Evaluation of Dislocation Mobility in Wurtzite Semiconductors
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Evaluation of Dislocation Mobility in Wurtzite Semiconductors Ichiro Yonenaga1 1 Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan ABSTRACT The indentation hardness and yield strength of various wurtzite-structured semiconductors, such as AlN, GaN, InN, and ZnO, were summarized together with those of 6H-SiC. From analysis of the data, the activation energy for motion of an individual dislocation was deduced to be 2–2.7 and 0.7–1.2 eV in GaN and ZnO, respectively, and the evaluated activation energy for dislocation motion showed a dependence on the dislocation energy in the minimum length. The results were evaluated in terms of homology and the basic mechanism of the dislocation process. Dislocation motion is thought to be primarily controlled by the atomic bonding character of the semiconductors. INTRODUCTION Aluminum nitride (AlN), gallium nitride (GaN), indium nitride (InN), zinc oxide (ZnO), and silicon carbide (SiC) are wide bandgap semiconductors. They are important for various practical applications for optoelectronic devices with a blue–ultraviolet wavelength range operating around room temperature (RT), various sensing modules, and high power devices. These materials generally have an extremely high density of grown-in dislocations due to the growth method currently under development such as MBE, MOCVD, or sublimation under severe growth conditions with certain substrates. Dislocations seriously affect the electrical and optical properties of a semiconductor crystal due to the formation of electronic levels in the bandgap. As a result, semiconductor device functions vary spatially at dislocation sites and are sometimes detrimentally lost to degradation. Dislocations are induced into a crystal under stress/strain stimulations through generation and multiplication during crystal growth and device processing. Thus, detailed knowledge on dynamic properties of dislocations and their relevant electrical and optical properties is essentially important as a basis for the control of dislocation generation and deformation during crystal growth and device processing. The present author’s group has revealed the dynamic behavior of dislocations and the mechanical strength of various crystals mainly with diamond and sphalerite (cubic-based) structures, such as Si, GaAs, and so forth [1-3]. In contrast, our knowledge of the dynamic behavior of dislocations and mechanical strength is far limited in wide band-gap semiconductors, partly due to the low symmetry of the crystal structure, such as the wurtzite (hcp-based) structure, due to rather low crystallinity, or limitation of the size available for dynamical characterizations. Here, we summarize mechanical strengths of wide bandgap single crystals in the hcpbased structure of wurtzite AlN, GaN, InN, ZnO, and 6H-SiC based on our previously reported results. Hardness data were obtained by indentation tests in a wide temperature range and yield strengths were obtained by a conventional compressive deformation method at elevated temperatures. Table I s
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