NEW-TYPE INTERFERENCE PATTERN GENERATED BY INTERNAL STRESS AROUND A MICROPIPE IN THE 6H-SiC SINGLE CRYSTAL. By H. Ohsato¹⁾, T. Kato¹⁾, M. Razeghi^2), T. Okuda¹⁾, ¹⁾Department of Materials Science and Engineering, Nagoya Institute of Technology, Nagoya 466, Japan, ²⁾Center for Quantum Devices, Northwestern University, IL 60208-3118, USA

SiC has been expected for substrate for GaN single crystal thin film which is available for blue laser diode, but the crystalline quality of SiC substrates is low grade affectedby internal stress around micropipes. Usually, sapphire ([[alpha]]- Al₂O₃) is the most commonly used for substrates, as it gives the best crystalline quality. Moreover GaN grown on sapphire has been used for blue LED and emission of blue laser has just succeeded. But there are many defects on the interface which cause short lifetime because of large atomic distance mismatch (ADM) between GaN and sapphire. On the other hand, good quality GaN epilayer has not grown on the SiC substrates in spite of small ADM. SiC single crystals made by modified Lely's method which could grow large single crystals have many micropipes along c-axis. Butterfly-type strain configurations around micropipes have been observed by the orthoscope under optical polarizing microscope in spite of adjusting c-axis direction to the optical axis of the microscope using universal stage. The butterfly-type pattern has been settled as a new-type interference pattern. A forth working upon the micropipe to one direction has been appreciated from the interference pattern with vibration directions (Fig.1). The vibration directions of the fast and slow wave are corresponding to the direction of composition and tension, respectively. Clarification of the growth mechanism of micropipes accompanied internal stress is available for growth of good quality GaN.