Naoyuki Nakada

GaN on Si Substrate with AlGaN/AlN Intermediate Layer

A single crystal GaN thin film was successfully grown on a Si (111) substrate by means of atmospheric pressure metalorganic chemical vapor deposition. Though there is a large difference in thermal expansion coefficients between GaN and Si, an intermediate layer consisting of AlN and AlGaN improved the quality of GaN on Si and reduced meltback etching during growth. Pits and cracks were not observed on the substrate and a mirror-like surface was obtained. The full-width at half maximum (FWHM) of the double-crystal X-ray rocking curve for GaN(0004) was 600 arcsec. Photoluminescence measurement at room temperature for a Si-doped film revealed a sharp band-edge emission with a FWHM of 62.5 meV, which is the narrowest value reported to date.

Improved characteristics of InGaN multiple-quantum-well light-emitting diode by GaN/AlGaN distributed Bragg reflector grown on sapphire

An InGaN multiple-quantum-well light-emitting diode (LED) containing a GaN/AlGaN distributed Bragg reflector has been grown on a sapphire substrate by metalorganic chemical vapor deposition. Comparing with the conventional LED, the output power has been improved from 79 to 120 μW under 20 mA direct current biasing condition and the external quantum efficiency has been also improved from 0.16% to 0.23% under 10 mA dc current.

High-Quality GaN on Si Substrate Using AlGaN/AlN Intermediate Layer

A single crystal GaN thin film was successfully grown on a Si(111) substrate by means of atmospheric-pressure metalorganic chemical vapor deposition. An intermediate layer consisting of AlN and AlGaN improved the quality of GaN on Si with a mirror-like surface and reduced the pits and cracks over the surface. The full width at half maximum (FWHM) of the double-crystal X-ray rocking curve for GaN(0004) was 600 arcsec. Photoluminescence measurement at 4.2 K for a nondoped film revealed a sharp band-edge emission with a FWHM of 8.8 meV, which is the narrowest value reported to date. GaInN multi-quantum-well structure was grown on this structure and showed a strong blue emission peaking at 470 nm. The results suggest GaN on Si with an AlGaN/AlN intermediate layer provides reliable light emitting devices on Si substrate.

Suppression of crack generation in GaN/AlGaN distributed Bragg reflector on sapphire by the insertion of GaN/AlGaN superlattice grown by metal-organic chemical vapor deposition

GaN/AlGaN distributed Bragg reflectors (DBRs) have been grown on sapphire by metal-organic chemical vapor deposition. A GaN/AlGaN superlattice (SL) was introduced prior to the growth of the DBR to suppress crack generation. By introducing the SL, GaN layers in the DBR were highly compressed and the in-plane lattice constants were close to those of AlGaN layers in the DBR. For the 30 pairs of GaN/Al0.41Ga0.59N DBRs, the reflectivity was improved from 93% to 98% by the introduction of the 100 periods of GaN/AlGaN SL, and the generation of cracks was effectively suppressed.

Correlation between electrical and surface properties of n-GaN on sapphire grown by metal-organic chemical vapor deposition

Lightly doped n-GaN epilayers were grown by metal-organic chemical vapor deposition (MOCVD) on sapphire substrates. The grown n-GaN epilayers were characterized using atomic force microscopy (AFM), X-ray diffraction (XRD), photoluminescence and Hall effect measurements. Enhanced PL intensity and low dark spot density (DSD) were observed on the aligned step structure n-GaN. The samples with these aligned step structure showed high electron mobilities with good structural and optical properties, while the samples with the anisotropic step structure showed broadened XRD FWHM values, low mobilities, and poor structural and optical properties. The low Hall mobility of n-GaN is due to the scattering of charged threading dislocations. A clear correlation was observed between Hall mobility and DSD by AFM. The AFM surface observation is also a better method for the evaluation of the electron mobility of lightly doped MOCVD grown n-GaN.