Organogelator-Templated Synthesis of Hollow TiO2 Nanotubes

Gregory Khitrov
2000 MRS bulletin  
Researchers at Sandia National Laboratories working with Cielo Communications have developed a 1.3-µm electrically pumped vertical cavity surface emitting laser (VCSEL) grown on gallium arsenide. This VCSEL is made mostly from stacks of layers of semiconductor materials common in shorter-wavelength lasers-aluminum gallium arsenide and gallium arsenide. The research team added to this structure a small amount of the material indium gallium arsenide nitride (InGaAsN), which was initially
more » ... by Hitachi of Japan in the mid-1990s. The researchers grew the structure by molecular-beam epitaxy in a single growth run. They reported at the Device Research Conference, held June 19-21 in Denver, that the top and bottom n-doped distributed Bragg reflector (DBR) mirrors contain 28 and 33 periods, respectively, and are fabricated from alternating quarterwavelength layers of Al 0.94 Ga 0.06 As and GaAs. They said that the relatively low doping in the Si-doped mirrors reduces the free-carrier absorption. They placed a tunnel diode at a node of the optical field in the GaAs layer nearest the cavity in the upper mirror to provide hole injection into the active region, and they oxidized the AlAs low-index layers adjacent to the optical cavity for electrical and optical oxide aperture confinement. They used an rf plasma nitrogen source to grow two 6-nmthick In 0.34 Ga 0.66 As 0.99 N 0.01 quantum wells (QW), contained in the optical cavity. As reported at the conference and in an article to appear in an upcoming issue of Electronic Letters, John Klem of Sandia and his colleagues achieved a single-mode output power of 60 µW at 20°C and continuous-wave operation up to 55°C. Operating at 1.3 µm (a wavelength of low dispersion in single-mode optical fiber) enables the VCSEL to be used for a wide variety of high-speed, mediumdistance data-communication applications, including Internet infrastructure, gigabit Ethernet, and fiber to the home. Peter Esherick, manager of the Compound Semiconductor Materials and Processes Department at Sandia, said, "We expect there to be great excitement over the device-fueled by the rapid expansion of Internet use and craving for faster Internet access.
doi:10.1557/mrs2000.133 fatcat:ru3n5vxex5f2bpaup7keg7x2qq