W. Stutius

Disordering of the ordered structure in MOCVD-grown GaInP and AlGaInP by impurity diffusion and thermal annealing

Ga0.5In0.5P and (AlxGa1−x)0.5In0.5P grown by metal-organic chemical vapor deposition (MOCVD) at temperatures below 700 °C show an ordered arrangement of the group III atoms on the column III sublattice. A periodic compositional modulation along the growth direction is also observed under certain growth conditions. This paper presents data showing that epitaxial layers of both Ga0.5In0.5P and (AlxGa1−x)0.5In0.5P grown on (001) GaAs substrates and containing the ordered phase can be converted to disordered alloys by thermal annealing under a variety of conditions at temperatures not exceeding the growth temperature. The disappearance of the ordered phase, as determined by TEM, is accompanied by a sift of the bandgap to higher energy by ≈90 meV. Ga0.5In0.5P and (AlxGa1−x)0.5In0.5P have been annealed in sealed ampoules under the following conditions: (1) thermal anneal with P4 overpressure, (2) Zn diffusion with Zn3P2 only, and (3) Zn diffusion with both Zn3P2 and P4. Similar bandgap shifts are obtained under all three conditions. It is further shown that selective disordering with either Zn or P4 can be achieved by using a patterned dielectric mask. The relative stabilities of the random and the ordered alloys are discussed in light of these disordering data.

Disordering of the ordered structure in metalorganic chemical vapor deposition grown Ga0.5In0.5P on (001) GaAs substrates by zinc diffusion

Transmission electron microscopy is used to study sublattice atomic ordering in as‐grown and Zn‐diffused epitaxial layers of Ga0.5In0.5P that are grown lattice matched to GaAs by low‐pressure metalorganic chemical vapor deposition. The as‐grown Ga0.5In0.5P layers exhibit an ordered trigonal structure with In‐Ga ordering occurring on only two sets of {111} planes. After a Zndiffusion is performed at 650 °C, the ordered structure is no longer observed in selected area diffraction patterns. Simultaneously, the room‐temperature photoluminescence peak shifts by ≊90 meV to higher energy, as compared to the undiffused samples. These data provide direct experimental evidence that Ga0.5In0.5P with an ordered distribution of Ga and In atoms on the column III sublattice can be converted to a random alloy by Zndiffusion.

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).

Layer interdiffusion in Se‐doped AlxGa1−xAs‐GaAs superlattices

Transmission electron microscopy and carrier concentration measurements are used to characterize the layer interdiffusion (Al‐Ga interdiffusion) mechanism of a Se‐doped AlxGa1−xAs‐GaAs superlattice (SL) under high‐temperature annealing. By varying the annealing environment and comparing the results with similarly annealed undoped SL’s and Mg‐doped SL’s, we find that the layer interdiffusion occurs through interaction of the Se impurity with native defects associated with As‐rich conditions, the most likely of which is the column III vacancy.

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).

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).

Zn disordering of a Ga0.5In0.5P‐(AlxGa1−x)0.5In0.5P quantum well heterostructure grown by metalorganic chemical vapor deposition

It is well established by now that epitaxial layers of (AlxGa1−x)0.5In0.5P and Ga0.5In0.5P grown on (001) GaAs substrates by metalorganic chemical vapor deposition at temperatures below 700 °C show an ordered arrangement of the group III atoms on the column III sublattice, resulting in a shift of the band gap to lower energies by ≊90 meV. In this letter we show that an (AlxGa1−x)0.5In0.5P‐Ga0.5In0.5P quantum well heterostructure containing the ordered phase can be converted to random alloy by a relatively short sealed‐tube zinc diffusion at a temperature of 600 °C, without affecting the dimensional or compositional stability of the quantum well. Complete intermixing of the quantum well with the cladding layers occurs at diffusion times longer than that required to disorder the column III ordered structure.

Dopant migration and lateral p‐n junctions in metalorganic vapor phase epitaxy of AlGaAs on nonplanar GaAs substrates

Lateral p‐n junctions have been demonstrated in the low pressure metalorganic vapor phase epitaxial growth of AlGaAs structures on nonplanar GaAs substrates. It is shown that the final distribution of dopant atoms is governed by the dopant migration over the structured surface evolving during the growth. This result has allowed the single‐step growth of index‐guided lasers with a built‐in lateral current confinement scheme.

Narrow far fields from extended‐window broad‐area lasers

Broad‐area lasers are fabricated with a long (80–100 μm), nonabsorbing window at each end. The window is shown to dramatically improve the spatial mode properties, stabilizing and smoothing the near field, and reducing the far field from 5°–15° to as low as 2°. This improvement comes at the expense of an increase in threshold current and reduction of quantum efficiency.

Variable resonator (variable Q) photopumped phonon‐assisted quantum well laser operation

Data are presented on a photopumped rectangular (w=40 μm, l=250 μm) quantum well heterostructure (QWH), with variable resonator Q along the sample, showing that phonon‐assisted laser operation predominates. To achieve variable resonator Q, the QWH sample is heat sunk embedded in In over half of its length (reflecting edges, high Q), as opposed to simple contact with a Au shim over the remaining half and no reflecting metal on the sample edges (low Q). Photopumping at the low Q, high Q boundary near the sample center turns on and off the n=1 confined‐particle recombination transition (E11 ) and sets a higher energy experimental (as well as calculated) reference, ℏω2 =E11, for the lower energy phonon‐assisted laser operation, ℏω1 =E11 −ℏωLO .