UV-photoassisted etching of GaN in KOH

Cho, Hyun; Auh, Keun Ho; Han, Jung; Shul, R. J.; Donovan, S. M.; Abernathy, C. R.; Lambers, E. S.; Ren, F.; Pearton, S. J.

doi:10.1007/s11664-999-0029-7

Cited by 21 publications

(22 citation statements)

References 21 publications

(41 reference statements)

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“…Second, an ultrasmooth rms roughness by PEC of 0.946 nm was obtained, better than that of RIE, which was 0.981 nm for the same n-GaN layer. This low surface roughness is the best reported to date for PEC-etched surfaces 6,13 and demonstrates a new way to achieve device-quality etched layers over a large area.…”

mentioning

confidence: 59%

Ultrasmooth GaN Etched Surfaces Using Photoelectrochemical Wet Etching and an Ultrasonic Treatment

Shelton

Zhu

Wong

et al. 1999

Electrochem. Solid-State Lett.

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We have studied the effect of ultrasonic agitation on the surface of n-type gallium nitride (GaN) layers grown on sapphire that were subjected to a selective photoelectrochemical etch. Solutions of various concentrations of KOH were used along with an ultraviolet lamp to oxidize the exposed GaN surface, resulting in an anisotropic etch. Smooth surfaces with root-mean-square (rms) roughness of ~4 nm were obtained for a narrow range of etching conditions. It was found that this window could be extended by using etch conditions which produced "whisker" growth. Subsequent ultrasonic agitation was then used to remove these whiskers and obtain smoother surfaces with the best rms roughness values being ~0.9 nm.The development of device processing techniques in the IIInitride (i.e., InAlGaN) material system has been crucial to the subsequent rise of blue and ultraviolet light-emitting diodes, laser diodes, photodetectors, and transistors. Traditional dry etching, used in mainstream semiconductor device production and development, has limitations in that surface damage can occur and the etch is not dopant selective, and thus does not provide an etch-stopping mechanism. Wet chemical etching has normally been used to solve these and related problems, but gallium nitride (GaN) does not have a simple wet etch that can be used to reliably and selectively etch smooth layers. 1,2 Recently, a chemical etching technique that goes beyond the simple wet etch has been developed. While some techniques have been used which require high temperature 3 or a more elaborate electrolysis apparatus, 4 the use of a photoelectrochemical (PEC) etch shows promise for the processing of GaN-based devices. This technique, which employs an ultraviolet (UV) light source to enhance the etch rate of GaN films, was first demonstrated by Minsky et al., 5 and subsequently studied by Youtsey et al. 6 From the experimental results, a model for the etching mechanism was proposed based on reaction kinetics and on how differently doped layers were etched. Reports have been made of a wide range of PEC-etched GaN surface morphologies, depending upon the etching conditions employed. Some indicate the formation of "whiskers" in n-type GaN that are thought to relate to threading dislocations, thus revealing the layer defect density. 7,8 Other reports show that smooth surfaces are achievable with this technique. 9,10 Determining the right conditions for a specific GaN sample to achieve smooth, device-quality etched layers is challenging because of the number of variables that determine etch rate and smoothness. These include, for example, (i) sample carrier concentration, (ii) UV light intensity, (iii) solution type, (iv) etchant concentration, (v) temperature, and (vi) agitation. In this work, the parameter space for GaN etching that relates to morphology has been studied, and the wider process latitude of whisker growth was exploited to achieve smooth layers via subsequent ultrasonic agitation.Experimental A series of n + -GaN layers were grown by low-pressure meta...

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confidence: 59%

Ultrasmooth GaN Etched Surfaces Using Photoelectrochemical Wet Etching and an Ultrasonic Treatment

Shelton

Zhu

Wong

et al. 1999

Electrochem. Solid-State Lett.

