Microstructure Characterization of Nonpolar ZnO and Zn_1-xMg_xO Epilayers Grown on (100) γ-LiAlO₂ by Chemical Vapor Deposition

Abstract

The defects and optical properties of nonpolar (1010) ZnO and Zn 0.9 Mg 0.1 O epilayers grown on (100) J-LiAlO 2 substrates by chemical vapor deposition were investigated by x-ray diffraction, transmission electron microscopy and cathodoluminescence. The x-ray rocking curves of the (1 1 00) reflection for the ZnO and Zn 0.9 Mg 0.1 O epilayers possessed low FWHM values of 504 and 216 arcsec, respectively. Misfit dislocations in high density exhibited at the epilayer/substrate interface with b= 3 1 [1210] for both samples. Basal stacking faults, threading dislocations and inversion domains were observed in the ZnO epilayer with densities on the order of 10 -5 cm -2 , 10 -9 cm -2 and 10 -4 cm -1 , respectively. On the other hand, only basal stacking faults and threading dislocations were found in the Zn 0.9 Mg 0.1 O epilayers. The densities of these defects were at least one order of magnitude lower than those of the ZnO one. The Zn 0.9 Mg 0.1 O epilayers exhibited a near band-edge emission at 3.5 eV whose intensity is about 15 times stronger than that of the ZnO epilayer at 3.3 eV. Monochromatic cathodoluminescence images acquired at the peak energy revealed that the basal stacking faults showed low emission intensities.

Spectral and Spatial Luminescence Distribution ofm-Plane ZnO Epitaxial Films Containing Stacking Faults: A Cathodoluminescence Study

“…3) Consequently, the growth of m-plane 4) or a-plane 5) ZnO has attracted much attention since the QCSE does not occur along nonpolar directions. However, high densities of basal plane stacking faults (BSFs) -on the order of 10 5 cm À1 -are frequently observed in nonpolar ZnO films regardless of the substrate and/or growth method, [6][7][8][9] while these planar defects are rarely observed in c-plane ZnO. According to Venne ´gue `s et al, 8) coalescence of nuclei during the first stage of growth is responsible for the generation of BSFs in a-plane ZnO.…”

“…Accordingly, we previously identified the BSFs of our m-plane ZnO epilayer to be I 1 BSFs. 9) In the current work, the corresponding optical properties are studied utilizing spatially resolved cathodoluminescence (CL) spectroscopy. We performed CL line scans across I 1 BSFs in order to experimentally examine the presence of a polarization field within the SF-related QWs.…”

“…18) Details of the growth process have been described elsewhere. 9,18) Secondary electron (SE) images were acquired using a Zeiss Ultra-55 field emission gun scanning electron microscope (SEM). The CL signals were collected and dispersed using a Gatan MonoCL3 system attached to the SEM.…”

“…2(c) is calculated to be 2:5 Â 10 4 cm À1 , which is in reasonable agreement with the density of I 1 BSFs (about 10 5 cm À1 ) obtained in our previous TEM results. 9) The smaller value derived from CL imaging is due to the reduced spatial resolution of CL in an SEM as compared with TEM measurements.…”