Impedance spectroscopy of the metal-oxide semiconductor (MOS) system has played a central role in the development of silicon-based complementary MOS (CMOS) technology over the past 50 years [1, 2]. With current research interest into alternative semiconductor channels to silicon for MOSFET and tunnel FET technologies, the measurement and interpretation of the overall impedance of the MOS structure requires detailed analysis to separate and quantify the contribution of interface states, and near interface traps (border traps), on the capacitance and conductance response, and to separate the contribution of these electrically active defect states from the ac response of minority carriers in the case of genuine inversion of the semiconductor/dielectric interface.

There has been considerable progress in recent years in reducing the interface state density (D_it) [3], [4], [5], in narrow gap In_xGa_1-xAs MOS structures to the point where genuine surface inversion can be observed for both n- and p-type In_0.53Ga_0.47As MOS capacitors, which is confirmed by analysis of the minimum capacitance of n- and p-type In_0.53Ga_0.47As MOS structure with doping concentration ranging from approximately 1x10¹⁶ to 1x10¹⁸ cm^-3 [6]. In this presentation we will provide an overview of the experimental relationship between specific functions of the capacitance (C) and conductance (G) for the case of narrow band gap III-V MOS structures which exhibit genuine surface inversion, where the capacitance and conductance of the MOS system as a function of ac angular frequency (ω) are related, and in particular, the peak values of G/ω and −dC/dlog_e(ω) (≡− ωdC/dω) are equal, and that these peak magnitudes occur at the same value of ω [7]. The relationship is also confirmed by physics based ac simulations of MOS structures and through analysis of the equivalent circuit model in inversion. Results will be presented for InGaAs and InGaSb MOS structures (Al₂O₃ and Al₂O₃/HfO₂ ALD oxides) where genuine inversion of the III-V/oxide surface is confirmed by the G/ω and −dC/dlog_e(ω) functions, which have peak values of C_ox²/2(C_ox+C_d) when the surface is inverted (where C_ox is the gate oxide capacitance and C_d is the maximum capacitance of the semiconductor surface in inversion). In the case of p type InGaSb MOS structures it is also notable that the accumulation frequency dispersion is very low (<0.7%/decade) indicating a reduced density of border traps at energies in the Al₂O₃ gate oxide aligning with the In_0.3Ga_0.7Sb valence band edge, which is approximately aligned with the lowest energy in the In_0.53Ga_0.47As conduction band gamma valley.

Finally, experimental results and physics based simulations will be presented, which indicate that the peak values of G/ω and −dC/dlog_e(ω) in inversion for any MOS system which demonstrates an inversion response within the typically range of temperatures and ac signal frequencies employed in experiments, opens a route to determine the gate oxide capacitance in inversion (where the gate oxide field and gate leakage are reduced), and that the angular frequency associated with the peak values of the G/ω and −dC/dlog_e(ω) functions allows the determination of the minority carrier generation rate in the semiconductor, which is relevant to the leakage currents in MOSFETs and the optical performance in photonic applications.

[1] E. H. Nicollian and J. R. Brews, MOS Physics and Technology. New York, NY, USA: Wiley, 1982

[2] E. H. Nicollian and A. Goetzberger, “The Si-SiO2 interface—Electrical properties as determined by the metal-insulator-silicon conductance technique,” Bell Syst. Tech. J., vol. 46, no. 6, pp. 1055–1133, 1967.

[3] É. O’Connor et al., J. Appl. Phys., vol. 109, no. 2, p. 024101, 2011.

[4] H.-D. Trinh et al., Appl. Phys. Lett., vol. 97, no. 4, pp. 042903-1–042903-3, 2010.

[5] T. D. Lin et al., “Realization of high-quality HfO2 on In0.53Ga0.47As by in-situ atomic-layer-deposition,” Appl. Phys. Lett., vol. 100, no. 17, p. 172110, 2012.

[6] E. O'Connor, K. Cherkaoui, S. Monaghan, B. Sheehan, I. M. Povey, and P. K. Hurley, Appl. Phys. Lett 110, 032902 (2017)

[7] Scott Monaghan, Éamon O’Connor, Rafael Rios, Fahmida Ferdousi, Liam Floyd, Eimear Ryan, Karim Cherkaoui, Ian M. Povey, Kelin J. Kuhn, and Paul K. Hurley, IEEE Transaction on Electron Devices, 61, 4176 (2014)