Effects of polarity and surface treatment on Ga- and N-polar bulk GaN

Foussekis, M.; Ferguson, Josephus D.; McNamara, J. D.; Baski, A. A.; Reshchikov, M. A.

doi:10.1116/1.4751276

Cited by 19 publications

(12 citation statements)

References 26 publications

(29 reference statements)

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“…The fast initial SPV decrease, i.e., an upwards band bending, for the as grown samples is caused by two fast processes . First, photogenerated holes further accumulate near the surface . The electron–hole‐pair generation by sub band gap illumination is possible inside the strong electric field due to the Franz–Keldish‐effect .…”

Section: Resultsmentioning

confidence: 99%

Surface photovoltage behavior of GaN columns

Deeb

Wei

Hartmann

et al. 2015

Physica Status Solidi (a)

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GaN columns are grown by metal organic vapor phase epitaxy (MOVPE) with a high silane flow, which often leads to rough sidewalls and related problems during a subsequent shell overgrowth by e.g., InGaN/GaN quantum wells. In order to get more information on the surface of GaN columns before overgrowth, surface photovoltage (SPV) measurements have been performed by photo‐assisted Kelvin probe force microscopy (KPFM) before and after chemical etching of the surface. Its electronic properties are demonstrated to be influenced by the silane injection during the samples' growth. Distinct differences are shown in the SPV behavior of GaN columns before and after etching with phosphoric acid. SPV decreases before etching, whereas after etching it increases like that on GaN bulk material. Silicon related surface states introduced during the growth are considered as the origin of the SPV behavior of the as grown samples. The change of this behavior after etching is attributed to the removal of the Si containing surface coating. Our investigations not only show the important role of silane injection during the growth on the SPV behavior of GaN columns, but it also reveals that the photo‐assisted KPFM technique is an easy and quick method to analyze surfaces.

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Section: Resultsmentioning

confidence: 99%

Surface photovoltage behavior of GaN columns

Deeb

Wei

Hartmann

et al. 2015

Physica Status Solidi (a)

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“…1(b, right diagram). 20,29,30,35 In this process, physisorbed oxygen species become chemisorbed by receiving electrons from the bulk. In the case of band-to-band excitation, the electrons can overcome the reduced nearsurface barrier.…”

Section: Results and Disscusionmentioning

confidence: 99%

“…Various studies reported about these processes on GaN layers. 29,30 For example, Foussekis et al investigated the fast and slow SPV responses in different gas environments using a single wavelength for both doped and undoped GaN layers. The SPV changes and, thus, the band bending under continuous illumination are explained by photo-induced adsorption of surface species in air ambient and photo-induced desorption in vacuum.…”

Section: Introductionmentioning

confidence: 99%

Photo-assisted Kelvin probe force microscopy investigation of three dimensional GaN structures with various crystal facets, doping types, and wavelengths of illumination

Deeb

Ledig

Wei

et al. 2017

Journal of Applied Physics

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Three dimensional GaN structures with different crystal facets and doping types have been investigated employing the surface photo-voltage (SPV) method to monitor illumination-induced surface charge behavior using Kelvin probe force microscopy. Various photon energies near and below the GaN bandgap were used to modify the generation of electron–hole pairs and their motion under the influence of the electric field near the GaN surface. Fast and slow processes for Ga-polar c-planes on both Si-doped n-type as well as Mg-doped p-type GaN truncated pyramid micro-structures were found and their origin is discussed. The immediate positive (for n-type) and negative (for p-type) SPV response dominates at band-to-band and near-bandgap excitation, while only the slow process is present at sub-bandgap excitation. The SPV behavior for the semi-polar facets of the p-type GaN truncated pyramids has a similar characteristic to that on its c-plane, which indicates that it has a comparable band bending and no strong influence of the polarity-induced charges is detectable. The SPV behavior of the non-polar m-facets of the Si-doped n-type part of a transferred GaN column is similar to that of a clean c-plane GaN surface during illumination. However, the SPV is smaller in magnitude, which is attributed to intrinsic surface states of m-plane surfaces and their influence on the band bending. The SPV behavior of the non-polar m-facet of the slightly Mg-doped part of this GaN column is found to behave differently. Compared to c- and r-facets of p-type surfaces of GaN-light–emitting diode micro-structures, the m-plane is more chemically stable.

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“…Because N-polar (Al,Ga)N is known to be easily oxidized 19,20 , with the effect stronger than on the Ga-polar surface, the need for surface protection is even more crucial in order to ensure a stable operation irrespectively of the environment conditions. Examining N-polar GaN/AlGaN structures with an in-situ MOCVD Si 3 N 4 a barrier height of ~ 1 eV at the Si 3 N 4 /GaN interface was determined via capacitance-voltage (C-V) measurements 21 .…”

Section: Contactless Electroreflectance Studies Coupled With Numericamentioning

confidence: 99%

SiNx/(Al,Ga)N interface barrier in N-polar III-nitride transistor structures studied by modulation spectroscopy

Janicki

Keller

et al. 2020

Sci Rep

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built-in electric field, and (2) a decrease in backbarrier doping that reduces the 2DEG density while leaving the potential well intact that attracts carriers from surface states. Methods Sample growth. All samples investigated in this study were grown by metal-organic chemical vapour deposition (MOCVD). C-plane sapphire substrates with 4° misorientation towards sapphire-a-plane were used to achieve smooth N-polar (Al,Ga)N films 4. A 1.4 μm thick semi-insulating (S.I.) GaN base layer was first deposited using the procedure reported previously. For all samples, the backbarrier layer consisted of a 20 nm thick graded Al x Ga 1−x N layer with x = 0.05 → 0.38 and a 10 nm thick Al 0.38 Ga 0.62 N film, followed by a 0.7 nm thick AlN interlayer, a GaN channel layer with thickness varying from 9 to 20 nm, a 0 or 2.6 nm thick Al 0.46 Ga 0.54 N cap layer, and a 0 or 5 nm thick in-situ SiN x film. The graded Al x Ga 1−x N layers were doped with Si to achieve n-type doping of 4 × 10 18 cm −2 (1st and 2nd series) or 5 × 10 18 cm −2 (3rd series). The SiN x film was grown at 1,030 °C using disilane and ammonia flows of 4.46 μmol/min and 268 mmol/min, respectively. 2DEG concentration measurements. Van der Pauw Hall measurements with indium contacts were performed at room temperature to determine the carrier concentrations. Contactless electroreflectance measurements. For CER measurements the samples were mounted in a capacitor with a half-transparent top electrode made from a copper-wire mesh. An air gap of ~ 0.5 mm was kept between the sample surface and the top electrode. An alternating voltage of ~ 3 kV provided the band bending modulation. Other relevant details on CER can be found in Refs. 32,33. Calculations. A commercial package nextnano++ was used for band profile and carrier concentration calculations 34 that provides solutions for coupled Schrödinger-Poisson equations.

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Effects of polarity and surface treatment on Ga- and N-polar bulk GaN

Cited by 19 publications

References 26 publications

Surface photovoltage behavior of GaN columns

Surface photovoltage behavior of GaN columns

Photo-assisted Kelvin probe force microscopy investigation of three dimensional GaN structures with various crystal facets, doping types, and wavelengths of illumination

SiNx/(Al,Ga)N interface barrier in N-polar III-nitride transistor structures studied by modulation spectroscopy

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