Comparison of surface photovoltage behavior for n-type versus p-type GaN

Foussekis, M.; Baski, A. A.; Reshchikov, M. A.

doi:10.1116/1.3605299

Cited by 15 publications

(24 citation statements)

References 19 publications

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“…Since the photogenerated voltage at the NW/HOPG contact has the same sign as that generated at the p-n junction, the photovoltage measured at the p-n junction (~1.2 V) is the result of the combined effect of the junction and the Schottky contacts at the n and p sides. s. Besides this, we observe a steady decrease of SPV during illumination, a characteristic that, as commented before, has been ascribed to the photoinduced chemisorption of oxygen [23]. The transfer of photo-generated electrons to the adsorbed oxygen species results in gradually decreasing VCPD.…”

Section: Resultsmentioning

confidence: 49%

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Direct assessment of p–n junctions in single GaN nanowires by Kelvin probe force microscopy

et al. 2016

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Making use of Kelvin probe force microscopy, in dark and under ultraviolet illumination, we study the characteristics of p-n junctions formed along the axis of self-organized GaN nanowires (NWs).We map the contact potential difference of the single NW p-n junctions to locate the space charge region and directly measure the depletion width and the junction voltage. Simulations indicate a shrinkage of the built-in potential for NWs with small diameter due to surface band bending, in qualitative agreement with the measurements. The photovoltage of the NW/substrate contact is studied by analysing the response of NW segments with p-and n-type doping under illumination. Our results show that the shifts of the Fermi levels, and not the changes in surface band bending, are the most important effects under above band-gap illumination. The quantitative electrical information obtained here is important for the use of NW p-n junctions as photovoltaic or rectifying devices at the nanoscale, and is especially relevant since the technique does not require the formation of ohmic contacts to the NW junction.2

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Section: Resultsmentioning

confidence: 49%

“…Discrimination between these contributions would require SPV measurements in well-controlled environments (N 2 and O 2 ) [23] and oxide-free samples. …”

Section: Resultsmentioning

confidence: 99%

Direct assessment of p–n junctions in single GaN nanowires by Kelvin probe force microscopy

et al. 2016

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“…No major difference is observed in the dependence of the SPV on light intensity for illumination with 270 and 342 nm photons. Foussekis et al [19,21] also have observed an increase of the SPV with increasing light intensity and determined similar values for the SPV. In observed, which indicate that two processes are involved in the decay of the CPD signal after switching off the light.…”

Section: Resultsmentioning

confidence: 59%

“…A large number of studies can be found in the literature dedicated to the investigation of surface-related effects on GaN using various techniques such as photoluminescence [9][10][11], photoconductivity [12][13][14][15][16][17], and contact potential difference measurements [18][19][20][21][22]. In the dark, n-type GaN grown on c-plane sapphire shows an upward band bending of approximately 1 eV due to trapping of electrons at surface states [23][24][25][26], which results in the formation of a positive space-charge region (SCR) close to the GaN surface.…”

Section: Introductionmentioning

confidence: 99%

“…Under illumination with ultraviolet (UV) light, the band bending can be reduced by 0.3-1.1 eV, corresponding to the so-called surface photovoltage (SPV) [11,[32][33][34]. The SPV has been measured in many studies which have used various techniques, such as x-ray photoelectron spectroscopy (XPS) [33,35], Kelvin probe force microscopy (KPFM) [22,34], and the macroscopic Kelvin probe technique [11,[18][19][20][21]32,36]. In these studies, it has been discussed that photogenerated electrons and holes are separated by the built-in electric field caused by the surface band bending.…”

Section: Introductionmentioning

confidence: 99%

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Kinetics of optically excited charge carriers at the GaN surface

2015

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In this work, we combine conductance and contact potential difference measurements in a consistent and systematic way, in steady-state and transient modes, both in the dark and under illumination. With this we obtain valuable information about the kinetics of charges at and close to the surface of GaN. We compare the processes involved in the accumulation and the decay of charge carriers generated via excitation with above and below band-gap light with varying light intensity. In particular, we probed the role played by localized defect states in the kinetics of photogenerated charges. These states are responsible for the trapping of photogenerated electrons in the space-charge region close to the surface, which explains the slow response of the photocurrent to illumination. These states are also involved in the transfer of electrons back to the surface after illumination, which results in the slow recovery of the photocurrent and the contact potential difference in the dark.A. WINNERL, R. N. PEREIRA, AND M. STUTZMANN PHYSICAL REVIEW B 91, 075316 (2015)

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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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Comparison of surface photovoltage behavior for n-type versus p-type GaN

Cited by 15 publications

References 19 publications

Direct assessment of p–n junctions in single GaN nanowires by Kelvin probe force microscopy

Direct assessment of p–n junctions in single GaN nanowires by Kelvin probe force microscopy

Kinetics of optically excited charge carriers at the GaN surface

Surface photovoltage behavior of GaN columns

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