Meoungwhan Cho

Demonstration of nonpolar a-plane InGaN/GaN light emitting diode on r-plane sapphire substrate

High crystalline a-plane (112¯0) GaN epitaxial layers with smooth surface morphology were grown on r-plane (11¯02) sapphire substrate by metalorganic chemical vapor deposition. The full width at half maximum of x-ray rocking curve was measured as 407 arcu2009sec along c-axis direction, and the root mean square roughness was 1.23 nm. Nonpolar a-plane InGaN/GaN light emitting diodes were subsequently grown on a-plane GaN template, and the optical output power of 0.72 mW was obtained at drive current of 20 mA (3.36 V) and 2.84 mW at 100 mA (4.62 V) with the peak emission wavelength of 477 nm.

Optimization of ZnSe growth on miscut GaAs substrates by molecular beam epitaxy

Abstract We report growth optimization of molecular beam epitaxy (MBE) grown ZnSe on GaAs (0xa00xa01) substrate tilted by 15° toward [1xa01xa00] in terms of beam equivalent pressure (BEP) ratio and growth temperature. A LT-ZnSe buffer was grown to reduce the formation of Ga–Se bonding, a well-known source of defect generation, due to interdiffusion through the heterointerface in the initial stage of growth. The ZnSe layer was further optimized by low-temperature-grown (LT-ZnSe) buffer. The optical and structural properties of the ZnSe film with LT-ZnSe and GaAs buffer are also analyzed by photoluminescence spectroscopy (PL), X-ray diffraction (XRD), and secondary ion mass spectroscopy (SIMS), which show very large intensity ratio of near-band-edge emission to deep level emission, narrow XRD peak width of (0xa00xa04) rocking curves, and abrupt ZnSe/GaAs heterointerface under the optimum growth condition, respectively. The optimum growth conditions are BEP ratio ( P Se / P Zn ) of 3 and growth temperature of 310°C with an LT-ZnSe buffer grown at 250°C.

Improvement in crystallinity of ZnSe by inserting a low-temperature buffer layer between the ZnSe epilayer and the GaAs substrate

Abstract This article demonstrates the effect of the thin low-temperature-grown ZnSe buffer layer (LT-ZnSe) in improving crystallinity of ZnSe-based films grown on GaAs substrate. Especially, the density of stacking fault defects, which is normally observed in ZnSe-based films grown on GaAs substrate, can be well reduced by inserting a thin ZnSe buffer layer grown at sufficiently low temperature between ZnSe/GaAs heterostructure. A ZnSe film with stacking fault densities as low as ∼2×10 6 /cm 2 was obtained by growing on the LT-ZnSe/GaAs buffer layers, in contrast, ∼8×10 8 /cm 2 was obtained by directly growing on GaAs substrate. The Frank-type stacking faults was dominant for films grown with LT-ZnSe, meanwhile, Shockley-type stacking faults was dominant for films grown without LT-ZnSe buffer. At the initial stages of ZnSe growth, three-dimensional growth mode is considerably suppressed with LT-ZnSe buffer. The improvement of crystallinity in the ZnSe film with LT-ZnSe and GaAs buffer is also evidenced by low-temperature photoluminescence spectroscopy and high-resolution X-ray diffraction, which show very large intensity ratio of near-band-edge emission to deep level emission and narrow X-ray diffraction peak width of (0xa00xa04) rocking curve with 92xa0arcsec, respectively.

Improvement of Light Extraction Efficiency and Reduction of Leakage Current in GaN-Based LED Via V-Pit Formation

Four types of GaN-based light-emitting diodes (LEDs) with V-pits formed in different regions were grown by metal-organic chemical vapor deposition. The position of the V-pits embedded in the layers of the LED structures was controlled by varying the growth temperature. We achieved the highest output power and lowest leakage current values with the LED structures comprising V-pits embedded in active regions and the p-GaN textured surface. The V-pit formation enhances the light output power and reverse voltage values by 1.3 times the values of the conventional LED owing to the enhancement of the light scattering probability and the effective filtering of threading dislocations.

Growth of self-standing GaN substrates

Large-sized and high-quality free standing GaN are required with the development of GaN-based devices. We have developed new techniques to reduce the price of GaN substrates. In this paper, we introduce a simple fabrication way of freestanding GaN substrate using hydride vapor phase epitaxy (HVPE). An evaporable buffer layer was applied for the fabrication of 2inch freestanding GaN to separate from a sapphire substrate, in other words, a freestanding GaN was fabricated only by HVPE (one-stop process) without any process.

Inversion domains triggering recovery of luminescence uniformity in epitaxially lateral overgrown thick GaN film

A 150 μm-thick GaN layer was grown by halide vapor phase epitaxy utilizing selective lateral overgrowth on a SiO2-prepatterned sapphire substrate. A series of optically active regions above the SiO2 mask was observed in cross sectional monochromatic cathodoluminescence images taken at 367 nm. These bright regions were, however, consistently terminated by triangular shaped domains at 60 to 80 μm thickness, leaving no sign of luminescence nonuniformity beyond the thickness. In conjunction with the recent results on the characteristics of inversion domains in GaN, we proposed that these triangular regions might be inversion domains.

A selective growth of III-nitride by MOCVD for a buried-ridge type structure

Abstract We report a novel structure of a selectively grown buried-ridge (SGBR) type nitride-based laser diode structure grown on sapphire and lateral epitaxial overgrowth (LEO) substrates by metal-organic chemical vapor deposition (MOCVD). The AlGaN layers were designed for current confinement into ridge as well as to enhance lateral optical confinement by introducing an index difference between MQW and AlGaN layers in the lateral direction. The I–V characteristics of SGBR structure on LEO substrate showed no leakage current upto a reverse bias of −10xa0V. From an EL image through transparent metal, we demonstrated that the current path was well defined into the ridge region.

Growth and characterization of ZnSe/BeTe superlattices

Abstract We have studied the growth and properties of ZnSe/BeTe superlattices by molecular beam epitaxy for two interface configurations, which are basically characterized by a “ZnTe” and a “BeSe” interface layer. The interface properties for the two interface configurations have been studied by means of reflection high energy electron diffraction, high resolution X-ray diffraction, and photoluminescence. It is shown that the optical and structural properties of ZnSe/BeTe superlattices are improved with a ZnTe interface compared to a BeSe interface.