GaAs Active Region Research Articles

Phonon-sideband MO-CVD quantum-well AlxGa1−xAs-GaAs heterostructure laser

Laser operation (4.2–300 °K) of multiple-quantum-well AlxGa1−xAs-GaAs heterostructures on a phonon (LO) sideband ∼36 meV below the lowest confined-particle transitions is described. Phonon-sideband laser data are presented on two different metalorganic chemical-vapor-deposited (MO-CVD) quantum-well heterostructures with four GaAs active regions (Lz∼50 and ∼90 Å) coupled by three AlxGa1−xAs (x∼0.35) barriers.

Low-current proton-bombarded (GaAl)As double-heterostructure lasers

Low-current cw stripe double-heterostructure (DH) lasers have been realized using a shallow proton-bombardment technique; unlike usual proton DH lasers they involve a resistive p (GaAl)As confinement layer and a rather highly doped GaAs active region both to reduce spreading current and stripe injected carrier outdiffusion. Threshold currents are on the order of 50 mA for a 12-μm-wide by 200-μm-long cavity.

Single-pass gain measurements on optically pumped Al<inf>x</inf>Ga<inf>(1-x)</inf>As-Al<inf>y</inf>Ga<inf>(1-y)</inf>As double-heterojunction laser structures at room temperature

Experiments are described in which the intensity and spectral distribution of amplified spontaneous radiation is measured on optically pumped Al x Ga (1-x) As-Al y Ga (1-y) As double-heterojunction structures as a function of the length of the region where the amplification takes place. From these data information is obtained on the gain versus wavelength dependence and gain saturation as a function of the excess carrier densities created. Furthermore, the optical absorption of a short unpumped region was also determined. Results are presented for structures with a GaAs active region ( y \approx 0 ) and for a structure with y \approx 0.10 . The results are compared with those of calculations based on various recombination models. Furthermore, a comparison is made with the values of the normalized threshold current density obtained on laser diodes fabricated from the same wafers.

Etched buried heterostructure GaAs/GaAlAs injection lasers

An injection laser is described in which a semicircular GaAs active region is completely surrounded by Ga1−xAlxAs by using selective etching and a single liquid-phase epitaxial growth.The active region dimensions can be made much more symmetric than those obtained with conventional stripe geometry lasers resulting in improved optical characteristics and low room-temperature threshold currents.

Continuous operation over 10 000 h of GaAs/GaAlAs double-heterostructure laser without lattice mismatch compensation

By improving the crystal growth conditions, continuous operation over 10 000 h has been achieved with a conventional metallic stripe geometry double-heterostructure laser without using additional Al to the GaAs active region or P to the adjacent GaAlAs layers, and this laser is still being operated.

Thermal characteristics of buried-heterostructure injection lasers

The thermal characteristics and CW operation of buried-heterostructure (BH) injection lasers, in which the GaAs active regions are completely buried in Ga <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</inf> Al <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> As, are described. The narrow active regions of these diodes facilitate effective heat dissipation. Thus, the CW operation of these lasers has been achieved without the p-GaAs layers usually grown in double-heterostructure (DH) lasers for electrical contacting purposes and with the heat dissipation through n-GaAs substrates. Even in this disadvantageous configuration, the temperature rise in the active regions of BH lasers at threshold is much smaller than that of p-side-down DH lasers. The calculation using an approximate formula can explain these low experimental values fairly well. Due to low operating current and effective heat dissipation, BH lasers can be operated continuously at room temperature on very small heat sinks such as TO-5 transistor headers.

GaAs–Ga1−xAlxAs buried-heterostructure injection lasers

Buried-heterostructure injection lasers which have the filamentary GaAs active regions completely surrounded by Ga1−xAlxAs are proposed and have been successfully fabricated by using two-step liquid-phase-epitaxial techniques. The active regions of these lasers can be made extremely small and do not have dimensional unbalances encountered in conventional injection lasers. The threshold current has been reduced to a value as low as 15 mA by applying current-confining geometry to this laser. A study of optical characteristics has revealed such improvements over ordinary lasers as Gaussian beam profile, fundamental mode (TE00) operation, mode reproducibility, and mode stability. Due to the superior thermal properties of these lasers cw operation was easily obtained.

Far-field emission patterns of single heterostructure GaAs lasers

The emission patterns of single heterostructure lasers have been calculated as a function of the refractive-index Step between the p GaAs active region and the n GaAs substrate. The conclusions that higher n doping levels should produce better optical confinement and a wider far-field pattern are supported by experimental measurements, from which the refractive index can be deduced.

GaAs : Si double-heterostructure LED's

The spontaneous-emission spectra of liquid-phase-epitaxial grown double-heterostructure light-emitting diodes with a Si-doped GaAs active region and Ga1−xAlxAs barrier regions have been measured as a function of the Si concentration in the growth solution and the thickness of the active region. The results indicate that a graded band-gap region is probably formed at the GaAs–Ga1−xAlxAs interface. The double-heterostructure light-emitting diodes are compared with homojunction diodes as potential excitation sources for upconverting phosphors.

GaAs–AlxGa1−xAs heterostructure laser with separate optical and carrier confinement

Heterostructure injection lasers in which the GaAs active region is the center layer of a five-layer dielectric slab waveguide have been investigated. The GaAs active layer is bounded on each side by an AlxGa1−xAs layer to confine the carriers. The two outside layers which are AlyGa1−yAs(y &amp;gt; x) confine the optical field. Lasers with this structure have been fabricated and room-temperature threshold current densities Jth300 as low as 650 A/cm2 have been obtained for 1-mm cavity lengths. Differential quantum efficiencies ηD for these separate optical and carrier confinement heterostructure (SCH) lasers were higher than generally encountered for double-heterostructure (DH) lasers with values as high as 65% for [inverted lazy s]300−μ−long cavities. The external quantum efficiency of several typical units was determined as a function of input current, and for one representative unit a maximum value of 39% was obtained at about four times Jth300. Emission in the fundamental TE mode was obtained for symmetrical structures with optical waveguide thicknesses in excess of 1 μ at currents many times Jth300. The angle of beam divergence perpendicular to the junction plane was found to depend on the thickness of the optical waveguide w with half-power point values varying from 51° to 33° for w between 0.8 and 1.56 μ. Calculation of the optical intensity distributions for the symmetrical SCH structure demonstrated the influence of the AlAs mole fraction and layer thickness on confinement of the optical intensity and suggest that it should be possible to achieve still lower threholds.