The impact of wet treatment using an (NH4)2S-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 (ρc < 1 × 10−4 Ω·cm2) was achieved with samples treated with an (NH4)2S-isopropanol solution, whereas the highest resistivity (ρc = 3.3 × 10−4 Ω·cm2) and surface roughness (Ra = 16 nm) were observed in samples prepared by standard methods. Annealing the contact system in an N2 + O2 + H2O atmosphere caused degradation through species inter-diffusion and metal-metal solid solution formation, irrespective of the preparation method. Standard prepared substrates developed a thin GaN-Au intermediate layer at the interface after heat treatment. Enhanced adhesion and the absence of GaN decomposition were observed in samples additionally cleaned with the (NH4)2S-solvent solution. Complete oxidation of nickel to NiO was observed in samples that underwent additional sulfur solution treatment. The intensity of metal species mixing and nickel oxidation was influenced by the metal diffusion rate and was affected by the initial state of the GaN substrate obtained through different wet treatment methods.

In 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 N2 atmosphere leads to degradation of the contact microstructure, resulting in diffusion of Ga, void formation on the interface and mixing of metals. Annealing in a mixture of N2 and O2 improves adhesion and reduces contact resistance. However, this process also induces GaN decomposition and species mixing. The mixing of metal–Ga and metal–metal remains unaffected by the method of thermal treatment but depends on gas composition for thin Pd contacts. To achieve low-resistance contacts (≈1 × 10−4 Ω cm2), we found that increasing the Pd thickness and using N2 + O2 as the annealing environment are effective measures. Nevertheless, the degradation effect of the annealed contact microstructure in the form of the void generation becomes evident as the thickness of Pd increases. Laser diodes (LDs) with optimized palladium-based contacts operate at a voltage of 4.1 V and a current density of 3.3 kA/cm².

This erratum corrects the funding of [Opt. Mater. Express 12, 991 (2022)10.1364/OME.445695].

Surface polarity plays a significant role in chemical etching of GaN in KOH solution, a process that is important for quality control and device fabrication. In this work, basic chemical mechanisms are proposed to explain the role of surface orientation in the chemical etching of the semiconductor. In addition, it is shown how prior photoetching of inert surfaces [the polar (0001), semipolar (101 (1) over bar), and nonpolar (1 (1) over bar 00) interfaces] enables chemical etching. Photoetching gives rise to the formation of nanocolumns on dislocations and to protrusions on nanoscale inhomogeneities. Subsequent etching in KOH solution leads to the development of distinctive features that depend on the crystal orientation of the surface and the presence of the inhomogeneities. The morphology of the photoetched surfaces was revealed by scanning electron microscopy, while X-ray photoelectron spectroscopy measurements were used to investigate the surface chemistry of these processes.

Gallium nitride (GaN) doped with germanium at a level of 1020 cm−3 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 0.990, which is comparable to undoped aluminium gallium nitride (AlGaN) with an aluminium composition of 6%. Germanium-doped GaN layers are lattice-matched to native GaN substrates; therefore, they introduce no strain, cracks, and wafer bowing. Their use, in place of strained AlGaN layers, will enable significant improvements to the production process yield.

Various experimental approaches of the wet nanoscale treatment have been proposed to account for features of the InAs, InSb and GaAs, GaSb semiconductor dissolution process in the (NH4)2Cr2O7–HBr–EG etching solution. Etching kinetics data showed that a crystal dissolution has diffusion-determined nature. The lowering of the solvent concentration from 80 to 0 vol.% in the solution was accompanied by a significant increase in the semiconductor etching speed. Depending on the solution composition, we have studied two types of crystal surface morphology, polished and passivated by the film, which was formed after chemical-dynamic (CDP) and/or chemical-mechanic polishing (CMP) in the solution, saturated by solvent and by oxidant, accordingly. It was found that in the polished etchants both CDP and CMP procedures lead to the formation of the mirror-like and super-smooth surface with nanoscale roughness less than 1 nm. The obtained results of surface state indicate that the (NH4)2Cr2O7–HBr–EG etchants could be used successfully for controllable CDP and CMP treatment of III–V semiconductors and formation of super-smooth surface.

