The Influence of Substrate Patterning on Threading Dislocation Density and Residual Stress in GaAs/Si Heteroepitaxial La
- PDF / 3,205,729 Bytes
- 5 Pages / 420.48 x 639 pts Page_size
- 39 Downloads / 231 Views
THE INFLUENCE OF SUBSTRATE PATTERNING ON THREADING DISLOCATION DENSITY AND RESIDUAL STRESS IN GaAs/Si HETEROEPITAXIAL LAYERS.
Hyunchul Sohn, Eicke R.Weber, Jay Tu*,Henry P. Lee**, and Shyh Wang* Department of Materials Science and Mineral Engineering, University of California, Berkeley. * Department of Electrical Engineering and Computer Sciences, University of California, Berkeley. ** Bell Communications Research, 331 Newman, Spring Road, Red Bank, NJ 07701 ABSTRACT The growth of GaAs films by MBE on mesa-type patterned Si substrates has been investigated. Mesa widths were varied from 10 Igm to 200 gtm and were prepared using chemical etching with Si 3N4 masks and reactive ion etching. The residual stress in the epitaxial layer was estimated using low temperature (7K) photoluminescence and the defect distribution was studied by cross sectional TEM, dislocation densities were in addition determined by etch pits. The residual stress and the dislocation density decreased monotonically with the reduction of growth area. By the incorporation of strained layers with the reduction of growth area, the etch pit density in GaAs layers on mesas was reduced further. INTRODUCTION The major problems of heteroepitaxial growth of GaAs on Si are the high density of threading dislocations(10 6 - 108 /cm2) and the high residual stress. The high residual stress in GaAs is attributed to the large difference in thermal expansion coefficients of GaAs and Si. Thermal stress is developed by the difference in contraction during cooling down from the growth temperature. It is well known that the measured residual stress(2.7 x10-ydynes /cm 2 ) in GaAs is lower than the theoretical value(4.0 x10 9 dynes /cm 2 ) calculated from the material constants under the assumption of complete stress relief at the growth temperature. Part of this differential stress is thought of being released by plastic deformation during cooling down, generating additional threading dislocations. The stress state in GaAs film grown on Si can be changed from biaxial tensile stress to uniaxial stress by chemical etching of GaAs film into stripes of small width[l]. Also post-growth patterning resulted in a substantial reduction in the uniform biaxial thermal stress[2]. In this paper, we report on the influence of the reduction of the growth area on the residual stress and the threading dislocation density in GaAs/Si layers. EXPERIMENTAL The Si wafers used in this experiment were misoriented 3.5 degree from towards . Si substrates were patterned into mesas by conventional photolithography. For one group of patterned Si substrates, Si 3N 4 masks were used. First, silicon nitride was deposited on Si wafers by thermal CVD and was etched by reactive ion etching(RIE) with a gas mixture of CH 3 F and 02, leaving squares whose sides were 10,15,20,45,100, or 200 4.m, respectively. These wafers were etched by a KOH solution to form mesas. The Si 3 N4 films on the top of mesas were removed by chemical etching. The other group of patterned Si substrates were prepared only by RIE us
Data Loading...