J. S. Major

Carbon diffusion in undoped, n‐type, and p‐type GaAs

The effects of background doping, surface encapsulation, and As4 overpressure on carbon diffusion have been studied by annealing samples with 1000 A p‐type carbon doping spikes grown within 1 μm layers of undoped (n−), Se‐doped (n+), and Mg‐doped (p+) GaAs. The layers were grown by low‐pressure metalorganic chemical vapor deposition using CCl4 as the carbon doping source. Two different As4 overpressure conditions were investigated: (1) the equilibrium pAs4 over GaAs (no excess As), and (2) pAs4 ∼2.5 atm. For each As4 overpressure condition, both capless and Si3N4‐capped samples of the n−‐, n+‐, and p+‐GaAs crystals were annealed simultaneously (825 °C, 24 h). Secondary‐ion mass spectroscopy was used to measure the atomic carbon depth profiles. The carbon diffusion coefficient is always low, but depends on the background doping, being highest in Mg‐doped (p+) GaAs and lowest in Se‐doped (n+) GaAs. The influence of surface encapsulation (Si3N4) and pAs4 on carbon diffusion is minimal.

Low‐threshold disorder‐defined buried heterostructure strained‐layer AlyGa1−yAs‐GaAs‐InxGa1−xAs quantum well lasers (λ∼910 nm)

The stability of strained‐layer Aly Ga1−yAs‐GaAs‐InxGa1−x As single quantum well heterostructures against thermal processing is examined using transmission and scanning electron microscopy. A self‐aligned impurity‐induced layer disordering process employing Si‐O diffusion is used to produce buried heterostructure stripe geometry lasers with a pseudomorphic InxGa1−x As quantum well active region. The 2‐μm‐wide stripe laser diodes exhibit high efficiency (η∼41%/facet), low threshold (Ith =7 mA), and high output power (Pout >20 mW/facet).

Column III and V ordering in InGaAsP and GaAsP grown on GaAs by metalorganic chemical vapor deposition

Data are presented showing that GaAs1−y Py grown on GaAs by metalorganic chemical vapor deposition (MOCVD) at relatively low temperature (∼640 °C) exhibits ordering on the column V sublattice. These data, with electron diffraction data and impurity‐induced layer disordering data, show that column III site and column V site ordering is possible for the quaternary InGaAsP grown on GaAs by MOCVD at relatively low temperature (∼640 °C). Ordered InGaAsP grown on GaAs shifts in photoluminescence wavelength ∼130 meV higher in energy with disordering by annealing or by impurity‐induced intermixing.

Disorder-defined buried-heterostructure AlxGa1−xAs-GaAs quantum well lasers by diffusion of silicon and oxygen from Al-reduced SiO2

We describe a convenient method utilizing chemical reduction of SiO2 by Al (from AlxGa1−xAs) to generate Si and O for impurity‐induced layer disordering (IILD) of AlxGa1−xAs‐GaAs quantum well heterostructures (QWHs). Experimental data show that Si‐O diffusion (from SiO2) is an effective source of Si for Si‐IILD and of O that compensates the Si donor, thus resulting in higher resistivity layer‐disordered crystal. The usefulness of the Si‐O IILD source for fabricating low‐threshold disorder‐defined buried‐heterostructure AlxGa1−xAs‐GaAs QWH lasers is demonstrated.

Column III vacancy‐ and impurity‐induced layer disordering of AlxGa1−xAs‐GaAs heterostructures with SiO2 or Si3N4 diffusion sources

Experiments are described determining the critical parameters for vacancy‐ and impurity‐induced layer disordering of AlxGa1−xAs‐GaAs quantum‐well heterostructure (QWH) crystals that utilize SiO2 and Si3N4 diffusion source layers. The SiO2‐ or Si3N4‐capped QWH crystal surface reaches equilibrium with the external annealing ambient by diffusion of Ga and As through the encapsulant layer, thus determining the crystal‐surface deviation from stoichiometry and the column III vacancy concentration for layer disordering. By proper design of the QWH crystal, encapsulant layer thickness, and annealing ambient, the SiO2 (Si3N4) can be employed as a column III vacancy source (or mask) or as a Si and O (or N) diffusion source to effect impurity‐induced layer disordering.

