Growth Of Gallium Nitride And Indium Nitride Films And Nanostructured Materials By Hydride Metalorganic Vapor Phase Epitaxy

Crack-free, 3 mum GaN films were grown on GaN/AlGaN/Si template at 850°C although cracks developed when the thickness exceeded 7 mum. It was possible, however, to grow crack-free polycrystalline 40 mum thick GaN on Si using InN NRs as a buffer material.

It was also found that the polycrystalline nature is as a result of polycrystalline nature of LT-GaN grown on the InN template. It was also shown that formation of completely enclosed uniformly distributed nanovoids were very essential to grow crack free thick GaN which is highly textured in 0002 orientation. It was also shown that GaN grown was very high quality crystal free of Indium. GaN growth on Indium metal deposited on Silicon was also studied. Depending on growth mode and conditions GaN 40 micron thick film and 100nm x 5000nm GaN wafers were successfully grown in same reactor.

This dissertation employs doping to investigate basic gallium nitride (GaN) crystal properties and to solve challenges of the hydride vapour phase epitaxy (HVPE) growth process. Whereas the first chapter is a short introduction to the history of the GaN single crystal growth, the 2nd chapter introduces to current crystal growth techniques, discusses properties of the GaN material system and the resulting influence on the applicable crystal growth techniques. HVPE, as a vapour phase epitaxy crystal growth method will be explained in greater detail, with focus on the used vertical reactor and its capabilities for doping. The 3rd chapter then focusses on point defects in GaN, specifically on intentionally introduced extrinsic point defects used for doping purposes, i.e. to achieve p-type, n-type or semi-insulating behaviour. Different dopants will be reviewed before the diffusion of point defects in a solid will be discussed. The in-situ introduction of iron, manganese, and carbon during crystal growth is employed in chapter 4 to compensate the unintentional doping (UID) of the GaN crystals, and therefore to achieve truly semi-insulating behaviour of the HVPE GaN. However the focus of this chapter lies on the characterisation of the pyroelectric coefficient (p), as semi-insulating properties are a necessary requirement for the applied Sharp-Garn measurement method. The creation of tensile stress due to in-situ silicon doping during GaN crystal growth is the topic of the 5th chapter. The tensile stress generation effect will be reproduced and the strain inside the crystal will be monitored ex-situ employing Raman spectroscopy. The n-type doping is achieved by using a vapour phase doping line and a process is developed to hinder the tensile strain generation effect. The 6th chapter concentrates on the delivery of the doping precursor via a solid state doping line, a newly developed doping method. Similar to chapter 5, the doping line is characterised carefully before the germanium doping is employed to the GaN growth. The focus lies on the homogeneity of the germanium doping and it is compared compared to the silicon doping and the vapour phase doping line. Benefits and drawbacks are discussed in conjunction with the obtained results. The germanium doping via solid state doping line is applied to the HVPE GaN growth process to measure accurately growth process related properties unique to the applied set of GaN growth parameters.

Gallium nitride is an important material for the production of next-generation visible and near-UV optical devices, as well as for high temperature electronic amplifiers and circuits; however there has been no bulk method for the production of GaN substrates for device layer growth. Instead, thick GaN layers are heteroepitaxially deposited onto non-native substrates (usually sapphire) by one of two vapor phase epitaxy (VPE) techniques: MOVPE (metalorganic VPE) or HVPE (hydride VPE). Each method has its strengths and weaknesses: MOVPE has precise growth rate and layer thickness control but it is slow and expensive; HVPE is a low-cost method for high rate deposition of thick GaN, but it lacks the precise control and heterojunction layer growth required for device structures. Because of the large (14%) lattice mismatch, GaN grown on sapphire requires the prior deposition of a low temperature MOVPE nucleation layer using a second growth process in a separate deposition system. Here we present a novel hybrid VPE system incorporating elements of both techniques, allowing MOVPE and HVPE in a single growth run. In this way, a thick GaN layer can be produced directly on sapphire. GaN growth commences as small (50-100 nm diameter) coherent strained 3-dimensional islands which coalesce into a continuous film, after which 2-dimensional layer growth commences. The coalescence of islands imparts significant stress into the growing film, which increases with the film thickness until catastrophic breakage occurs, in-situ. Additionally, the mismatch in thermal expansion rates induces compressive stress upon cooling from the growth temperature of 1025°C. We demonstrate a growth technique that mitigates these stresses, by using a 2-step growth sequence: an initial high growth rate step resulting in a pitted but relaxed film, followed by a low growth rate smoothing layer. As a result, thick (> 50 [Mu]m) and freestanding films have been grown successfully. X-ray rocking curve linewidth of 105 arcseconds and 10K PL indicating no "yellow" emission indicate that the material quality is higher than that produced by conventional MOVPE. By further modifying the hybrid system to include a metallic Mn source, it is possible to grow a doped semi-insulating GaN template for use in high frequency electronics devices.

A VLS growth mechanism is proposed, however, a VS growth mechanism can be achieved at high N/In ratios. SEM and TEM analysis revealed a core-shell nanowire structure with a single crystal InN core and a poly-crystalline In2O3 shell. Nanowire growth occurs along the [0002] direction with diameters and lengths ranging from 100 to 300 nm and 10 to 40 microns, respectively for a 1 hr growth. H-MOCVD growth of InN nano- and microrods occurred on different substrates and the nanorod structure was studied by TEM. The polarity of the substrate directly affected the nanorod tip shape and prismatic stacking faults are suggested as the cause for the flower-like growth habit. Variation of growth parameters, such as temperature, N/In ratio, and Cl/In ratio proved to be ineffective at changing the aspect ratio of the nanorods. Increased growth duration produces microrod size dimensions regardless of the chosen growth conditions.

ABSTRACT: InN and In-rich compositions of In[subscript x]Ga[subscript 1-x]N, have potential for a variety of device applications including solar cells. This work addresses the growth of high quality InN by metalorganic vapor phase epitaxy. To better understand the material a thermodynamic assessment of the In-N-C-H system was performed to yield the In-N P-T diagram. In addition, the InN critical thickness was calculated for several candidate substrates to guide substrate selection. Furthermore, computational fluid dynamics was used to design an improved reactor. A vertical NH3 tube design produced the lowest reported [omega]-2[theta] rocking curve FWHM value of (574 arcsec) for InN grown on GaN/Al2O3 (0001). The film surface was also mirror-like as judged by AFM (RMS roughness = 4.2 nm). The PL peak energy of 0.82 eV was obtained for InN grown on Si, consistent with recent reports of a considerably lower of bandgap energy.

This book discusses the important technological aspects of the growth of GaN single crystals by HVPE, MOCVD, ammonothermal and flux methods for the purpose of free-standing GaN wafer production.

Indium gallium nitride nanostructures were grown at a temperature of 600oC and a total V/III ratio of 10,000. Below an indium fraction of 0.20 nanostructures were observed with diameters between 200 and 350 nanometers. The diameters were found to decrease with increasing indium fraction. Texturing in the (0001) c-plane direction was also enhanced as the indium fraction was increased. At indium fractions above 0.20 the formation of metal droplets within a porous indium gallium nitride film were observed. There are several untried deposition recipes that can yet be attempted to grow the nanostructures over the entire compositional range of the indium gallium nitride alloy.

The GaN samples grown for this dissertation were studied by various techniques to characterize their structural, optical, and electrical properties.