Norikatsu Koide

Effects of the buffer layer in metalorganic vapour phase epitaxy of GaN on sapphire substrate

Abstract High-quality GaN film with a smooth surface, free from cracks, can be grown on a sapphire substrate by metalorganic vapour phase epitaxy (MOVPE) using a thin AlN buffer layer. The most essential role of the buffer layer is found to be (i) the supply of the nucleation sites with the same crystal orientation as the substrate, and (ii) the promotion of the lateral growth of GaN due to the decrease in interfacial free energy between the substrate and the epitaxial GaN film.

Doping of GaN with Si and properties of blue m/i/n/n+ GaN LED with Si-doped n+-layer by MOVPE

The doping of GaN with silicon (Si) has been studied using SiH4 as the Si source gas. A Si-doped n-type GaN film with a free electron concentration of 1016-1018cm-3 and resistivity of 1−10-2Ω cm at RT can be easily obtained by controlling the flow rate of SiH4 during growth. Blue m/i/n/n+ LEDs have been fabricated for the first time using a Si-doped n+-GaN layer. The EL peak wavelength was ≁ 485 nm, and brightness was ≁ 50 mcd at a forward current of 10mA.

Room-Temperature Low-Threshold Surface-Stimulated Emission by Optical Pumping from Al0.1Ga0.9N/GaN Double Heterostructure

The difference in the refractive index at around λ=0.37 µm between GaN and Al0.1Ga0.9N is found to be about 0.19. With use of AlGaN/GaN double heterostructures, the threshold power for surface-stimulated emission by optical pumping at room temperature has been markedly decreased to about one-twentieth that of a bulk GaN layer. The mechanism of the stimulated emission in this system is discussed.

Characterization of the Shallow and Deep Levels in Si Doped GaN Grown by Metal-Organic Vapor Phase Epitaxy

Si doped GaN with room temperature free carrier concentration 1.1× 1017 cm-3 studied using the Hall effect exhibits exponential carrier freeze-out over a large range with activation energy 28.0± 0.5 meV; however, resistivity dependence on temperature suggests carrier hopping occurs at low temperature. GaN with greater Si concentration displays metallic impurity band conduction following the two-band model. Deep level transient spectroscopy results show a negligible concentration of other deep donors from native defects or unintentionally included impurities indicating that the active shallow donor is uniquely Si; however, photoluminescence tests show broad yellow emission with peak energy ~ 2.2 eV commonly observed in Si doped GaN.

MOVPE growth of GaN on a misoriented sapphire substrate

Abstract The effects of slight misorientation from a (0001) singular plane on sapphire (α-Al 2 O 3 ) substrates on the surface morphology and luminescence properties of MOVPE-grown GaN films have been studied. Macrostep morphology with periodic terraces (singular plane) and risers (clustered steps) has been observed for the first time on epitaxial GaN films grown on 3°–10° misoriented sapphire substrates toward both the [ 1 0 1 ¯ 0 ] sapphire and [ 1 2 ¯ 1 0 ] sapphire directions. In addition, it is found that the macrostep causes inhomogeneity of cathodoluminescence (CL) and electroluminescence (EL) patterns in Zn-doped GaN films, suggesting that the Zn-luminescence center formation depends on the growth planes of the terrace and riser.

Series Resistance in n-GaN/AlN/n-Si Heterojunction Structure

A nominally nondoped GaN was grown on an (111)Si substrate using an AlN intermediate layer and the electrical resistance of a GaN/AlN/Si heterojunction was studied in relation to the growth conditions of the AlN intermediate layer. Cross-sectional reflection electron microscopy (REM) images showed that the AlN intermediate layer is of pyramid-like microcrystals with a thin area in between. A clear correlation was found between the film thickness in the thin area and the apparent resistance of a sample. The growth conditions of the AlN intermediate layer were studied to achieve a low electrical resistance, maintaining the mirror flat surface morphology of a top GaN layer.

Carbon Incorporation on (1101) Facet of AlGaN in Metal Organic Vapor Phase Epitaxy

Using C2H2 as the source material, the incorporation of carbon into a (1101)AlGaN facet was studied in metal organic vapor phase epitaxy. The cathodo luminescence (CL) spectra for the sample surface were dominated by two near-band-edge emission peaks, assigned as a donor bound exciton (DBE) peak and a carbon-related exciton peak. The emission intensity of the carbon related exciton peak was enhanced by carbon doping, and the enhancement was more efficient on the (1101) facets than on the (0001) facet. It was found that more carbon is incorporated in a sample with high Al composition on the (1101) facets. In the case of Mg doping, on the other hand, the optical properties on the (1101) facets are nearly the same as those of the (0001) facet.

A local vibration mode in a carbon doped (1-101)AlGaN

Behavior of carbon (C) doping in a (1-101)AlGaN has been investigated by grazing incidence FTIR analyses at room temperature. The sample was grown by MOVPE on (1-101)facets of GaN triangular stripes made on (111)Si substrate. Intentional C doping was performed by introducing C2H2 into the reactor during the growth. In the FTIR spectra, a C related LVM mode was found out at 950 cm-1 which was associated with A1(LO) mode of AlN at 890cm-1. The behavior was similar to the results found in an un-intentionally Al doped GaN sample. Linear chain model with an effective mass gives the LVM energy of Al-C bond at 930 cm-1, a little lower than the experimental observation. The C doping on the N site might be performed forming a complex with additional elements.

Selective growth and impurity incorporation in semipolar GaN grown on Si substrate

Semipolar nitrogen terminated (1-101)GaN film was grown on a patterned (001)Si substrate using selective area metal organic vapor phase epitaxy. By using a high temperature grown AlN buffer layer upon oblique (111) Si facets on the substrate, we achieved a GaN crystal film with low dislocation density. Because the growth of GaN crystal was selforganized on the facets, we achieved two dimensional growth mode automatically, and the surface roughness was as small as 0.2nm. Incorporation of magnesium (Mg) and carbon (C) in the (1-101) GaN was studied extensively. It was found that the Mg doping efficiency is superior on (1-101) face to that on (0001) face. In case of C doping, a shallow acceptor level was generated in (1-101) face and p-type conduction was realized.

Acceptor Level due to Carbon in a (1–101)AlGaN

Carbon doping into N terminated GaN and AlGaN epitaxial layer is investigated. We found strong carbon related emission band which is insensitive to the annealing effect. The results suggested a shallow acceptor level which was slightly increased by the increase of the Al composition. A possible mechanism of the shallow level is discussed.