Z. L. Liau

Wafer fusion: A novel technique for optoelectronic device fabrication and monolithic integration

Centimeter‐size single‐crystal InP or GaAs wafers have been fused together entirely, face to face or side by side, after a heat treatment in a graphite/quartz reactor which can press the wafers together through differential thermal expansion. Diodes formed by fusing p‐ and n‐type wafers showed normal current‐voltage characteristics and light emission. Fusion between lattice‐mismatched wafers (i.e., InP and GaAs) has also been demonstrated.

Semiconductor wafer bonding via liquid capillarity

Liquid surface tension has been used to pull different semiconductor wafers to very close contact and strong bonding. Bonded wafers, such as GaAs/GaP, were heat treated without pressure application to achieve wafer fusion. The bonding process has been analyzed, and criteria for surface tension, wafer flatness, and elasticity have been derived.

Microchannel heat sinks for two-dimensional high-power-density diode laser arrays

The operation of a two-dimensional GaInAsP/InP diode laser array with CW power dissipation up to 500 W/cm/sup 2/ into a Si microchannel heat sink is discussed. The approximately 1*4-mm/sup 2/ laser array was used to characterize the heat sink, and the value of 0.040 degrees C cm/sup 2//W was obtained for the thermal resistance per unit area. The extrapolated value for a 1-cm/sup 2/ heated area is 0.070 degrees C cm/sup 2//W. >

Low‐threshold InGaAs strained‐layer quantum‐well lasers (λ=0.98 μm) with GaInP cladding layers and mass‐transported buried heterostructure

Buried‐heterostructure quantum‐well lasers fabricated by mass transport are reported for In0.18Ga0.82As/GaAs/Ga0.5In0.5P strained‐layer structures grown by atmospheric pressure organometallic vapor‐phase epitaxy. Threshold current densities as low as 85 A/cm2 are measured for broad‐stripe lasers, and buried‐stripe devices show threshold currents as low as 3 mA and differential quantum efficiencies as high as 34% per facet without coatings.

Surface-emitting GaInAsP/InP laser with low threshold current and high efficiency

A buried‐heterostructure laser has been developed whose output is deflected to a direction perpendicular to the substrate surface by a monolithically integrated 45° (parabolic) mirror. The latter is fabricated by smoothing a chemically etched multistep structure using a mass‐transport phenomenon. The present devices show threshold current as low as 12 mA, differential quantum efficiency as high as 47% and a surface‐emitting far‐field pattern with a main lobe as narrow as 12°.

Near-diffraction-limited diode laser arrays by wavelength beam combining

We demonstrate 35 W output peak power with M2 approximately 1.35 in both dimensions from a 100 element, 100 microm pitch slab-coupled optical waveguide laser diode array using wavelength beam combining.

GaInAsP/InP Double-heterostructure lasers

A method and apparatus is described wherein a buried double heterostructure laser device is formed utilizing epitaxial layers of quaternary III-V alloys of gallium indium arsenide phosphide and wherein the buried layer is formed by first etching the p-type top layer of the structure down to the quaternary active layer forming a mesa. A second etchant is then provided which preferentially etches the active layer. This etchant is used to undercut the top layer by removing the active layer on both sides of the top mesa surface providing a narrow strip of active layer underneath the undercut mesa. The undercut is then filled in by a heat treatment process which results in migration or transport of the binary top layer and binary bottom layer to fill in the undercut, leaving the active layer buried in the binary material. In an alternate embodiment of the invention, the two-step etching process plus the transport phenomena is utilized to form the mirror surface of a laser device. The device may include a support mesa and control mesa structure and may also be used to fabricate optical waveguide structures.

3.9‐μm InAsSb/AlAsSb double‐heterostructure diode lasers with high output power and improved temperature characteristics

Double‐heterostructure diode lasers emitting at ∼3.9 μm have exhibited pulsed operation at temperatures up to 170 K and cw operation up to 105 K, with single‐ended cw output power of 30 mW at 70 K. The laser structure, grown on GaSb substrates by molecular‐beam epitaxy, has an InAsSb active layer and AlAsSb cladding layers. The lowest pulsed threshold current density is 36 A/cm2 obtained at 60 K. The characteristic temperature is 20 K over the entire temperature range.

Gallium phosphide microlenses by mass transport

Arrays of high quality refractive microlenses have been formed in GaP substrates by mesa etching followed by a heat treatment in which the multistep mesas were smoothed due to surface energy minimization. A smooth lens surface and an accurately controlled lens profile have been obtained. Microlenses of 130 μm diameter and 200 μm focal length have been used to collimate the outputs of GaInAsP/InP and GaAs/GaAlAs diode lasers and have yielded a nearly diffraction‐limited beam divergence of 0.68°.

Large‐numerical‐aperture microlens fabrication by one‐step etching and mass‐transport smoothing

Precision f/1 microlenses have been fabricated in GaP by smoothing a multiple‐mesa structure etched with a designed width and length variation. High‐resolution lithography and ion‐beam‐ assisted etching were used for mesa definition and resulted in accurate lens profiles after mass‐transport smoothing at 900–1070 °C. This much simplified fabrication technique is highly promising for efficient, diffraction‐limited micro‐optical elements.