InGaN Growth Research Articles

Characterization of a-plane InGaN multiple-quantum wells grown on maskless lateral epitaxially overgrown a-plane GaN

We investigated the properties of nonpolar a-plane InGaN∕GaN multiple-quantum wells (MQWs) grown on maskless lateral epitaxial overgrowth (LEO) a-plane GaN∕r-sapphire. Many surface defects with asymmetric V-shape were observed on a-plane InGaN MQWs grown on the defective regions which were seed and coalescence regions. In the low defect regions, the surface defect density of a-plane InGaN MQWs was ∼1.0×107∕cm2, which was higher than that of conventional c-plane LEO-GaN, by measuring atomic force microscope and scanning tunneling electron microscope. The cathode luminescence intensity distribution of a-plane InGaN MQWs was significantly dependent on the distribution of surface asymmetric V-defect. Therefore, we suggest that the optical properties of a-plane InGaN active layer were affected by the asymmetric V-defects which were generated by interaction between the epitaxial defects and the limit of InGaN growth kinetics.

Luminescence characterization of InGaN/GaN vertical heterostructures grown on GaN nanocolumns

ABSTRACTThe photoluminescence of MBE-grown InGaN/GaN vertical heterostructures on c-axis oriented GaN nanocolumns is investigated. Nanocolumnar InGaN heterostructures exhibit luminescence efficiencies greater than 20% for peak emission wavelengths as long as 540 nm. Compared to otherwise identical InGaN samples with larger median column diameters, the luminescence is blue-shifted and exhibits reduced efficiency for diameters less than about 50 nm. Growth of InGaN on GaN columns with a broad distribution of diameters results in broad-band photoluminescence that appears white to the eye and has efficiency as high as 23%.

InGaN Growth with Indium Content Controlled by GaN Growth Plane

ABSTRACTHighly spatially resolved cathodoluminescence (HRCL) imaging and electron backscattering pattern (EBSP) study of InGaN microcrystals were achieved. InGaN grown by the nitridation of a mixture of GaN microcrystals and indium sulfide powders with ammonia at 1000°C had crystal habit with twelve prismatic planes. The prismatic planes were grouped into two groups: the first group is pentagonal shaped planes yielding blue CL (420nm) and rectangular planes without luminescence. EBSP showed that the pentagonal shaped planes are indexed to the {11-20} a-plane and the rectangular plane to the {1-100} m-plane. HRCL imaging showed InGaN accumulated at the V pits on the basal plane. The obevation indicated that the crystal qualty of InGaN and the indium contents incorpated were controlled by the indices of GaN growth planes on which InGaN grew.

InGaN Thin Films Grown by ENABLE and MBE Techniques on Silicon Substrates

ABSTRACTThe prospect of developing electronic and optoelectronic devices, including solar cells, that utilize the wide range of energy gaps of InGaN has led to a considerable research interest in the electronic and optical properties of InN and In-rich nitride alloys. Recently, significant progress has been achieved in the growth and doping of InGaN over the entire composition range. In this paper we present structural, optical, and electrical characterization results from InGaN films grown on Si (111) wafers. The films were grown over a large composition range by both molecular beam epitaxy (MBE) and the newly developed “energetic neutral atomic-beam lithography & epitaxy” (ENABLE) techniques. ENABLE utilizes a collimated beam of ∼2 eV nitrogen atoms as the active species which are reacted with thermally evaporated Ga and In metals. The technique provides a larger N atom flux compared to MBE and reduces the need for high substrate temperatures, making isothermal growth over the entire InGaN alloy composition range possible. Electrical characteristics of the junctions between n- and p-type InGaN films and n- and p-type Si substrates were measured and compared with theoretical predictions based on the band edge alignment between those two materials. The predicted existence of a low resistance tunnel junction between p-type Si and n-type InGaN was experimentally confirmed.

Influence of High Indium Composition InGaN on Lattice Matched ZnO Sacrificial Substrates

MOCVD growth of InGaN on ZnO substrates has achieved indium concentration as high as 43% as observed by high-resolution X-ray diffraction (HRXRD). The uniqueness of this finding is the absence of phase separation and the higher indium incorporation compared to growth on thick GaN/sapphire. Transmission electron microscopy (TEM) shows perfectly matched GaN and ZnO lattices. In addition, atomic layer deposition (ALD) transition layers have been grown in order to provide a transition layer on ZnO substrates to block Zn diffusion and allow for future substrate removal for thin nitride fabrication.

