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Exploring the border traps near the valence band in the - system using above-band-gap optical excitation
P. Kumar, H. G. Medeiros, S. Race, M. I. M. Martins, P. Ammann, M. E. Bathen, T. Prokscha, and U. Grossner
Phys. Rev. Applied 21, 064065 – Published 27 June 2024
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Abstract
Studying near-valence-band () defects at the insulator–-type - interface is challenging due to the low minority carrier concentration. Herein, we present a technique for characterizing the border traps near in an -type - MOS capacitor by generating holes using above-band-gap optical excitation (OE). A rise in capacitance was observed under OE (due to hole capture by border traps), remaining stable long after the optical stimulus was removed, resulting in a persistent photocapacitance effect. We show the dynamics of the capture process and perform a quantification of the captured holes in samples with thermally grown oxide and different postoxidation annealing treatments.
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- Received 7 February 2024
- Revised 22 April 2024
- Accepted 3 June 2024
DOI:https://doi.org/10.1103/PhysRevApplied.21.064065
![Exploring the border traps near the valence band in the ${\mathrm{Si}\mathrm{O}}_{2}$-$\mathrm{Si}\mathrm{C}$ system using above-band-gap optical excitation (10) Exploring the border traps near the valence band in the ${\mathrm{Si}\mathrm{O}}_{2}$-$\mathrm{Si}\mathrm{C}$ system using above-band-gap optical excitation (10)](https://i0.wp.com/cdn.journals.aps.org/files/icons/creativecommons.png)
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
- Research Areas
CapacitanceChargeElectron emissionPhotoinduced effect
- Physical Systems
Field-effect transistorsInterfacesWide band gap systems
Condensed Matter, Materials & Applied Physics
Authors & Affiliations
P. Kumar1,*, H. G. Medeiros1, S. Race1, M. I. M. Martins1,2, P. Ammann1, M. E. Bathen1, T. Prokscha2, and U. Grossner1
- 1Advanced Power Semiconductor Laboratory, ETH Zürich, Physikstrasse 3, Zurich 8092, Switzerland
- 2Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institute, Forschungsstrasse 111, Villigen PSI 5232, Switzerland
- *Contact author: kumar@aps.ee.ethz.ch
Article Text
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Vol. 21, Iss. 6 — June 2024
Subject Areas
- Optoelectronics
- Semiconductor Physics
![Exploring the border traps near the valence band in the ${\mathrm{Si}\mathrm{O}}_{2}$-$\mathrm{Si}\mathrm{C}$ system using above-band-gap optical excitation (14) Exploring the border traps near the valence band in the ${\mathrm{Si}\mathrm{O}}_{2}$-$\mathrm{Si}\mathrm{C}$ system using above-band-gap optical excitation (14)](https://i0.wp.com/cdn.journals.aps.org/development/journals/images/author-services-placard.png)
Images
Figure 1
Change in capacitance of the device (see Table1 for sample details) as a function of time for an applied optical excitation for (a)–(c) the MOS capacitor and (d) the Schottky diode case. Panels (b),(c) show the rise and decay of the capacitance transient, respectively, for the MOS capacitor and illustrate the presence of a fast and a slow exponential component in the rise and decay. Results shown in (a)–(d) were performed with an LED. (e) Capacitance versus time under optical excitation using a laser with variable photon energy. Small increase in capacitance is observed during the OE experiment when . Increase in capacitance also persists after the laser is turned off. For , a rapid increase in capacitance is observed.
Figure 2
Proposed model for the MOS capacitor to illustrate the generation, trapping, and recombination of charges under different operating conditions. Hole trapping at the border traps is proposed to be responsible for the rise in capacitance under the applied optical excitation.
Figure 3
Parabolic approximation in the nonradiative multi-phonon (NMP) model to account for the deformation of the defect site. Upon optical excitation, the defect level can transform from State 01 (red parabola) into State 02 (black parabola). After optical excitation is removed, the barrier to transition from State 02 to State 01 is .
Figure 4
(a) Rising capacitance of the sample upon the application of optical excitation using an LED as a function of applied bias. Extracted time constant is shown as a function of gate bias (b) and temperature (c). (d) Dependence of the time constant on the optical power is illustrated. Measurement is performed at 293 K and 0-V dc bias.
Figure 5
Hole-capture rate evaluated as from Eq.(1) for the thermally oxidized and annealed samples (left, ; middle, 1300NO1300; right, 1300Ar1300) during the OE experiment with a fixed temperature of 293 K and variable bias. It is observed that, for all the samples, the capture rate increases as a larger negative bias is applied to the MOS capacitors.
Figure 6
(a) TCAD simulation of the oxide-semiconductor structure under varying gate bias. Inset, variation in the energy difference () between a chosen defect level in the oxide and , depending on the gate bias. (b) CC diagram for the border traps. Although the energy difference between the defect level and increases from to for increasing negative gate bias, the energy barrier for the transition from State 01 to 02 reduces from to .
Figure 7
(a) Representative example of the optical excitation experiment. (b) Capacitances , , and are located on the - curve, and corresponding voltages are extracted. (c) Using information about the initial and final capacitances and voltage, the concentrations of trapped positive charges in the oxide are calculated and shown as a function of applied gate bias for the three samples.
Figure 8
Hole-capture rate evaluated for the thermally oxidized and annealed samples (left, ; middle, 1300NO1300; right, 1300Ar1300) during the OE experiment with a fixed bias of 0 V and variable temperature. It is observed that the hole-capture process is fairly independent of temperature over the measured range.