Energy Gap Of Silicon Research Articles

The Effect of Hot Electron Injection on Interface Charge Density at the Silicon to Silicon Dioxide Interface

The avalanche injection of hot electrons at the silicon to silicon dioxide interface causes an anomalous N‐shaped shift of flatband voltage in accordance with the injected charge density and generates an interface state with widely distributed time constants. To explain the N‐shaped behavior, we propose a model which assumes electron trapping in the silicon dioxide and the generation of the donor‐type interface state. It is also observed that the orientation of silicon substrate strongly affects the generated interface‐state density. The generated interface‐state density of a (100) capacitor has a value approximately half that of a (111) capacitor. The energy level of the generated interface state is distributed near the middle of the energy gap of silicon. The dominant electron capture cross sections are approximately for both (100) and (111) capacitors.

Space-charge generation properties of gold in MOS structures

The generation lifetime, capture cross section, and thermal emission rates for the gold acceptor level in bulk silicon have been studied using MOS techniques. The experimental methods used were the pulsed high-frequency capacitance-time and nonequilibrium linear-voltage-ramp techiniques at various temperatures. By correlating the results of the above measurements, the capture cross section σ and trap energy Et of the gold acceptor state were determined as a function of temperature in the range 235–265 °K. It was observed that σ increases with increasing temperature and has a value of the order of 1.0×10−15 cm2. On the other hand, the trap energy Et was found to decrease with increasing temperature, suggesting that it varies in unison with the silicon energy gap. Finally, from the above results the thermal emission rates en and ep were determined, with the assumption that the degeneracy factor and gA=1. For the temperature range investigated, the ratio en/ep varied from 30 at 235 °K to 20 at 265 °K.

The energy levels and the defect signature of sulfur-implanted silicon by thermally stimulated measurements

Two energy levels of sulfur in the upper half of the energy gap of silicon were obtained by isothermal transient capacitance and thermally stimulated current measurements on samples prepared by sulfur implantation and high-temperature annealing. The measured energy levels are in good agreement with two levels for sulfur introduced by a closed-tube diffusion but disagree with one of two levels measured for implanted sulfur after low-temperature annealing.

Existence of an isotope shift for the sulfur deep level in silicon

The deep energy level of the isotope 34S in the upper half of the energy gap of silicon is examined by isothermal transient capacitance measurements on ion-implantation-predeposited diode structures. The resulting energy level at Ec−0.512 eV is found to be 0.014 eV closer to the conduction band edge than the corresponding deep level for the isotope 32S in similarly prepared samples. The existence of an isotope shift for the deep sulfur level is interpreted as implying vibronic coupling between the electronic states of the sulfur center and the silicon lattice.

Temperature effects in Schottky-barrier solar cells

It has been reported recently that the short-circuit current Isc of silicon Schottky-barrier solar cell increases with increasing operating temperature. The increase in Isc has been attributed to the availability of extra photons, belonging to the long-wavelength range of the solar spectrum, due to the lowering of the forbidden energy gap of silicon with increasing temperature. The purpose of the present letter is to show that the contribution to the increase of Isc due to the mechanism mentioned above is negligible and cannot explain the experimental results. Instead, it has been found that good agreement with experimental results is obtained when the increase in Isc with increasing temperature is calculated by taking the change of the absorption coefficient of the semiconductor with temperature at all wavelengths.

Characteristics of a water absorber in front of a silicon solar cell

In a system for converting sunlight to both electric power and heat, a selective absorber between the sun and a semiconductor solar cell may provide a substantial thermal output without seriously reducing the electrical output. Calculations for water in front of a typical silicon solar cell show, for example, that a water layer 1 cm thick absorbs 16.3% of the incident energy (chiefly photons having energies below the energy gap of silicon) while reducing the electric power output only slightly, from 13.8 to 13.1%. Experimental results confirm this finding.

Dependence of the indirect energy gap of silicon on hydrostatic pressure

A diamond anvil optical cell is employed to measure the pressure dependence of the fundamental indirect Γ- X transition of crystalline Si. The result is E (eV) = (1.110 ± 0.002) − (1.41 ± 0.06) × 10 −3P where the pressure P is in kbar. Between 115 and 126 a transformation takes place to a phase opaque to electromagnetic radiation of wavelength between 0.3 and 2.0 μm. We believe this is the same phase transition reported by Minomura and Drickamer. A pseudopotential calculation assuming a relatively soft core is carried out and its results are in rather good agreement with experiment.

