Clarence Dunnrowicz

Characterization of AlGaInN diode lasers with mirrors from chemically assisted ion beam etching

Current-injection InGaAlN heterostructure laser diodes grown by metalorganic chemical vapor deposition on sapphire substrates are demonstrated with mirrors fabricated by chemically assisted ion beam etching. Due to the independent control of physical and chemical etching, smooth vertical sidewalls with a root-mean-squared roughness of 4–6 nm have been achieved. The diodes lased under pulsed current-injection conditions at wavelengths in the range from 419 to 423 nm. The lowest threshold current density was 25 kA/cm2. Lasing was observed in both gain-guided and ridge-waveguide test diodes, with cavity lengths from 300 to 1000 μm; and output powers of 10–20 mW were achieved. Laser performance is illustrated with light output-current and current–voltage characteristics and with a high-resolution optical spectrum.

Flip-chip bonding on 6-/spl mu/m pitch using thin-film microspring technology

Bonding-pad densities on high-performance integrated-circuit chips are beginning to exceed the limits of available interconnect technologies. Also, stresses due to thermal mismatch in flip-chipped packages are reducing time to contact failure. We have addressed both of these problems by microlithographically fabricating highly elastic cantilever springs in linear arrays on pitches down to 6 /spl mu/m. We have soldered test arrays of 52 springs on this pitch to Si chips with 100% contact yield and good solder wetting to every spring. The fine-pitch capability also facilitates off-chip routing; the very high compliance of the springs should avoid thermal fatigue; and the low thermal conductance along the springs should allow fast-cycle soldering of chips to multichip modules as well as replacement of chips subsequently testing faulty.

Demonstration of an InGaN/GaN-based optically pumped multiquantum well distributed feedback laser using holographically defined third-order gratings

We demonstrate an optically pumped InGaN/GaN-based multiquantum well distributed feedback laser in the blue spectral region. The third-order grating providing feedback was defined holographically and dry etched into the upper waveguiding layer by chemically assisted ion-beam etching. When aligning the stripe-shaped pump beam either parallel or perpendicular to the grating grooves, we found a considerably lower pumping threshold, higher slope efficiency, a slightly longer emission wavelength, and a much narrower linewidth for the geometry with the pump beam orthogonal to the grating lines. A nearly constant emission wavelength of 400.85 nm and a linewidth of 0.7 A were observed under various pump intensities. To the best of our knowledge, this is the narrowest linewidth ever reported for an optically pumped device in this material system.

Stripe-width dependence of threshold current for gain-guided AlGaInN laser diodes

The threshold current density of narrow-stripe gain-guided nitride laser diodes increases very rapidly as the stripe width is made narrow. To examine this behavior, waveguide simulations, incorporating the complex refractive indices associated with optical gain, have been used to analyze the lateral optical modes of gain-guided laser diodes. Threshold current was then determined from the gain–current relationship of our laser material, which was obtained experimentally. These evaluations reveal that gain guiding, coupled with a carrier-induced index depression, offer a reasonable explanation for the rapid increase in threshold when the stripe width becomes less than 5 μm.

Low-threshold InAlGaAs vertical-cavity surface-emitting laser arrays using transparent contacts

We present top-emitting all-epitaxial planar laterally oxidized vertical-cavity surface-emitting lasers employing transparent indium–tin–oxide electrodes. The transparent contacts facilitate device fabrication and offer significantly denser device packing than similar planar laterally oxidized structures using metal contacts. The InAlGaAs-based devices operate at a wavelength of 817 nm with a minimum threshold current of 175 μA.

Characterization of InGaN/AlGaN multiple-quantum-well laser diodes

This paper discusses the design and characteristics of III-nitride based multi-quantum well (MQW) laser diodes grown on a- as well as c-plane sapphire substrates by metal organic chemical vapor deposition (MOCVD). Threshold current densities as low as 4.8 kA/cm 2 have been observed on devices with CAIBE etched mirrors and a SiO 2 /TiO 2 high reflective coating on both facets. The lowest threshold currents obtained were around 55 mA (U th = 9.5V) for 3μm * 300μm ridge-waveguide laser diodes devices which allow room temperature pulsed operation up to 70% duty cycle (devices mounted p-side up). From cavity length studies the distributed loss in our structures was determined to be of the order of 35-45 cm -1 . At threshold this corresponds to a maximum modal gain of about 110 cm -1 or a material gain of about 2200 cm -1 .

Characterization of InGaN/GaN-Based Multi-Quantum Well Distributed Feedback Lasers

We present a device fabrication technology and measurement results of both optically pumped and electrically injected InGaN/GaN-based distributed feedback (DFB) lasers operated at room temperature. For the optically pumped DFB laser, we demonstrate a complex coupling scheme for the first time, whereas the electrically injected device is based on normal index coupling. Threshold currents as low as 1.1 A were observed in 500 μm long and 10 μm wide devices. The 3 order grating providing feedback was defined holographically and dry-etched into the upper waveguiding layer by chemically-assisted ion beam etching. Even when operating these lasers considerably above threshold, a spectrally narrow emission (3.5 Å) at wavelengths around 400 nm was seen.

MOCVD growth and characterization of AlGaInN multiple quantum well heterostructures and laser diodes

We demonstrate room temperature, pulsed, current-injected operation of InGaAlN heterostructure laser diodes with mirrors fabricated by chemically assisted ion beam etching. The multiple quantum well devices were grown by organo‐metallic vapor phase epitaxy on c-face sapphire substrates. The emission wavelengths of the gain-guided laser diodes were 400 nm. The lowest threshold current density obtained was 6 kA cm 2 with maximum output powers of 50 mW per facet. Optically-pumped distributed-feedback laser operation was also achieved.

CHARACTERIZATION OF InGaN/GaN-BASED MULTI-QUANTUM WELL DISTRIBUTED FEEDBACK LASERS

We present a device fabrication technology and measurement results of both optically pumped and electrically injected InGaN/GaN-based distributed feedback (DFB) lasers operated at room temperature. For the optically pumped DFB laser, we demonstrate a complex coupling scheme for the first time, whereas the electrically injected device is based on normal index coupling. Threshold currents as low as 1.1 A were observed in 500 μm long and 10 μm wide devices. The 3 rd order grating providing feedback was defined holographically and dry-etched into the upper waveguiding layer by chemically-assisted ion beam etching. Even when operating these lasers considerably above threshold, a spectrally narrow emission (3.5 A) at wavelengths around 400 nm was seen.