Interface state density

Low inversion channel mobility on a vertical sidewall due to high interface state density at the p-SiC/SiO interface and high fixed charge density in the insulator. 

Significant improvement in the inversion channel mobility reported in [30] became possible due to a dramatic reduction in the interface state density by postoxidation annealing standard thermal oxides in an NO atmosphere. An extensive experimental and theoretical study exists showing that NO postoxidation anneal improves the dH-SiC/SiO interface quality and inversion channel mobility (e.g., [31-33]). It has also been shown for NO-annealed oxides that the electron injection barrier height increases to values close to the theoretical value at RT that will... 

The success of CD CdS in photovoltaic cells has driven related research with potential applications in other semiconductor devices. Since the CD process seems to play a role in the favorable properties of the CdS windows by decreasing interface recombination, studies of its passivation properties on other interfaces and surfaces have been carried out, with considerable success. For example, when a very thin film (ca. 6 nm) was deposited between InP and SiOi, the resulting reduction of the interface state density led to improved electrical properties of metal-insulator-semiconductor capacitors and field effect transistors (FETs)... 

A simple way of studying the interfaces is to use multilayer samples, which contain many interfaces and to apply the techniques normally used for bulk measurements. Fig. 9.20 shows ESR data of the silicon nitride interface for such samples (Tsai, Street, Ponce and Anderson 1986b). The total thickness of each sample, 0.6 pm, and the thicknesses of the nitride and a-Si H layers are equal the only difference is in the thicknesses of the individual layers and therefore in the number of interfaces. The dependence of the ESR spin density on this parameter shows that the interfaces dominate most of the spin measurements. It is not possible, however, to separate out the effects of the top and bottom interfaces, both of which are present in equal number. The top nitride interface is presumably the main source of the signal, since it has the larger interface state density. 

Minimization of the density of slow states and interface states is of technological importance for held effect transistors. Presently available nitrides are of sufficient quality that the slow states have no signihcant effect on electrons at normal temperatures, but some hole trapping occurs. The use of a bottom nitride structure reduces the interface state density to an almost negligible amount. The remaining problem associated with the interface of the transistors is the generation of metastable interface defects in the a-Si H him due to the accumulation bias. 

J. L. Dort, J. Joseph, J. R. Martin, and P. Qechet, pH dependence of the Si/SiOj interface state density for EOS systems, quasi-static and AC conductance methods, J. Electroanal. Chem. 193, 75, 1985. 

The oxidized layer charge densities and interface state densities are reported in table 11. 

Table II Charge densities in the oxide layer and interface state densities for the oxide layer growth with stirring and without stirring (during 150 s). 

MIS Steady Charge Density (cm 2) Mobile Charge Density (cm 2) Interface State Density (cm 2)... 

Recently Vaccaro et al. [15, 249] found that chemical bath deposition is also an effective method to passivate metal insulator semiconductor (MIS) devices based on InP. They showed that deposition of a very thin CdS layer from an ammonia bath (2 nm) between InP and Si02 lead to spectacular improvement in the electrical properties of the devices. The reason was attributed to a reduction by at least one order of magnitude of the interface state density at the InP surface as compared to the reference structure. They show that the CBD deposition leads to a reduction of the phophorus vacancies densities at the interface and also to elimination of residual oxides. 

Alternatively, a metal insulator junction is an ohmic contact for electron flow if < X (for hole flow if and if the interface state density in the insulator band gap is sufficiently small that the metal Fermi energy will not be pinned in the insulator band gap [125]. The accumulation layer which then forms can act as a virtual cathode for electrons ( < x) or anode for holes ( >... 

Fig. 1. Interface-state density of c-Si measured by deep-level transient current spectroscopy on thermally oxidized, unannealed, (11 l)-oriented silicon. [From Johnson et al (1983).]...

The interface-state density of a-Si H measured by Suzuki et al. (1982) is shown in Fig. 2. The peaks observed in Fig. 1 have not yet been found in a-Si H, and the correlation of the states in the lower and upper half of the gap has still to be investigated, but the similarity of the shapes of g, E) and the g -value of the surface spins suggest that the origin of these states is the same for crystalline and amorphous Si. 

Fig. 2. Interface-state density of a-Si H deposited on thermally oxidized SiOj at 300°C. Densities were measured by Suzuki el al. (1982) by combining the field-eflFect and capacitance-voltage methods. [From Suzuki el al. (1982).]...

Interface State Density ( crn eV" l-4xl012 lxlO11 5xl010... 

Heat treatment of HP0-Ge02 ammonia ambient results in low interface state density even for poor quality oxides as the starting material. 

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