Probing band-tail states in silicon metal-oxide-semiconductor heterostructures with electron spin resonance

Abstract

We present an electron spin resonance (ESR) approach to characterize shallow electron trapping in band-tail states at Si/SiO2 interfaces in metal-oxide-semiconductor (MOS) devices and demonstrate it on two MOS devices fabricated at different laboratories. Despite displaying similar low temperature (4.2 K) peak mobilities, our ESR data reveal a significant difference in the Si/SiO2 interface quality of these two devices, specifically an order of magnitude difference in the number of shallow trapped charges at the Si/SiO2 interfaces. Thus, our ESR method allows a quantitative evaluation of the Si/SiO2 interface quality at low electron densities, where conventional mobility measurements are not possible.

Description of low temperature bandtail states in two-dimensional semiconductors using path integral approach

“…9, 23 We found that it has similar characteristic to those of sample A, 5 but different characteristic from those of sample B. 5 This indicates that the effect of the charged impurities is not the dominated effect in sample B. Thus, we consider only the effect of the interface roughness in this work.…”

“…This was applied to the three-dimensional electron gas 1,2 and to the 2DEG as in Si/SiGe 3 and MgZnO/ZnO. 4 Recently, there has been an experimental measurement on the bandtail states in Si/SiO 2 heterostructures at low temperature around 370 mK-3 K. 5 We showed in this paper that the existing semiclassical model gives incomplete description to the reported bandtail states. Then, we used path integral theory to suggest a function form of the low temperature bandtail states of a 2DEG with dense and random impurities, and provided much better description to the experimental data.…”

“…At the final stage, we shall use Eqs. (11) and (13) to describe the experimental measurement of 2DEG bandtail in Si=SiO 2 heterostructures (Sample B) at low temperature of 370 mK-3 K. 5 At low temperatures, it is well-known that the charged impurities and the interface roughness affect the electronic properties of a 2D system. 9 To clarify which is the dominated effect, we consider the bandtail from the charged impurities which has been previously investigated in Si=SiO 2 heterostructures.…”

“…5 Within the nonparabolic band of Si, the in-plane effective mass is of m ¼ 0:2m 0 , the free electron DOS is equal to 1:6 Â 10 11 meV À1 cm À2 with two-fold valley degeneracy, 5 and the growth-direction effective mass is of m z ¼ 0:916m 0 . 24 For the roughness parameters, Thongnum et al 3 showed that the interface roughness limited mobility is l ¼ 2 5=2 em 2 z a 6 n 1=2 s =p 4 hm 2 D 2 L. Without further input parameters from the experiment, there still are a few parameters which are needed to be identified.…”

(Invited) Spin Coherence in Si and Applications to Quantum Information Processing

“…The "X" on the vertical axis on the right is the density of states in the lowest subband (two valleys) for a 2-dimensional system in silicon (after ref. 18). …”