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Synthesis of InGaAs quantum wells, lattice matched to InP by metalorganic vapour phase epitaxy poses severe problem because arsenic is incorporated into the growing solid much more readily than phosphorus. Therefore growth of InP after growing InGaAs is likely to have a transition layer of InGaAsP/InAsP of uncontrolled composition even though the arsine flow is switched off, because of trace amounts of arsine in the growth reactor. A common technique used to minimise the problem is to introduce a suitable pause in the growth sequence during the transition from InGaAs layer to InP layer in order to minimise the arsine content in the growth chamber, before starting the growth of InP. We find from photoluminescence (PL) measurements that this pause is not sufficient to optimise the well quality. The halfwidth of PL can be improved further by growing an intermediate layer of InGaAsP between InGaAs and InP, such that the quantum well structure consists of 5 layers in the sequence: InP/InGaAsP/InGaAs/InGaAsP/InP. The optimisation of pause sequence is made during the switching steps: (i) pause PI- in the transition from InGaAsP to InGaAs and (ii) pause P2- in the transition from InGaAs to InGaAsP. The nominal composition of the well is In0.53 Ga0.47 As with thickness of 100°A. The nominal composition of the intermediate layer is In0.72Gt0.28gAs0.6P0.4 Two Ga sources have been used during the growth of In0.53 Ga0.47As and In0.72Ga0.28As0.6P0.4, while the In source is kept the same. The PL emmision peak lies at 0.815 eV at 9 K, with halfwidth ~ 6 meV which is close to the state of art. In comparison, the PL measurement from QW samples with three layer sequence InP/InGaAs/InP with pauses at both interfaces of InGaAs gave halfwidth of more than 10 meV. Lattice matching of all the layers used in the above studies is checked separately on thick layers grown under similar growth conditions, by using X-ray diffraction measurements.
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