Selective Area Intermixing Research Articles

Design of low-threshold photonic-crystal surface-emitting lasers with confined gain regions by using selective area intermixing

Photonic-crystal surface-emitting lasers have many promising properties over traditional semiconductor lasers and are regarded as the next-generation laser sources. However, the minimum achievable lasing threshold of PCSELs is still several times larger than that of VCSELs, and limiting its applications especially if the required power is small. Here, we propose a new design that reduces the gain region in the lateral plane by using selective quantum-well intermixing to reduce the threshold current of PCSELs. By performing theoretical calculations, we confirmed that the threshold current can be lowered by a factor of two to three while keeping the PCSEL’s advantage of small divergence angle.

Selective area intermixing of III–V quantum-dot lasers grown on silicon with two wavelength lasing emissions

The ability to tailor the bandgap of III–V compound semiconductors spatially, across the wafer is highly desirable for monolithically integrating photonic components with multi-functions. Using rapid thermal annealing with SiO2 and TiO2 capping layers as a selective area intermixing technique, we have demonstrated selective area bandgap tuning of III–V quantum dot (QD) material on a silicon (Si) substrate. Electrically pumped InAs/GaAs QD lasers directly grown on Si with dual-wavelength lasing emissions of 1275 and 1313 nm have been fabricated by this technique. This result indicates that the selective area intermixing technique can potentially be used in optical integrated circuits for Si photonics.

Monolithically integrated InGaAsP multiple quantum well tunable laser diode for integrated optic surface plasmon resonance sensing

We demonstrate an InGaAsP multiple quantum well tunable laser diode consisting of two gain sections with different bandgap energy levels. This tunable laser is used as a probing source for an optical sensor that makes use of surface plasmon resonance (SPR). Lasers fabricated on a single monolithic substrate can have widely differing output wavelengths. Therefore, by controlling the extent of the intermixing, the bandgap energy of the material can be accurately tuned over a broad spectral range. The regions of different bandgap energies are achieved using selective area intermixing of the multiple quantum wells, through impurity-free vacancy-induced disordering. By varying the current combination that was injected to each section, the laser wavelength can be effortlessly tuned from 1538 to 1578 nm with relatively constant output power. The free spectral range of the tunable laser is found to be 0.25 nm. This tunable laser was launched into an optical SPR sensor head that was fabricated on an inverted rib dielectric waveguide to provide an input light source for the SPR sensor. The average sensitivity of the SPR sensor devices was determined to be S = 334 nm RIU − 1.

Ultraviolet laser quantum well intermixing based prototyping of bandgap tuned heterostructures for the fabrication of superluminescent diodes

The ultraviolet laser induced quantum well intermixing process has been investigated for prototyping of multiple bandgap quantum well (QW) wafers designed for the fabrication of superluminescent diodes (SLDs). The process takes advantage of a krypton fluoride excimer laser (λ=248nm) that by irradiating an InP layer capping GaInAs/GaInAsP QW heterostructure leads to the modification of its surface chemical composition and formation of point defects. A subsequent rapid thermal annealing step results in the selective area intermixing of the investigated heterostructures achieving a high quality bandgap tuned material for the fabrication of broad spectrum SLDs. The devices made from a 3-bandgap material are characterized by ~100nm wide emission spectra with relatively flat profiles and emission exceeding 1mW.

Quantum dot selective area intermixing for broadband light sources

We report a comparison of different capping materials on the intermixing of modulation p-doped InAs/In(Ga)As quantum dots (QD). QD materials with different caps are shown to exhibit significant difference in their optical properties during the annealing process. The selective area intermixing technique is demonstrated to laterally integrate two and three different QD light emitting devices with a single electrical contact. A spectral bandwidth of 240nm centered at 1188nm is achieved in a device with two sections. By calculating the point spread function for the obtained emission spectra, and applying the Rayleigh criteria for resolution, an axial resolution of 3.5μm is deduced. A three section device realizes a spectral bandwidth of 310nm centered at 1145nm. This corresponds to an axial resolution of 2.4μm. Such a small predicted axial resolution is highly desirable in optical coherence tomography system and other coherence-based systems applications.

The conduction band absorption spectrum of interdiffused InGaAs/GaAs quantum dot infrared photodetectors

We report on a theoretical study of the relationship between interdiffusion and the conduction band optical absorption of In(Ga)As/GaAs quantum dots. Quantum dot geometries are progressively interdiffused based on Fick’s model and the quantum dot strain, band structure and optical absorption cross-section are calculated numerically. Quantifying the effects of interdiffusion on quantum dot optical absorption is important for applications that utilize post-growth techniques such as selective area intermixing.

Integration of waveguide-type wavelength demultiplexing photodetectors by the selective intermixing of an InGaAs-InGaAsP quantum-well structure

Using the selective intermixing of an InGaAs-InGaAsP multiquantum-well (MQW) structure, a wavelength demultiplexing photodetector which can demultiplex two widely separated wavelengths was fabricated. An InGaAs-InGaAsP MQW with a u-InP cladding layer and a n-InGaAs cap layer, grown by metal organic chemical vapor deposition was used. Selective area intermixing of the InGaAs-InGaAsP MQW structure was done by a rapid thermal annealing after the deposition and patterning of the SiO/sub 2/ dielectric layer on the InGaAs cap layer. The integrated structure consists of shorter and longer wavelength sections, separated by an absorber section. Shorter wavelength and absorber sections were intermixed with the SiO/sub 2/ dielectric layer. At a wavelength of 1477 nm, the output photocurrent ratio was enhanced as the length of the absorber region increased and a ratio of over 30 dB was observed, while at a wavelength of 1561 nm, an output photocurrent ratio of 18.9 dB was observed.

Intermixing of multiple quantum wells for all-optical integrated circuits

All-optical waveguide switches that can potentially be implemented in all-optical integrated circuits are described. These switches are presently made in either single or multiple semiconductor quantum well structures. Selective-area intermixing of the quantum wells is presented as a most viable means of achieving the passive waveguide sections for the interconnections between the switches.