P. Gavrilovic

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.

Temperature profile along the cavity axis of high power quantum well lasers during operation

Measurements of the temperature distribution along the cavity of 0.5 W AlGaAs quantum well lasers are presented. The spatial distribution of temperature was determined by measuring the spectral shift of electroluminescence emitted through a window in the GaAs substrate metallization. The average temperature of the active layer is 10–15 K higher than the heatsink temperature at 0.5 W output. Facet temperatures can exceed the average active layer temperature by over 100 K. Data are also presented illustrating the temperature profile at different drive currents between threshold and the maximum operating current. A temperature profile of a laser with a damaged front facet is presented, showing a hot region that is twice the size of the defect.

Persistent spectral hole burning at liquid nitrogen temperature in Eu 3+‐doped aluminosilicate glass

The observation of persistent spectral hole burning (PSHB) in Eu3+‐doped aluminosilicate glass at 77 K is reported in this letter. The homogeneous linewidth of the 7F0→ 5D0 transition is measured to be ∼0.5 A by both PSHB and fluorescence line narrowing techniques. The ratio of inhomogeneous‐to‐hole widths at 77 K is 45. The 7F0→ 5D0 transition is visible directly in transmission due to the high concentration of Eu3+.

High‐power, single‐frequency diode‐pumped Nd:YAG microcavity lasers at 1.3 μm

A single‐frequency output power of 210 mW on the 1.3 μm transition was obtained from a monolithic YAG laser doped with 4.2% Nd. Lasers fabricated from high Nd‐concentration YAG crystals oscillated simultaneously on the 1.319 and 1.338 μm lines at high pump power, but in a single axial mode at both wavelengths. The oscillation frequency was continuously temperature‐tunable at a rate of 3.6 GHz/ °C over a range of 170 GHz (10 A). The emission was linearly polarized with an extinction ratio ≳1000:1. In two‐wavelength operation, the 1.319 and 1.338 μm transitions were orthogonally polarized.

Photoluminescence measurement of the facet temperature of 1 W gain‐guided AlGaAs/GaAs laser diodes

The output facet temperature of high‐power AlGaAs/GaAs single quantum well (SQW) laser diodes was measured during operation. The front output facets were passivated with Al2O3 coatings. The spectral shift of photoluminescence from the cladding layers was used to determine the temperature rise at the front facet with increasing output power. The spatial resolution of the technique allowed to look at each cladding layer individually and to study the correlation between the near‐field pattern and the temperature profile along the active layer. The local temperature on the facet at 1 W total optical power (corresponding to an average linear power density of 10 mW/μm) was found to vary between 25 and 45 K above the average active layer temperature and to exceed the heat‐sink temperature by up to 70 K. This represents a significant reduction of facet temperature in comparison to earlier reports and can be attributed to high‐quality passivation coatings.

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).