Complementary study of defects in GaN by photo-etching and TEM

Eur. Phys. J. Appl. Phys.

Macht

et al. 2004

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Abstract. Photochemical (PEC) etching and transmission electron microscopy (TEM) have been used to study the defects in hetero-epitaxial GaN layers. TEM proved that PEC etching reveals not only dislocations but also nanopipes in the form of protruding, whisker-like etch features. It is shown by diffraction contrast techniques that the nanopipes are screw coreless dislocations. An example is shown of the transformation of a normal full-core screw dislocation into a nanopipe. The PEC/TEM experiments indicate the presence of electrically active (recombinative) species in the vicinity of the nanopipes.PACS. 61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Section: Introductionmentioning

confidence: 87%

Nanopipes in GaN: photo-etching and TEM study

Lazar

Eur. Phys. J. Appl. Phys.

Macht

et al. 2004

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“…The photocurrent-time characteristic was recorded during etching that allows in-situ control and modification of the etching process. It has been already shown by TEM calibration, that PEC etching reveals dislocations and inversion domains (IDs) [12][13][14]19]. The main limitations of this method are: (i) it is not possible to etch the high-resistive samples, (ii) no etching occurs on heavily n-doped GaN single crystals (for n above 10 19 cm −3 the space charge layer width W sc becomes very small according to the relationship n ~ 1/W sc 2 , resulting in tunnelling of photo-carriers and lack of holes for dissolution of GaN [20]).…”

mentioning

confidence: 97%

“…The delay in using simple and quick etching vs. X-ray and TEM, has been caused by the very high chemical resistance of nitrides. From the recent studies it follows however, that two approaches are the most promising in revealing and analysing defects in different types of GaN, namely photo-electrochemical (PEC or electroless) [12][13][14] and molten bases [11,15] etching. In the present communication these two techniques are briefly characterized and some representative examples are shown on the use of these methods for studying defects in GaN single crystals and epitaxial layers.…”

mentioning

confidence: 99%

“…The main drawback is that in the hetero-epitaxial samples containing high density of nano-pipes or screw dislocations, the pits formed on them are "growing" much quicker than the pits on mixed or edge dislocations, that might lead to the erroneous estimation of the total density of defects. PEC etching was shown to reveal crystallographic defects in non-intentionally doped and n-type hetero-epitaxial GaN layers [12][13][14]19], but failed in revealing defects in heavily ndoped GaN single crystals (carrier concentration above 1 × 10 19 cm…”

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confidence: 99%

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Characterization of GaN single crystals by defect‐selective etching

Macht

Kamler

et al. 2003

phys. stat. sol. (c)

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In this communication it is shown that both "orthodox" etching in molten KOH -NaOH eutectic (E etch and its modification) and photo-etching in aqueous KOH solution (PEC method) permit quick assessment of density, distribution and, after appropriate calibration, type of defects in GaN single crystals and epitaxial layers. Characteristic features of both etching methods are briefly discussed. It is shown that dislocations and micro-defects can be revealed in the form of etch pits (in "orthodox" E etch) and as etch hillocks (PEC method) on both Ga-and N-polar surfaces. The reliability of both methods has been confirmed by direct TEM calibration and by using indentation method. Very low dislocation density (EPD ≤ 2 × 10 2 cm −2 ) in the undoped GaN single crystals and MOCVD-grown epitaxial layers has been confirmed by this study.Introduction High-pressure grown GaN single crystals constitute an attractive substrate material for manufacturing lattice matched (i.e. low defect-density) high performance III-V opto-electronic device structures [1][2][3]. At the early stage of the development of sizable GaN single crystals and homo-epitaxial layers, the structural quality of the material was determined using X-ray diffraction [4-6] and transmission electron microscopy (TEM) [7][8][9]. These techniques demonstrated superior quality of the GaN single crystals and the layers grown on them over hetero-epitaxial layers, but failed in precise determining of the density of dislocations due to the intrinsic limits of the methods.More recently, the structural quality of GaN crystals and epitaxial layers has been examined by defectselective etching [10][11][12]. The delay in using simple and quick etching vs. X-ray and TEM, has been caused by the very high chemical resistance of nitrides. From the recent studies it follows however, that two approaches are the most promising in revealing and analysing defects in different types of GaN, namely photo-electrochemical (PEC or electroless) [12][13][14] and molten bases [11,15] etching. In the present communication these two techniques are briefly characterized and some representative examples are shown on the use of these methods for studying defects in GaN single crystals and epitaxial layers.

“…Electroless photo-etching (PEC) can reveal not only the crystallographic defects (e.g. dislocations), but also electrically active chemical non-homogeneities (differences in free-carrier concentrations) [1,2]. An advantage of this method is the possibility for either large area or local etching (only the illuminated part of the sample is etched) to map the non-homogeneities on the chosen surface of the sample [3].…”

Section: Introductionmentioning

confidence: 99%

The influence of free-carrier concentration on the PEC etching of GaN: A calibration with Raman spectroscopy

Lewandowska

Journal of Crystal Growth

Kelly

et al. 2007

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Large areas of electrically active regions of in-homogeneities have been revealed by the electroless photo-etching (PEC) method in GaN layers grown by the hydride vapor phase epitaxy (HVPE) technique.Variations in the local etch rate have been correlated with the variations in the free-carrier concentrations as determined by microRaman spectroscopy. The etch rate decreased linearly with the log of the carrier concentration. The latter could change by more than two orders of magnitude on the same sample. r