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“…A recent development is the demonstration of photoelectrochemical (PEC) wet etching which has resulted in significantly higher etch rates for GaN [44][45][46][47][48][49][50][51][52][53]. The PEC process utilizes photogenerated electron-hole pairs to enhance oxidation and reduction reactions taking place in an electrochemical cell.…”

Section: Photoelectrochemical Wet Etchingmentioning

confidence: 99%

“…The reaction kinetics in the latter etching is believed to be diffusion-controlled. Using similar etching procedure in KOH solutions, Cho et al [47] reported etch rates greater than 100 nm/min and an activation energy of ~ 0.8 kCal.mol -1 under diffusioncontrolled kinetics.…”

Section: Photoelectrochemical Wet Etchingmentioning

confidence: 99%

Dry and Wet Etching for Group III – Nitrides

Adesida

Youtsey

Ping

et al. 1999

MRS Internet j. nitride semicond. res.

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The group-III nitrides have become versatile semiconductors for short wavelength emitters, high temperature microwave transistors, photodetectors, and field emission tips. The processing of these materials is significant due to the unusually high bond energies that they possess. The dry and wet etching methods developed for these materials over the last few years are reviewed. High etch rates and highly anisotropic profiles obtained by inductively-coupled-plasma reactive ion etching are presented. Photoenhanced wet etching provides an alternative path to obtaining high etch rates without ion-induced damage. This method is shown to be suitable for device fabrication as well as for the estimation of dislocation densities in n-GaN. This has the potential of developing into a method for rapid evaluation of materials.

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“…8,10,[23][24][25][26] The most common method of wet etching for n-type Group-III nitrides is photoelectrochemical (PEC) etching. 19,20,22,[27][28][29][30][31][32][33][34][35][36][37][38][39][40] There have been several fundamental investigations of this process 35,36,40 using techniques such as linear sweep voltammetry, rotating disk voltammetry, electrochemical impedance and Mott-Schottky analysis. Photogenerated holes lead to electrochemical etching of the semiconductor while the corresponding electrons are involved in a reduction process at the cathode.…”

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confidence: 99%

A Study of the Photoelectrochemical Etching of n-GaN in H₃PO₄ and KOH Electrolytes

Heffernan

Lynch

Buckley

2019

ECS J. Solid State Sci. Technol.

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We investigated the photoelectrochemical etching of n-GaN in H 3 PO 4 and KOH as a function of electrolyte concentration, potential and light intensity. Etch rates measured by stylus profilometry were compared with coulometric and amperometric values. In both electrolytes, etch rates increased with concentration, reaching a maximum at 3.0 mol dm −3 and decreasing at higher concentrations. The increase in etch rate with concentration of either H 3 PO 4 or KOH reflects the amphoteric nature of gallium and the decrease above 3.0 mol dm −3 is attributed to common-ion effects. Profilometric etch rates were lower than coulometric and amperometric etch rates reflecting formation of a surface film. SEM and profilometry demonstrated that thick surface films are formed at lower concentrations. Etch rates increased linearly with light intensity indicating a carrier-limited etching regime: a quantum efficiency of 57.6% was obtained. At light intensities greater than ∼35 mW cm −2 the etch rates showed evidence of saturation. AFM and SEM images of the etched GaN surfaces showed a distinctive ridge-trench structure with a hexagonal appearance. Photoluminescence spectra of the etched GaN show a significant increase in the defect-related yellow luminescence peak suggesting correlation to the formation of the ridge structures, which may represent dislocations terminating at the surface.

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UV-photoassisted etching of GaN in KOH

Cited by 21 publications

References 21 publications

Ultrasmooth GaN Etched Surfaces Using Photoelectrochemical Wet Etching and an Ultrasonic Treatment

Ultrasmooth GaN Etched Surfaces Using Photoelectrochemical Wet Etching and an Ultrasonic Treatment

Dry and Wet Etching for Group III – Nitrides

A Study of the Photoelectrochemical Etching of n-GaN in H₃PO₄ and KOH Electrolytes

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UV-photoassisted etching of GaN in KOH

Cited by 21 publications

References 21 publications

Ultrasmooth GaN Etched Surfaces Using Photoelectrochemical Wet Etching and an Ultrasonic Treatment

Ultrasmooth GaN Etched Surfaces Using Photoelectrochemical Wet Etching and an Ultrasonic Treatment

Dry and Wet Etching for Group III – Nitrides

A Study of the Photoelectrochemical Etching of n-GaN in H3PO4 and KOH Electrolytes

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A Study of the Photoelectrochemical Etching of n-GaN in H₃PO₄ and KOH Electrolytes