Steve Johnston is a senior scientist on the Microscopy and Imaging team of the Materials Science center of NREL. He received his B.S. in Engineering from the Colorado School of Mines (CSM); M.S. from the University of Illinois, Urbana-Champaign, in Electrical Engineering; and Ph.D. from CSM in Materials Science. He worked for more than two years at Texas Instruments with clean-room semiconductor processing and measurement equipment. He has experience with NREL in minority-carrier lifetime, capacitance-related, and imaging-based measurement techniques for solar cell materials.

Research Interests

Microwave reflection photoconductive decay, transient free-carrier absorption, and time-resolved photoluminescence for minority-carrier lifetime and light-beam induced current for quantum efficiency and diffusion length measurements.

Electroluminescence imaging, photoluminescence imaging, and lock-in thermography for material and cell characterization.

Capacitance/voltage, admittance spectroscopy, and deep-level transient spectroscopy for characterization of carrier concentration and defect and impurity levels.

Education

B.S. in Engineering, Colorado School of Mines, 1991

M.S. in Electrical Engineering, University of Illinois, Urbana-Champaign, 1995

Ph.D. in Materials Science, Colorado School of Mines, 1999

Featured Work

S. Johnston, K. Zaunbrecher, R. Ahrenkiel, D. Kuciauskas, D. Albin, W. Metzger, "Simultaneous measurement of minority-carrier lifetime in single-crystal CdTe using three transient decay techniques," IEEE Journal of Photovoltaics, 4(5), 1295–300 (2014)

S. Johnston, H. Guthrey, F. Yan, K. Zaunbrecher, M. Al-Jassim, P. Rakotoniaina, M. Kaes, "Correlating multicrystalline silicon defect types using photoluminescence, defect-band emission, and lock-in thermography imaging techniques,"IEEE Journal of Photovoltaics, 4(1), 348–354 (2014).

S. Johnston, T. Unold, I. Repins, A. Kanevce, K. Zaunbrecher, F. Yan, J.V. Li, P. Dippo, R. Sundaramoorthy, K.M. Jones, B. To, "Correlations of Cu(In,Ga)Se2 imaging with device performance, defects, and microstructural properties,"Journal of Vacuum Science & Technology A, 30(4), 04D111 (2012)

S. Johnston, T. Unold, I. Repins, et al., "Imaging characterization techniques applied to Cu(In,Ga)Se2 solar cells," Journal of Vacuum Science & Technology A, 28(4), 665–670 (2010).

S.W. Johnston, R.K. Ahrenkiel, D.J. Friedman, S.R. Kurtz, "Deep-level transient spectroscopy in InGaAsN lattice-matched to GaAs," IEEE PVSC, New Orleans (2002).

S.W. Johnston, R.S. Crandall, A. Yelon, "Evidence of the Meyer-Neldel rule in InGaAsN alloys and the problem of determining trap capture cross sections,"Appl. Phys. Lett., 83, 908–910 (2003).

S.W. Johnston, R.K. Ahrenkiel, C.W. Tu, Y.G. Hong, "Measurement of charge-separation potentials in GaAs1-xNx," J. Vac. Sci. Technol. A, 21(5), 1765–1769 (2003).

S.W. Johnston, R.S. Crandall, "Evidence of the Meyer-Neldel Rule in InGaAsN Alloys:  Consequences for Photovoltaic Materials," MRS Spring Meeting, San Francisco, CA, April 21–25, 2003.

S.W. Johnston, S.R. Kurtz, D.J. Friedman, A.J. Ptak, R.K. Ahrenkiel, R.S. Crandall, "Observed trapping of minority-carrier electrons in p-type GaAsN during deep-level transient spectroscopy measurement," Appl. Phys. Lett., 86, 072109 (2005).

S.W. Johnston, S. Kurtz, D.J. Friedman, A.J. Ptak, R.K. Ahrenkiel, R.S. Crandall, "Electron traps in p-type GaAsN characterized by deep-level transient spectroscopy," Conference Record of the Thirty-First IEEE Photovoltaic Specialist Conference, 599 (2005).

S.W. Johnston, S.R. Kurtz, "Comparison of a dominant electron trap in n-type and p-type GaNAs using deep-level transient spectroscopy," J. Vac. Sci. Technol. A, 24(4), (2006).

