John E. Epler

Donor‐induced disorder‐defined buried‐heterostructure AlxGa1−xAs‐GaAs quantum‐well lasers

A simple form of a buried heterostructure Al x Ga1−x As‐GaAs quantum‐well laser is described that is realized by impurity‐induced layer disordering (d o n o r‐i n d u c e d disordering). The layer disordering [and the resulting band‐gap shift to higher energy (and lower index)] is accomplished by Si diffusion in a stripe pattern defined by a Si3N4 mask. Single‐mode lasers of stripe width 3 and 6 μm are demonstrated that operate continuously at 300 K in the threshold current range of 10–25 mA and with single‐facet power levels as high as 10–20 mW.

Transverse modes of gain‐guided coupled‐stripe lasers: External cavity control of the emitter spacing

By means of an external grating cavity, the dispersion relation of the transverse modes of gain‐guided coupled‐stripe laser diodes is determined. The parabolic relation obtained indicates (despite the stripes) a relatively flat gain profile similar to a broad area laser. Accordingly, higher order transverse modes are possible and are demonstrated with near and far fields exhibiting one and two emitters per stripe.

Supermodes of multiple‐stripe quantum‐well heterostructure laser diodes operated (cw, 300 K) in an external‐grating cavity

The far‐field supermode patterns of a phase‐locked multiple‐stripe quantum‐well heterostructure (QWH) laser diode are described as a function of injection current and emission wavelength, the latter controlled by an external grating. The external‐grating cavity is used to isolate single or multiple supermodes of the multiple‐stripe QWH laser (Pout>170 mW cw, λ∼7400 A). The progression of supermode patterns consists of a discrete set of mode configurations for each longitudinal mode of the spectrum. The progression is cyclic with a ∼2.8‐A period which corresponds to the longitudinal mode spacing of the diode. Under high gain conditions, i.e., near the center of the recombination‐radiation spectrum or at higher current levels, continuous tunability is observed with gradual transitions between supermode eigenstates. As the gain is reduced (low current), the number of supermodes observed decreases until only the in‐phase pattern, i.e., each emitter at the same phase, remains above threshold. The far‐field pat...

Far‐field supermode patterns of a multiple‐stripe quantum well heterostructure laser operated (∼7330 Å, 300 K) in an external grating cavity

A multiple‐stripe quantum well heterostructure laser diode operated in an external grating cavity is shown to exhibit the far‐field radiation patterns of the ‘‘supermode’’ eigenstates predicted by coupled mode analysis. Data (∼7330u2009A) are presented on a gain‐guided laser array at various continuous (cw, 300 K) operating currents to illustrate the progression of the supermodes from double‐lobed patterns (phase shift between emitters) to a single‐lobed pattern (no phase shift between emitters). As the cavity wavelength is scanned a cyclical progression (2.8‐A period) of far‐field patterns (supermodes) is observed.

Broadband tuning (ΔE∼100 meV) of Alx Ga1−xAs quantum well heterostructure lasers with an external grating

Alx Ga1−xAs‐GaAs quantum well heterostructure laser diodes are shown to be tunable over a 100‐meV range when operated continuously (cw) at room temperature in an external cavity with a grating to control feedback. The gain profile of the n=1 and n′=1′ (electron‐to‐heavy hole and electron‐to‐light hole, e→hh and e→lh) transitions and the n=2 electron‐to‐heavy hole transitions are clearly outlined by the intensity profile of the selected laser lines. The partial homogeneous broadening of the gain profile agrees with rapid carrier relaxation in the well. The diodes contain a single 60–90‐A GaAs well and are grown by metalorganic chemical vapor deposition.

