| AVS 66th International Symposium & Exhibition | |
| Atomic Scale Processing Focus Topic | Wednesday Sessions |
| Session AP+BI+PS+TF-WeM |
| Session: | Surface Reaction Analysis and Emerging Applications of Atomic Scale Processing |
| Presenter: | Akira Uedono, University of Tsukuba, Japan |
| Authors: | A. Uedono, University of Tsukuba, Japan T. Nabatame, NIMS, Japan W. Egger, Universität der Bundeswehr München, Germany T. Koschine, Universität der Bundeswehr München, Germany C. Hugenschmidt, Technische Universität München, Germany M. Dickmann, Technische Universität München, Germany M. Sumiya, NIMS, Japan S. Ishibashi, AIST, Japan |
| Correspondent: | Click to Email |
Positron annihilation is a useful technique for characterizing vacancy-type defects in semiconductors, and it has been successfully used to detect defects in GaN. This technique is also useful for detecting open spaces in thin amorphous films deposited on semiconductor substrates. When a positron is implanted into condensed matter, it annihilates with an electron and emits two 511-keV gamma quanta. The energy distribution of the annihilation gamma rays is broadened by the momentum component of the annihilating electron-positron pair. A freely diffusing positron may be localized in a vacancy-type defect because of Coulomb repulsion from positively charged ion cores. Because the momentum distribution of the electrons in such defects differs from that of electrons in the bulk material, these defects can be detected by measuring the Doppler broadening spectra of the annihilation radiation. Because the electron density in open spaces or vacancy-type defects is lower than that in the bulk, the lifetime of positrons trapped by such regions is longer than that of positrons in the delocalized state. Thus, the measurement of the positron lifetime also provides information of open spaces and vacancies in solid. In the present work, open spaces and defects in the Al2O3(25 nm)/GaN structure were probed by using monoenergetic positron beams.
Al2O3 films were deposited on GaN by atomic layer deposition at 300oC. Temperature treatment above 800°C leads to the introduction of vacancy-type defects in GaN due to outdiffusion of atoms from GaN into Al2O3. The width of the damaged region was determined to be 40-50 nm from the Al2O3/GaN interface, and some of the vacancies were identified to act as electron trapping centers. In the Al2O3 film before and after annealing treatment at 300-900oC, open spaces with three different sizes were found to coexist. The density of medium-sized open spaces started to decrease above 800°C, which was associated with the interaction between GaN and Al2O3. Effects of the electron trapping/detrapping processes of interface states on the flat band voltage and the defects in GaN were also discussed.
The present research suggests that the interaction between amorphous Al2O3 and GaN introduces not only vacancy-type defects in GaN but also changes the matrix structure of Al2O3 film. We also revealed that the electron trapping/detrapping processes of interface charge states are influenced by the defects introduced in GaN.