R.K. Ahrenkiel, S.W. Johnston, W.K. Metzger, P. Dippo, "Relationship of band-edge luminescence to recombination lifetime in silicon wafers," Journal of Electronic Materials, 37(4), 396–402 (2008).

R.K. Ahrenkiel, S.W. Johnston, "Interaction of microwaves with photoelectrons in semiconductors," Journal of Vacuum Science & Technology B, 26(4), 1508–1515 (2008).

R.K. Ahrenkiel, S.W. Johnston, "Lifetime analysis of silicon solar cells by microwave reflection," Solar Energy Materials and Solar Cells, 92(8), 830–835 (2008).

S.W. Johnston, N.J. Call, B. Phan, R.K. Ahrenkiel, "Applications of imaging techniques for solar cell characterization," 34th IEEE Photovoltaic Specialists Conference, 7–12 June 2009, Philadelphia, PA (2009).

R.K. Ahrenkiel, S.W. Johnston, "An optical technique for measuring surface recombination velocity," Solar Energy Materials and Solar Cells, 93(5), 645–649.

R. Krause, H. Hovel, E. Marshall, G. Pfeiffer, Z. Li, L. Clevenger, K. Petrarca, D. Shahrjerdi, K. Prettyman, S. Johnston, "Advantages and shortcomings of UMG silicon in photovoltaic device production," Photovoltaics International, 8th Edition, Second Quarter, 38–50 (2010).

F. Liu, C.-S. Jiang, H. Guthrey, S. Johnston, M.J. Romero, B.P. Gorman, M.M. Al-Jassim, "Optical response of grain boundaries in upgraded metallurgical-grade silicon for photovoltaics," Solar Energy Materials & Solar Cells, 95, 2497–2501 (2011).

S. Johnston, F. Yan, J. Li, K. Zaunbrecher, M.J. Romero, M. Al-Jassim, O. Sidelkheir, A. Blosse, "Temperature-dependent photoluminescence imaging and characterization of a multi-crystalline silicon solar cell defect area," 37th IEEE Photovoltaic Specialists Conference (PVSC 37), 19–24 June 2011, Seattle, WA.

F. Yan, S. Johnston, K. Zaunbrecher, M. Al-Jassim, O. Sidelkheir, K. Ounadjela, "Defect-band photoluminescence imaging on multi-crystalline silicon wafers," Physica Status Solidi-Rapid Research Letters, 6(5), 190–192 (2012). DOI: 10.1002/pssr.201206068

S.W. Johnston, F. Yan, D. Dorn, K. Zaunbrecher, M. Al-Jassim, O. Sidelkheir, K. Ounadjela, "Comparison of photoluminescence imaging on starting multicrystalline silicon wafers to finished cell performance," 38th IEEE Photovoltaics Specialists Conference, June 3–8, 2012, Austin, TX.

S.W. Johnston, F. Yan, K. Zaunbrecher, M. Al-Jassim, O. Sidelkheir, K. Ounadjela, "Quality characterization of silicon bricks using photoluminescence imaging and photoconductive decay," 38th IEEE Photovoltaics Specialists Conference, June 3–8, 2012, Austin, TX.

M.K. Hudait, Y. Zhu, S.W. Johnston, D. Maurya, S. Priya, R. Umbel, "Ultra-high frequency photoconductivity decay in GaAs/Ge/GaAs double heterostructure grown by molecular beam epitaxy," Applied Physics Letters, 102(9), 093119 (2013). DOI: 10.1063/1.4794984

P. Hacke, R. Smith, K. Terwilliger, S. Glick, D. Jordan, S. Johnston, M.Kempe, S. Kurtz,  "Acceleration factor determination for potential-induced degradation in crystalline silicon PV modules," 2013 IEEE International Reliability Physics Symposium, 4B.1.1-5 (2013). DOI: 10.1109/IRPS.2013.6532009

S. Grover, C.W. Teplin, J.V. Li, D.C. Bobela, J. Bornstein, P. Schroeter, S. Johnston, H. Guthrey, P. Stradins, H.M. Branz, D.L. Young, "Device physics of heteroepitaxial film c-Si heterojunction solar cells," IEEE Journal of Photovoltaics, 3(1), 230–235 (2013). DOI: 10.1109/JPHOTOV.2012.2223455

P. Hacke, R. Smith, K. Terwilliger, S. Glick, D. Jordan, S. Johnston, M. Kempe, S. Kurtz, "Testing and analysis for lifetime prediction of crystalline silicon PV modules undergoing degradation by system voltage stress," IEEE Journal of Photovoltaics, 3(1), 246–253 (2013). DOI: 10.1109/JPHOTOV.2012.2222351

