Investigation of Misfit Dislocation Configurations in MBE-Grown InGaAs Layers on Misaligned GaAs (001) Substrates
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INVESTIGATION OF MISFIT DISLOCATION CONFIGURATIONS IN MBE-GROWN InGaAs LAYERS ON MISALIGNED GaAs (001) SUBSTRATES
P.Wemer,* N.D. Zakharov,* Y. Chen,* Z. Liliental-Weber,* J. Washburn,* J.F. Klem,** J.Y. Tsao.** *Lawrence Berkeley Laboratory, Berkeley, CA ** Sandia National Laboratories, Albuquerque, NM ABSTRACT
The configurations of misfit dislocations in In0.2Ga0.8As/GaAs(00l) hetero structures grown on slightly misoriented substrates was investigated by transmission electron microscopy (TEM). Layers 6 nm, 20 nm and 40 nm thick were grown by MBE. The substrate was tilted in [110], [1 To], [120], [210] and [010] directions at angles between 00 and 100. Only in the 40 nm thick layers networks of 600 and 900 dislocations were formed. Misfit dislocations were found at the interface in directions. In the substrate tilting range between 00 and 40 the changes in dislocation density can be explained by the different character of ac and PIdislocations. For a substrate tilting above 60 the different dislocation sets show an increased anisotropy. The misfit dislocations at the interface were decorated by In atoms. The influence of three-dimensional crystal growth on increasing surface roughness is discussed. I. Introduction In recent years the growth of InGaAs epitaxial thin films has become the topic of numerous investigations due to their application in optoelectronics. However, only in a limited number of cases can a perfect match between the lattices of the film and the substrate be realized. One case is InO.53GaO.4 7 As layers grown on InP(001) substrate. Since a high crystalline film perfection is needed for good device performance the goal of many investigations is to reduce the density of misfit dislocations or to pin them near or at the interface, where they have almost no influence on the optoelectronical properties of the layers. InGaAs films on GaAs (001) substrates seem to be a useful system for studying the initial stages of the crystal growth of strained layers and the generation of misfit dislocations. Misfit dislocations found in the InGaAs heterosystem are of the Lomer type (900 edge, Burgers vector b=1/2a( 1101 in the interface) 1 , as well as the 600 type 3 (b= 1/2a{ 101) inclined to the interface plane). All these misfit dislocations lie at the interface in the directions. It was recently reported that, in a InGaAs/GaAs(001) structure with high In concentration (x>0.4), edge-type misfit dislocations inclined at 450 to the film surface can be 2 generated by glide in 1110) slip planes. In AIII-BV crystals, parallel opposite-sign 600 dislocations are not chemically equivalent. 4 For the so-called a-dislocations the extra half-plane terminates with a row of group-Ill atoms, whereas the core of f3-dislocations is characterized by a row of group-V atoms. The a- and 13-dislocations also show different behavior. 60) dislocation can glide on four different ( 1111 planes. For InGaAs/GaAs(001) heterostructures there are four different 600 dislocations, with edge components of their Burgers vector directed in [112
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