In this work, Ni/ZnO:Al and Au/ZnO:Al structures are proposed as efficient ohmic contacts to p-GaN. Through a careful selection of deposition parameters and annealing environment, we not only achieve the formation of high-quality ohmic contacts but also gain insights into the interfacial reactions, enhancing the understanding of conventional Ni/Au contact formation on p-GaN. In particular, the notion that the presence of NiO at the interface is enough for an ohmic contact to form is challenged by showing that in fact it has to be NiO formed at the interface from metallic Ni and additional oxygen.
View Article and Find Full Text PDFA nonradiative recombination channel is proposed, which does not vanish at low temperatures. Defect-mediated nonradiative recombination, known as Shockley-Read-Hall (SRH) recombination, is reformulated to accommodate Coulomb attraction between the charged deep defect and the approaching free carrier. It is demonstrated that this effect may cause a considerable increase in the carrier velocity approaching the recombination center.
View Article and Find Full Text PDFThe impact of wet treatment using an (NH)S-alcohol solution on the interface state of the p-GaN/Ni/Au/Pt contact system and laser diode processing was investigated. Sulfur wet cleaning resulted in reduced surface roughness and contact resistivity. The lowest specific contact resistance ( < 1 × 10 Ω·cm) was achieved with samples treated with an (NH)S-isopropanol solution, whereas the highest resistivity ( = 3.
View Article and Find Full Text PDFThis work reports on the possibility of sustaining a stable operation of polarization-doped InGaN light emitters over a particularly broad temperature range. We obtained efficient emission from InGaN light-emitting diodes between 20 K and 295 K and from laser diodes between 77 K and 295 K under continuous wave operation. The main part of the p-type layers was fabricated from composition-graded AlGaN.
View Article and Find Full Text PDFUsing the example of III-V nitrides crystallizing in a wurtzite structure (GaN, AlN, and InN), this review presents the special role of hydrostatic pressure in studying semiconductor properties. Starting with a brief description of high-pressure techniques for growing bulk crystals of nitride compounds, we focus on the use of hydrostatic pressure techniques in both experimental and theoretical investigations of the special properties of nitride compounds, their alloys, and quantum structures. The bandgap pressure coefficient is one of the most important parameters in semiconductor physics.
View Article and Find Full Text PDFIn this paper, we investigate the effect of Pd thickness and heat treatment on Pd/Ni/Au/p-GaN metal contacts. The as-deposited samples exhibit a smooth morphology and non-linear I-V characteristics. Heat treatment in a N atmosphere leads to degradation of the contact microstructure, resulting in diffusion of Ga, void formation on the interface and mixing of metals.
View Article and Find Full Text PDFMicromachines (Basel)
February 2023
The main objective of this work is to demonstrate and validate the feasibility of fabricating (Al, In) GaN laser diodes with etched facets. The facets are fabricated using a two-step dry and wet etching process: inductively coupled plasma-reactive ion etching in chlorine, followed by wet etching in tetramethylammonium hydroxide (TMAH). For the dry etching stage, an optimized procedure was used.
View Article and Find Full Text PDFIn this study, we propose a solution for realization of surface emitting, 2D array of visible light laser diodes based on AlInGaN semiconductors. The presented system consists of a horizontal cavity lasing section adjoined with beam deflecting section in the form of 45° inclined planes. They are placed in the close vicinity of etched vertical cavity mirrors that are fabricated by Reactive Ion Beam Etching.
View Article and Find Full Text PDFGallium nitride (GaN) doped with germanium at a level of 10 cm is proposed as a viable material for cladding layers in blue- and green-emitting laser diodes. Spectral reflectometry and ellipsometry are used to provide evidence of a reduced index of refraction in such layers. The refractive-index contrast to undoped GaN is about 0.
View Article and Find Full Text PDFMost optoelectronic devices share the same basic epitaxial structure - a stack of quantum wells (QWs) sandwiched between p- and n-doped layers. In nitride semiconductors, where holes have 20-times lower mobility than electrons, the holes are able to populate only the topmost 1-2 QWs. The inability to distribute the holes in a large-enough number of QWs is a cause of high Auger recombination in nitride LEDs.
View Article and Find Full Text PDFThe effect of growth temperature and precursor flow on the doping level and surface morphology of Ge-doped GaN layers was researched. The results show that germanium is more readily incorporated at low temperature, high growth rate and high V/III ratio, thus revealing a similar behavior to what was previously observed for indium. V-pit formation can be blocked at high temperature but also at low V/III ratio, the latter of which however causing step bunching.
View Article and Find Full Text PDFIn this work we investigate the role of threading dislocations in nitride light emitters with different indium composition. We compare the properties of laser diodes grown on the low defect density GaN substrate with their counterparts grown on sapphire substrate in the same epitaxial process. All structures were produced by metalorganic vapour phase epitaxy and emit light in the range 383-477 nm.
View Article and Find Full Text PDFWe studied degradation mechanisms of ultraviolet InGaN laser diodes emitting in the UVA range. Short wavelength nitride devices are subjected to much faster degradation, under the same packaging and testing conditions, than their longer wavelength counterparts. Transmission electron microscopy analysis of the degraded laser diodes showed pronounced damage to facets in the area of the active layer (waveguide, quantum wells, and electron blocking layer).
View Article and Find Full Text PDFWe have fabricated tunnel-junction InGaN micro-LEDs using plasma-assisted molecular beam epitaxy technology, with top-down processing on GaN substrates. Devices have diameters between 5 µm and 100 µm. All of the devices emit light at 450 nm at a driving current density of about 10.
View Article and Find Full Text PDFWe studied mechanisms of recombination in InGaN quantum wells in polar and semipolar structures. Photoluminescence measurements show that the optical emission linewidths for polar and semipolar structures are almost identical suggesting the same level of indium fluctuations in quanutm wells. Their "peak-energy-versus-temperature" relations demonstrate very pronounced "s-shape" effect.
View Article and Find Full Text PDFIn this paper we demonstrate 450 nm (Al,In)GaN graded index separate confinement heterostructure travelling wave optical amplifier with a double 'j-shape' waveguide. The length of the amplifier is 2.5 mm and the width of the ridge is 2.
View Article and Find Full Text PDFVisible light communications using a Gallium-nitride (GaN) laser diode is reported. Devices, which are cased in TO packages, show modulation bandwidths of up to 1.4 GHz.
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