Dislocation density in GaN determined by photoelectrochemical and hot-wet etching

Visconti, Paolo; Jones, K. M.; Reshchikov, M. A.; Cingolani, R.; Morkoç̌, H.; Molnar, R. J.

doi:10.1063/1.1329330

Cited by 144 publications

(87 citation statements)

References 19 publications

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“…The dark contrast seen in the unannealed samples (A*, B*) is quite likely pits corresponding to the surface termination of mixed dislocations. 13 The density of the pits is approximately 6 9 10 7 cm À2 to 8 9 10 7 cm À2 , which is consistent with values of threading dislocation densities (TDDs) found in literature for as-grown Ge film on Si. 9 The pits are not visible in the annealed samples, indicating a reduction in TDD by high-temperature annealing.…”

supporting

confidence: 74%

Poisson Ratio of Epitaxial Germanium Films Grown on Silicon

Bharathan

Narayan

Rozgonyi

et al. 2012

Journal of Elec Materi

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An accurate knowledge of elastic constants of thin films is important in understanding the effect of strain on material properties. We have used residual thermal strain to measure the Poisson ratio of Ge films grown on Si h001i substrates, using the sin 2 w method and high-resolution x-ray diffraction. The Poisson ratio of the Ge films was measured to be 0.25, compared with the bulk value of 0.27. Our study indicates that use of Poisson ratio instead of bulk compliance values yields a more accurate description of the state of in-plane strain present in the film.

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supporting

confidence: 74%

Poisson Ratio of Epitaxial Germanium Films Grown on Silicon

Bharathan

Narayan

Rozgonyi

et al. 2012

Journal of Elec Materi

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“…The threading dislocation density (TDD) of GaN substrates is approximately 2.2 × 10 6 cm −2 , which is two or three orders of magnitude less than that of hetero-epitaxial layers grown on sapphire substrates. 32 The electrochemical current was supplied through the Au-ohmic contact on the back side of the substrate, and the electrochemical process was performed using a standard cell with three electrodes: an n-type GaN working electrode, a Pt counter electrode, and a Ag/AgCl reference electrode (see Fig. 1b).…”

mentioning

confidence: 99%

Correlation between Structural and Photoelectrochemical Properties of GaN Porous Nanostructures Formed by Photo-Assisted Electrochemical Etching

Kumazaki¹,

Watanabe²,

Yatabe³

et al. 2014

J. Electrochem. Soc.

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We investigated the correlation between structural and photoelectrochemical properties of GaN porous nanostructures formed by photo-assisted electrochemical etching. The porous nanostructures were formed during light irradiation of the top-surface of homo-epitaxial layers grown on freestanding GaN substrates. The pore depth, wall thickness, and surface morphology of porous nanostructures were strongly influenced by the way holes generated by the light irradiation were supplied. Such structural features influenced the optical properties of GaN porous nanostructures. The photoluminescence peaks measured on GaN porous nanostructures were shifted to higher energies because of the quantum confinement in the thin GaN walls between pores. Formation of porous nanostructure decreased the photoreflectance of the GaN surface, and the smallest reflectance was obtained from the porous sample having large pores on its surface after the ultrathin layer with small pores had been removed by surface-etching. The photoelectrochemical response measured on GaN porous nanostructures in a NaCl electrolyte were drastically enhanced by the unique features of those structures, such as low photoreflectance and large surface area. The largest photocurrents were obtained from the sample from which H 3 PO 4 treatment had removed the ultrathin layer without thinning the pore walls. Photoelectrochemical systems based on semiconductor photoelectrodes have recently attracted much attention due to their potential use in the next generation of green technologies such as water splitting for fuel cells, artificial photosynthesis, and so on.1-5 Among the photoelectrode materials, GaN is one of the most attractive because of its chemical stability and its potential to achieve direct photoelectrolysis by solar power without the consumption of electric power. [6][7][8] In addition, the bandgap energy of GaN-based materials can be varied from about 0.65 to 6.0 eV by alloying them with InN and AlN, which enables us to design various functional photoelectrodes not only for spectral matching of solar light but also for the electrochemical reduction of CO 2 to carbohydrate. 9 One of the common approaches to improving conversion efficiency is to form nanostructures on the photoelectrode surface in order to increase its surface area. Most reported GaN nanostructures have been made using selective-area growth 10,11 or a dry etching process such as reactive ion etching. 12,13 There are, however, severe limitations on increasing the density of nanostructures because most approaches use lithography for defining the size and position of the nanostructures. And when a dry etching process is involved, the etching damage induced by ion bombardment is not negligible [14][15][16] and could significantly degrade the photoelectrochemical efficiency.One alternative approach is an electrochemical-fabrication process, which can form various semiconductor nanostructures in a self-assembled fashion. The most well-known application of an electrochemical process is the formation...

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“…The densities of TD defects for three samples are also listed in Table I. For LED-A, the density of TD defects is estimated by counting for etching pits density and it is the same as that of LED-B [24]. According to Table I, the are estimated to be 27.5 33 and 40 for LED-A, LED-B, and LED-C, respectively.…”

Section: Light Extraction Efficiencymentioning

confidence: 99%

Study of GaN-Based Light-Emitting Diodes Grown on Chemical Wet-Etching-Patterned Sapphire Substrate With V-Shaped Pits Roughening Surfaces

Lee

Kuo

et al. 2008

J. Lightwave Technol.

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Abstract-We investigate the mechanism responding for performance enhancement of gallium nitride (GaN)-based light-emitting diode (LED) grown on chemical wet-etching-patterned sapphire substrate (CWE-PSS) with V-Shaped pit features on the top surface. According to temperature-dependent photoluminescence (PL) measurement and the measured external quantum efficiency, the structure can simultaneously enhance both internal quantum efficiency and light extraction efficiency. Comparing to devices grown on planar sapphire substrate, the threading dislocation defects of LED grown on CWE-PSS are reduced from 1.28 10 9 cm 2 to 3.62 10 8 cm 2 , leading to a 12.5% enhancement in internal quantum efficiency. In terms of the theoretical computing of radiation patterns, the V-Shaped pits roughening surface can be thought of as a strong diffuser with paraboloidal autocorrelation function, increasing the escape probability of trapped photons and achieving a 20% enhancement in light extraction efficiency. Moreover, according to the measurement of optical diffraction power, CWE-PSS demonstrated superior guided light extraction efficiency than that of planar sapphire substrate, thus an extra 7.8% enhancement in light extraction efficiency was obtained. Therefore, comparing to the conventional LED, an overall 45% enhancement in integrated output power was achieved.

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Dislocation density in GaN determined by photoelectrochemical and hot-wet etching

Cited by 144 publications

References 19 publications

Poisson Ratio of Epitaxial Germanium Films Grown on Silicon

Poisson Ratio of Epitaxial Germanium Films Grown on Silicon

Correlation between Structural and Photoelectrochemical Properties of GaN Porous Nanostructures Formed by Photo-Assisted Electrochemical Etching

Study of GaN-Based Light-Emitting Diodes Grown on Chemical Wet-Etching-Patterned Sapphire Substrate With V-Shaped Pits Roughening Surfaces

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