Igor Vurgaftman

Single-Mode Room-Temperature CW Interband Cascade Lasers Covering the ? = 3-4 ?m Spectral Band

Interband cascade lasers emitting at 3.6 ?m operated to a maximum temperature of 335 K and produced 59 mW of cw power at room temperature. Single-mode cw emission with 12 mW of power was demonstrated.

Development of quantum and interband cascade lasers on silicon (Conference Presentation)

We are developing midwave infrared (mid-IR) quantum cascade lasers (QCLs) and interband cascade lasers (ICLs) bonded to silicon. The heterogeneous integration of mid-IR photonic devices with silicon promises to enable low-cost, compact sensing and detection capabilities that are compatible with existing silicon photonic and electronic technologies. The first Fabry-Perot QCLs on silicon were bonded to pre-patterned silicon-on-nitride-on-insulator (SONOI) substrates. Lateral tapers in the III-V mesas transferred the optical mode from the hybrid III-V/Si active region into the passive silicon waveguides, with feedback provided by reflections from both the III-V tapers and the polished passive silicon facets. Lasing was observed at   4.8 m with threshold current densities as low as 1.6 kA/cm2 when operated in pulsed mode at T = 20 oC. The first mid-IR DFB lasers integrated on silicon employed gratings patterned into the silicon waveguides before bonding. Over 200 mW of pulsed power was generated at room temperature, and operated to 100 °C with T0 = 199 K. Threshold current densities were measured below 1 kA/cm2.The grating imposed considerable wavelength selectivity and 22 nm of thermal tuning, even though the emission was not spectrally pure. Ongoing research focuses on flip-chip bonding to improve heat sinking for continuous-wave operation, and arrayed waveguide gratings for beam combining. ICLs have also been bonded to silicon and the GaSb substrate has been chemically removed with an InAsSb etch-stop layer. Tapered ICL ridges designed for lasing in a hybrid III-V/Si mode have been processed above passive silicon waveguides patterned on SOI. A goal is to combine the power generated by arrays of QCLs and ICLs residing on the same chip into a single, high-quality output beam.

Mid-infrared interband cascade light-emitting devices with improved radiance

We report interband cascade light-emitting devices (ICLEDs) emitting at λ ≈ 3.1mm, which produce generate higher radiance, output power, and efficiency than any other mid-infrared LEDs operating in continuous wave (cw) mode near and above room temperature. This is achieved in part by splitting the 22 LED stages into four groups placed at the antinodes of the near-normal optical field when the device is mounted epitaxial-side-down on a reflective metal contact. At an applied bias of 9.4 V and injection current of 0.6 A, an ICLED with mesa diameter 400 mm produces 2.9 mW of cw output power at T = 25°C, which corresponds to a radiance of 0.73 W/cm2/sr. The wall-plug efficiency ranges from 0.4% at low powers to 0.05% at the maximum output power.

An Integrated Electrically Driven Coherent Source of Surface Plasmon Polaritons

We demonstrate a versatile electrically-driven source of coherent SPPs by end-coupling a quantum-well laser to an integrated plasmonic waveguide with coupling efficiency of ?36%. The SPP peak power generated at room temperature is 36 mW.

Artificially ordered BiSb alloys: growth and transport properties

We propose a new approach for potentially achieving high-ZT materials: artificially ordered alloy structures. We have prepared artificially ordered Bi/Sb alloys with different (Bi/Sb) periods from 7.7 /spl Aring/ to 55 /spl Aring/ by MBE. Atomic-scale ordering effects on the structural and transport properties have been studied. The formation of an ordered alloy was confirmed by the presence of XRD superlattice satellites. Using electrical resistivity, thermopower, and magneto-transport measurements, we have observed a semimetal-semiconductor transition in an ordered BiSb superlattice. The intentional ordering of the layered Bi-Sb structure has produced a new phase and the measured differences in the electronic spectrum relative to the random alloy are a consequence of its atomic structure.

Bi1-xSbx alloy thin film and superlattice thermoelectrics

We have grown Bi1-xSbx alloy thin films on CdTe(111)B over a wide range of Sb concentrations (0≤x≤0.183) using MBE. We have observed several differences with the bulk system. The 3.5 and 5.1% Sb alloys show semiconducting behavior, and the Sb concentration with the maximum bandgap is shifted to a lower Sb concentration, from 15% in bulk to 9%. The power factor S2/ρ (where S is thermoelectric power(TEP) and ρ electrical resistivity) peaks at a significantly higher temperature (250K) than previously reported for the bulk alloy (80K). The magnetotransport properties of Bi1-x,Sbx thin films (x = 0, 0.09, and 0.16) and Bi/CdTe superlattices have been determined by applying the Quantitative Mobility Spectrum Analysis (QMSA) and multicarrier fitting to the magneticfield- dependent resistivities and Hall coefficients, using algorithms which account for the strong anisotropy of the mobilities. The calculated S values are in good agreement with experimental results. The structural stability of bulk Bi is studied using the local density linear muffin-tin orbital method. It is shown that the internal displacement changes the Bi electronic structure from a metal to a semimetal, in qualitative agreement with a Jones-Peierls-type transition. The total energy is calculated to have a double well dependence on the internal displacement, and to provide a stabilization of the trigonal phase. We show that an increase of the trigonal shear angle leads to a semimetal-semiconductor transition in Bi.