Spin-dependent and localisation effects at Si/SiO₂device interfaces

Abstract

This paper discusses the defect structure of MOS device materials, in particular the evidence relating to dangling bond defects at the Si/SiO, interface. Over two decades and more, the characterisation of such defect states has given information on paramagnetic (S = +) centres at the interface. The most remarkable feature of the thermally oxidised Si surface is the very small density of interface defects ( -10l5 m-2) compared to the bare semiconductor surface. These states have energies throughout the Si band gap, and their charge may be changed by changing the Fermi level in the band gap. Ionic contamination of the thermal oxide may affect the electrostatics of the MOS material. Some ionic defects (such as Na+) move under the influence of an applied field and cause device characteristics to drift with time, in addition there is a positive 'fixed oxide charge' located within about 3 nm of the Si/SiO, interface. Other centres exist throughout the bulk of the oxide, which can trap both positive and negative charge. The control of interface state density and oxide charge density is extremely important for the production of reliable devices. Given the very small defect levels, rather sensitive techniques have to be used to measure the concentration and characterise the structure of defects in Si/SiO, materials. Here we discuss the use of spin-dependent spectroscopies such as electron spin resonance, optical detection of magnetic resonance and spindependent recombination as aids to elucidating defect structure. We also discuss some experiments on p-channel MOSFETS in which an inversion layer of holes is created at the interface when turned on by a sufficiently negative gate voltage. Inversion layers in MOSFETS at low temperatures are used for the investigation of conduction in two dimensions. Such experiments at low temperatures on the localisation of carriers are shown here to give information on both positive and negative charge trapped near the interface.

Recombination at silicon dangling bonds

“…The P b center was identified by its dependence on the angle between the B 0 field and the sample surface (shown in the inset of Fig. 2), an anisotropic behavior well documented in the literature [17]. Fig.…”

Recombination centers inGaAs/Al0.4Wimbauer1, Brandt2, Bayerl3 et al. 1998Phys. Rev. B

“…Its field position corresponds to gϭ2.001 and the peak-to-peak linewidth is ⌬H pp ϭ18 G. The g value close to the free electron value is not a very specific defect feature, but the halfwidth of the resonance is surprisingly small for a defect in GaAs or Al 0.4 Ga 0. 6 As, as all nuclei of the host carry nuclear spin and thus interact with the defect electron via hyperfine interaction. As discussed below, this leads to magnetic resonance linewidths that typically are an order of magnitude higher for defects in GaAs and Al 0.4 Ga 0.6 As compared to the defect observed here.…”

“…Most EDMR experiments reported so far deal with defects in bulk semiconductors, thin films, or simple p/n diode structures. 6,7 While such experiments have been very successful for semiconductors with indirect band gaps, such as Si, 3 SiC, 8 and GaP, 9 experiments on direct band-gap semiconductors are rare, with GaN light-emitting diodes 8,10 and a study of lowtemperature GaAs ͑Ref. 8͒ being the only examples known to the authors.…”

Improvement of charge-pumping electrically detected magnetic resonance and its application to silicon metal–oxide–semiconductor field-effect transistor

“…The signal intensity [peak height in (b)] ΔI cp was ∼100 fA, which means that ΔI cp =I cp (= 10 nA) was on the order of 10 −5 . This value is comparable to or slightly smaller (worse) than those obtained using the conventional (constant bias) EDMR, 17,21) presenting a striking contrast to the case of the SiC=SiO 2 interface, where CP EDMR appears to provide far more distinct signals than constant-bias EDMR. 29) Figure 3(c) shows a close-up view of the noise floor.…”

“…It usually monitors, under constant (gate) bias conditions, a small change ΔI in the device current I due to electron spin resonance. 13) Among several mechanisms causing EDMR, spin-dependent recombination (SDR) [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] yields the highest signals (typically, ΔI=I = 10 −5 -10 −4 ) and is suitable for accessing deep centers such as MOS interface defects.…”