The Initial Stages of Growth of Ordered GaInP and GalnAs Grown by Metal Organic Vapor Phase Epitaxy
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ABSTRACT We have used atomic force microscopy (AFM) and Raman spectroscopy to investigate the development of the surface morphology of (001) direct and vicinal GaInP and GaInAs grown under conditions to produce strong CUPtB ordering. Raman spectroscopy provided direct evidence of CuPtB ordering in layers as thin as 10 nm for GaInP and 5 nm for GaInAs. We find that the morphology of GaInP and GaInAs on (001)6B substrates consists of ridges, which are aligned predominately along the [110] direction (A-direction). These ridges are well developed even at layer thicknesses of 2 nm, and their sides consist of step-bunches and near (001) terraces. On (001) direct substrates, the GaInP morphology is similar to that obtained on 6B substrates, although the step bunches have no preferential orientation, while GaInAs (001) growth proceeds by a combination of 2D-island and step flow growth. We discuss possible reasons for the differences in the morphology of ordered GaInP and GaInAs. The results of this work suggest it may be difficult to produce abrupt heterointerfaces in structures containing ordered GalnP and GaInAs alloys. INTRODUCTION The strong modifications to the band structure in III-V ternary alloys due to spontaneous atomic ordering have recently been explored for use in device applications such as light emitting diodes[ 1], solar cells[2], modulation doped structures[3] and low-threshold ordered laser diodes[4]. Ordering leads to a band gap reduction, which enables combinations of ordered and disordered alloys to be used for engineering the band structure of various optoelectronic devices. Both homostructures and heterostructures containing a partially ordered alloy in conjunction with a disordered alloy of the same or different chemical composition have been fabricated and studied[3, 5, 6]. These so-called order/disorder (O/D) structures may have important technological applications, and they will require atomically abrupt interfaces for optimal performance, especially in devices relying on quantum wells formed from the ordered alloy material. Recently, a number of studies employing high-resolution transmission electron microscopy (TEM) and atomic force microscopy (AFM) have investigated the interface and surface structure of ordered Gao.s 2Ino.48P[7-13] and Gao.47In0. 53As[14-16] alloys (hereafter called GaInP and GaInAs) grown by metalorganic vapor phase epitaxy (MOPVE). These studies investigated how the growth parameters influence the surface structure and degree of ordering. The details of the surface morphology are highly dependent upon the substrate orientation and growth conditions and the morphology evolves as the layer grows. Ordered GaInP grown on (001) direct substrates was found to have a wedding-cake-like or honeycomb-like morphology [7, 8, 17] with islands several nm high consisting of monolayer (ML) or bilayer (BL) steps and (001) terraces. The relative number of ML and BL steps depended on the growth conditions[7) and P precursor[18]. For a very thick (10 ltm) double-variant (001) layer, Friedman e
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