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Article type: Cover
2009 Volume 36 Issue 3 Pages
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Article type: Index
2009 Volume 36 Issue 3 Pages
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Article type: Index
2009 Volume 36 Issue 3 Pages
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Article type: Index
2009 Volume 36 Issue 3 Pages
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2009 Volume 36 Issue 3 Pages
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Hiroshi Fujioka, Shigefusa Chichibu
Article type: Article
2009 Volume 36 Issue 3 Pages
147-
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Noriyuki Kuwano
Article type: Article
2009 Volume 36 Issue 3 Pages
148-154
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Microstructure characterization is essentially important since the functional performance of device materials depends strongly upon their microstructure. In this report, fundamentals of structure defects and transmission electron microscopy (TEM) were described, and practical analysis methods for Burgers vectors and crystal polarity were explained with a special reference of the rotation relationship between TEM image and diffraction pattern that was occasionally a confusing issue.
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Akira Uedono, Shoji Ishibashi, Nagayasu Oshima, Toshiyuki Ohdaira, Ryo ...
Article type: Article
2009 Volume 36 Issue 3 Pages
155-165
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Positron annihilation is a nondestructive technique for investigating point defects in solids. When a positron is implanted into materials, it annihilates with an electron and emits two 511-keV γ quanta. From measurements of Doppler broadening spectra of the annihilation radiation and the positron lifetimes, one can detect vacancy-type defects such as monovacancies and vacancy clusters. The defect species and their concentrations can be estimated from a comparison between the Doppler broadening spectra and positron lifetime obtained through the experiments and those calculated using first-principles calculation. Relationships between point defects, electrical and optical properties of GaN, AlN, and InN were studied. We have shown that positron annihilation is a powerful tool for studying vacancy-type defects in group-III nitrides.
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Shigefusa Chichibu, Akira Uedono
Article type: Article
2009 Volume 36 Issue 3 Pages
166-177
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Threading dislocations (TDs) in (Al, In, Ga) N are known to affect the internal quantum efficiency (IQE) of near-band-edge (NBE) emissions in bulk films and quantum structures. However, principal roles of point defects such as vacancies on the luminescent properties has not been fully understood. In this article, impacts of point defects on IQE of NBE emissions and on the intensity of deep emission bands in (Al, Ga) N films are described, based on the results of steady-state and time-resolved photoluminescence (TRPL) and positron annihilation measurements. The nonradiative recombination process in GaN is shown to be governed not by single point defects, but by certain defects introduced with the incorporation of V_<Ga>, such as V_<Ga>-defect complexes. Similar conclusion is drawn for Al_xGa_<1-x>N alloy films. In addition to nonradiative process, cation vacancy concentration was found to correlate with the relative intensity of characteristic deep emission bands in AlN and Al_xGa_<1-x>N alloy films.
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Akio Kaneta, Mitsuru Funato, Yoichi Kawakami
Article type: Article
2009 Volume 36 Issue 3 Pages
178-190
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We have performed nanoscopic optical characterization for c-plane and semipolar (112^^-2) In_xGa_<1-x>N/GaN quantum wells (QWs) by a scanning near field optical microscope. For the blue-emitting c-plane QW, there is no correlation between PL intensity distribution and positions of threading dislocations. This can be attributed to potential fluctuations in the In_xGa_<1-x>N QW, because carriers/excitons captured at the potential minima hardly reach threading dislocations. On the other hand, PL intensity was clearly correlated with threading dislocations in the green-emitting QW. It was revealed that as the In composition increases, (a) Inrich regions, which act as potential minima, are associated with dislocations, and (b) the internal piezoelectric field is strengthened, which elongates radiative recombination lifetime and diffusion length, as a consequence. Both (a) and (b) enhance probability for carriers/excitons to be captured at dislocations. On the other hand, for the (112^^-2) QW, relatively uniform PL intensity distribution was observed. The internal electric field reduced by the (112^^-2) semipolar crystallographic orientation causes faster radiative recombination lifetime. Therefore, carriers/excitons recombine before traveling a long distance, which may lead to the observed uniform distribution. Additionally, the maximum internal quantum efficiency was 50% at 520nm for the (112^^-2) QWs, which suggests that (112^^-2) QWs are suitable for green emitters.
