Atomic Force Microscopy and Raman Spectroscopy Study of Strain Relaxation in InGaAs ON GaAs(100) Grown by Chemical Beam
- PDF / 1,569,529 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 69 Downloads / 169 Views
RO,
ABSTRACT The correlation of surface morphology with strain relaxation in the Ino.15Gao.ssAs epilayer on GaAs(100) grown by chemical beam epitaxy using unprecracked monoethylarsine has been investigated. The surface morphology of InGaAs was analyzed by atomic force microscopy as the epilayer thickness was increased from 0.025 to 1.668 p m. The changes in the surface morphology indicated that surface roughening is related to the process of strain relaxation in the film. The strain-induced shifts in the GaAs-like longitudinal optical phonon in the Raman spectrum also indicated that the strains in the InGaAs epilayer relax via step-wise process with increasing the film thickness beyond the critical thickness, which agrees well with the changes of surface mophology. INTRODUCTION Epitaxially grown InGaAs films have become the topic of numerous investigations due to their potential in optoelectronics. InGaAs/GaAs heterostructures have a lattice misfit at the interface(0- 7%), which causes lattice strain in the layer and
may create defects such as dislocations beyond the critical thickness.[1-31 The critical thickness is the epilayer thickness above which the interface to the substrate becomes incoherent, and the epilayer materials become fully or partially relaxed. Relaxation process, however, is not well understood for the films beyond the critical thickness and hence it becomes a requirement to have knowledge of the relaxation process in the film as well as the factors that influence it for device applications. From in situ reflection high energy electron diffraction(RHEED) measurements, Whaley and Cohen[4] reported surface roughening during growth of the pseudomophic InGaAs layer. In addition to surface roughness, the presence of corrugations on InGaAs surfaces with dislocated interfaces was also reported by Kavanagh et al.[1] These corrugations were thought to have been originated from surface steps. Accordingly, a higher density of corrugations appeared on surfaces with higher interfacial lattice mismatch. In all these studies, however, a correlation of the surface morphology with strain in the film was not made, particularly beyond the critical thickness. The epitaxial growth of InGaAs has been generally achieved by molecular beam epitaxy(MBE), where the film material is brought to the surface in elemental form, or by organometallic vapor phase epitaxy(OMVPE), where use is made of the decomposition of a molecular compound of the film material in the gas phase as well as on the substrate surface. However, in CBE using unprecracked hydrides,[5] the process used here, all the molecules dissociate only on the hot substrate surface, and release the atoms of the film material and the rest of fragment species subsequently desorb from the
surface.
These
studies
have
shown
that
hydrogen
atoms
dissociated
21 Mat. Res. Soc. Symp. Proc. Vol. 355 01995 Materials Research Society
from
unprecracked hydrides play an important role in removing hydrocarbon -containing species from the growing surface, resulting in
Data Loading...
