M. Ettenberg

Calculated stresses in multilayered heteroepitaxial structures

A useful closed‐form expression for stresses within individual layers of a multilayer composite has been obtained as a function of position within the layer. Equal and isotropic elastic constants were assumed in the calculation, although the error introduced by this assumption is found to vary by no more than the difference in elastic constants. Unequal elastic constants may be handled via computer solutions. The stresses within heterojunction AlxGa1−xAs/GaAs lasers are calculated as an example of the technique. The addition of Al to the active GaAs region is shown to have a drastic effect upon the active‐region stress, changing it from tension to compression. This change of sign in stress is correlated with improvements in operating lifetimes of lasers.

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.

The temperature dependence of threshold current for double‐heterojunction lasers

The temperature dependence of the threshold current has been examined for the double‐heterojunction lasers (AlGa)As, (InGa) (AsP)/InP, and (InGaAs)/(InGa)P with emission wavelengths between 0.8 and 1.4 μm. For all lasers studied, the threshold current density was found to follow the exponential relationship Jth(T) ∝ exp(T/T0), where the constant T0 was found to be directly related to the energy‐band‐gap step, ΔEg, between the recombination region and the adjacent confining layers. The value of T0 was found experimentally to obey the relationship T0=AΔEg, with the constant A having values between 200 and 300 °K/eV for the three types of lasers studied.

Low‐threshold double heterojunction AlGaAs/GaAs laser diodes: Theory and experiment

A detailed study is presented of AlxGa1−xAs/GaAs double heterojunction lasers combining very thin recombination regions (d?0.1 μm) with high Al concentration differences at the heterojunctions. These devices have exceptionally low threshold current densities (475–1000 A/cm2 depending on the structural details), which increase by a median value of 1.35 between 22 and 70 °C. The differential quantum efficiency decrease in that same temperature interval is small. The device parameters have been analyzed in terms of available theory connecting the radiation confinement to the width of the recombination region and the dielectric step at the heterojunctions. Both the threshold current density dependence on the width of the recombination region and the far‐field beam pattern are in reasonable agreement with theory. Assuming no change in carrier or optical flux confinement for large Al concentration differences, the temperature dependence of the threshold current density is found to be somewhat steeper than calcu...

Low‐threshold 1.25‐μm vapor‐grown InGaAsP cw lasers

Vapor‐grown double‐heterojunction lasers of InGaAsP/InP have been prepared with cw room‐temperature threshold currents of 85 mA and differential quantum efficiencies exceeding 50% at 1.25 μm. From several lasers, fundamentaal‐lateral‐ and fundamental‐longitudinal‐mode operation have been observed over moderate current ranges. Over 1000 h of room‐temperature cw operation has been observed to date without significant degradation.

The effect of gas‐phase stoichiometry on deep levels in vapor‐grown GaAs

A deep (0.82 eV) impurity level has been observed via transient capacitance measurements in GaAs prepared under various gas‐phase stoichiometries. The density of these impurities increased with increasing AsH3/GaCl ratio in the vapor phase ranging from 2×1013 cm−3 for a 1/3 ratio to 9×1013 cm−3 for a 3/1 ratio. The minority‐carrier lifetime in these same samples decreased from 15 to 5 nsec with increasing AsH3/GaCl ratio. These deep levels, which serve as recombination centers for lifetime reduction, appear to originate from point defects introduced by deviations from stoichiometry toward the As‐rich side.

Accelerated step‐temperature aging of AlxGa1−xAs heterojunction laser diodes

Double‐heterojunction Al0.3Ga0.7As/Al0.08Ga0.92As lasers (oxide‐striped and Al2O3 facet coated) were subjected to step‐temperature aging from 60 to 100 °C. The change in threshold current and spontaneous output was monitored at 22 °C. The average time required for a 20% pulsed threshold current increases from about 500 h, when operating at 100 °C, to about 5000 h at 70 °C. At 22 °C, the extrapolated time is about 106 h. The time needed for a 50% spontaneous emission reduction is of the same order of magnitude. The resulting ’’activation energies’’ are ∼0.95 eV for laser degradation and ∼1.1 eV for the spontaneous output decrease.

Universal stain/etchant for interfaces in III‐V compounds

The application of the A‐B dislocation etch to the delineation of interfaces in III‐V compounds is described. The etchant is easy to use and has worked on all III‐V compounds tested to date.

cw room‐temperature InxGa1−xAs/InyGa1−yP 1.06‐μm lasers

Room-temperature cw laser operation at wavelengths between 1.06 and 1.12 ..mu..m has been obtained from double-heterojunction structures of In/sub x/Ga/sub 1-x/As/In/sub y/Ga/sub 1-y/P prepared by vapor-phase epitaxy. These devices have pulsed threshold current densities as low as 1000 A/cm/sup 2/ and external differential quantum efficiencies as high as 55%. Their active laser cavities are between 0.14 and 0.36 ..mu..m thick, providing fundamental transverse-mode operation with far-field patterns 50 to 60degree wide. (AIP)Room‐temperature cw laser operation at wavelengths between 1.06 and 1.12 μm has been obtained from double‐heterojunction structures of InxGa1−xAs/InyGa1−yP prepared by vapor‐phase epitaxy. These devices have pulsed threshold current densities as low as 1000 A/cm2 and external differential quantum efficiencies as high as 55%. Their active laser cavities are between 0.14 and 0.36 μm thick, providing fundamental transverse‐mode operation with far‐field patterns 50 to 60° wide.

Effects of dislocation density on the properties of liquid phase epitaxial GaAs

A study has been made of the effect of dislocation density on the properties of p‐type GaAs (Ge‐doped, p = 1 × 1019 cm−3) grown homoepitaxially on GaAs and heteroepitaxially on GaP. It has been found that dislocation densities > 5 × 106 cm−2 reduce the minority‐carrier diffusion length in the p‐type material and, consistent with this reduction, degrade the junction electroluminescence and p‐layer photoluminescence. At high dislocation densities (> 5 × 106 cm−2), it is also found that subgrains form in the GaAs epitaxial layers grown either heteroepitaxially on GaP or homoepitaxially on GaAs. It is surmised that the dislocations polygonize during growth to form subgrain boundaries rather than form due to nucleation at the substrate. Finally, the results indicate that the electron diffusion length is limited to the average dislocation spacing with the dislocations acting as nonradiative recombination centers for electrons.