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Yoshihiro Ishitani, Masayuki Fujiwara, Akihiko Yoshikawa
Article type: Article
2009 Volume 36 Issue 3 Pages
191-199
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InN is a promising material of high performance infrared optoelectronic and electronic devices, since it has the bandgap energy of 0.63eV at room temperature and effective electron mass of about 0.05m_0. However, samples have high residual electron density of more than 10^<17>cm^<-3> and the dislocation density of the order of 10^9 or 10^<10>cm^<-2>. In this report we show that the edge type dislocation is one of the main causes of electron and hole scattering centers. These analyses are based on the measurements of carrier properties in the bulk region except for the surface or interface with substrate by infrared analysis utilizing the large dispersion of refractive index in the infrared region.
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Hiroshi Amano, Motoaki Iwaya, Satoshi Kamiyama, Isamu Akasaki
Article type: Article
2009 Volume 36 Issue 3 Pages
200-204
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Inversion domains having pyramidal shape are observed in both highly Mg-doped GaN and AlN grown on c-plane sapphire substrate by MOVPE. Mg concentration dependence of the effective activation energy of Mg in AlGaN shows similar behavior to that in GaN. Effective acceptor energy decreases with a negative one-third-powers law. There is an maximum hole concentration at room temperature in AlGaN because of the generation compensating donor states which may be related to inversion domains. Growth on a-plane template shows slightly higher hole concentrations compared with that on +c-plane growth.
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Tamotsu Hashizume
Article type: Article
2009 Volume 36 Issue 3 Pages
205-213
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This paper reviews deep electronic levels of GaN and AlGaN, which have mainly been detected by electrical characterization methods such as admittance spectroscopy, deep-level transient spectroscopy (DLTS) and current spectroscopy. Although many data on deep levels have been reported for n-GaN, their origins correlating with crystalline defects and/or impurities are not clear yet. Several deep levels have been reported for AlGaN with relatively low Al compositions. In addition, recent data on near-midgap levels in Al_<0.25>Ga_<0.75>N are presented. Finally, near-surface deep levels and surface electronic states of GaN and AlGaN are reviewed, focusing on their formation during the device processing steps and their effects on the electrical properties of "free" surfaces and insulator-semiconductor interfaces.
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Kenji Shiojima
Article type: Article
2009 Volume 36 Issue 3 Pages
214-221
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AlGaN/GaN high-electron-mobility transistors have been intensively studied as high-temperature high-power high-frequency electron devices. In this article, four topics, which related to the effects of crystal quality on device characteristics are reported. (i) Correlation between current-voltage (I-V) characteristics and dislocations was evaluated by using sub-micron diameter n-GaN Schottky contacts. The diodes showed that neither mixed nor edge dislocation affected I-V characteristics. (ii) Evaluation of Schottky barrier height was conducted for low-Mg-doped p-GaN. Large Schottky barrier height of 2.4eV was obtained and memory effects were observed. (iii) Thermal stability of 2 dimensional electron gas was evaluated. The carrier concentration was sensitive to AlGaN crystal quality. (iv) The electron velocity in short-gate HEMTs with different crystal quality was evaluated. The measured velocities were virtually the same for all devices.
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Shigetaka Tomiya, Masao Ikeda
Article type: Article
2009 Volume 36 Issue 3 Pages
222-228
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Reduction of structural defects in GaN- based laser diodes is of critical importance for high efficient and high reliable performance. Therefore, it is very important to understand their characteristics,. Since their crystal structure is different from that of conventional zinc-blende-based III-V materials such as GaAs, different kinds of structural defects are nucleated in the epitaxial films for GaN-based laser diodes. Here we review on transmission electron microscope analysis of various kinds of structural defects observed in these epitaxial films.
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Nobuhiko Sarukura
Article type: Article
2009 Volume 36 Issue 3 Pages
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Koichi Kakimoto
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2009 Volume 36 Issue 3 Pages
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Satoru Ueno
Article type: Article
2009 Volume 36 Issue 3 Pages
231-232
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Keiichiro Fujita
Article type: Article
2009 Volume 36 Issue 3 Pages
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Shinichi Hirano
Article type: Article
2009 Volume 36 Issue 3 Pages
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Article type: Appendix
2009 Volume 36 Issue 3 Pages
235-237
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Article type: Appendix
2009 Volume 36 Issue 3 Pages
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Article type: Appendix
2009 Volume 36 Issue 3 Pages
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Article type: Appendix
2009 Volume 36 Issue 3 Pages
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Article type: Appendix
2009 Volume 36 Issue 3 Pages
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Article type: Appendix
2009 Volume 36 Issue 3 Pages
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