AVS 50th International Symposium
    Semiconductors Thursday Sessions
       Session SC-ThM

Paper SC-ThM4
Strain Relaxation of Step-graded InAsP Buffers on InP Grown by Molecular Beam Epitaxy

Thursday, November 6, 2003, 9:20 am, Room 326

Session: Heteroepitaxy and Strain Engineering
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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Compositionally graded metamorphic 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 based on the InGaAsP material system. 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 In(Al,Ga)As buffers is advantageous for such applications since decoupling the growth rate (Indium flux) from the composition control (As:P flux ratio) results in superior morphological properties of relaxed layers. Here, we discuss the strain relaxation properties of step-graded InAs@sub y@P@sub 1-y@ out to a nominal composition of y = 0.4, representing a total misfit of ~ 1.2% with respect to InP. For this study, InAs@sub y@P@sub 1-y@ buffers were grown on both on-axis and 2° off-cut (001) InP substrates under identical solid source 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 ~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, and a comparison to cation based graded layers will be made to optimize the growth of these buffers.