Jacques Beauvais

Low-energy ion-implantation-induced quantum-well intermixing

In this paper, we present the attractive characteristics of low-energy ion-implantation-induced quantum-well intermixing of InP-based heterostructures. We demonstrate that this method can fulfil a list of requirements related to the fabrication of complex optoelectronic devices with a spatial control of the bandgap profile. First, we have fabricated high-quality discrete blueshifted laser diodes to verify the capability of low-energy ion implantation for the controlled modification of bandgap profiles in the absence of thermal shift. Based on this result, intracavity electroabsorption modulators monolithically integrated with laser devices were fabricated, for the first time, using this postgrowth technique. We have also fabricated monolithic six-channel multiple-wavelength laser diode chips using a novel one-step ion implantation masking process. Finally, we also present the results obtained with very low-energy (below 20 keV) ion implantation for the development of one-dimensional and zero-dimensional quantum confined structures.

A Nanodamascene Process for Advanced Single-Electron Transistor Fabrication

A process design based on a nanowire structure is demonstrated with the fabrication of metallic single-electron transistors. The method is capable of subattofarad resolution resulting in transistors that exhibited Coulomb blockade up to approximately 430 K. An analysis showed that these devices have sufficient operational margin to sustain process fluctuations and still operate within the temperature limits of conventional silicon field effect transistors.

BLUESHIFTING OF INGAASP/INP LASER DIODES BY LOW-ENERGY ION IMPLANTATION

A new method based on low-energy implantation is presented for the fabrication of laser diodes with shifted emission wavelength. The laser diodes are based on InGaAsP/InGaAs/InP material, with compressively strained active layers. Low-energy implantation (18 keV As+) is used to generate vacancies near the surface of an incomplete laser structure, for which the epitaxial growth was interrupted 45 nm above the active layers of the device. The vacancies are subsequently diffused through the quantum wells by rapid thermal annealing. This diffusion causes a local intermixing of atoms at the interfaces of the active layers, which induces an increase of the band gap energy. The implantation/anneal process can be repeated several times to increase the amount of intermixing, thereby further shifting the emission wavelength. Once this process is completed, the upper optical confinement layer of the structure is overgrown using chemical beam epitaxy. Operational lasers with blueshifts as large as 35 nm were obtained.

Blueshifting of InGaAsP-InP laser diodes using a low-energy ion-implantation technique: comparison between strained and lattice-matched quantum-well structures

Blueshifted InGaAsP-InGaAs-InP laser diodes have been fabricated using a technique that includes a low-energy ion implantation, used to generate point defects near the surface of the structure, followed by a thermal anneal which causes the diffusion of these defects through the quantum wells (QWs). This diffusion of point defects induces a local intermixing of atoms in the QWs and barriers, which results in a decrease in the emission wavelength of the devices. Results obtained with strained and lattice-matched QW structures are compared. For lattice-matched structures, electroluminescence wavelength shifts as large as 76 nm were obtained. Strained QW structures presented a much smaller blueshift (/spl ap/10 nm). In both cases, we observed no significant change of the threshold current caused by the intermixing process.

Room Temperature Single-Electron Transistor Featuring Gate-Enhanced on -State Current

A single-electron transistor operating at room temperature was successfully fabricated by an improved nanodamascene process. It consists in a gated titanium nanowire interspersed by two very closely spaced tunnel junctions constituting a Coulomb island. The improvement in the process concerns the presence of an individual control gate close to the island, paving the way toward the fabrication of single-electron circuits. Moreover, a final oxidizing plasma treatment was used to tune the tunnel junction capacitances and, thus, the device operating temperature. As expected, electrical characteristics showed Coulomb blockade at room temperature, with an unexpectedly high on-state current.

Method for fabricating submicron silicide structures on silicon using a resistless electron beam lithography process

A novel resistless lithography process using a conventional electron beam system is presented. Metallic lines with widths of less than 50 nm were produced on silicon substrates. The process is based on localized heating with a focused electron beam of thin platinum layers deposited on silicon. It is demonstrated that silicide formation occurs at the Pt-Si interface. By using a dilute solution of aqua regia, it is possible to obtain a sufficient difference in etch rates between exposed and unexposed regions of the platinum thin film to selectively remove only the unexposed areas.

Improved characteristics of a terahertz set-up built with an emitter and a detector made on proton-bombarded GaAs photoconductive materials

We report the coherent generation and detection of terahertz radiation from antenna-type devices made by using proton-bombarded GaAs photoconductive materials. Our combined emitter/detector set-up allows us to obtain a large bandwidth going from 0.1 up to 2 THz. We compare the performance of antenna emitters fabricated using mono- and multi-energy proton implantation in semi-insulating GaAs. Improved emission of terahertz radiation with a comparable bandwidth has been obtained using multi-energy proton implantation. Our results show that creating more defects in the optical absorption region gives rise to higher damage threshold biasing and larger saturation optical pumping power levels.

Pulsed photoconductive antenna terahertz sources made on ion-implanted GaAs substrates

In this work we show that improved performances of terahertz emitters can be obtained using an ion implantation process. Our photoconductive materials consist of high-resistivity GaAs substrates. Terahertz pulses are generated by exciting our devices with ultrashort near-infrared laser pulses. The ion implantation introduces non-radiative centres, which reduce the carrier lifetime in GaAs. The presence of the charged defects also induces a redistribution of the electric field between the antenna electrodes. This effect has a huge influence on the amplitude of the radiated terahertz field. Results obtained as a function of the laser excitation power are discussed and a comparison of the performance of these devices with a conventional antenna-type emitter is given.

Nano patterning on optical fiber and laser diode facet with dry resist

Semiconductor micro and nanofabrication lithography techniques for application in microelectronics as well as in micromechanics and optoelectronics can gain significantly from using a dry resist process, since it enables the deposition of a very uniform lithographically sensitive layer on a potentially very small area. This would otherwise be extremely difficult to achieve by using a traditional spin coated resist, such as poly(methylmethacrylate) (PMMA). We demonstrate the use of an electron sensitive sterol based evaporated electron beam resist to fabricate high-resolution features (down to 100 nm) on a small surface area. This electron beam resist has a sensitivity comparable to PMMA and is deposited using a simple thermal evaporation. Two practical applications are explored: first, this resist makes it possible to fabricate a Fresnel zone plate lens on the tip of an optical fiber in order to demonstrate the principle and the potential of highly efficient coupling of diode laser emission into the fiber...

A novel fabrication technique for multiple-wavelength photonic-integrated devices in InGaAs-InGaAsP laser heterostructures

We report the fabrication of multiple wavelength chips in InGaAs-InGaAsP laser structure using a novel ion implantation induced quantum-well (QW) intermixing technique. This technique first consists of using a gray mask photolithography and reactive ion etching process to create a SiO/sub 2/ implant mask with variable thickness on the sample. This is followed by a single 360-keV phosphorus ion implantation at a dose of 1/spl times/10/sup 14/ cm/sup -2/ at 200/spl deg/C, which creates different amounts of point defects in the sample depending on the local thickness of the SiO/sub 2/ mask. A subsequent thermal annealing step induces QW intermixing through the diffusion of the point defects across the structure. With this technique, we have successfully fabricated 10-channel multiple wavelength laser diodes, with lasing wavelength spreading over 85 nm (between 1.47 and 1.55 /spl mu/m), monolithically integrated on a single chip. Only a limited increase of threshold current density of 17% (i.e., from 1.2 to 1.4 kA/cm/sup 2/), has been observed between the least intermixed and the most intermixed lasers.