Selective Area Epitaxy of GaAs Optical Waveguides by Laser Assisted Chemical Vapor Deposition
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631 Mat. Res. Soc. Symp. Proc. Vol. 397 01996 Materials Research Society
EXPERIMENT LCVD Growth System The LCVD system consists of a vertical MOCVD reactor operated at atmospheric pressure, an Ar ion laser operated at multiple wavelength (488nm 514nm) and a computer controlled X-Y laser beam scanner (2-3 pm positioning resolution). An optical grade quartz window, welded onto our cylindrical Si0 2 growth tube, is flushed with a small flow of H2 during annealing to prevent deposition that would interfere with the incoming laser light. Trimethylgallium (TMG, -10°C), arsine (AsH 3, 100%), and silane (1000 ppm, in H 2) were used as source gases; Pd diffused H2 was the carrier gas. GaAs substrates were attached to a graphite susceptor which was RF heated to a substrate temperature of 400'C. An Ar ion laser, whose spot size at the substrate surface is controlled by the position of a focusing lens, was
repeatedly scanned in a straight line over a local area of the substrate to induce maskless selective deposition of GaAs. Negligible deposition occurs outside of the laser irradiated area for the temperatures used in these experiments. Other details of the experimental apparatus have been reported elsewhere 2 . It should be noted that with this LCVD apparatus, we have previously reported the successful maskless deposition of several other electronic and optoelectronic devices including p-n junctions 3 , PIN photodetectors 4 , MESFETs', and high speed MSM detectors 6 . All of these devices performed at least as well as conventionally grown devices of similar dimensions. These selectively grown devices constitute a core of electronic and optoelectronic components necessary for the monolithic integration of optoelectronic circuits. In this paper we present another key OEIC component, GaAs optical waveguides, that have been selectively grown by LCVD and exhibit comparable properties to conventionally fabricated waveguides of similar structure.
Selective Growth of Strip-loaded and Channel Waveguides Strip-loaded and channel waveguides have been selectively grown with our LCVD system. The strip-loaded structure, shown in Figure 1 a, consists of a "loading strip" which is selectively deposited on a core\cladding layer of AIxGal ,As\GaAs. The loading strip may be realized by a heavily doped (n') GaAs rib, having a smaller refractive index than GaAs. In this type of structure, light is confined in the GaAs layer lying directly beneath the loading strip. Confinement in the vertical dimension results from the GaAs refractive index exceeding that of the AIxGalxAs cladding and n+-GaAs strip. Lateral confinement is achieved because the n÷-doped loading-strip makes the effective refractive index underneath the rib greater than the refractive index to either side of the rib. The second type of waveguide structure grown by LCVD is a channel waveguide. This structure, shown in Figure lb, consists of a relatively thick GaAs line selectively deposited on an AIxGal-xAs cladding layer. Light launched into the GaAs channel remains confined ther
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