Detailed study about influence of oxygen on trap properties in SiOxNy by the thermally stimulated current and maximum entropy method

The trap amount depending on trap energy levels [N_t(E_t)] in various silicon oxynitride films were investigated. Using the thermally stimulated current and the maximum entropy method, we determined N_t(E_t) with very high energy resolution. In N_t(E_t), many E_t were observed between 1.2 and 1.6 eV. Interestingly, their amounts significantly depended on the film compositions. The influence of oxygen on N_t(E_t) is also discussed.     

The linear stage of evolution of electron-hole avalanches in semiconductors

A complete analytical solution of the problem of the linear stage of evolution of electron-hole avalanches in the uniform time-independent electric field E _ext is derived. The theory accounts for the drift, diffusion, and impact ionization of electrons and holes, thus providing a means for calculating the space-time distributions of fields and charges as well as all the basic parameters of the avalanches up to the onset of nonlinear effects at the time t _a . Formulas for the group velocity of the avalanches and for the velocity of its leading fronts are derived. It is shown that the time t _a must be determined from the condition that the impact ionization coefficient α in the center of the avalanche be reduced by a specified small quantity η. A transcendent equation is derived, which allows the calculation of the time t _a as a function of the quantity η, the unperturbed coefficient α(E _ext), and other parameters of the semiconductor. It is found that, when α(E _ext) is increased by two orders of magnitude, the total number of electron-hole pairs generated up to the point t _a decreases by nearly three orders of magnitude.     

A Theoretical Model for the HgCdTe Electron Avalanche Photodiode

A ballistic model is presented for electron avalanche multiplication in the conduction band of HgCdTe, based upon the concept of an optical phonon limited mean free path for the electron, λ _e. The model predicts avalanche gain as a function of applied bias voltage V, and a threshold voltage for impact ionization V _th. Impact ionization probabilities are calculated analytically using a simplified band structure model for HgCdTe and used to estimate values for the threshold energy for impact ionization. A simple ballistic model is developed to correlate the relationship between electron energy and applied bias voltage, based upon the relevant electron scattering mechanisms in HgCdTe. A comparison with published gain–voltage data suggests that the process is limited by optical phonon scattering, and the relationship between electron energy and applied bias voltage, for a uniform electric field F = V/W, across a diode depletion width W, is given by E = α(E)V, where α(E) = [λ _e(E)/W]. For high electron energies λ _e(E) is independent of E and α(E) depends only on the dielectric parameters of the material. Using this simple model it is easy to predict electron avalanche gain versus voltage for any parametric combination of diode geometry, bandgap, and operating temperature.     

Study of the electrical properties of Cd<Subscript>x</Subscript>Hg<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Te

On the basis of the temperature and field dependences of the Hall coefficient R _H , it was found that samples with a low electron density are, as a rule, compensated, and the degree of compensation changes upon thermal conversion of the conductivity of the sample to p type. For n-Cd_xHg_1?xTe, the ionization energy of the donor level was found from the temperature dependences of resistivity ρ(T): E _d =24–32 meV. For the same samples, after their thermal conversion to p type, the ionization energies of acceptors, which are related to doubly charged vacancies V _Hg ⁺⁺ , were determined: E _a =32 and 48 meV. In addition, a deep level E _t , related to an unknown amphoteric impurity, was found (E _t ?E _v ≈0.7E _g ).     

Characteristic properties of macroporous silicon sintering in an argon atmosphere

The temperature and time dependences of the sintering of macroporous silicon in Ar or Ar + 3% H₂ are studied. The contribution of various mechanisms governing this process is determined. The specific features of the sintering of macroporous silicon are examined by means of isochronous and isothermal annealing of the samples with ordered and random macropores in the temperature range 1000–1225°C. It is found that the sintering of macroporous silicon under atmospheric pressure in an inert gas flow containing 2 × 10–4% O₂ is greatly affected by thermal etching. Thermal etching competes with the substance-transfer processes characteristic of sintering and hinders the formation of a defect-free surface crust. The reason for etching consists in that gaseous silicon monoxide is generated and then carried away by the gas flow. The etching effect is dominant in the low-temperature range and is independent of whether H₂ is added. The values obtained for the activation energy of the silicon diffusion coefficient, E _a = 2.57 eV, and for the exponent n = 3.31–3.74 in the time dependence of the pore radius, r ~ t ^1/n are indicative of a mixed substance-transfer mechanism via the surface and volume diffusion of silicon atoms.     

Small-signal response of bulk traps in MNOS devices

The small-signal response of bulk traps in MNOS devices is presented. Excellent correlation is obtained between theory (previous paper) and experiment for the trap conductance as a function of temperature and frequency, from which the trap density (N_t), trap energy (E_t) and trap cross-section (σ) are obtained for generating trap centres.     