Correlation between luminescence and compositional striations in InGaN layers grown on miscut GaN substrates

The influence of the miscut angle of GaN substrate on compositional and optical properties of InxGa1−xN epilayers (0.05<x<0.1) was examined using x-ray diffraction, photoluminescence (PL), cathodoluminescence, and Z-contrast scanning electron microscopy. We show that single atomic steps bunch during growth of InGaN and form macrosteps. Indium is incorporated differently at treads and risers of these macrosteps, which causes the layer to decompose and induces the formation of compositional growth striations. Since the growth step density increases with growing miscut angle of the substrate, the average indium concentration decreases and the average PL peak energy blueshifts and broadens with increasing miscut angle. The presented work enables understanding on microscopic scale effects related to the inhomogeneous distribution of indium in InGaN layers on miscut substrates, which is significant from the point of view of optoelectronic applications.

Metalorganic chemical vapor deposition of InGaN layers on ZnO substrates

InGaN layers have been grown on (0001) ZnO substrates by metalorganic chemical vapor deposition utilizing a low temperature grown thin GaN buffer. Good quality InGaN films with a wide range of In composition were confirmed by high-resolution x-ray diffraction. Even at high indium concentrations no In droplets and phase separation appeared, possibly due to coherent growth of InGaN on ZnO. Photoluminescence showed broad InGaN-related emissions with peak energy lower than the calculated InGaN band gap, possibly due to Zn/O impurities diffused into InGaN from the ZnO substrate. An activation energy of 59 meV for the InGaN epilayer is determined.

Characterization of interface fluctuations and emission mechanisms in InGaN/AlGaN multiple quantum wells

The InGaN/AlGaN multiple- quantum- well heterostructures were fabricated by metal-organic chemical vapor deposition system. Samples were grown with different indium and aluminum content during the growth of InGaN well layers and AlGaN barrier layers. The exciton-localization effect on the performance of the samples is investigated by means of temperature-dependent photoluminescence measurements. The dependence of optical characteristics on temperature is consistent with recombination mechanisms involving band-tail states. For sample with higher indium content in the well layer, the localization effect is enhanced; in contrast, the effect is weakened for sample with higher aluminum content in the barrier layer.

Phosphor-free white-light light-emitting diode of weakly carrier-density-dependent spectrum with prestrained growth of InGaN∕GaN quantum wells

The authors grew a white-light InGaN∕GaN quantum-well (QW) light-emitting diode epitaxial structure with its electroluminescence spectrum close to the ideal condition in the Commission International de l’Eclairage chromaticity based on the prestrained metal-organic chemical vapor deposition technique. The prestrained growth leads to the efficient yellow emission from three InGaN∕GaN QWs of increased indium incorporation. The color mixing for white light is implemented by adding a blue-emitting QW at the top of the yellow-emitting QWs. The blueshifts of the blue and yellow spectral peaks of the generated electroluminescence spectra are only 1.67 and 8nm, respectively, when the injection current increases from 10to70mA. Such small blueshifts imply that the piezoelectric fields in their QWs are significantly weaker than those previously reported.

Nitrogen supply rate dependence of InGaN growth properties, by RF-MBE

Nitrogen flow rate dependence of InGaN growth mechanism on sapphire (0 0 0 1) was studied. The indium content of the InGaN layer can be controlled by changing the nitrogen supply rate by structural and optical investigations. In case of lower nitrogen flow rate, the formation of phase separation due to dissociation of InN and condensation of indium on the growing surface were observed. In case of higher nitrogen flow rate (under N-rich condition), on the other hand, the indium content became uniform and the photoluminescence (PL) emission showed single peak. It is considered that the causes of phase separation formation were suppressed and nonequilibrium condition was enhanced by the increase of the nitrogen supply rate and the growth rate. Judging from the estimated thermal activation energies and degree of fluctuation in the indium content by PL line-width, however, the non-radiative recombination centers within the spontaneously formed potential wells as well as in the extended states were formed in case of excess nitrogen supply rate. The structural defects that were caused by the suppression of the surface migration of group-III atoms with excessive activated nitrogen might have worked as non-radiative recombination centers. Thus, a slightly N-rich condition is desirable for the realization of the uniform InGaN alloy composition and the high optical quality, especially at relatively high growth temperature.

