L.M.F. Kaufmann

Analysis of 6-nm AlGaAs SQW low-confinement laser structures for very high-power operation

This paper reports experimental results on single quantum-well separate confinement heterostructures (SQW SCH) with low-confinement factor, designed for very high-power operation. The maximum power output for AR/HR coated 3-mm-long devices, measured in very short pulsed conditions (100 ns/1 kHz), from 10-/spl mu/m-wide stripes was as high as 6.4 W before catastrophic optical degradation. If scaled to continuous-wave (CW) conditions, this value would be 800-1100 MW, which would mean a factor of 22.7 times more than reported for the best devices with normal design for threshold minimization. The absorption coefficient for the symmetrical structure is as low as 1.1 cm/sup -1/, in spite of the low trapping efficiency of carriers in the quantum well (QW). The maximum differential efficiency is 40% (both faces, uncoated devices) for symmetrical structure and 33% for the asymmetrical one (all measurements in pulsed conditions). Threshold current densities were 800 A/cm/sup 2/ for 5-mm-long devices in the symmetrical case and 2200 A/cm/sup 2/ in the asymmetrical one. The effects of inefficient carrier trapping in the QW on the threshold current densities and differential efficiency are discussed.

Stress-induced effects by the anodic oxide in ridge waveguide laser diodes

This paper studies, both theoretically and experimentally, stress-induced effects on the lateral far-field behavior for ridge-type semiconductor laser diodes where anodic oxide is used for the definition of the stripe width. These effects consist of antiguiding under the stripe region, and of two positive waveguiding features near the stripe edges. For low-threshold devices, these effects may be more important than thermal effects, depending on the stress in the oxide. They put a lower limit on the built-in index guiding to be introduced by lateral etch outside the ridge region in order to maintain fundamental mode operation for wider stripes. The magnitude of these effects may be as large as /spl Delta/n/sub ef/=1/spl times/10/sup -3/. An analytical mathematical model is deduced for computing stresses and strains for a certain ridge-shaped interface which bounds the elastic medium.

Controlled Anodic Oxidation for High Precision Etch Depth in AlGaAs III‐V Semiconductor Structures

Controlled anodic oxidation for achieving a better control of etch depth in AlGaAs semiconductor structures is studied. The rates of material consumption and oxide thickness growth for p ++ -GaAs and p-Al 0.38 Ga 0.89 As are given for the citric acid/glycol/water electrolyte. The etch profiles for GaAs/Al 0.45 Ga 0.55 As and GaAs/Al 0.50 Ga 0.40 As layer sequences in laser diode structures are presented. The underetch is rather high and depends on oxidation conditions (constant voltage or constant current). The profile obtained is very rough for constant voltage oxidation and much better when using constant current conditions. The latter also improves the uniformity of oxide growth. The etch rate of the anodic oxide in diluted HCl is much larger for GaAs than for AlGaAs.

High-power operation of low-confinement laser-diode structure

Low confinement laser diode structure permits lower modal gain, longer devices and wider stripes. The optimum value of the confinement factor is correlated with the modal attenuation coefficient. For an 1 cm-1 modal attenuation coefficient, the optimum operation is obtained in 12 micrometers stripe and 0.007 confinement factor. In such structures, fundamental lateral mode is preserved at power higher than 1 W.

Microwave analysis of double barrier resonant tunneling diodes

Accurate microwave measurements up to 40 GHz have been carried out on GaAs/AlAs Double Barrier Resonant Tunneling (DBRT) diodes over the whole bias range of its DC characteristic. The resulting small-signal scattering parameters (S-parameters) have been analysed afterwards in terms of equivalent circuits. The analysis demonstrates that the most suitable equivalent circuit of the DBRT structure has to include, apart from the circuit elements used to model the Esaki tunnel diode, an intrinsic inductance which is related to the life time of the quantum well quasi-state involved in the tunneling process. The bias dependency of the equivalent circuit parameters and the maximum oscillation frequency of the DBRT device have been obtained.