Participation of the electron subsystem of a crystal in the reactions of defect-complex decomposition in semiconductors

The reactions of defect-complex decomposition in semiconductors are considered. The contribution from the electron subsystem to the reaction rate is taken into account by adding a change in the electron-subsystem energy of a crystal (as a result the reaction) to the energy barrier of the reaction. The theoretical and experimental data are compared by the example of the reactions of E-center decomposition in the n-type phosphorus-doped silicon. The dependence of temperature of isochronous annealing of E centers on a donor-impurity concentration is explained. The first stage of annealing (T _ann≈400 K) in a low-resistivity silicon is caused by the decomposition of the E center and can be explained using the model of a vacancy as the double acceptor center with a negative correlation energy and values of vacancy charge-exchange levels E _V (0/-)=E _c -0.99 eV, E _V (-/—)=E _c =?0.39 eV. From the comparison between calculated and experimental data, the dissociation energy of E center and the degeneracy factor are obtained to be U _a0≈0.96 eV and $g_E^ - /g_E^0 = 1/16$ , respectively.     

Electrically active centers formed in silicon during the high-temperature diffusion of boron and aluminum

The parameters of electrically active centers formed during the high-temperature diffusion of boron and aluminum into silicon in various media are studied by the Hall method and capacitance spectroscopy. It is found that the variation in the resistivity of the n base of the structures with p-n junctions fabricated in the study is controlled by the formation of three donor levels Q1, E4, and Q3 with the energies E _c - 0.31, E _c - 0.27, and E _c - 0.16 eV. Diffusion in a chlorine-containing atmosphere introduces only a single level E4, but its concentration is 2.5 times lower, compared with diffusion in air. The values of the ionization energy of the Q3 level, measured under equilibrium (Hall effect) and nonequilibrium (capacitance spectroscopy) conditions, almost coincide. The deepest level E1 with an energy of E _c - 0.54 eV, formed upon diffusion in both media, has no effect on the resistivity in the n base of the structures.     

Electrical and thermoelectric properties of ZnO under atmospheric and hydrostatic pressure

Temperature (for T = 77–400 K) and pressure (for P ≤ 8 GPa) dependences of conductivity σ(T,P). Hall coefficient R _H(T, P), and Seebeck coefficient Q(T) were studied in single-crystal n-ZnO samples with the impurity concentration N _i = 10¹⁷ ? 10¹⁸ cm^?3 and free-electron concentration n = 10¹³?10¹⁷ cm^?3. Single crystals were grown by the hydrothermal method. Dependence of the ionization energy of a shallow donor level on the impurity concentration E _d1(N _d) is determined, along with the pressure coefficients for the ionization energy ?E _d1/?P and static dielectric constant ?x/?P. A deep defect level with the energy E _d2 = 0.3 eV below the bottom of the conduction band is found. The electron effective mass is calculated from the obtained data on the kinetic coefficients R _H(T) and Q(T).     

The small signal admittance of carbon implanted p-n diodes

In this paper we consider, in detail, how the introduction of radiation damage centres, produced by the implanation of carbon ions, affects the small signal admittance of silicon p-n diodes. Thermally stimulated capacitance measurements are used to obtain the charge states and activation energies of the damage centres. For carbon doses between 1 × 10¹¹ cm^?2 and 1 × 10¹² cm^?2 two trapping levels are observed with activation energies of E_t?E_v=0·31 eV and E_c?E_t=0·37 eV, and for doses between 5 × 10¹² cm^?2 and 5 × 10¹³ cm^?2 an extra level appears with an energy of E_c?E_t=0·25 eV. A study is made of the effects of these damage centres on the small signal capacitance and conductance of the diodes under forward bias. The results are interpreted in terms of a conductivity modulation effect, and it is proposed that this technique yields valuable information on the profile of the damage centres.     

Decrease in the binding energy of donors in heavily doped GaN:Si layers

The properties of Si-doped GaN layers grown by molecular-beam epitaxy from ammonia are studied by photoluminescence spectroscopy. It is shown that the low-temperature photoluminescence is due to the recombination of excitons bound to donors at Si-atom concentrations below 10¹⁹ cm^?3. At a Si-atom concentration of 1.6 × 10¹⁹ cm^?3, the band of free excitons is dominant in the photoluminescence spectrum; in more heavily doped layers, the interband recombination band is dominant. A reduction in the binding energy of exciton-donor complexes with increasing doping level is observed. With the use of Haynes rule, whereby the binding energy of the complex in GaN is 0.2 of the donor ionization energy E _D , it is shown that E _D decreases with increasing Si concentration. This effect is described by the dependence {ie1134-1}, where E _D ^otp is the ionization energy of an individual Si atom in GaN. The coefficient that describes a decrease in the depth of the impurity-band edge with increasing Si concentration is found to be α = 8.4 × 10^?6 meV cm^?1.     