Growth of In-rich InGaN films on sapphire via GaN layer by RF-MBE

Growth temperature dependence of In-rich InGaN growth properties for each Ga/(Ga+In) supply ratio by radio-frequency plasma assisted molecular beam epitaxy was investigated. The luminescence property of In-rich InGaN films up to 20% of Ga improved compared with that of InN because their growth temperatures could be set at high and high purity InGaN films were obtained. This effect can be partly interpreted as a result of the larger bond strength of Ga–N than that of In–N. However, the InGaN films tend to be Ga-rich in case of relatively high growth temperatures. Also, InGaN dot-like structures at intermediate composition were grown as a result of the combination effect of phase separation due to the immiscibility of GaN into InN and local strain due to lattice mismatch between InGaN and underlying GaN buffer layer.

InGaN/GaN MQW structures prepared with various In and Ga flow rates

InGaN/GaN multiple quantum well (MQW) structures were prepared by metalorganic vapour phase epitaxy (MOVPE) with various InGaN growth conditions. It was found that growth rate and photoluminescence (PL) peak wavelength were determined by Ga and In flow rates, respectively. It was also found that the sample prepared with high InGaN growth rate exhibited low ν-defect related pits and good crystal quality. For the samples prepared with low growth rate, we could also improve the sample quality by increasing In/(In + Ga) flow rate ratio.

Surface modifications and optical properties of blue InGaN single quantum well by in‐situ thermal treatments

We investigated the surface modifications and optical properties of blue InGaN single quantum well (SQW) using the in-situ annealing process with different two temperatures. The surface of blue InGaN SQW was significantly modified from spiral surface to step-like surface structure as well as the degradation of InGaN PL emission efficiency after in-situ annealing process at a 1030 °C for 3 min in the metalorganic chemical vapor deposition (MOCVD) system. However, the surface of InGaN SQW was modified from spiral surface to spinodal pattern surface structure after in-situ annealing process at the InGaN growth temperature of 750 °C. These results implied that the surface atoms of InGaN could significantly rearranged by the thermal treatments at the high temperatures just after the InGaN growth. This surface reconstruction process can be caused by the desorption, the evaporation, and the surface migration of surface adatoms to reduce the thermodynamical instability. Moreover, it is possible to be happened the spinodal related phase separation of InGaN SQW under the in-situ annealing process with the InGaN growth temperature. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

InGaN Layers Grown on Al2O3/ZnO Substrates Prepared by Atomic Layer Deposition

AbstractAtomic layer deposition (ALD) of Al2O3 is used as a passivation layer on ZnO substrates before nitride growth by metalorganic chemical vapor deposition (MOCVD). This layer is being used to prevent Zn diffusion from the substrate, protect the ZnO surface from H2 back etching, and promote high quality nitride growth. ALD-Al2O3 films were grown at 100°C and then annealed in a furnace at various times at 1100°C for crystallization of the passivation layer. XRD results showed both Al2O3 and ZnAl2O4 phases at different intensities for 50 and 20nm ALD-AlM2O3 films. In addition, the InGaN layer has been successfully grown on the passivated ZnO substrate. Findings show that a short annealing time for the ALD-Al2O3 layer will be optimal for InGaN growth.

Epitaxial growth and optical properties of semipolar (112¯2) GaN and InGaN∕GaN quantum wells on GaN bulk substrates

GaN and InGaN∕GaN multiple quantum well (MQW) were grown on semipolar (112¯2) GaN bulk substrates by metal organic vapor phase epitaxy. The GaN homoepitaxial layer has an atomically flat surface. Optical reflection measurements reveal polarization anisotropy for the A, B, and C excitons. Free A excitons dominate the photoluminescence (PL) spectrum at 10K and are accompanied by a weaker, sharp doublet emission due to neutral donor-bound excitons. The InGaN∕GaN MQW grown on a GaN homoepitaxial layer involves fast radiative recombination processes. The PL decay monitored at 428nm can be fitted with a double exponential curve, which has lifetimes of 46 and 142ps at 10K. These values are two orders of magnitude shorter than those in conventional c-oriented QWs and are attributed to the weakened internal electric field. The emissions from GaN and MQW polarize along the [11¯00] direction with polarization degrees of 0.46 and 0.69, respectively, due to the low crystal symmetry.

