Takashi Matsuoka

InN polarity determination by convergent-beam electron diffraction

To establish an accurate determination technique for the polarity of InN by convergent-beam electron diffraction (CBED), we clarified the influence of the electron incidence direction, film thickness, and the temperature factor B on CBED patterns by simulation. The electron incidence direction of [11¯00] and a film thinner than 50nm were found to be preferable for easy and reliable polarity determination. Using an InN film grown on a (0001¯) GaN template on (0001) sapphire by metalorganic vapor-phase epitaxy, observation of the CBED pattern in the thin region of the film was confirmed from the simulation result. This InN film was clearly determined to have N polarity and the value of B was estimated to be less than 2.0A2.

Red to blue wavelength emission of N-polar

N-polar (−c-plane) InGaN light-emitting diodes with emission wavelengths ranging from blue to green to red were fabricated on a c-plane sapphire substrate by metalorganic vapor phase epitaxy. The optimization of growth conditions for −c-plane InGaN/GaN multiple quantum wells was performed. As a result, the extension of the emission wavelength from 444 to 633 nm under a constant current of 20 mA was achieved by changing the growth temperature of quantum wells from 880 to 790 °C.

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With respect to N-polar GaN grown on a sapphire substrate, the effects of Mg doping on the surface morphology, and the optical, and electrical properties are precisely investigated. By doping Mg, hillocks observed on the surface of GaN can be suppressed, while step bunching becomes severe. The atomic terrace width is extended with increasing Mg/Ga precursor ratio. Mg doping can promote the surface migration of Ga adatoms on a GaN surface during growth. In the case of heavily Mg-doped GaN, atomic steps become wavy. From photoluminescence spectra, the dominant transition was found to change from near-band-edge transition to donor–acceptor-pair transition. Hall-effect measurement shows p-type conduction at room temperature for a sample grown with the Mg/Ga precursor ratio of 4.5 × 10−3. The activation energy is 143 meV, which is comparable to that of Mg in the conventional Ga-polar (0001) GaN.

InGaN light-emitting diodes grown by metalorganic vapor phase epitaxy

Indium was introduced as a surfactant during metalorganic vapor phase epitaxial growth of nitrogen-polar GaN on c-plane sapphire tilted from 0.2 to 1.0° toward m-axis. For each sample with different tilted angle, the surfactant effect was confirmed from a scanning electron microscope and an atomic force microscope observations. In particular, for the tilted angle of 0.2°, all the hillocks, which usually exist on the nitrogen-polar GaN films on sapphire substrates with low tilted angles, disappeared. The microscopic terrace width was enlarged, and the surface roughness became small irrespective of the tilted angle, however, for the samples with higher tilted angles, the occurrence of the giant step bunching was rather enhanced. Therefore, it was confirmed that indium introduced during the nitrogen-polar GaN growth surely plays a role as a surfactant.

Enhancement of surface migration by Mg doping in the metalorganic vapor phase epitaxy of N-polar

The miscible region of InGaAlBN quinary system was simulated by using the strictly-regular-solution approximation. The interaction parameter to obtain excess enthalpies caused by mixing was calculated using the delta-lattice-parameter model. The results show that the miscible regions of the InGaAlBN are located near the InN-rich region, near BN, and near the line connecting GaN to AlN. This means that InGaAlBN quinary system makes it possible to design infrared optical devices with InN or In-rich InGaN as an active layer without any strain, which shortens device lifetime. InGaAlBN devices could possibly outperform the InGaAsP devices presently used in optical communications systems.

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The effect of the metastable zincblende (ZB) InN inclusion in the stable wurtzite (WZ) InN on the threading dislocation densities (TDDs) of an InN film grown by pressurized-reactor metalorganic vapor phase epitaxy has been studied by X-ray diffraction measurements. InN films are directly grown on c-plane sapphire substrates with nitrided surfaces at 1600 Torr with the different growth temperature from 500 to 700 °C. Films including ZB-InN show the correlation between the ZB volume fraction and the edge component of TDDs, not the screw component of TDDs. This result can be crystallographically understood by a simple model explaining how the ZB structure is included, i.e., ZB domains existing side-by-side with WZ domains and twined ZB domains. This can be clearly observed by electron backscatter diffraction.

