Study of the Interface Properties in InGaP/GaAs multi quantum wells by Low-Pressure MOVPE from liquid sources

The Al-free InGaP/GaAs heterostructure is an interesting alternative to AlGaAs/GaAs system in a wide range of micro- and optoelectronic applications [1-3]. Nevertheless, the required ML-abruptness of both normal and inverse InGaP-GaAs interfaces is not obtainable, due to both the As/P intermixing and the In memory effect during the MOVPE growth process in which a standard gas switch sequence (GSS) is adopted [4]. As a consequence, unintentional InGaAsP intermediate layers are formed at the interfaces, so that the optical properties of the InGaP/GaAs quantum wells (QW's) are affected by unexpected, low-energy photoluminescence (PL) contributions [5], whereas either the hindrance of the QW emission or its line-shape width increasing, are expected. In this work different lattice-matched InGaP/GaAs single and multi QW structures were grown on exact, S.I. (001)GaAs substrates at 600°C by low-pressure MOVPE, with the use of the TMGa, TMIn, TBAs and TBP precursors; GaAs quantum well thickness varied in the range 3-8 nm. In order to enhance the direct interface abruptness, different GSS's were exploited for the interface growing, and few ML-thick GaAsP interlayers (IL), were inserted at the GaAs-on-InGaP interface [6]. Low-temperature photoluminescence (PL), High resolution X Ray Diffraction (HRXRD), Transmission Electron Microscopy (TEM) analysis and Photo Reflectance Spectroscopy (PR) measurements were performed on the grown heterostructures for correlating the interface properties and the width of the QW emission with the parameters of the growth method adopted. A model to predict the expected PL energy emission from the GaAs QW's, referred to an ideal square QW's with finite potential barriers, was employed to compare the theoretical and experimental results.