FIB

2015 Nanotechnology

HPY Publications , , , , ,

Paul_Nanotechnology“Electron beam induced current in the high injection regime”, P. M. Haney, H. P. Yoon, P. Koirala, R. W. Collins, and N. B. Zhitenev, Nanotechnology 26, 295401, 2015.

1. Center for Nanoscale Science and Technology, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA.
2. Maryland NanoCenter, University of Maryland, College Park, MD 20742.
3. Dept. of Physics and Astronomy, University of Toledo, Toledo, OH, 43606.

ABSTRACT. Electron beam induced current (EBIC) is a powerful technique which measures the charge collection efficiency of photovoltaics with sub-micron spatial resolution. The exciting electron beam results in a high generation rate density of electron–hole pairs, which may drive the system into nonlinear regimes. An analytic model is presented which describes the EBIC response when the total electron–hole pair generation rate exceeds the rate at which carriers are extracted by the photovoltaic cell, and charge accumulation and screening occur. The model provides a simple estimate of the onset of the high injection regime in terms of the material resistivity and thickness, and provides a straightforward way to predict the EBIC lineshape in the high injection regime. The model is verified by comparing its predictions to numerical simulations in one- and two-dimensions. Features of the experimental data, such as the magnitude and position of maximum collection efficiency versus electron beam current, are consistent with the  three dimensional model.

LINK

2015 IEEE Photovoltaic Specialists Conference

HPY Publications , , ,

pvsc_2015_poster“Local Photocarrier Dynamics in CdTe Solar Cells Under Optical and Electron Beam Excitations”, H. P. Yoon, P. M. Haney, Y. Yoon, S. An, J. I. Basham, and N. B. Zhitenev, 42th IEEE Photovoltaic Specialists Conference, p. 1, 2015. (DOI: 10.1109/PVSC.2015.7356020)

1. Center for Nanoscale Science and Technology, National Institute of Standards and Technology, Gaithersburg, Maryland, 20899, USA.
2. Maryland Nanocenter, University of Maryland, College Park, Maryland, 20742, USA

ABSTRACT. We compare local carrier dynamics in n-CdS / p-CdTe solar cells, where the electron-hole pairs are generated by either near-field optical illumination or highly focused electron beam excitation. An ion beam milling process was used to prepare a smooth surface of cross-sectional devices. The spatially resolved photocurrent images confirm high carrier collection efficiency at grain boundaries. An analytical model was used to extract material parameters at the level of single grains. We find that the minority carrier diffusion lengths extracted from both local measurement techniques are in excellent agreement, but are smaller than the values determined from macro-scale measurements.

LINK

2014 Microscopy and Microanalysis

HPY Publications , , , ,

MandM“Effects of Focused-Ion-Beam Processing on Local Electrical Measurements of Inorganic Solar Cells“, H. P. Yoon, P. M. Haney, J. Schumacher, K. Siebein, Y. Yoon, and N. B. Zhitenev, Microscopy and Microanalysis 20 (S3), 544-545, 2014.

1.Center for Nanoscale Science and Technology, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
2. Maryland Nanocenter, University of Maryland, College Park, MD 20742, USA

ABSTRACT. Quantitative determination of electronic properties at high spatial resolution is crucial for the development of high-efficiency solar cells. Electron beam induced current (EBIC) is a powerful technique in which electron-hole pairs are created in proximity to an exposed surface, and the carrier collection efficiency is measured as a function of excitation position. Cross-sections of device are often created by focused ion beams (FIB) due to the flexibility of the patterning and milling processes. However, the irradiating Ga ions of the FIB fabrication may introduce unintended artifacts, affecting local electronic properties. In this study, we investigate the impact of the FIB process observed in EBIC measurements and two-dimensional finite element simulations.

LINK

2014 7th Annual FIB SEM Workshop

HPY Publications , , ,

usermeeting
“Effects of Focused-Ion-Beam Processing on Local Measurements of Semiconductor Solar Cells”, H. P. Yoon, P. M. Haney, J. Schumacher, K. Siebein, Y. Yoon, and N. B. Zhitenev, presented by H. Yoon at the 7th Annual FIB SEM Workshop in Laurel, MD, February 2014.

1. Center for Nanoscale Science and Technology, National Institute of Standards and Technology, Gaithersburg, Maryland, 20899, USA. 2. Maryland Nanocenter, University of Maryland, College Park, Maryland, 20742, USA

ABSTRACT. Quantitative determination of electronic properties at high spatial resolution is crucial for the development of high-efficiency solar cells. Electron beam induced current (EBIC) is a powerful technique in which electron-hole pairs are created in proximity to an exposed surface, and the carrier collection efficiency is measured as a function of excitation position. Cross-sections of device are often created by focused ion beams (FIB) due to the flexibility of the patterning and milling processes. However, the irradiating Ga ions of the FIB fabrication may introduce unintended artifacts, affecting local electronic properties. In this talk, we discuss the impact of the FIB process observed in EBIC measurements and two-dimensional finite element simulations. A series of EBIC data was obtained on a single crystalline solar cell at different electron beam voltages and beam currents to examine the depth and carrier injection level dependence inside the depletion region and away from the p-n junction. Quantitative analysis shows that the EBIC efficiency of the FIB sample is much lower (< 40 %) than that of the cleaved sample (100%) at low beam voltages (<10 keV). We discuss the effects of FIB processing of other types of photovoltaic devices including CdTe and CIGS solar cells.

LINK (NDR contents are not presented)