Tem Study of Stacking Faults Formed in Pairs in a ZnSe Epitaxial Layer on a GaAs(00l) Buffer Layer
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I-I, Tsukaguchi-
ABSTRACT Structure of stacking faults in a ZnSe epitaxial layer grown on a GaAs(00 1) buffer layer was determined with transmission electron microscopy. Two stacking faults were formed in pairs on (111) and ( I1) planes with the same polarity and met at a point which is a few atomic layers away from the interface between ZnSe and GaAs. Partial dislocations were found to be the Shockley type ones with a Burgers vector of 1/6. Atomic force microscopy showed that hillocks were formed in pairs at a surface where the pair of stacking faults existed in the layer. Moreover, it was observed that the pair of stacking faults elongated along the direction by gliding on the {I }faulted planes under annealing at 200°C for 30min. Formation mechanisms of the pair of stacking faults have been discussed. INTRODUCTION Crystalline defects are known to cause a degradation on the properties of electronic semiconductor devices[l]. Since it is very important to grow high quality thin films on substrates, great efforts have been focused on epitaxial growth technique. In the case that epitaxial layers are not lattice matched to substrates, the layers are subject to lattice strain and finally misfit dislocations should be introduced in the layers[2]. Both in low lattice mismatched heteroepitaxial systems and even in lattice matched homoepitaxial systems, crystalline defects can be formed in the epitaxial layers from the interface[3]. It suggests that initial growth of epitaxial layers must be well controlled. Structure of the defects strongly depends on the formation mechanism. Therefore, it is very important to study the structure of the defects for obtaining high quality epitaxial layers with a
small density of the defects. ZnSe-based II-VI semiconductors are promising materials for blue and blue-green light emitting devices. ZnSe epitaxial layers have been generally grown on GaAs(001) substrates. Since the lattice mismatch in this system is 0.27% at room temperature, the ZnSe epitaxial layers are subject to a compressive stress and critical thickness at which generation of misfit dislocations will begin is known to be about 120nm[4]. There have been many reports about crystalline defects introduced in the ZnSe epitaxial layers[5]-[7]. Petruzzello et al. reported that stacking faults occurred in pairs in the ZnSe epitaxial layer with the thickness of 87nm[5]. They grew the ZnSe films on GaAs(001) substrates by molecular beam epitaxy(MBE) using ZnSe as a source material. The stacking faults lay preferably on two kinds of (Il I} planes with the same polarity, and the partial dislocations were of the Frank type with a Burgers vector of b= 1/3[l 11 ]. However they did not show the polarity of the fault planes or the procedure to determine the dislocations as the Frank type. We have developed gas source MBE(GSMBE) on the growth of ZnSe epitaxial layers because it has the high controllability of the gas flow rate. In the ZnSe epitaxial layer grown by GSMBE with the thickness of about 100nm, stacking faults occurred in pairs.
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