Masahito Yamaguchi

Growth of GaN free from cracks on a (111)Si substrate by selective metalorganic vapor-phase epitaxy

The selective metalorganic vapor-phase epitaxy of wurtzite GaN was performed on a (111) silicon substrate using SiO2 grid mask pattern. Within window regions of (0.2–0.5) mm×(0.2–0.5) mm, GaN films free from cracks were achieved. The full width at half maximum of the (0004) X-ray rocking curve was as narrow as 388 arcs and that of the band edge emission was 18.6 meV at 77 K. The band edge emission peak energy was redshifted. The redshift is reduced slightly in a sample grown on small windows. This suggests that the biaxial strain due to the thermal expansion coefficient mismatch is partly relaxed on small windows.

Optical and electrical properties of (1-101)GaN grown on a 7° off-axis (001)Si substrate

Uniform growth of (1-101)GaN was performed on coalesced stripes of GaN which had been prepared by selective metalorganic vapor phase epitaxy on a 7° off-axis (001)Si substrate via an AlN intermediate layer. The cathodoluminescence spectra at 4 K exhibited a donor bound excitonic emission at 358 nm followed by defect-related emission peaks at 363, 371, and 376 nm. The 363 and 376 emission bands are observed upon the coalescence region. The Hall measurements exhibited p-type conduction at 80–300 K (the hole carrier density 6.3×1012 cm−2 and hole mobility 278 cm2/V s at 100 K). The activation energy of the acceptor was estimated to be 60 meV. The possible origin of the p-type conduction is discussed in relation to the unintentionally doped carbon.

Selective Area Growth of GaN on Si Substrate Using SiO 2 Mask by Metalorganic Vapor Phase Epitaxy

Selective area growth (SAG) of GaN on (111) Si substrate was studied using AlGaN as an intermediate layer. A hexagonal dot with a (0001) plane on the top and of a 5 µm or a submicron size was obtained using a patterned dot structure of silicon dioxide (SiO2) mask. The facet structure revealed that the axis of hexagonal GaN is parallel to the axis of the Si substrate. The cathodoluminescence (CL) spectrum at 133 K exhibited a strong near-band-edge emission band for the submicron dots, which suggests excellent crystallinity. Epitaxial lateral overgrowth (ELO) of GaN on the Si substrate is demonstrated.

The formation of crystalline defects and crystal growth mechanism in InxGa1 - xN/GaN heterostructure grown by metalorganic vapor phase epitaxy

Abstract The composition pulling effect at the initial growth stage of In x Ga 1− x N grown on a GaN epitaxial layer is studied in relation to the lattice mismatch between In x Ga 1− x N and the GaN epitaxial layer. TEM observation of the In x Ga 1− x N/GaN heterostructure reveals that the degradation of the In x Ga 1− x N layer is caused by pit formation, which is converted from the edge dislocations penetrating to the In x Ga 1− x N layer from the GaN layer. By increasing the layer thickness, the crystalline quality becomes worse, and In x Ga 1− x N consists of two types of regions: a homogeneous, good crystalline quality layer and a bad crystalline quality layer. Crystalline quality of In x Ga 1− x N is good near the interface of In x Ga 1− x N/GaN, and EDX composition analysis shows that the composition of In x Ga 1− x N near the interface is close to that of GaN.

AlGaN-Based Deep Ultraviolet Light-Emitting Diodes Fabricated on Patterned Sapphire Substrates

Deep ultraviolet (DUV) light-emitting diodes (LEDs) on patterned sapphire substrates (PSSs) have been clearly demonstrated. AlN templates grown on PSSs had average threading dislocation densities (TDDs) of as low as 5×107 cm-2. Flip-chip DUV LEDs fabricated on PSSs demonstrated a significantly high performance. The 266 nm LED exhibited an output power of 5.3 mW and an external quantum efficiency (EQE) of 1.9% at 60 mA DC, and the 278 nm LED had 8.4 mW output and an EQE of 3.4%. Moreover, the 70% lifetime was more than 700 h at 20 mA.

Hydride vapor-phase epitaxy growth of high-quality GaN bulk single crystal by epitaxial lateral overgrowth

Selective area growth (SAG) of GaN using the HVPE method was carried out to obtain a high-quality GaN bulk single crystal. Selectivity of the GaN growth was excellent and the GaN layer had no cracks. The FWHM (195 arcsec) of the X-ray rocking curve for (0004) diffraction was narrower than that (348 arcsec) of the sample grown by the conventional method. Overgrowth of the GaN on the SiO 2 mask was enhanced in the direction. Cathode luminescence intensity of this overgrowth region was much stronger than that of the window region. It was found that a reduction in stress is achieved by narrowing the window area, and the epitaxial lateral overgrowth on the mask is effective in obtaining high-quality GaN layer.

Efficient spin injection into GaAs quantum well across Fe3O4 spin filter

We demonstrate efficient spin injection into GaAs across an Fe3O4 electrode. Spin polarization of electrons injected into a GaAs quantum well becomes significantly large below 120 K, reaching a value of 33% at 10 K. The large spin polarization is likely due to spin filtering effect across the insulating ferrimagnetic Fe3O4 layer at the interface. The results indicate that spin filtering effect across Fe3O4 is a very promising means to enhance the spin injection efficiency into semiconductors.

Reduction of Efficiency Droop in Semipolar (1101) InGaN/GaN Light Emitting Diodes Grown on Patterned Silicon Substrates

The semi-polar InGaN-based LEDs exhibits low efficiency droop because the reduction of the polarization field not only made the band diagram smoother but also restricted electron overflow to the p-GaN layer as shown in simulations.

Selective Area Growth of GaN Using Tungsten Mask by Metalorganic Vapor Phase Epitaxy

We studied selective area growth (SAG) of GaN using a tungsten (W) mask with an atmospheric metalorganic vapor phase epitaxy (MOVPE) system. No GaN polycrystals were observed on the W mask regions, and the selectivity of GaN growth on window regions proved to be excellent. The GaN stripes developed into different shapes depending on the direction of stripe mask patterns. If the stripe was along , a triangular shape with {1101} facets was formed. If the stripe was along , a trapezoidal shape with a smooth (0001) surface on top and rough surfaces on both sides was obtained. The lateral overgrowth of GaN on the W mask occurred in both cases. The growth mechanisms and the facet formation were similar to those found in SAG using a SiO2 mask.

Partial strain relaxation by stacking fault generation in InGaN multiple quantum wells grown on (11¯01) semipolar GaN

We have investigated the structural properties and relaxation phenomenon of InGaN multiple quantum wells (QWs) on (11¯01) semipolar GaN templates grown on patterned (001) silicon substrates by selective area growth technique. Our studies by transmission electron microscopy and x-ray diffraction reciprocal space mapping reveal that QWs emitting light at 540 nm experience significant strain relaxation along the in-plane [11¯02¯] direction by the generation of an array of basal stacking faults (BSF). The generation of BSFs in 540 nm QWs could be an important factor limiting its luminescence efficiency.