High‐power disorder‐defined coupled stripe AlyGa1−yAs‐GaAs‐InxGa1−xAs quantum well heterostructure lasers

Data are presented describing continuous (cw) room‐temperature laser operation of Al y Ga1 − y As‐GaAs‐In x Ga1 − x As quantum wellheterostructure (QWH) phase‐locked arrays. The ten‐stripe arrays have 3 μm emitters, with emitter to emitter spacing of 4 μm, and are patterned onto the QWH crystal using a self‐aligned Si‐O impurity‐induced layer disordering (IILD) procedure. The IILD process is devised to provide limited layer intermixing to ensure optical coupling (across ∼1 μm). The coupled stripe QWH lasers exhibit narrow twin‐lobed far‐field patterns that show unambiguously phase locking in the highest order supermode. The cw output power of the lasers (differential quantum efficiency 52%) is shown from threshold (∼75 mA) to over 280 mW (both facets, no optical coatings).

Al‐Ga interdiffusion in heavily carbon‐doped AlxGa1−xAs‐GaAs quantum well heterostructures

Impurity‐induced layer disordering experiments on AlxGa1−xAs‐GaAs quantum well heterostructures (QWHs) that are doped heavily with carbon are described. The data show that carbon doping retards Al‐Ga interdiffusion relative to an undoped crystal, and that interdiffusion in C‐doped QWHs is not enhanced by a Ga‐rich (versus As‐rich) annealing ambient. The data are inconsistent with most Fermi‐level‐effect models for layer disordering that do not include chemical impurity dependence or sublattice dependence, and that do not consider the possibility of inhibited Al‐Ga interdiffusion in extrinsic crystals.

Broadband long‐wavelength operation (9700 Å≳λ≳8700 Å) of AlyGa1−yAs‐GaAs‐InxGa1−xAs quantum well heterostructure lasers in an external grating cavity

Data are presented on p‐n Al y Ga1−y As‐ GaAs‐In x Ga1−x As quantum wellheterostructure lasers showing that the large band filling range of a combined GaAs‐In x Ga1−x As quantum well makes possible a very large tuning range in external grating operation. Continuous 300 K laser operation is demonstrated in the 8696–9711 A range (Δλ∼1000 A, Δℏω∼150 meV) and pulsed operation in the 8450–9756 A range (Δλ∼1300 A, Δℏω∼200 meV). The band filling and gain profile are shown to be continuous from the In x Ga1−x As quantum well (L z ∼125 A, x∼0.2) up into the surrounding GaAs quantum well (L z ∼430 A).

Si impurity‐induced layer disordering of Alx Ga1−x ‐GaAs quantum‐well heterostructures by As‐free open‐tube rapid thermal annealing

Data are presented describing Si impurity‐induced layer disordering (IILD) and Al‐Ga interdiffusion in AlxGa1−x As‐GaAs quantum‐well heterostructures (QWHs) using open‐tube rapid thermal annealing (900–1000 °C) in a flowing N2/H2 ambient. The data show that Al‐Ga interdiffusion is enhanced by n‐type crystal doping and suppressed by p‐type doping. By surrounding the active layers of the heterostructure with layers of opposite doping, we show that the surrounding layers modify the interdiffusion by controlling the diffusion of point defects to the active layers of the heterostructure. Data are presented showing the effects of dielectric encapsulation (SiO2, Si3N4 ) on Al‐Ga interdiffusion. The data show that regardless of doping SiO2 enhances interdiffusion as compared to Si3N4. To achieve more thorough layer intermixing of AlxGa1−x As‐GaAs QWHs, Si IILD is also investigated in the high‐temperature As‐poor regime. The experimental data show that in a high‐temperature As‐poor annealing ambient, little or no ...

Instability of partially disordered carbon‐doped AlGaAs/GaAs superlattices

Superlattices of Al0.3Ga0.7As/GaAs grown by metalorganic chemical vapor deposition and heavily doped with carbon using CCl4 were annealed for 24 h at 825 °C under a variety of ambient and surface encapsulation conditions. Pronounced changes in photoluminescence from the annealed superlattices with storage time at room temperature, as opposed to an excellent reproducibility of that from the as‐grown, not annealed samples, are reported. These changes may be indicative of degraded thermal stability of the annealed superlattice crystals due to high‐temperature‐induced lattice defects. The systematic failure to fabricate buried‐heterostructure quantum well lasers via impurity‐induced layer disordering in similarly doped AlGaAs/GaAs crystals, which may be related to the same effect, is also discussed.