Photoelectrochemical etching of epitaxial InGaN thin films: self-limited kinetics and nanostructuring

Abstract

We report here the characteristics of photoelectrochemical (PEC) etching of epitaxial InGaN semiconductor thin films using a narrowband laser with a linewidth less than ~1 nm. In the initial stages of PEC etching, when the thin film is flat, characteristic voltammogram shapes are observed. At low photo-excitation rates, voltammograms are S-shaped, indicating the onset of a voltage-independent rate-limiting process associated with electron-holepair creation and/or annihilation. At high photo-excitation rates, voltammograms are superlinear in shape, indicating, for the voltage ranges studied here, a voltage-dependent rate-limiting process associated with surface electrochemical oxidation. As PEC etching proceeds, the thin film becomes rough at the nanoscale, and ultimately the self-limiting etch kinetics lead to an ensemble of nanoparticles. This change in InGaN film volume and morphology leads to a characteristic dependence of PEC etch rate on time: an incubation time, followed by a rise, then a peak, then a slow decay.

III‐nitride quantum dots for ultra‐efficient solid‐state lighting

“…One potential method to create QDs with low inhomogeneous broadening, smaller QD sizes, and higher QD densities is quantum‐sized controlled photoelectrochemical etching (QSC‐PEC) . In QSC‐PEC, an initial QW or large‐scale nanostructure is PEC etched using above‐bandgap laser light for photoexcitation.…”

Deterministic Placement of Quantum-Size Controlled Quantum Dots for Seamless Top-Down Integration

“…Nevertheless, the self-assembled nature of such QDs result in large uncertainty in QD location and significant fluctuations in QD size . As a result, integrating bottom-up growth techniques with nanophotonic designs, such as high-quality factor (Q-factor) microcavities, often involve complex alignment procedures and can face low device yields. ,− Recently, a top-down wet-etch approach , has been demonstrated for the fabrication of III-nitride QDs using quantum-size-controlled photoelectrochemical (QSC-PEC) etching. This approach has the advantage of starting with a pregrown planar epitaxial III-nitride film and subsequently wet-etching the film to fabricate monodisperse QDs of desired size (controlled emission wavelength) in potentially desirable locations.…”

“…Thus, QSC-PEC etching is a technique that self-terminates after quantum-size effects begin to suppress absorption and the subsequent photogeneration of carriers. Previous work demonstrated the feasibility of QSC-PEC etching on an unpatterned III-nitride platform, containing an uncapped In x Ga 1– x N QW . As a consequence, the QDs exhibited no preferential in-plane placement.…”

“…III-Nitride materials are inherently difficult to wet-etch. However, light-assisted photoelectrochemical (PEC) etching has been shown to greatly improve the etching of such material systems. , A typical PEC etch setup is illustrated in Figure b. In the setup, a III-nitride sample is immersed in an electrolyte solution.…”

“…Previous work demonstrated the feasibility of QSC-PEC etching on an unpatterned III-nitride platform, containing an uncapped In x Ga 1−x N QW. 34 As a consequence, the QDs exhibited no preferential in-plane placement.…”