S. C. Smith

High‐performance planar native‐oxide buried‐mesa index‐guided AlGaAs‐GaAs quantum well heterostructure lasers

High‐performance planar ‘‘buried‐mesa’’ index‐guided AlGaAs‐GaAs quantum well heterostructure (QWH) lasers have been fabricated by oxidation (H2O vapor+N2 carrier gas, 425–525 °C) of a significant thickness of the high composition AlxGa1−xAs upper confining layer (outside the active stripe). The oxide provides excellent current confinement for low‐threshold laser operation and a low refractive index (n∼1.6) for transverse optical confinement and index guiding. Laser diodes with ∼4 μm‐wide active regions exhibit 300 K continuous (cw) laser thresholds of 8 mA, with single longitudinal mode operation to 23 mW/facet, and maximum output powers of 45 mW/facet (uncoated). Devices fabricated on a lower confinement AlxGa1−xAs‐GaAs QWH crystal (x≲0.6 instead of x≳0.8) with ∼4 μm‐wide active stripes exhibit 300 K cw thresholds of 9 mA and total external differential quantum efficiencies of 66%. Peak output powers ≳80 mW/facet (uncoated) with linear L‐I characteristics over the entire operating range are observed. In...

Planar native‐oxide AlxGa1−xAs‐GaAs quantum well heterostructure ring laser diodes

Native‐oxide planar AlxGa1−xAs‐GaAs quantum well heterostructure ring laser diodes (25‐μm‐ wide annulus, 250‐μm inside diameter, 300‐μm outside diameter) are demonstrated. The curved cavities (full‐ring, half‐ring, and quarter‐ring) are defined by native oxidation (H2O vapor+N2 carrier gas, 450 °C) of the entire upper confining layer inside and outside of the annulus. The native oxide provides current confinement and a sufficiently large lateral index step, and thus photon confinement, to support laser oscillation along the ring. Half‐ring laser diodes fabricated in a self‐aligned geometry exhibit continuous wave (cw) 300‐K thresholds as low as ∼105 mA (∼500‐μm circular cavity length), high total external differential quantum efficiencies (∼49%), and cw output powers of ≳40 mW.

Low‐threshold disorder‐defined native‐oxide delineated buried‐heterostructure AlxGa1−xAs‐GaAs quantum well lasers

Impurity‐induced layer disordering (IILD) along with oxidation (native oxide) of high‐gap AlxGa1−xAs confining layers is employed to fabricate low‐threshold stripe‐geometry buried‐heterostructure AlxGa1−xAs‐GaAs quantum well heterostructure (QWH) lasers. Silicon IILD is used to intermix the quantum well and waveguide regions with the surrounding confining layers (beyond the laser stripe) to provide optical and current confinement in the QW region of the stripe. The high‐gap AlxGa1−xAs upper confining layer is oxidized in a self‐aligned configuration defined by the contact stripe and reduces IILD leakage currents at the crystal surface and diffused shunt junctions. AlxGa1−xAs‐GaAs QWH lasers fabricated by this method have continuous 300 K threshold currents as low as 5 mA and powers ≳ 3l mW/facet for ∼ 3‐μm‐wide active regions.

Native‐oxide masked impurity‐induced layer disordering of AlxGa1−xAs quantum well heterostructures

Data are presented showing that the native oxide that can be formed on high Al composition AlxGa1−xAs (x≳0.7) confining layers on AlyGa1−yAs‐AlzGa1−zAs (y≳z) superlattices or quantum well heterostructures serves as an effective mask against impurity diffusion (Zn or Si), and thus against impurity‐induced layer disordering. The high quality native oxide is produced by the conversion of high Al composition AlxGa1−xAs (x≳0.7) confining layers, which can be grown on a variety of heterostructures, via H2O vapor oxidation (≳400 °C) in an N2 carrier gas.

Native‐oxide‐defined coupled‐stripe AlxGa1−xAs‐GaAs quantum well heterostructure lasers

Data are presented on the continuous‐wave (cw) room‐temperature (300 K) operation of multiple stripe AlxGa1−xAs‐GaAs quantum well heterostructure (QWH) laser arrays defined with native oxide contact masking. Use of the native AlxGa1−xAs(x≳0.7) oxide allows the fabrication of high‐performance devices without depositing foreign oxide or dielectric layers (SiO2 or Si3N4). Arrays of ten 5‐μm‐wide emitters on 7 μm centers are coupled and operate at powers as high as 300 mW per facet, or at wider stripe spacing (5 μm emitters on 10 μm centers) as high as 400 mW per facet. These data indicate that current blocking layers of native oxide, formed from AlxGa1−xAs with H2O vapor in N2 carrier gas (400 °C, 3 h), can be used in the construction of high‐power multiple stripe QWH arrays with excellent performance characteristics.