High-density InGaN nanodots grown on pretreated GaN surfaces

High-density InGaN nanodots are successfully grown on pretreated GaN surfaces. The GaN surfaces were covered by SiO2 layers firstly, and then the SiO2 layers were removed before the growth of InGaN on the GaN. After this process, the growth of InGaN on the GaN surfaces changed to a three-dimensional mode. However, on the GaN surface without the SiO2 treatment, the growth of InGaN maintained a two-dimensional growth mode as usual. The InGaN nanodots are 26to68nm in diameter, 3.6–15nm in height, and up to 9×1010cm−2 in density, which can be controlled by growth duration and substrate temperature. Comparing with the InGaN thin film grown on untreated GaN surface with the same growth conditions, the InGaN nanodots showed stronger photoluminescence in longer wavelength range at room temperature. The formation mechanism of the nanodots is described based on the GaN surface states changed by SiO2 coverage. This approach enables fabrication of dense and controllable InGaN nanodots.

The effect of Si on the growth mode of GaN

AbstractIn the growth of InGaN on a SiH4‐exposed GaN surface, a change in the growth mode is observed for low SiH4 doses. To help explain this observation the potential energy surface of Ga and N adatoms on a GaN (0001) surface containing an isolated Si atom in the terminating layer was calculated using plane wave density functional theory. The surface Si atom decreases the diffusion barrier of Ga and N adatoms relative to the corresponding diffusion barriers on the ideal GaN (0001) surface. In addition, the adatom binding energies were not significantly affected by the Si surface atom. It was therefore concluded that the observed transition in growth mode of GaN cannot be simply explained by the presence of isolated Si atoms on the GaN surface. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

InN‐based layers grown by modified HVPE

AbstractThis paper contains results on InN and InGaN growth by Hydride Vapor Phase Epitaxy (HVPE) on various substrates including sapphire and GaN/sapphire, AlGaN/sapphire, and AlN/sapphire templates. The growth processes are carried out at atmospheric pressure in a hot wall reactor in the temperature range from 500 to 750 ºC. Continuous InN layers are grown on GaN/sapphire template substrates. Textured InN layers are deposited on AlN/sapphire and AlGaN/sapphire templates. Arrays of nano‐crystalline InN rods with various shapes are grown directly on sapphire substrates. X‐ray diffraction rocking curves for the (002) InN reflection have the full width at half maximum (FWHM) as narrow as 270 arcsec for the nano‐rods and 460 arcsec for the continuous layers. InxGa1–xN layers with InN content up to 10 mol.% are grown on GaN/sapphire templates. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Growth and morphology of MOVPE grown InGaN/GaN islands

AbstractThe dependence of the surface morphology on the growth temperature of InGaN/GaN(0001) samples grown by metal organic vapour phase epitaxy has been investigated using scanning probe microscopy. By lowering the growth temperature, the thermal diffusion of the InGaN is reduced which results in an increase of the island density. For 1.3 nm InGaN deposition at 650 °C, large spiral disc‐like InGaN islands with atomically flat top surfaces are observed which preferentially nucleate at GaN substrate defects. In contrast, InGaN growth at 600 °C leads to a homogeneous nucleation of small islands with a granular appearance. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

InGaN blue cathodoluminescence phosphors synthesized with long reaction time in a new reactor

AbstractInGaN microcrystals were grown by two‐stage growth method for 10 hours in a new reactor without clogging an exhaust tube by fine particles. Obtained InGaN showed double peaked cathodoluminescence spectra, violet peak at 385‐389 nm and blue at 438‐444 nm when excited at 5‐15 kV. The uniformity of the blue emission spectra among the crystals were improved for those grown for the 10‐hour reaction time. The yields of emissive GaN and InGaN crystals were not improved. The compatibility of the position of the violet band of the InGaN crystals to that of the GaN crystals and the resemblance of morphology of the GaN and InGaN crystals imply the growth of InGaN on GaN facets in two‐stage growth. The cause of the deterioration of the CL efficiency of the grown InGaN crystals at a low acceleration voltage was discussed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)