H. F. Lockwood

AN EFFICIENT LARGE OPTICAL CAVITY INJECTION LASER

A new GaAs injection laser structure is described in which the optical cavity thickness is very large and is varied independently of that of the pair recombination region. Large optical cavities are possible because the radiation propagates predominantly in low‐loss n‐type material. The problem of catastrophic degradation is greatly reduced because of the lower optical flux density.

Al2O3 half‐wave films for long‐life cw lasers

Long‐term operating‐life data are reported for (AlGa)As cw laser diodes. The use of half‐wave Al2O3 facet coatings is shown to eliminate facet erosion, allowing stable diode operation at constant current for periods in excess of 10 000 h.

Large‐Optical‐Cavity (AlGa) As–GaAs Heterojunction Laser Diode: Threshold and Efficiency

Detailed operating properties and first‐order theory of the large‐optical‐cavity (LOC) laser diode are described, including threshold current density, efficiency, mirror damage under pulsed operation, and cw operation at room temperature. This new structure differs from the single‐heterojunction and conventional double‐heterojunction laser in that the optical‐cavity thickness can be made very large and is varied independently of the pair recombination region which is always less than a diffusion length thick. Large optical cavities are possible with high differential quantum efficiencies at room temperature because the radiation propagates predominantly in low‐loss n‐type material, allowing the design of lasers for specific applications. The problem of catastrophic degradation in the wide‐cavity devices is reduced because of the lower optical flux density. The threshold current density depends on the width of the mode‐guiding region, increasing with increasing thickness of that region. Power conversion efficiency values of 22% have been achieved at room temperature with narrow‐cavity lasers.

Degradation of AlxGa1−xAs heterojunction electroluminescent devices

Experimental results are presented correlating the operating life of (AlGa)As heterojunction diodes with recombination region doping and Al concentration. For a given doping level, the operating life is shown to increase with the addition of Al. The relationship between spontaneous emission degradation and lasing properties has also been studied.

LOW‐THRESHOLD LOC GaAs INJECTION LASERS

We report new results with the large optical cavity (LOC) injection lasers previously described. It is shown that by narrowing the n region adjacent to the junction, the threshold current decreases without decreasing the differential quantum efficiency. Furthermore, epitaxial growth of all layers was used, and diffusion was avoided. Fabry‐Perot mode threshold current densities as low as 1700 A/cm2 were obtained with differential quantum efficiencies of about 50% and power conversion efficiencies of 20% at room temperature.

Lasing Transitions in p+‐n‐n+ (AlGa) As–Ga As Heterojunction Lasers

A study of the lasing and spontaneous emission from p+‐n‐n+ heterojunction lasers with lightly doped n‐type active regions shows that the stimulated emission is not due to a simple band‐to‐band recombination process. It is further shown that the 300 K gain coefficient dependence on the junction current differs greatly from that predicted on the basis of band‐to‐band lasing involving a parabolic density‐of‐states distribution.

Measurements of refractive index step and of carrier confinement at /AlGa/As-GaAs heterojunctions.

The refractive index difference at the GaAs lasting wavelength of [inverted lazy s] 9000 A has been experimentally determined, from the measured beam profile, for a range of (AlGa)As–GaAs heterojunctions of practical interest. Good agreement is found with values calculated from the change in band gap with increasing Al in (AlGa)As. We have also shown by direct measurement that the loss of electron confinement at p+‐p heterojunctions follows a thermally activated process with activation energy equal to the difference in band gap at the heterojunction.

Radiation trapping in laser diodes

This paper is concerned with the problem of cavity geometries which exhibit anomalously low radiative efficiencies. While the ideas presented apply to any type of cavity, the experiments and discussion refer specifically to the type of cavity of importance in commercial injection lasers, a Fabry‐Perot cavity with cleaved end facets and sawed sidewalls. In this study, it is shown that the lowering of the external efficiency is probably associated with the excitation of internally circulating modes, analogous to those found in lasers with four cleaved sides. A dual‐cavity diode structure is employed to demonstrate that it is the sidewall loss which controls the excitation of the internally circulating modes. To determine the geometric conditions for internal mode excitation in single and double heterojunction diodes, an extensive study was made of the combination of length, width, and facet reflectivity which lead to efficiency decreases. It is assumed that the internal modes are excited when the distribute...

Effect of edges on the reliability of GaAs and (AlGa) as heterojunction leds

The effect of various diode geometries on the degradation rate of heterojunction diodes with either GaAs or (AlGa)As in the recombination region has been studied. It is shown that GaAs diodes are particularly sensitive to edge-related degradation which varies with the current density J as J3/2. The addition of Al to the recombination region considerably reduces the degradation rate of diodes both with and without exposed edges, and data are reported for Al0.1Ga0.9As stripe-contact edge-emitting structures operating for over 20,000 hours with no change in output at 1000 A/cm2.

Experimental properties of injection lasers. III. Current dependence of polarization

The power distribution function which describes the shape and current dependence of the lateral beam is applied to a phenomenological model of weakly polarized injection lasers. It predicts that the polarization of coherent power should drop rapidly from an infinite value at threshold to near unity at high drive. Careful measurement of polarization of a laser representative of the model, with especial attention to rejection of the spontaneous emission, supports this conclusion. The form of the power distribution function used in the analysis implies that lasers with strong polarization at high drive have large threshold differences of the two polarizations, suggesting that present theories of the source of polarization are inadequate. The difficulty of interpreting the present results in terms of spatial hole burning or inhomogeneities is pointed out.