Kelvin probe force microscopy of semiconductor surface defects

Rosenwaks, Y.; Shikler, Rafi; Glatzel, Thilo; Sadewasser, Sascha

doi:10.1103/physrevb.70.085320

Cited by 192 publications

(154 citation statements)

References 22 publications

(22 reference statements)

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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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“…The (110) surface of GaAs and other III-V semiconductors have been previously demonstrated to display charging of their step edges. 2,3,4 The sign of the charge was found to depend on the doping of the semiconductor, but a detailed understanding in terms of the geometric and electronic structure of the step edges was lacking. From a theoretical perspective, steps of various orientations on GaAs(110) have been studied.…”

Section: Introductionmentioning

confidence: 99%

Structure and electronic spectroscopy of steps on GaAs(110) surfaces

et al. 2012

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Steps on GaAs(110) surfaces, with step-normal vectors parallel to [001], are studied by scanning tunneling microscopy and spectroscopy. Two possible orientations of the steps occur, with outward normal vectors of [001] or [ 1 00 ], which in simple bulk-terminated form have Ga (cations) or As (anions) on their edges, respectively. The latter type of step in n-type or undoped material is found to retain its bulk-terminated form. A band of states is observed extending out from the valence band, associated with the dangling bonds of the terminating As atoms. It is argued that compensation of the dangling bonds on the step edges is the driving force for the step structure, producing reconstruction of the step edges in certain cases.

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“…It has been applied to characterize various types of solids used in electronic devices such as ionic crystal thin films, 2 semiconductors, 3 organic solar cell structures, 4 and nanographenes 5 in order to study the sample lateral variations of surface potentials and work functions and infer the electronic structures.…”

Section: Introductionmentioning

confidence: 99%

Simulating and interpreting Kelvin probe force microscopy images on dielectrics with boundary integral equations

Shen

Barnett

Pinsky

2008

Review of Scientific Instruments

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Reduced leakage current, enhanced ferroelectric and dielectric properties in (Ce,Fe)-codoped Na0.5Bi0.5TiO3 film Appl. Phys. Lett. 100, 022909 (2012) Modified Johnson model for ferroelectric lead lanthanum zirconate titanate at very high fields and below Curie temperature Appl. Phys. Lett. 100, 022907 (2012) Engineering titanium and aluminum oxide composites using atomic layer deposition J. Appl. Phys. 110, 123514 (2011) High dielectric tunability of (100) oriented PbxSr1xTiO3 thin film coordinately controlled by dipole activation and phase anisotropy J. Appl. Phys. 110, 124107 (2011) Kelvin probe force gradient microscopy of charge dissipation in nano thin dielectric layers J. Appl. Phys. 110, 084304 (2011) Additional information on Rev. Sci. Instrum. Kelvin probe force microscopy ͑KPFM͒ is designed for measuring the tip-sample contact potential differences by probing the sample surface, measuring the electrostatic interaction, and adjusting a feedback circuit. However, for the case of a dielectric ͑insulating͒ sample, the contact potential difference may be ill defined, and the KPFM probe may be sensing electrostatic interactions with a certain distribution of sample trapped charges or dipoles, leading to difficulty in interpreting the images. We have proposed a general framework based on boundary integral equations for simulating the KPFM image based on the knowledge about the sample charge distributions ͑forward problem͒ and a deconvolution algorithm solving for the trapped charges on the surface from an image ͑inverse problem͒. The forward problem is a classical potential problem, which can be efficiently solved using the boundary element method. Nevertheless, the inverse problem is ill posed due to data incompleteness. For some special cases, we have developed deconvolution algorithms based on the forward problem solution. As an example, this algorithm is applied to process the KPFM image of a gadolinia-doped ceria thin film to solve for its surface charge density, which is a more relevant quantity for samples of this kind than the contact potential difference ͑normally only defined for conductive samples͒ values contained in the raw image.

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Kelvin probe force microscopy of semiconductor surface defects

Cited by 192 publications

References 22 publications

Surface potential of chalcopyrite films measured by KPFM

Surface potential of chalcopyrite films measured by KPFM

Structure and electronic spectroscopy of steps on GaAs(110) surfaces

Simulating and interpreting Kelvin probe force microscopy images on dielectrics with boundary integral equations

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