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The growth behaviour of GaN selective area growth (SAG) by MOVPE on two types of nano-patterned GaN substrates has been investigated. Samples were characterized by SEM, AFM and TEM. Results indicate that well formed nano-pyramids with base size of ∼150 nm, and sharp tips are readily grown through mask patterns defined by electron beam lithography (EBL). A growth rate of nearly zero on the {10$ \bar 1 $1} nano-facets, effectively self-limiting growth (SLG), has been observed under a wide range of growth conditions using a conventional growth mode. In contrast, pulsed growth is able to change the SLG behaviour, and thereby control the size of pyramids, even to coalesce the pyramids to form flat, smooth GaN films. SLG-like behaviour of GaN SAG on patterns defined by nano-imprint lithography (NIL) is also observed and enabled nano-pyramids to form. However, GaN SAG on NIL patterns shows accelerated growth in some pores at the early stage of the growth. This accelerated growth is attributed to the possible presence of screw-type dislocations in the pore. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

This paper presents the results using an alternative defects and strain minimizing technique with nanostructures as the compliant layer to grow III-V nitrides onto foreign substrates. Defects reduction and stress relaxation had been observed through HRTEM on GaN grown on sapphire and silicon. Results of LED devices on silicon with performance compatible with those on sapphire are presented.

A mixed pulsed and normal GaN epitaxial lateral overgrowth (ELO-GaN) by epitaxy metalorganic vapour phase epitaxy (MOVPE) is reported in this study. Monitoring by using an in situ spectroscopic reflectometer has shown that a varying vertical growth rate during the pulsed growth was observed as in the normal ELO-GaN growth process, however, the growth rate was dramatically reduced in pulsed growth. Cross-section scanning electron microscope (SEM) images have shown that a lateral to vertical growth ratio (LTVGR) of 7 was obtained under a set of growth conditions on a template with a GaN trench and SiO 2 mask width of 5 and 15 μ m , respectively, and with the stripes aligned in the GaN 〈 1 ¯ 1 0 0 〉 crystallographic direction. Two types of growth instability associated with pulsed growth were observed under some growth conditions. One is the formation of large steps on the ELO-GaN stripes before coalescence; the other is the formation of hexagonal pyramids on the coalesced surface. The origin of pyramidal formation was found exactly on the coalescence boundaries. A mixed pulsed and normal ELO-GaN growth technique has been established to eliminate the large steps, and formation of pyramids can be avoided by switching to normal growth conditions before ELO-GaN stripes coalesce. The thickness of ELO-GaN has been successfully controlled below 1 μ m before coalescence, and below 3 μ m for a fully coalesced ELO-GaN film by this technique. Atomic force microscope (AFM) has confirmed that ELO-GaN films grown by this technique are of high structural quality.

Undoped GaN (u-GaN) films were grown by low pressure metalorganic vapour phase epitaxy (LP-MOVPE) on sapphire substrates. In situ optical monitoring was applied to the growth process either using a LayTec EpiR-DA TT spectroscopic reflectometer or Filmetrics F30. Refractive indices of u-GaN films at 1060 degrees C were obtained in a spectral range from 370-900 nm. A peak at 412 5 rim in refractive index spectra was observed, which most likely corresponds to the band-gap of hexagonal GaN at a temperature of 1060 degrees C. Refractive indices below this band-gap are fitted well to the first-order Sellmeier formula. As an example of the applications of the refractive indices, the effective film thicknesses of GaN during the resumption from 3 dimensional (3D) to 2 dimensional (2D) growth have been calculated from the spectra recorded by a LayTec system using the optical constants obtained. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Epitaxial lateral overgrowth (ELO) has been used to reduce threading dislocation (TD) densities in GaN. This paper reports transmission and scanning electron microscopy studies of TDs in GaN films grown by ELO on GaN nanocolumns produced either during growth by MBE (method 1), or by self-organised patterning on a uniform layer grown by MOCVD (method 2). In method 1, isolated nanocolumns grew without TDs, but some TDs formed when nanocolumns coalesced. Although some of these TDs extended through the overlayer, extensive lateral migration of others, depending on the dislocation type, led to dislocation annihilation, lowering the overall TD density. In method 2, a similar process of lateral migration of TDs was observed during ELO, resulting in a continuous GaN overlayer with TD densities less than 108 cm–2. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In this work, the results are presented of a nanorod LED array. If the lateral size of the nanorods is small enough, it is possible to achieve a degree of lateral confinement. If the nanorods are ordered into a suitable photonic lattice, then this will reduce the lateral spontaneous emission and enhance emission along the vertical axis via the Purcell effect. Additionally there is a degree of dislocation filtering that can occur [1]. However, one potential drawback of this device is the large free surface that borders the multi-quantum well active region. Nevertheless, it has been shown that the surface recombination in the nitride materials is the lowest of all III-V semiconductors. Results of SEM, PL, EL, and far field pattern are presented to compare the progressive effect of using photo-assisted electroless and wet etching [2]. It can be seen that over time the photo-assisted electroless method clearly delineates the active MQW region, possibly as a result of the different etch rate of InGaN. Alternatively, a purely chemical etching method was used. With a narrowing of the nanorods, there is a progressive blue shift of the photoluminescence peak. The optical image of the emission shows that there are well-defined lines of enhanced light propagation that match the symmetry of the nanorod array, thus showing there is a photonic crystal effect.

