For materials of varying band gap, we compare energy levels of atomically localized defects calculated within a semilocal and a hybrid density-functional scheme. Since the latter scheme partially relieves the band gap problem, our study describes how calculated defect levels shift when the band gap approaches the experimental value. When suitably aligned, defect levels obtained from total-energy differences correspond closely, showing average shifts of at most 0.2 eV irrespective of band gap. Systematic deviations from ideal alignment increase with the extent of the defect wave function. A guideline for comparing calculated and experimental defect levels is provided.

Defect energy levels in density functional calculations: alignment and band gap problem.

Abstract The electron thermal emission and capture rates and the electron impact ionization rate of trapped electrons at the sulfur donor centers in the depletion region of reverse biased silicon p-n junctions have been measured by the dark capacitance and current transient methods. Least square fits of the low field data give the following electron thermal emission rates: en0t = 1.64 × 1010(T/300°K)2exp [−276/kT] sec for the neutral center and en−1t = 1.03 × 1012 (T/300°K)2 exp [−528/kT] sec for the singly ionized center where kT is in meV. The thermal activation energies are then 276 and 528 meV respectively. The hole emission rates are much smaller and not determined. The electric field dependences of the thermal emission rates of electrons are considerably smaller than that predicted by the Poole-Frenkel theory applied to the ground state: en0t increased by 1.5 at 130°K from 0.2 to 1.0 × 105 V/cm and en−1t by 3 at 200°K. Electron capture coefficients are obtained from capacitance transient during steady state electron injection into the junction depletion layer either by transistor emitter or by optical generation at the surface next to the junction. The electron capture rate at the doubly charged center, cn−2t, decreases from 5 × 10−7 cm3/sec at 3 × 104 V/cm to 10−7 cm3/sec at 1.0 × 105 V/cm with essentially no temperature dependence. The electron capture rate at the singly ionized centers, cn−1t, obtained at 82°K was about two orders of magnitude smaller than cn−2t but had essentially the same electric field dependence. The electron impact ionization rate of trapped electrons at the neutral centers and its electric field dependences were also determined at 82°K.

Emission and Capture of Electrons at Sulfur Centers in Silicon.

Computer simulations of small filling pulse deep level transient spectroscopy (DLTS) measurements of Si/SiO2 interface states in metal‐oxide semiconductor (MOS) capacitors, demonstrate that the time dependence of the surface potential during emission and capture of charge carriers must be considered for a correct interpretation of DLTS data. It is demonstrated that not only the amplitude but also the shape of DLTS spectra are influenced by the interface state density Nit. Accurate values of Nit and capture cross sections are obtained for exponential as well as nonexponential emission of charge carriers by fitting simulated to experimental data. This solves the problem of nonexponential transients due to a time dependent surface potential for high interface state densities. Measurements on irradiated MOS samples verify that numerical simulations can be used for accurate determination of interface state parameters. An observed discrepancy between the amplitudes of the measured and simulated DLTS signals is ...

Deep‐level transient spectroscopy: Increased accuracy of interpretation of silicon/silicon dioxide interface state data by the assistance of computer simulations

Vanadium‐doped silicon has been investigated using a photocapacitance method on n+‐p and p+‐n junctions. The photoionization cross‐section spectra showed two levels at 0.47 eV below the conduction band and 0.485 eV above the valence band, and the complementary optical transition threshold energies were 0.665 and 0.77 eV, respectively. For the Ec−0.47‐eV level, the electron photoionization cross section at the threshold energy depends significantly on temperature. This would be due to the photothermal ionization process via the excited states. For the Ev+0.485‐eV level, the sum of the threshold energies in electron and hole emission processes was greater than the band gap. This indicates that phonon broadening due to lattice relaxation occurs in the photoionization spectrum. According to the configuration coordinate model, the local phonon energy and the lattice relaxation energy are approximately 350 K and 0.13 eV, respectively.

Photoionization cross sections in vanadium-doped silicon

Structures, chemical properties, and chalcogen-dimer formation energies in silicon were investigated using quantum-chemical ab initio calculations by the Hartree-Fock method. The equilibrium geometrical configuration, electron-density distribution, and the parameters of the chemical bonding of lattice atoms were determined. Lattice relaxation around impurity defects is shown to contribute substantially to the total energy of a crystal. The chalcogen-dimer stability associated with a decrease in the total energy of a crystal, which accompanies its formation, was predicted. Estimates obtained for the dimer-formation energy agree well with available experimental data on their formation reactions. The geometrical configuration, and the electronic and chemical properties of impurity clusters involving up to six chalcogen atoms are discussed.

Chalcogen dimers in silicon

Deep impurity levels due to ion‐implanted tellurium in n–silicon are studied. Two donor levels at Ec−0.13 and Ec−0.56 eV are obtained using deep level transient spectroscopy. Thermal electron capture cross sections for both levels are too large to be measured. Electron photoionization cross section spectrum confirms the Ec−0.56 level and also reveals an excited state 0.45 eV above the ground state.

Deep levels related to ion‐implanted tellurium in silicon

A simple technique for the fabrication of Schottky-barrier diodes with near ideal characteristics is discussed. The fabrication employs a two mask process with an isotropic etching step to round off the corners of the metallurgical junction. A self-aligned MOS guard ring is also incorporated, the use of which is optional.

Etch-induced MOS guard-ring-protected schottky-barrier diodes

A DLTS technique for surface state capture cross-section measurement of MOS diodes

Some new observations on the phenomenon of photocapacitane on n-type silicon MOS structures under low intensities of illumination are reported. The difference between the illuminated and dark C---characteristics is automatically followed as a function of the applied bias thereby obtaining the differential photocapacitance and the resulting characteristics has been termed as the Low Intensity Differential Photocapacitance (LIDP). For an MOS capacitor, the LIDP characteristics is seen to go through a well defined maximum. The phenomenon has been investigated under different ambient conditions like light intensity, temperature, dependance of the frequency of the light etc. and it has been found that the phenomenon is due to a band excband excitation. In this connection, a novel sensitive technique for the measurement of the capacitance based upon following the frequency changes of a tank circuit is also described in some detail. It is also shown that the phenomenon can be understood by a simple theoretical model.

Low-intensity differential photocapacitance of MOS structures

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Deep levels related to ion‐implanted tellurium in silicon

Etch-induced MOS guard-ring-protected schottky-barrier diodes

A DLTS technique for surface state capture cross-section measurement of MOS diodes

Low-intensity differential photocapacitance of MOS structures