GaN/sapphire

To promote the research on the growth of high-quality InN films attractive to the application for both optical and electronic devices, the pressurized-reactor metalorganic-vapor-phase epitaxy (PR-MOVPE) system which can overcome the high equilibrium-vapor-pressure of nitrogen between solid and vapor phases is originally developed. In addition to this system, the N-polar growth technique developed in the growth of GaN is introduced. As a result, the dense InN films with atomic steps are successfully grown. From the struggle of the research on high quality InN, the subject of the phase purity is also arisen. The pole figure measurements make the growth condition for a pure InN with a wurtzite structure. The phase purity is almost determined by the growth temperature. These results will pave the way to high-quality InN.

Improvement of surface morphology of nitrogen-polar GaN by introducing indium surfactant during MOVPE growth

In this paper, we report the metalorganic vapor phase epitaxial (MOVPE) growth of InN using a NiO-based pellet-type NH3 decomposition catalyst. The use of the catalyst significantly changes the growth behavior of InN, which is dependent on the growth temperature (T g). Continuous InN films without the incorporation of metallic In and a cubic phase are grown at T g = 400–480 °C. An InN film grown at T g ≈ 450 °C has a full-width at half maximum (FWHM) of 376 arcsec in the X-ray rocking curve for InN(0002) reflection. At T g ≥ 500 °C, the deposition rate of InN rapidly decreases and the deposited films become discontinuous with large (ca. 1 µm) pyramidal grains of InN. Depositions are scarcely obtained at T g ≥ 600 °C. Such changes in the growth behavior of InN are governed by the NH3 decomposition.

Calculation of Phase Separation in Wurtzite In1-x-y-zGaxAlyBzN

The metastable zincblende (ZB) phase in N-polar (0001¯) (−c-plane) InGaN/GaN multiple quantum wells (MQWs) grown by metalorganic vapor phase epitaxy is elucidated by the electron backscatter diffraction measurements. From the comparison between the −c-plane and Ga-polar (0001) (+c-plane), the −c-plane MQWs were found to be suffered from the severe ZB-phase inclusion, while ZB-inclusion is negligible in the +c-plane MQWs grown under the same growth conditions. The ZB-phase inclusion is a hurdle for fabricating the −c-plane light-emitting diodes because the islands with a triangular shape appeared on a surface in the ZB-phase domains. To improve the purity of stable wurtzite (WZ)-phase, the optimum conditions were investigated. The ZB-phase is dramatically eliminated with decreasing the V/III ratio and increasing the growth temperature. To obtain much-higher-quality MQWs, the thinner InGaN wells and the hydrogen introduction during GaN barriers growth were tried. Consequently, MQWs with almost pure WZ phase...

Effect of Phase Purity on Dislocation Density of Pressurized-Reactor Metalorganic Vapor Phase Epitaxy Grown InN

Nitrogen-polar (N-polar) InGaN films were grown on a GaN template/c-plane sapphire substrate by metal–organic vapor phase epitaxy (MOVPE). The effects of c-plane sapphire substrate miscut angle on the indium (In) content and crystal properties of N-polar InGaN films were investigated. The In content increased with increasing miscut angle in the vicinal region of less than 1.1°. This tendency is different from that of group-III-polar InGaN growth because of the difference in the atomic arrangement on the terraces and at step edges between these two inverted polar surfaces. In the case of N-polar growth, a spontaneous two-dimensional nucleation on terraces is difficult and the intentional introduction of steps is effective compared with group-III-polar growth. Furthermore, by observing the surface morphologies of GaN templates in view of both macroscopic and microscopic scales, a clear relationship between the macroscopic surface structure of GaN template and the In content of InGaN was revealed.