AVS 51st International Symposium
    Semiconductors Tuesday Sessions
       Session SC-TuA

Paper SC-TuA3
Strain Relaxation of MBE-grown Step-Graded Metamorphic InAsP Buffers on InP Substrates

Tuesday, November 16, 2004, 2:00 pm, Room 304C

Session: Semiconductor Heteroepitaxy and Nanostructures
Presenter: M.K. Hudait, The Ohio State University
Authors: M.K. Hudait, The Ohio State University
Y. Lin, The Ohio State University
S.A. Ringel, The Ohio State University
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Step-graded metamorphic InAsP buffers grown on InP substrates to increase the substrate lattice constant are of interest to support a range of high-speed electronic and infrared optoelectronic devices. Recent work by our group has shown that grading the composition of the anion sublattice using InAsP buffers as opposed to the group-III cation sublattice using InAlAs buffers is advantageous for MBE growth for such applications since decoupling the growth rate from the composition control results in superior morphological and thermophotovoltaic device properties. Here, we discuss the strain relaxation properties of step-graded InAs@sub y@P@sub 1-y@ (y=0.32-0.4) buffers, representing a total misfit of ~1.1-1.2% with respect to InP. For this study, InAsP buffers were grown on both (100) and 2° off-cut (100) InP substrates under identical MBE growth conditions with an average grading rate of 20% As/µm. The relaxation of each layer within each buffer was measured along [1-10] and [110] directions using TAXRD to evaluate asymmetric relaxation and tilt relative to the initial substrate orientation. For both substrate types, the strain relaxation was found to be symmetric and greater than 90% for the top InAs@sub 0.4@P@sub 0.6@ layer. This indicates that @alpha@ ([1-10] direction) and @beta@ ([110] direction) slip systems have similar activation energies for dislocation nucleation. Moreover, a small epilayer tilt of ~20-190 arcsec was observed for both substrate orientations, which indicates that tilt generated by @alpha@ and @beta@ dislocations will be in proportion to the substrate offcut resolved in [110] and [1-10] directions, respectively. The relation between these observations and properties of group-V and group-III core dislocations will be made to optimize the growth of these buffers. Correlations with the strain relaxation properties, surface morphology and cross-sectional interface properties will also be made as a function of substrate misorientation.