The features of the InAs, InSb, GaAs, and GaSb ultra-smooth surface have been investigated using chemical–mechanical polishing with the (NH4)2Cr2O7–HBr–CH2(OH)CH2(OH)-etching solutions. The etching rate of the semiconductors has been measured as a function of the solution saturation by organic solvent (ethylene glycol). It was found that mechanical effect significantly increases the etching rate from 1.5 to 57 µm/min, and the increase of the organic solvent concentration promotes the decrease of the damaged layer-removing rate. According to AFM, RS, HRXRD results, the treatment with the (NH4)2Cr2O7–HBr–ethylene glycol solutions produces the clean surface of the nanosize level (Ra < 0.5 nm).

The chemical dissolution of InAs, InSb, GaAs and GaSb crystals in (NH4)(2)Cr2O7-HBr-C6H8O7 etching solutions has been investigated. The dissolution rate of the semiconductor materials has been measured as a function of etchant composition, stirring rate and temperature. The limiting stages of dissolution process, regions of the polishing and unpolishing solutions have been established. The polishing etchant compositions and conditions for chemical-dynamic polishing of the InAs, InSb, GaAs and GaSb crystals have been proposed and optimized.

We have studied the chemical dissolution of InAs, InSb, GaAs, and GaSb crystals in (NH4)2Cr2O7–HBr–C6H8O7 solutions. The dissolution rate of the crystals has been measured as a function of etchant composition, and the kinetics of the chemical interaction of the semiconductors with solutions have been investigated in detail. The dissolution rate has been shown to be diffusion-limited. Citric acid helps to reduce the etch rate and improves the polishing performance of the etching solutions.

We have studied the nature and kinetics of the chemical interaction of InAs, InSb, GaAs, and GaSb crystals with aqueous (NH4)2Cr2O7–HBr solutions. The dissolution rate of the crystals has been measured as a function of etchant composition, solution stirring rate, and temperature. The results demonstrate that the dissolution rate of the semiconductors is diffusion-limited. We have determined the composition ranges of polishing solutions, optimized their compositions, and found conditions for the dynamic chemical polishing of the semiconductors. Ultrasmooth polished semiconductor surfaces have been obtained, with R a ≈ 1 nm.

This paper presents results on the kinetics and mechanism of the physicochemical interaction of InAs, InSb, GaAs, and GaSb semiconductor surfaces with (NH4)2Cr2O7–HBr–C4H6O6 etching solutions under reproducible hydrodynamic conditions in the case of laminar etchant flow over a substrate. We have identified regions of polishing and nonpolishing solutions and evaluated the apparent activation energy of the process. The surface morphology of the crystals has been examined by microstructural analysis after chemical etching. The results demonstrate that the presence of C4H6O6 in etchants helps to reduce the overall reaction rate and extend the region of polishing solutions.

The features of InAs, InSb, GaAs, and GaSb dissolution in the (NH4)2Cr2O7−HBr−H2O etching compositions have been investigated. The chemical-dynamic polishing in the reproducible hydrodynamic conditions has been used. It was established that the arsenides etching rate changed similarly and achieved the maximum values in the oxidant saturated mixture (22 vol.%). It was found that the antimonides dissolution rate increases when the (NH4)2Cr2O7 concentration is increasing also. It was established that all etching compositions are polishing for InAs and GaAs, and in the case of InSb and GaSb the polishing solutions occupy about 50 % of the investigated concentrated regions. It was shown that the dissolution rate of all crystals decreases to 0,1 μm/min and the quality of the antimonides surface degrades when the H2O concentration is increasing. The substrates dissolution has the diffusion nature. Using metallographic analysis and atomic force microscopy it was confirmed a good quality of InAs, InSb, GaAs and GaSb surface obtained after chemical treatment in the (NH4)2Cr2O7−HBr−H2O polishing solutions.

The paper presents the results of experimental determination of the influence of the initial concentration of tartaric acid on the features of the chemical interaction of InAs, InSb, GaAs and GaSb with (NH4)2Cr2O7‑HBr‑C4H6O6 etching solutions. It was established that C4H6O6 decreases the general crystals dissolution rate because it increases the etching compositions viscosity, and also enhances the polishing properties of the etching solutions. The comparative analysis of the etching mixtures composition changes influence demonstrates that the using of 40 % C4H6O6, in comparison with 27 %, provides the higher quality polishing of the crystals surface.