GaN and its alloys with InN and AlN are materials systems that have enabled the revolution in solid-state lighting and high-power/high-frequency electronics. GaN-based materials naturally form in a hexagonal wurtzite structure and are naturally grown in a (0001) c-axis orientation. Because the wurtzite structure is polar, GaN-based heterostructures have large internal electric fields due to discontinuities in spontaneous and piezoelectric polarization. For optoelectronic devices, such as light-emitting diodes and laser diodes, the internal electric field is generally deleterious as it causes a spatial separation of electron and hole wave functions in the quantum wells, which, in turn, likely decreases efficiency. Growth of GaN-based heterostructures in alternative orientations, which have reduced (semipolar orientations) or no polarization (nonpolar) in the growth direction, has been a major area of research in recent years. This issue highlights many of the key developments in nonpolar and semipolar nitride materials and devices.
James S. Speck, Guest Editor for this issue of MRS Bulletin, can be reached at the Materials Department, University of California, Santa Barbara, CA 93117, USA; and e-mail firstname.lastname@example.org.
Speck is a professor and chair of the Materials Department at the University of California, Santa Barbara (UCSB). He received his BSME degree in metallurgical engineering from the University of Michigan in 1983 and his SM and ScD degrees in materials science from the Massachusetts Institute of Technology in 1985 and 1989, respectively. At UCSB, Speck's early work focused on epitaxial oxide films on semiconductors, ferroelectric thin films, and strain relaxation in highly misfitting epitaxial systems. He has worked extensively on the materials science of GaN and related alloys. Major aspects of Speck's work on nitrides include elucidating basic growth modes and defect generation, the development of MBE growth of GaN, and the development of nonpolar and semipolar GaN. Speck received the Quantum Device Award from the International Symposium on Compound Semiconductors in 2007, was named an inaugural MRS fellow in 2008, and received the JJAP Best Paper Award in 2008.
Shigefusa F. Chichibu, Guest Editor for this issue of MRS Bulletin, can be reached at the Center for Advanced Nitride Technology, Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2–1–1 Katahira, Aoba, Sendai 980–8577, Japan; tel. 81–22–217–5360; e-mail email@example.com.
Chichibu is a professor at the Center for Advanced Nitride Technology, Institute of Multidisciplinary Research for Advanced Materials at Tohoku University in Japan.
He obtained B.E., M.E., and PhD degrees from Keio University in 1986, 1988, and 1994, respectively. He has been working on III nitride materials such as localized quantum well excitons in InGaN quantum well blue and green light-emitting diodes and also on nonpolar (AlInGa)N materials. He received the JJAP paper award (2008), DoCoMo Mobile Science Award (2008), and the Marubun Research Award (2004).