Kelvin probe force microscopy for characterization of semiconductor devices and processes

Tanimoto, Masafumi

doi:10.1116/1.589136

Cited by 109 publications

(48 citation statements)

References 7 publications

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“…The strength of KPFM is the capability to measure contact potential with a high spatial resolution, as demonstrated by imaging different materials [11], different doping in semiconductors [32] and localized charges [33]. Looking at the work function images in Figs.…”

Section: Lateral Variations In the Work Functionmentioning

confidence: 99%

Surface potential of chalcopyrite films measured by KPFM

Sadewasser

2006

Physica Status Solidi (a)

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Atomic force microscopy is widely used to characterize the surface topography of a variety of samples. Kelvin probe force microscopy (KPFM) additionally allows determining images of the surface potential with nanometer resolution. The KPFM technique will be introduced and studies on surfaces of chalcopyrite semiconductors for solar cell absorbers will be presented. It is shown that operation in ultra-high vacuum (UHV) is required to obtain meaningful work function values. Different methods for obtaining UHV-clean surfaces are presented and KPFM studies on these are compared. Surfaces where prepared by in-vacuum deposition, inert-gas transfer, in-vacuum decapping of a protective Se-cap and a peel-off method. Finally, a sputter-annealing cycle also allows to obtain well-suited surfaces for KPFM studies. Employing KPFM, variations in the local surface potential at grain boundaries of polycrystalline CuGaSe2 films were observed. A potential drop indicates the presence of charged defects at grain boundaries. Furthermore, different electronic activity was found for different grain boundaries, as concluded from studies under illumination. Using laterally resolved surface photovoltage, a Cu2−xSe impurity phase could be observed in CuGaSe2.Copyright line will be provided by the publisher 1 Introduction Photovoltaic energy conversion is one route followed in the quest for a sustainable energy supply in the future. Thin film solar cell technologies offer a high cost reduction potential compared to standard silicon wafer technology. With their high power conversion efficiencies on the laboratory scale, thin film solar cells from the Cu-chalcopyrite materials system are a promising candidate for this technology; in fact, pilot production lines have recently been started. Currently, the highest efficiency of nearly 20% is obtained for Cu(In, Ga)Se 2 containing ≈ 30% of Ga [1]. A typical solar cell consists of a metallic Mo layer on a float glass substrate, a polycrystalline p-type Cu-chalcopyrite absorber layer with a typical thickness of 2 µm, a thin buffer layer (typically CdS) and the n-type double layer window (ZnO). A NiAl grid provides the front contact. A wide variety of growth techniques for the chalcopyrite absorber have been studied, including evaporation, sputtering and subsequent rapid thermal processing in chalcogen atmosphere, chemical vapor deposition, metal organic vapor phase epitaxy and electrochemical deposition. In such multilayered structures the various interfaces play a crucial role, as they are prone to contain electronically active defects causing electronic losses in the device. The polycrystalline character of the materials introduces additional effects, as for example varying composition in different grains and grain boundaries [2]. Recently, also compositional variations on the nanometer scale have been proposed [3]. Therefore, studies of surfaces and interfaces are highly important in order to further the understanding of these materials and eventually increase their efficiency towards the theore...

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Section: Lateral Variations In the Work Functionmentioning

confidence: 99%

Surface potential of chalcopyrite films measured by KPFM

Sadewasser

2006

Physica Status Solidi (a)

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“…For instance, KPFM has been utilized for the label-free detection of biomolecules [11,12] and for surface photovoltage measurements in optically active proteins [13]. Similarly, KPFM has been useful in mapping electrostatic potential profiles across working devices [14], surface photo-voltage in photovoltaics [15][16][17], and charging dynamics in ferroelectric [18][19][20] and dielectric materials [21].…”

Section: Introductionmentioning

confidence: 99%

Open loop Kelvin probe force microscopy with single and multi-frequency excitation

et al. 2013

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Abstract. Conventional Kelvin probe force microscopy (KPFM) relies on closed loop (CL) bias feedback for the determination of surface potential (SP). However, SP measured by CL-KPFM has been shown to be strongly influenced by the choice of measurement parameters due to non-electrostatic contributions to the input signal of the bias feedback loop. This often leads to systematic errors of several hundred mV and can also result in topographical crosstalk. Here, open loop (OL)-KPFM modes are investigated as a means of obtaining a quantitative, crosstalk free measurement of the SP of graphene grown on Cu foil, and are directly contrasted with CL-KPFM. OL-KPFM operation is demonstrated in both single and multi-frequency excitation regimes, yielding quantitative SP measurements. The SP difference between single and multilayer graphene structures using OL-KPFM was found to be 63 ± 11 mV, consistent with values previously reported by CL-KPFM. Furthermore, the same relative potential difference between Al 2 O 3 -coated graphene and Al 2 O 3 -coated Cu was observed using both CL and OL techniques. We observe an offset of 55 mV between absolute SP values obtained by OL and CL techniques, which is attributed to the influence of non-electrostatic contributions to the input of the bias feedback used in CL-KPFM.

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“…SPM has been successfully applied to semiconductor, 19 organic, 20 and ferroelectric 21,22 surfaces, as well as to defects, 23,24 and photoinduced 25,26 and thermal phenomena 27,28 in these materials. A number of SPM studies on grain boundary related phenomena have also been reported.…”

Section: Introductionmentioning

confidence: 99%

Potential and Impedance Imaging of Polycrystalline BiFeO₃ Ceramics

Kalinin

Suchomel

Davies

et al. 2002

Journal of the American Ceramic Society

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Electrostatic-force-sensitive scanning probe microscopy (SPM) is used to investigate grain boundary behavior in polycrystalline BiFeO 3 ceramics. Scanning surface potential microscopy (SSPM) of a laterally biased sample exhibits potential drops due to resistive barriers at the grain boundaries. In this technique, the tips acts as a moving voltage probe detecting local variations of potential associated with the ohmic losses within the grains and at the grain boundaries. An approach for the quantification of grain boundary, grain interior, and contact resistivity from SSPM data is developed. Scanning impedance microscopy (SIM) is used to visualize capacitive barriers at the grain boundaries. In SIM, a dc-biased tip detects the variations of local potential induced by the lateral ac voltage applied to the sample. Unlike the traditional dc and ac transport measurement, both of these techniques are sensitive to the variation of local potential (SSPM) or local voltage oscillation amplitude and phase (SIM), rather than to current. Therefore, special attention is paid to the relationship between SSPM and SIM images and data obtained from traditional impedance spectroscopy and dc transport measurements. For BiFeO 3 ceramics excellent agreement between the local SIM measurements and impedance spectroscopy data are demonstrated.

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Kelvin probe force microscopy for characterization of semiconductor devices and processes

Cited by 109 publications

References 7 publications

Surface potential of chalcopyrite films measured by KPFM

Surface potential of chalcopyrite films measured by KPFM

Open loop Kelvin probe force microscopy with single and multi-frequency excitation

Potential and Impedance Imaging of Polycrystalline BiFeO₃ Ceramics

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Kelvin probe force microscopy for characterization of semiconductor devices and processes

Cited by 109 publications

References 7 publications

Surface potential of chalcopyrite films measured by KPFM

Surface potential of chalcopyrite films measured by KPFM

Open loop Kelvin probe force microscopy with single and multi-frequency excitation

Potential and Impedance Imaging of Polycrystalline BiFeO3 Ceramics

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Potential and Impedance Imaging of Polycrystalline BiFeO₃ Ceramics