable oxide and the implementation of this oxide into high performance vertical-cavity surface emitting lasers (VCSELs). The rate of lateral oxidation is shown to be linear with an Arrhenius temperature dependence. The measured activation energies vary with Al composition, providing a high degree of oxidation selectivity between AlGaAs alloys. Thus buried oxide layers can be selectively fabricated within the VCSEL through small compositional variations in the AlGaAs layers. The oxidation of AlGaAs alloys, as opposed to AlAs, is found to provide robust processing of reliable lasers. The insulating and low refractive index oxide provides enhanced electrical and optical confinement for ultralow threshold currents in oxide-apertured VCSELs.
Date: June 1, 1996
Creator: Choquette, K.D.; Geib, K.M.; Chui, H.C.; Hou, H.Q. & Hull, R.
Partner: UNT Libraries Government Documents Department

Mirror reflectivity and doping considerations for high performance oxide-confined vertical cavity lasers

Description: We report the effects of mirror doping and reflectivity in 850 and 780 nm oxide-confined vertical cavity surface emitting lasers. Decreased doping throughout the n-type mirror produces significantly higher quantum efficiency, while the optimum reflectivity is dependent upon the gain material.
Date: January 1, 1996
Creator: Geib, K.M.; Choquette, K.D.; Chui, H.C.; Hou, H.Q. & Hammons, B.E.
Partner: UNT Libraries Government Documents Department

Dynamic Range of Vertical Cavity Surface Emitting Lasers in Multimode Links

Description: The authors report spurious free dynamic range measurements of 850nm vertical cavity surface emitting lasers in short multimode links for radio frequency communication. For a 27m fiber link, the dynamic range at optimal bias was greater than 95dB-Hz{sup 2/3} for modulation frequencies between 1 and 5.5 GHz, which exceeds the requirements for antenna remoting in microcellular networks. In a free space link, they have measured the highest dynamic range in an 850nm vertical cavity surface emitting laser of 113dB-Hz{sup 2/3} at 900MHz. We have also investigated the effects of modal noise and differential mode delay on the dynamic range for longer lengths of fiber.
Date: July 7, 1999
Creator: Lee, H.L.T.; Dalal, R.V.; Ram, R.J. & Choquette, K.D.
Partner: UNT Libraries Government Documents Department

High efficiency oxide confined vertical cavity surface emitting lasers

Description: Optical loss is studied in devices with either two aligned apertures above and below the active region or with a single effective aperture above the active region. The latter exhibit slope efficiencies of up to 1 W/A.
Date: August 1, 1995
Creator: Lear, K. L.; Kilcoyne, S. P.; Schneider, R. P., Jr.; Choquette, K. D. & Hadley, G. R.
Partner: UNT Libraries Government Documents Department

Comprehensive numerical model for cw vertical-cavity surface-emitting lasers

Description: The authors present a comprehensive numerical model for vertical-cavity surface-emitting lasers that includes all major processes effecting cw operation of axisymmetric devices. In particular, the model includes a description of the 2D transport of electrons and holes through the cladding layers to the quantum well(s), diffusion and recombination processes of these carriers within the wells, the 2D transport of heat throughout the device, and a multi-lateral-mode effective index optical model. The optical gain acquired by photons traversing the quantum wells is computed including the effects of strained band structure and quantum confinement. They employ the model to predict the behavior of higher-order lateral modes in proton-implanted devices, and to provide an understanding of index-guiding in devices fabricated using selective oxidation.
Date: March 1, 1995
Creator: Hadley, G.R.; Lear, K.L.; Warren, M.E.; Choquette, K.D.; Scott, J.W. & Corzine, S.W.
Partner: UNT Libraries Government Documents Department

Highly uniform and reproducible visible to near-infrared vertical-cavity surface-emitting lasers grown by MOVPE

Description: The authors present the growth and characterization of vertical-cavity surface emitting lasers (VCSELs) from visible to near-infrared wavelength grown by metalorganic vapor phase epitaxy. Discussions on the growth issue of VCSEL materials include the control on growth rate and composition using an in situ normal-incidence reflectometer, optimization of ultra-high material uniformity, and comprehensive p- and n-type doping study in AlGaAs by CCl{sub 4} and Si{sub 2}H{sub 6} over the entire Al composition range. They will also demonstrate the recent achievements of selectively-oxidized VCSELs which include the first room-temperature continuous-wave demonstration of all-AlGaAs 700-nm red VCSELs, high-performance n-side up 850-nm VCSELs, and low threshold current and low-threshold voltage 1.06 {micro}m VCSELs using InGaAs/GaAsP strain-compensated quantum wells.
Date: May 1, 1997
Creator: Hou, H.Q.; Choquette, K.D.; Hammons, B.E.; Breiland, W.G.; Crawford, M.H. & Lear, K.L.
Partner: UNT Libraries Government Documents Department

Threshold properties of a microcavity laser with submicroampere threshold current

