Single and Double Variant Cupt-B Ordered Galnas
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ABSTRACT Nominally lattice-matched GaInAs layers grown by metal organic vapor phase epitaxy on InP substrates have been studied using high-resolution x-ray diffraction (HRXRD) to determine the growth conditions under which ordering is introduced. HRXRD provides an independent means to quantify the order parameter of semiconductor heterostructures as well as the ordering on different {111 planes, i.e., double variant ordering. This independent means to determine ordering provides for a better understanding of the effects of ordering on the electronic and optical properties. Double variant ordering was observed for epitaxial layers grown on exact (001) InP substrates, with an order parameter of about 0.1 in both variants. For substrates that were miscut by 6 degrees, single variant ordering was detected. In these cases, an order parameter as high as 0.66 was measured for certain growth conditions. The layers grown on vicinal substrates are all of high crystalline quality, those on (001) substrates exhibit some mosaic spread. INTRODUCTION It has been well established that atomic ordering, which is commonly observed in epitaxially grown III-V alloys, effects the alloys' electronic and optical properties.1 Ordering reduces the band gap with respect to the random alloy, changes the band structure, and establishes optical polarization. These effects are of considerable interest to the semiconductor community for the development of high-quality, band gap engineered materials. Many studies of atomic ordering have been reported, particularly in GaInP, including analyses of the electronic
effects using photoluminescence (PL)2 , and structural analyses using transmission electron microscopy (TEM)3 , scanning tunneling microscopy 4 , and x-ray diffraction (XRD). 5' 6 Recent works have reported on CUPtB in technologically important Ga×Inl-,As grown on InP using photocurrent sgectroscopy 7 , TEM 8, and ultrahigh frequency photoconductive decay measurements . The current paper presents a direct, quantitative measurement of the degree of order in GaInl-,As samples using high-resolution XRD (HRXRD). CuPt is the most commonly observed type of ordering in ternary III-V epilayers grown on [001] oriented substrates. It consists of (11) planes rich in alternating group-rn constituents. Group-V rich surface reconstructions typically lead to ordering of the (I 11) and/or (1 11)planes, referred to as the CuPtJ variants. Epilayers grown on exact [001] substrates typically contain approximately equal amounts of the two B variants. Epilayers grown on substrates tilted towards a (101)B plane contain more of that (011)1 variant than the other. A substrate tilt of 6' has been shown to produce nearly single variant CUPtB ordering.iO EXPERIMENT Eight GaInI -As samples were studied with HRXRD. The samples were grown by low pressure metal organic vapor phase epitaxy at a total pressure of 75 Torr on InP substrates. The precursors were arsine (AsH 3), phosphine, triethylgallium and trimethylindium. The carrier gas was hydrogen for sample 3, with a gr
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