The influence of temperature on spreading resistance measurement

The resistance of the contact used in spreading resistance measurements on silicon has been measured as a function of temperature. The results can be described by assuming a potential barrier in series with the true spreading resistance and it is shown that thermal emission over this barrier and (at low resistivities) tunnelling through the barrier influence significantly the contact resistance. The observed relationship between contact resistance and resistivity is explained by this model when the pressure effect on the silicon energy gap is taken into account.

Contact Properties of Metal-Silicon Schottky Barriers

Barrier heights of Schottky diodes prepared by vacuum depositions of metals onto chemically etched silicon surfaces were investigated by measuring the current-voltage and capacitance-voltage characteristics. The barrier height varied remarkably with the work function of metal and the sum of the barrier heights measured on n-type and p-type silicon was nearly equal to the energy gap of silicon. The results were well explained by applying the theory of Cowley and Sze, leading to the conclusion that the Fermi level is not always pinned at the semiconductor surface.

Radiative Spectra from Shallow Donor-Acceptor Electron Transfer in Silicon

Radiation associated with shallow donor-acceptor electron transfer in silicon has been examined in the liquid-helium temperature region for various combinations of group-V donors and group-III acceptors. The spectra for all impurities are quite similar, exhibiting TA- and TO-phonon---assisted lines, as well as a no-phonon line in all but the (Sb,B)-doped sample. A (P,In) sample exhibits an unusual extra line which is attributed to an LA-phonon---assisted transition. A theory analogous to that of Thomas, Hopfield, and Augustyniak, modified to take account of anisotropic donor wave functions, is used to analyze the line shapes and determine rate constants and the impurity-pair Coulomb energy for pairs that decay at different times after impurity neutralization. This leads to a direct measurement of the indirect silicon energy gap of 1.166\ifmmode\pm\else\textpm\fi{}0.0010 eV and an exciton binding energy of 0.0102\ifmmode\pm\else\textpm\fi{}0.0015 eV, when combined with infrared-absorption measurements near the indirect gap. The analysis also indicates that optically determined impurity ionization energies are correct, and that the thermally determined impurity activation energies and their concentration dependence probably result from carrier redistribution effects rather than modification of the impurity ionization energies of the majority of the impurities.

Stability and surface charge in the MOS system†

Results are presented which show that the surface charge and the stability of the MOS system are not directly related. The centres responsible for the surface charge are located close to the silicon surface and their density is independent of the silicon resistivity, the slice pre-oxidation treatment, the silicon surface potential over a wide range of the silicon energy gap and the oxide growth rate. The surface charge is, however, a function of the oxide thickness and the time and temperature of post oxidation annealing in nitrogen.

Effect of uniaxial stress on silicon and germanium

Values for the pressure dependence of the energy gap of germanium and silicon are derived from measurements on p-n junctions under localised stress along main crystallographic directions. The results are compared with values obtained from the deformation potential theory.

Surface States on Silicon and Germanium Surfaces

Interface states are found in the upper half of the energy gap of silicon and germanium. On weakly oxidized surfaces, they lie 0.42 and 0.13 ev above the intrinsic position of the gap with approximate densities ${10}^{11}$ to ${10}^{12}$ and ${10}^{10}$ to ${10}^{11}$ for silicon and germanium, respectively. On well-oxidized surfaces, interface states are found approximately 0.44 to 0.48 ev and 0.18 ev above the intrinsic position of the gap with densities of around ${10}^{12}$ and ${10}^{11}$ to ${10}^{12}$ for silicon and germanium, respectively. At large bias voltages, high electric fields exist in the oxide film. Changes in the structure of the interface states in the upper half of the gap of silicon are found. A model is given which can account for the experimental observation.

Properties of silicon power rectifiers

THE STATIC electrical properties of small-area silicon P-N junction rectifiers prepared by the alloy fusion process have been described by Pearson and Sawyer1 in 1952. Since that time rectifiers of the same type and having about the same P-N junction area (in the order of 0.0005 to 0.001 square centimeter (cm)) have become commercially available. The development of these rectifiers confirms theoretical expectations as to the superior electrical properties of silicon over germanium for semiconductor devices. These superior properties, which include extremely low reverse currents, high rectification ratios, and the ability to operate successfully at high ambient temperatures, are attributed to the wider energy gap in silicon (1.15 electron volts) as compared to germanium (0.75 electron volt).