Low indium content quantum well structures
View Patent ↗A method of suppression of Indium carry-over in the MOCVD growth of thin InGaAsP quantum wells, with low Indium content, on top of thick GaInAsP, with high Indium content. These quantum wells are essential in the stimulated emission of 808 to 880 nm phosphorous-based laser structures. The Indium carryover effect is larger in large multi wafer reactors and therefore is this invention focused on large multiwafer MOCVD reactors. This invention improves the quality of the quantum well, as measured by photo-luminescence spectra and uniformity of wavelength radiation.
1. A method of simultaneously growing in a horizontal low pressure planetary MOCVD reactor a plurality of wafers having a gallium arsenide substrate for use in laser diodes, comprising the steps of:
a) planetarily rotating each of said plurality of wafers while growing thereon a high Indium content wave guide foundation layer exhibiting a high indium vapor pressure;
b) introducing into said reactor a short interval of trimethylgallium and phosphine to encapsulate residual indium deposited upstream of the wafer in a pseudomorphic layer of InGaP, utilizing residual indium remaining from the formation of said foundation layer; and
c) growing a low Indium containing In x Ga 1-x As 1-y P y quantum well active region with precise Indium control, without disturbance by said residual Indium.
2. A method according to claim 1 wherein said active layer is a quantum well layer having the composition In x Ga 1-x As 1-y P y where x and y are small and adjusted to produce radiation at a specified wavelength.
3. A method according to claim 1 wherein said short interval of trimethylgallium gas deposits a layer of gallium phosphide having a nominal thickness of less than 1 nanometer over the surface of said plurality of wafers.
4. A semiconductor structure for a laser diode which does not emit spurious Q-line radiation, comprising
a GaAs substrate;
an In 0.48 (Al α Ga 1-α ) 0.52 InP wave guide layer adjacent said substrate; and
an active region having a thin, low in containing strata next to said waveguide layer, said active region having the composition In x Ga 1-x As 1-y P y where x and y are small and adjusted to produce radiation at a specified wavelength and wherein x is lower than α of said waveguide layer.
5. A semiconductor structure according to claim 4 wherein said waveguide layer is encapsulated in a pseudomorphic GaP layer having an average thickness less than one nanometer.
6. A semiconductor structure according to claim 5 wherein said adjustment of x and y avoids the zone of poor miscibility.
7. A semiconductor structure according to claim 6 wherein said adjustment of x and y establishes a predetermined lattice mismatch strain.