This paper reports the characteristics of gallium nitride layers that have been grown on top of an etched array of nanorods. Nanoimprint lithography has been used to create nanorods on a wafer-scale that are subsequently passivated to allow selective regrowth from their tips by MOVPE. The first epitaxial growth step favoured lateral growth and the second resulted in a planar coalesced layer of gallium nitride. It was found that smooth planarised overgrowth required careful timing of the growth transition between the two steps and that the crystallographic quality of the overgrown layer was very sensitive to the nanorod template properties, in particular the amount of unpassivated nanorod surface. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Nano-pendeo-epitaxial GaN films have been grown by metalorganic vapour phase epitaxy on nanocolumns fabricated on thin GaN-on-Si(111) templates. Optical and structural performances of the films are improved, crack densities are reduced, and self-separation of GaN films from the substrates at the nanocolumns has been realized. The success of the nano-pendeo-epitaxy of GaN films is attributed to the following three techniques developed in this study: (1) the growth of high quality ultrathin GaN/AlN templates on on Si(111) substrates, (2) the fabrication of uniform nanocolumns across the 2-inch wafer surface, and (3) the in situ conversion of the exposed silicon surfaces of the fabricated nanocolumns to silicon nitride. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A resonance tunnelling LED structure having a high efficiency, low droop and negligible wavelength shift with current is reported in this study. The LED structure contains a thick InGaN bottom spacer between an n-GaN contact layer and a multiple quantum well (MQW) active region, and a thin InGaN top spacer between the MQW and an AlGaN electron blocking layer (EBL). The observed high efficiency and negligible wavelength shift with applied current are attributed to the thick InGaN bottom spacer that nucleates V-pits and acts as a strain control layer for the MQW. The thick InGaN layer also provides an electron reservoir for efficient electron tunnelling injection into the MQW and reduces the electropotential difference between the n-emitter and the p-emitter, to suppress current leakage at high driving current and reduce droop. The top InGaN spacer was designed to act as a magnesium back-diffusion barrier and strain relief layer from EBL so as to obtain high efficiency.

Cd1-yZnyTe (CZT) wafers with (111) orientations, which serve as the common substrates for Hg1-xCdxTe (MCT) epitaxial deposition, were treated with different processes of mechanical polishing and chemical etching and then tested by x-ray diffraction unit with the same experimental conditions. The conclusion is that the sample surface treatment dramatically influences the values of DCRC FWHM. The most desirable process and its experimental conditions for accurate measurement of DCRC FWHM have also been reported in this paper.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We report the influence of growth conditions on the qualities of CdTe, HgTe and HgCdTe layers grown by MOVPE, CdTe and HgTe layers were grown onto 2 degree(s)(100)GaAs substrates. HgCdTe layers were grown onto hybrid substrates 2 degree(s)(100)CdTe/GaAs with 3 micrometers buffers using interdiffused multilayer process. Surface morphology and compositional uniformity of HgCdTe layers have been investigated. Although the growth conditions have not been optimized, the layers have smooth and specular surface with remarkable featureless except some occasions with elongated hexagonal features. The morphology is sensitive to slight variations of concentrations of reactants, and (100)CdTe/(100)GaAs layers can be grown in a narrow range at Cd-rich conditions. Compositional uniformity of (Delta) x equals +/- 0.005 mol.CdTe over 1 cm2 area of HgCdTe layers have been reached for both LWIR and MWIR material. The grown layers can be p- or n-type, depending upon the buffer thickness, Hg concentrations during growth and postgrowth treatment and the substrate temperatures.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

In order to meet with the epitaxial growth of large area Hg1-xCdxTe (MCT) with various compositions for infrared focal plane arrays, CdTe and Cd1-yZnyTe (y equals 0.020, 0.025 and 0.040 for various x) crystals with 120 mm length and 20 - 40 mm diameter have been successfully synthesized and grown by the vertical Bridgman method. These crystals were grown unseededly or seededly and free of any macroscopic defects e.g. micro-cave and crackles. Wafers with areas from 12 X 18 mm2 to 30 X 35 mm2 in the orientation have been obtained from large grain of the ingot. Effects of changing the ampoule base shape upon the crystal growth have also been investigated. A necked ampoule bottom is preferred to ones employing seeding. Assessments of the samples have included infrared transmission (range 2.4 - 24 micrometers ), etch pit density, X-ray photography and three-crystal rocking curve measurement. Good quality MCT epitaxial films (areas of 12 X 18 mm2 and 20 X 20 mm2), as demonstrated by good surface topography, electrical parameters, have been grown by liquid phase epitaxy and metal organic chemical vapor epitaxy onto CdTe(CT) and Cd1-yZnyTe(CZT) substrate materials produced in our study.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Transmission and scanning electron microscopy are used to examine the role of an intermediate nanorod layer in reducing threading defect densities in GaN/(0001)sapphire. Films grown by molecular beam epitaxy under N-rich conditions showed Ga-polar nanorods growing out of a more compact N-polar layer. The nanorods sometimes contained extended threading defects, which were faulted dipoles lying on {10-10} planes with a displacement vector of ±1/2[0001], which act as sources for spiral growth. By overgrowing the nanorods under Ga-rich conditions, continuous epilayers were formed with threading defect densities down to 108 cm−2. In a second approach, nanorods produced by etching through a self-organised layer of Ni islands were overgrown by metal-organic chemical vapour deposition, to produce overlayers with defect densities down to 5*107 cm−2. In both cases, the mechanisms by which the nanorod layer reduces the threading defect density are identified.

A photonic crystal has been created on the p-layer of an InGaN light-emitting diode wafer by selective area growth, thus avoiding the etch processes that are detrimental to the active region. Nanopyramid arrays with either hexagonal or Archimedian lattices were grown in apertures defined by nanoimprint lithography. Electroluminescence measurements show that the pyramids improve the on-axis light output by up to 1.9–2.0 times. This technique could be extended to higher aspect ratio nanostructures that will have stronger coupling between the guided modes and the photonic crystal.