We report studies of spin-dependent recombination at the Si/SiO2 interface in electron irradiated (100) and (111) p-channel metal-oxide-silicon field-effect transistors and metal-oxide-silicon wafers. Electron spin resonance transitions on the Pb center increase the recombination current at the Si/SiO2 interface by 2–3 parts in 104. The results are interpreted using a model involving the recombination of electrons and holes at Pb centers with which they are spatially correlated.

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.

We report spin-dependent generation of electron-hole pairs at the Si/SiO2 interface detected via microwave-induced changes in the recombination current through a gate-controlled diode.

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