Broadband operation of coupled-stripe multiple quantum well AlGaAs laser diodes

A recently developed AlGaAs multiple stripe, multiple quantum well superluminescence light‐emitting diode (SLED) with an extremely low reflectivity front‐facet coating is operated as a high‐power laser in an external grating cavity over an unusually broad tuning range. The SLED diode is operated continuously (cw) in a tuning range Δℏω∼94 meV and a power output from the grating cavity of 75 mW (optical flux ∼500 mW within the compound cavity). Data are presented showing the output power as a function of wavelength at currents of 750 mA (7660 A<λ<8040 A) and 1.0 A (7620 A<λ<8085 A). The threshold current in pulsed laser operation is measured over a range of 130 meV.

Hydrostatic pressure measurements (≲12 kbar) on single‐ and multiple‐stripe quantum‐well heterostructure laser diodes

Short wavelength Alx’Ga1−x’As‐AlxGa1−xAs (x’∼0.85, x∼0.22) quantum‐well heterostructure (QWH) laser diodes (well size Lz ≊400 A) that operate continuously (cw) at 300 K are subjected to hydrostatic pressure (≲12 kbar). The emission spectrum and the light intensity versus current (L‐I) curves are monitored to determine the pressure dependence of the direct (Γ) band gap and the threshold current. The band gap exhibits a linear pressure dependence with a noticeable change in slope at ∼4.5 kbar, similar to previously reported results for AlxGa1−xAs‐GaAs QWH diodes. The threshold current increases monotonically with pressure, reflecting the increasing loss of carriers to the X and L bands. The short‐wavelength cw limit of the system, i.e., a gain‐guided laser with a 400‐A AlxGa1−xAs (x∼0.22) quantum well and no separate waveguide region, is determined to be ∼6980 A.

Pressure dependence of AlxGa1−xAs light emitting diodes near the direct‐indirect transition

High‐pressure studies on high quality AlxGa1−xAs double heterostructure light emitting diodes (LEDs) grown by liquid phase epitaxy (LPE) are presented. The AlxGa1−xAs active region varies in composition from x∼0.25 to x∼0.53, i.e., through the important region of the direct‐indirect crossover (x≡xc≊0.45). The pressure coefficient of the Γ conduction band is observed to decrease (∼1 meV/kbar for x∼0.25 to x∼0.53) with increasing Al concentration, which is in accord with alloy disorder and band‐edge bowing. Indirect‐gap (X) recombination radiation of significant intensity is observed and provides evidence for the high quality of the LPE diodes. High‐pressure measurements, and the corresponding increase in energy of the direct band edge and decrease in the indirect band edge, show that the light emission is a strong function of the carrier distribution in the Γ and X conduction‐band minima. Comparison LEDs fabricated from a crystal (x∼0.37) grown by metalorganic chemical vapor deposition exhibit nearly simil...

Mode‐locked coupled‐stripe quantum well laser operation (λ∼7350 Å) in a tunable (Δℏω∼37 meV>kT) external grating cavity

The performance of an actively mode‐locked coupled‐stripe Alx’Ga1−x’As‐AlxGa1−xAs quantum well laser in a tunable external cavity is described. Pulses as short as 50 ps are measured and a tuning range of Δℏω∼37 meV>kT, which is not the limit, is demonstrated. The existence of the transverse modes of coupled‐stripe lasers increases significantly the spectral density of available lasing modes (for mode locking) compared with a single‐stripe laser.

Thermal behavior and stability of room-temperature continuous Al/sub x/Ga/sub 1-x/As-GaAs quantum well heterostructure lasers grown on Si

Thermal characteristics of p-n Al/sub x/Ga/sub 1-x/As-GaAs quantum-well heterostructure (QWH) diode lasers grown on Si substrates have been investigated. Continuous operation at 300 K for over 10 h has been demonstrated for lasers mounted with the junction side away from the heat sink (junction-up) and the heat dissipated through the Si substrate. Junction-up diodes grown on Si substrates had measured thermal impedances 38% lower than those grown on GaAs substrates, with further reductions possible. Measured values were consistent with calculated values for these structures. Low sensitivity of the lasing current to temperature has also been observed, with T/sub 0/ values as high 338 degrees C. >