Linda J. Olafsen

Near-room-temperature mid-infrared interband cascade laser

A 25-stage interband cascade laser with a W active region and a third hole quantum well for the suppression of leakage current has exhibited lasing in pulsed mode up to 286 K. A peak output power of 160 mW/facet and a slope efficiency of 197 mW/A per facet (1.1 photons per injected electron) were measured at 196 K. Above 200 K, the characteristic temperature was higher (T0=53 K) and the threshold current densities lower than for a previously reported W interband cascade laser without the third hole quantum well.

Auger coefficients in type-II InAs/Ga1−xInxSb quantum wells

Two different approaches, a photoconductive response technique and a correlation of lasing thresholds with theoretical threshold carrier concentrations have been used to determine Auger lifetimes in InAs/GaInSb quantum wells. For energy gaps corresponding to 3.1–4.8 μm, the room-temperature Auger coefficients for seven different samples are found to be nearly an order-of-magnitude lower than typical type-I results for the same wavelength. The data imply that at this temperature, the Auger rate is relatively insensitive to details of the band structure.

High-temperature continuous-wave 3–6.1 μm “W” lasers with diamond-pressure-bond heat sinking

Optically pumped type-II W lasers emitting in the mid-infrared exhibited continuous-wave (cw) operating temperatures of 290 K at λ=3.0 μm and 210 K at λ=6.1 μm. Maximum cw output powers for 78 K were 260 mW at λ=3.1 μm and nearly 50 mW at λ=5.4 μm. These high maximum temperatures were achieved through the use of a diamond-pressure-bonding technique for heat sinking the semiconductor lasers. The thermal bond, which is accomplished through pressure alone, permits topside optical pumping through the diamond at wavelengths that would be absorbed by the substrate.

Above-room-temperature optically pumped midinfrared W lasers

We report temperature-dependent pulsed lasing performance, internal losses, and Auger coefficients for optically pumped type-II W lasers with wavelengths in the range of 3.08–4.03 μm at room temperature. All lased to at least 360 K, and produced 1.5–5 W peak power at 300 K. Internal losses at 100 K were as low as 10 cm−1, but increased to 90–360 cm−1 at 300 K. Room temperature Auger coefficients varied from 5×10−28 cm6/s at the shortest wavelength to 3×10−27 cm6/s at the longest.

Large magnetoresistance in postannealed Bi thin films

We have observed a large increase in the magnetoresistance (MR) of molecular beam epitaxy grown Bi thin films, which were subjected to a postannealing procedure 3 °C below the Bi melting point. We have achieved an increase in the MR by a factor of 2560 at helium temperatures compared with of 343 for an as-grown film. The enhancement of the MR in the annealed films is due to higher electron and hole mobilities (μe≈1×106 cm2/V s at 5 K) relative to those of the as-grown films (μe≈9×104 cm2/V s at 5 K). The enhancement of the mobility in the annealed films is also supported by the observation of Shubnikov–de Haas oscillations.

Negative luminescence from type-II InAs/GaSb superlattice photodiodes

Strong negative luminescence is displayed by type-II InAs/GaSb superlattice diodes under reverse bias. The negative emittance at room temperature is as high as 1.5 μW/cm2 meV at 4.9 μm, and the negative efficiency at 3.5 μm is 41% of the emission from a perfect blackbody at that temperature. The main features of the data are reproduced by a detailed photodiode simulation.

High-efficiency midinfrared “W” laser with optical pumping injection cavity

We describe an optical pumping injection cavity (OPIC) edge-emitting laser which employs GaSb/AlAsSb distributed Bragg reflectors above and below the type-II “W” active region to form an etalon for the pump beam. A pulsed W–OPIC laser emitting at 3.1–3.4 μm displays an incident threshold pump intensity of only 8 kW/cm2 at 300 K, and incident power conversion efficiencies per facet of 9% at 77 K and 4% at 275 K.

Type-II quantum-well “W” lasers emitting at λ=5.4–7.3 μm

A series of optically pumped type-II quantum-well “W” lasers with wavelengths ranging from 5.4 to 7.3 μm operated at temperatures up to at least 220 K for pulsed operation. The peak output power at 80 K was 1.1 W/facet for a device emitting at λ=7.0 μm. Internal losses were characterized for the temperature range between 40 and 190 K. Auger coefficients determined from an analysis of the threshold pump intensities were found to be suppressed by up to an order of magnitude compared to type-I III–V semiconductors with the same energy gaps.

Continuous-wave type-II "QW" lasers emitting at /spl lambda/=5.4-7.1 μm

Optically pumped type-II QW lasers emitting in the 5.4-7.1 -/spl mu/m wavelength range and at continuous-wave (CW) temperatures up to 210 K are demonstrated. At 80 K, the maximum CW output power from a 40-/spl mu/m-wide pump stripe is 48 mW at 5.41 /spl mu/m and 31 mW at 6.05 /spl mu/m. Epitaxial-side-down heat sinking is provided by a new diamond-pressure-bond mounting technique, which requires minimal processing and maintains topside optical access.

Large magnetoresistance in post-annealed polycrystalline and epitaxial Bi thin films

We have observed a large increase in the magnetoresistance (MR) of polycrystalline and epitaxial thin Bi films, which were subjected to a post-annealing procedure at 3°C below the Bi melting point. We have achieved an increase in the MR by a factor of 2560 at 5 K as compared with 343 for an as-grown epitaxial film due to enhanced carrier mobilities.