Process for forming a positive index waveguide

A process of preparing a laser comprising

• providing a monocrystalline substrate comprised of a III-V semiconductor,
• epitaxially growing on the substrate N and P conductivity type cladding layers having a concentration of 10.sup.16 to 10.sup.18 conductivity imparting ions per cubic centimeter separated by an active layer,
• the substrate and the layers together forming a monocrystlline III-V compound structure, wherein the group V ions are arsenic and the group III ions are at least one of gallium and aluminum,
• characterized in that a laterally confined positive index laser presenting a planar surface is formed by
• providing a first substrate portion having a conductivity imparting ion concentration of from 1 to 3.times.10.sup.18 ions per cubic centimeter,
• epitaxially growing on the first substrate portion an isolating substrate portion being comprised of gallium aluminum arsenide containing from 30 to 60 mole percent aluminum and having a resistivity of greater than 10.sup.7 ohm-cm, said isolating substrate portion forming one major surface of the substrate,
• providing on the one major surface a protective layer of silica or silicon nitride defining an opening,
• through the opening creating a channel in the substrate through the isolating substrate portion of the first substrate portion to expose an unprotected portion of the substrate beneath the one major surface,
• forming a laser waveguide region by selectively depositing epitaxially in sequence
• a first gallium arsenide layer having a first conductivity type ion concentration of from 10.sup.17 to 5.times.10.sup.18 ions per cc,
• a first cladding layer comprised of aluminum arsenide or gallium aluminum arsenide containing at least 90 mole percent aluminum having a first conductivity type ion concentration of from 10.sup.16 to 10.sup.19 ions per cc,
• an active layer comprised of gallium arsenide having a substantially lower conductivity imparting ion concentration than the first cladding layer,
• a second cladding layer comprised of aluminum arsenide or gallium aluminum arsenide containing at least 90 mole percent aluminum having a second conductivity type ion concentration of from 10.sup.16 to 10.sup.18 ions per cc, and
• a surface gallium arsenide layer having a second conductivity type ion concentration of greater than 10.sup.19 ions per cc,
• epitaxially depositing the laser waveguide layers selectively in the channel and on the gallium aluminum arsenide isolating portion of the substrate forming side walls of the channel by conducting deposition at a temperature in the range of from 650.degree. to 750.degree. C. at a pressure of less than 10 torr. from an atmosphere comprised of arsine gas and at least one of trialkyl aluminum and trialkyl gallium gas, alkyl being independently in each occurrance selected from methyl and ethyl, with the ratio of arsine to remaining gas being from 10:1 to 30:1.
• terminating epitaxial deposition with the surface gallium arsenide layer lying at or beneath the one major surface by a distance of 3000 Angstroms or less to form a planar surface therewith, and
• deposting on the planar surface at least one layer bridging the substrate and the laser waveguide region,
• so that the laser waveguide region acts as a wave propagation medium, the epitaxially deposited substrate portion acts as a lateral isolation medium for the waveguide region, and the planar surface formed by the waveguide region and the substrate one major surface facilitates formation of the bridging layer.