Optical channel waveguides in AlGaAs multiple-quantum-well structures formed by focused ion-beam-induced compositional mixing

Optical channel waveguiding in a AlGaAs multiple-quantum-well structure was demonstrated in a channel formed by compositional mixing induced by focused ion beam (FIB) implantation. Selective mixing was achieved by FIB implanting Si/sup ++/ with a dose of 5*10/sup 14/ cm/sup -2/ followed by rapid thermal annealing at 950 degrees C for 10 s. Raman microprobe spectra were used to characterize the lateral variation of compositional mixing. Channel waveguide loss of 17.2 dB/cm was measured, compared to 10-12 dB/cm measured for planar waveguiding. Mode field pattern measurements indicate that a change in effective index of 2.7*10/sup -4/ was induced, corresponding to an approximate mixing depth of 270 nm.<<ETX>>

Self‐aligned native‐oxide ridge‐geometry AlxGa1−xAs‐GaAs quantum well heterostructure laser arrays

Process conditions for fabricating ridge geometry AlxGa1−xAs‐GaAs quantum well heterostructure laser arrays utilizing a high quality self‐aligned native oxide of AlxGa1−xAs are presented. Wet oxidation is performed, after etching ridges, via H2O vapor in a N2 or N2/H2(10%) carrier gas at 435–445 °C for 15–20 min. The formation of a uniform smooth oxide was found to be critically dependent on the crystal environment prior to the oxidation process. Characteristics of devices fabricated by this process are presented.

Native‐oxide coupled‐cavity AlxGa1−xAs‐GaAs quantum well heterostructure laser diodes

Data are presented demonstrating AlxGa1−xAs‐GaAs quantum well heterostructure laser diodes consisting of an array of coupled cavities (19 μm long on 22 μm centers, ∼250 μm total length) arranged lengthwise in single 10‐μm‐wide laser stripes. The cavities are defined by a native oxide formed from a significant portion of the high‐gap AlxGa1−xAs upper confining layer. The native oxide (grown at 425 °C in H2O vapor+N2 carrier gas) confines the injected carriers and optical field within the cavities, resulting in reflection and optical feedback distributed periodically along the laser stripe. These diodes exhibit single‐longitudinal‐mode operation over an extended range (relative to similar diodes fabricated without multiple cavities). At high current injection levels, longitudinal‐mode spectra demonstrate unambiguously oscillation from the internal coupled cavities.

Native‐oxide‐masked Si impurity‐induced layer disordering of AlxGa1−xAs‐AlyGa1−yAs‐AlzGa1−zAs quantum‐well heterostructures

Data are presented showing that the native oxide that can be formed on high Al composition AlxGa1−xAs (x≳0.7) confining layers commonly employed on AlxGa1−xAs‐AlyGa1−yAs‐AlzGa1−zAs (y≳z) superlattices or quantum‐well heterostructures serves as an effective mask against Si diffusion, and thus impurity‐induced layer disordering. The high‐quality native oxide is produced by the conversion of high‐composition AlxGa1−xAs (x≳0.7) confining layers via H2O vapor oxidation (≳400 °C) in N2 carrier gas.

High‐performance diffusion disordered AlxGa1−xAs lasers via a self‐aligned process and conventional open‐tube annealing

Process conditions for fabricating Si‐O impurity‐induced layer disorder defined AlxGa1−xAs‐GaAs buried heterostructure quantum well lasers utilizing a fully self‐aligned planar process and conventional As free open‐tube‐furnace annealing are presented. An SiO2 layer, deposited by sputtering, was used as a diffusion source for Si and O impurities as well as a source for Ga vacancies that enhance impurity diffusion and allow for a reduction in the required annealing temperature and time. A self‐aligned native oxide of the AlxGa1−xAs cladding layer was used to form a Zn diffusion mask and dielectric layer. Lasers fabricated using this process exhibited threshold currents as low as 2.72 mA and external differential quantum efficiencies of 79% at room temperature in continuous operation.