R.K. Ahrenkiel, A. Feldman, J. Lehman, S.W. Johnston, "novel free-carrier pump-probe analysis of carrier transport in semiconductors," IEEE Journal of Photovoltaics, 3(1), 348–352 (2013). DOI: 10.1109/JPHOTOV.2012.2215581

J.N. Duenow, J.M. Burst, D.S. Albin, D. Kuciauskas, S.W. Johnston, R.C. Reedy, W.K. Metzger, "Single-crystal CdTe solar cells with V-oc greater than 900 mV,"Applied Physics Letters, 105(5), 53903–53903 (2014).

O. Yaffe, T. Ely, R. Har-Lavan, D.A. Egger, S. Johnston, H. Cohen, L. Kronik, A. Vilan, D. Cahen, "Effect of molecule-surface reaction mechanism on the electronic characteristics and photovoltaic performance of molecularly modified Si," Journal of Physical Chemistry C, 117(43), 22351–22361 (2013).

J.J. Sheng, D. Leonhardt, S.M. Hana, S.W. Johnston, J.G. Cederberg, M.S. Carroll, "Empirical correlation for minority carrier lifetime to defect density profile in germanium on silicon grown by nanoscale interfacial engineering,"J. Vac. Sci. Technol. B, 31(5), (2013).

N. Katz, M. Patterson, K. Zaunbrecher, S. Johnston, J. Hudgings, "High-resolution imaging of defects in CdTe solar cells using thermoreflectance,"Electronics Letters, 49(24), 1559–1561 (2013).

M.O. Reese, J.M. Burst, C.L. Perkins, A. Kanevce, S.W. Johnston, D. Kuciauskas, T.M. Barnes, W.K. Metzger, "Surface passivation of CdTe single crystals," IEEE Journal of Photovoltaics, 5(1) 382–385.

R.K. Ahrenkiel, S.W. Johnston, D. Kuciauskas, J. Tynan, "Dual-sensor technique for characterization of carrier lifetime decay transients in semiconductors," Journal of Applied Physics, 116(21), 214510.

A. Kanevce, D. Kuciauskas, D.H. Levi, A. Allende Motz, S. Johnston, "Two dimensional numerical simulations of carrier dynamics during time-resolved photoluminescence decays in two-photon microscopy measurements in semiconductors," Journal of Applied Physics, 118(4), 045709.

S.C. Siah, M.T. Winkler, D.M. Powell, S.W. Johnston, A. Kanevce, D.H. Levi, T. Buonassisi, "Proof-of-concept framework to separate recombination processes in thin silicon wafers using transient free-carrier absorption spectroscopy," Journal of Applied Physics, 117(10), 105701.

M.A. Lloyd, S.-C. Siah, R.E. Brandt, J. Serdy, S.W. Johnston, J. Hofstetter, Y.S. Lee, B. McCandless, T. Buonassisi, "Two-step annealing study of cuprous oxide for photovoltaic applications," IEEE Journal of Photovoltaics, 5(5), 1476–1481.

H. Guthrey, S. Johnston, D.N. Weiss, S. Grover, K. Jones, A. Blosse, M. Al-Jassim, "Three-dimensional minority-carrier collection channels at shunt locations in silicon solar cells," Solar Energy, 135, 163–168 (2016).

B. Nemeth, D.L Young, M.R. Page, V. Lasalvia, S. Johnston, R. Reedy, P. Stradins, "Polycrystalline silicon passivated tunneling contacts for high efficiency silicon solar cells," Journal of Materials Research, 31(6), 671–681 (2016).

A.W. Welch, L.L. Baranowski, P. Zawadzki, C. DeHart, S. Johnston, S. Lany, C.A. Wolden, A. Zakutayev,"Accelerated development of CuSbS₂ thin film photovoltaic device prototypes," Prog. Photovolt: Res. Appl., 24, 929–939 (2016).

S.A. Jensen, J.M. Burst, J.N. Duenow, H.L. Guthrey, J. Moseley, H.R. Moutinho, S.W. Johnston, A. Kanevce, M.M. Al-Jassim, W.K. Metzger, "Long carrier lifetimes in large-grain polycrystalline CdTe without CdCl₂," Applied Physics Letters, 108, 263903 (2016).