Description: We report the threshold characteristics of small oxide-confined vertical-cavity surface emitting lasers. Abrupt threshold transitions 105 times the spontaneous emission background are obtained at injection currents as low as 470 nanoampere.
Date: February 1, 1996
Creator: Choquette, K.D.; Hou, H.Q.; Lear, K.L.; Chow, W.W.; Mar, A.; Geib, K.M. et al.
Partner: UNT Libraries Government Documents Department

Comparison of Techniques for Bonding VCSELs Directly to Ics

Description: This paper reports the successful bonding of 8 x 8 and 4 x 4 VCSEL arrays to Si CMOS and GaAs MESFET integrated circuits and to GaAs substrates. Three different bonding techniques are demonstrated and their electrical, optical and mechanical characteristics are compared. All three techniques remove the substrate from the VCSEL wafer, leaving individual VCSELs bonded directly to locations within the integrated circuit.
Date: March 26, 1999
Creator: Choquette, K.D.; Geib, K.M.; Hayes, E.M. Wilmsen, C.W.; Hou, H.Q. & Pu, R.
Partner: UNT Libraries Government Documents Department

Proton Irradiation Effects in Oxide-Confined Vertical Cavity Surface Emitting Laser (VCSEL) Diodes

Description: Recent space experience has shown that the use of commercial optocouplers can be problematic in spacecraft, such as TOPEX/Poseidon, that must operate in significant radiation environments. Radiation--induced failures of these devices have been observed in space and have been further documented at similar radiation doses in the laboratory. The ubiquitous use of optocouplers in spacecraft systems for a variety of applications, such as electrical isolation, switching and power transfer, is indicative of the need for optocouplers that can withstand the space radiation environment. In addition, the distributed nature of their use implies that it is not particularly desirable to shield optocouplers for use in radiation environments. Thus, it will be important for the space community to have access to radiation hardened/tolerant optocouplers. For many microelectronic and photonic devices, it is difficult to achieve radiation hardness without sacrificing performance. However, in the case of optocouplers, one should be able to achieve both superior radiation hardness and performance for such characteristics as switching speed, current transfer ratio (CTR), minimum power usage and array power transfer, if standard light emitting diodes (LEDs), such as those in the commercial optocouplers mentioned above, are avoided, and VCSELs are employed as the emitter portion of the optocoupler. The physical configuration of VCSELs allows one to achieve parallel use of an array of devices and construct a multichannel optocoupler in the standard fashion with the emitters and detectors looking at each other. In addition, detectors similar in structure to the VCSELs can be fabricated which allows bidirectional functionality of the optocoupler. Recent discussions suggest that VCSELs will enjoy widespread applications in the telecommunications and data transfer fields.
Date: March 11, 1999
Creator: Armendariz, M.G.; Barnes, C.E.; Choquette, K.D.; Guertin, S.; Hash, G.L.; Schwank, J.R. et al.
Partner: UNT Libraries Government Documents Department

High-speed modulation of vertical cavity surface emitting lasers

Description: This report summarizes work on the development of high-speed vertical cavity surface emitting lasers (VCSELs) for multi-gigabit per second optical data communications applications (LDRD case number 3506.010). The program resulted in VCSELs that operate with an electrical bandwidth of 20 GHz along with a simultaneous conversion efficiency (DC to light) of about 20%. To achieve the large electrical bandwidth, conventional VCSELs were appropriately modified to reduce electrical parasitics and adapted for microwave probing for high-speed operation.
Date: March 1, 1998
Creator: Hietala, V.M.; Armendariz, M.G.; Choquette, K.D. & Lear, K.L.
Partner: UNT Libraries Government Documents Department

Combined photonics and MEMs function demonstration

Description: The authors have recently demonstrated two prototypes where photonics and microelectromechanical system (MEMs) technologies have been integrated to show proof-of-principle functionality for weapon surety functions. These activities are part of a program which is exploring the miniaturization of electromechanical components for making weapon systems safer. Such miniaturization can lead to a low-cost, small, high-performance ``systems-on-a-chip``, and have many applications ranging from advanced military systems to large-volume commercial markets like automobiles, rf or land-based communications networks and equipment, or commercial electronics. One of the key challenges in realization of the microsystem is integration of several technologies including digital electronics; analog and rf electronics, optoelectronics (light emitting and detecting devices and circuits), sensors and actuators, and advanced packaging technologies. In this work the authors describe efforts in integrating MEMs and photonic functions and the fabrication constraints on both system components. Here, they discuss two examples of integration of MEMs and a photonic device. In the first instance, a MEMs locking device pin is driven by a voltage generated by photovoltaic cells connected in series, which are driven by a laser. In the second case, a VCSEL emitting at 1.06 {micro}m is packaged together with a metallized MEMs shutter. By appropriate alignment to the opening in the shutter, the VCSEL is turned on and off by the movement of the Si chopper wheel.
Date: January 1, 1998
Creator: Blum, O.; Warren, M.E.; Hou, H.Q.; Choquette, K.D.; Rogers, M.S.; Sniegowski, J.J. et al.
Partner: UNT Libraries Government Documents Department