MD2 Novel 0.98pmlnGaAs/AIGaAs Quantum Well Lasers Structures Grown by Organomettallic Vapor Phase Epitaxy

W. S. Hobson, S. J. Pearton, J . L. Lopata, N. K . Dutta, M . C. Wu, and Y . K . Chen

AT&T Bell Laboratories 600 Mountain Avenue

Murray Hill, New Jersey 07974 (908) 582-2220

SUMMARY ABSTRACT

There is considerable interest in high power InGaAdAlGaAs quantum well lasers emitting

at 980 nm for use as the pump source for erbium-doped fiber amplifiers. Laser characteristics of

particular importance for this application include model stability under high power operation

and optical beam divergence. In addition, it is also useful to consider laser structure which

simplify the epitaxial growth and subsequent laser processing. We have fabricated several

novel laser structures which address some of these issues. These include periodic index

separate confinement heterostructures (PINSCH) for minimizing the optical beam divergence, a

buried heterostructure (BH) formed by a single growth over mesas etched into the substrate in

the (OZ) direction, the introduction of InGaP stop-etch layers into the AlGaAs cladding layers

to simplify processing, and BH lasers formed by regrowth of various layers.

The optical beam divergence is of importance since it governs the fraction of emitted power

which can be effectively coupled into the fiber. Graded-index separate confinement

heterostructures (GRINSCH) have resulted in the lowest thresholds and highest external

differential quantum efficiencies, but typically exhibit large (e.g. 50') transverse far field

angles. The PINSCH structure consists of cladding layers each comprised of eight periods of

Aloe4 G Q . ~ As/GaAs which provide both optical and electrical confinement. The transverse

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is expanded over that of the GRINSCH since approximately three

aAs periods are required until the optical field decays; consequently, the

rse beam divergence is reduced. We have utilized organometallic vapor phase

) to grow the PINSCH structures and used secondary ion mass spectrometry,

microscopy, and transmission electron microscopy to characterize the layers.

of the PINSCH and GRINSCH lasers grown using similar conditions were

sverse fare field angle of the PINSCH laser is reduced to 23" compared to

46" for the GRWSCH, while there is a modest increase in threshold current (19 mA vs. 10 mA).

guided BH lasers provide increased modal stability compared to weakly

ures such as ridge waveguide lasers. We have produced BH lasers by using

wth over nonplanar GaAs substrates formed by etching mesas in the [OE]

s in a discontinuous layer structure in which p-AlGaAs surrounds the laser

the top of the mesa. Previously, in other materials systems, growth over

e [ O i l ] direction have resulted in BH lasers. However, a subsequent ion

ired for lateral electrical confinement. We have examined the resultant

ated lasers had thresholds of 30 mA for cavity lengths of 250 pm and

per facet. Other laser characteristics will be discussed.

report on the incorporation of InGaP stop etch layers. The use of these layers

mesa dimensions to be achieved without the risk of overetching. Broad area

well GRINSCH lasers with 500 pm cavity length exhibited threshold current

mA/cm2, only slightly higher than usual (-160 mA/cm2). Various BH

will also be discussed.

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