Evaluation of the effective threshold energy of the Interband impact ionization in a deep-submicron silicon n-channel MOS transistor

Using the ensemble Monte Carlo method allowing for the main features of charge-carrier transport in conditions of strong electric fields, a deep-submicron silicon n-channel MOS transistor with a channel length of 50 nm is simulated. In the Keldysh impact ionization model with a soft threshold in a channel of the simulated transistor, the effective threshold energy of this process is calculated.     

Electron trap behaviour in Te-doped GaAs0.6P0.4

An electron trap spectrum has been obtained in Te-doped GaAsP by DLTs and transient capacitance measurements. The two traps identified display non-exponential emission and capture characteristics, the capture rate depending on temperature. The dominant trap A has an activation energy, E_a = 0.20 ± 0.02 eV and a constant concentration in the epilayer of typically 0.1N_d, trap B has an activation energy, E_a = 0.4 eV.The defect is donor related and characterised by non-radiative capture and lattice-relaxation multiphonon emission. Photocapacitance measurements provide the electron photoionization cross-section of the centre, and in agreement, a phonon broadened lineshape theory gave a threshold of 0.62 eV supporting the large lattice relaxation model. Evidence for persistent photoconductivity is also presented.     

Special features of radiation-defect annealing in silicon <Emphasis Type="Italic">p-n</Emphasis> structures: The role of Fe impurity atoms

Deep-level transient spectroscopy is used to study the formation of complexes that consist of a radiation defect and a residual impurity atom in silicon. It is established that heat treatment of the diffused Si p⁺-n junctions irradiated with fast electrons lead to the activation of a residual Fe impurity and the formation of the FeVO (E_0.36 trap) and FeV₂ (H_0.18 trap) complexes. The formation of these traps is accompanied by the early (100–175°C) stage of annealing of the main vacancy-related radiation defects: the A centers (VO) and divacancies (V₂). The observed complexes are electrically active and introduce new electron (E_0.36: E _t ^e =E _c -0.365 eV, σ _n =6.8×10^?15 cm²) and hole (H_0.18: E _t ^h =E _v +0.184 eV, σ _p =3.0×10^?15 cm²) levels into the silicon band gap and have a high thermal stability. It is believed that the complex FeVO corresponds to the previously observed and unidentified defects that have an ionization energy of E _t ^e =E _c ?(0.34–0.37) eV and appear as a result of heat treatment of irradiated diffused Si p⁺-n junctions.     

Methodology for predicting off-state reliability in GaN power transistors

Results of a lifetest across temperature and drain voltage on off-state high power GaN FET test structures are presented. The times to failure (t_f) are fitted to a combination of the Arrhenius model (ln(t_f) ∼ inverse temperature) and the linear field model (ln(t_f) ∼ drain voltage). The estimated activation energy (E_a) is 2.1 eV and the estimated linear field parameter (γ) is 0.03 V⁻¹. Reliability parameters estimated from the test structure data are used to predict the FIT rate for a product level FET using linear scaling of the gate width. Further, the effect of a burn-in and a transient voltage under a duty cycle on the FIT rate are modeled. The FIT rate of the product level FET is larger than that of the test structure. The burn-in and transient voltage similarly reduce the reliability. Contour plots are given that allow trade-offs between these factors in order to meet reliability requirements.     

Ionization energy of copper in Hg0.8Cd0.2Te crystals under conditions of light and intermediate doping

Resistivity and the Hall effect were studied in copper-doped p-Hg _0.8 Cd _0.2 Te crystals in the temperature range of 4.2–125 K and the range of Cu concentrations from 2.6×10¹⁵ to 2×10¹⁸ cm^?3. It is shown that the conventional method for determining the ionization energy of impurities from the slope of the dependence R _H (T) is inapplicable in this case. In order to obtain the correct results, it is necessary to take into account the structure of the impurity band and the screening of the impurity charge with free charge carriers. A simplified model of the impurity band is suggested; this model makes it possible to calculate the ionization energy of acceptors under conditions of light doping and a small degree of compensation. This approach is used to find that ionization energy of copper depends only slightly on the copper concentration at T=0 and is equal to E _A =7.6 meV for an isolated acceptor, which coincides with the theoretical value. At finite temperatures, the ionization energy of acceptors decreases appreciably as a result of screening.     

A study of deep traps at the SiO2/6H-SiC interface relying upon the nonequilibrium field effect

The nonequilibrium field effect associated with deep surface states at the SiO₂/6H-SiC interface has been observed and studied in a 6H-SiC MOSFET of depletion-accumulation type. An analysis of the relaxation of channel conductance at elevated temperatures upon filling of the surface traps with nonequilibrium carriers has shown that the energy distribution of the surface traps has the form of a narrow Gaussian peak in the upper half of the 6H-SiC band gap, with a peak energy E _C ?E _tm = 1.19eV, peak width ΔE _t ≈85 meV, and electron capture cross section σ_n≈10^?14 cm². These surface states are believed to have the fundamental nature of “oxidation defects” similar to P _b centers in the SiO₂-Si system (of dangling silicon bonds).     

Noise due to donors in n-channel silicon JFETs

We have measured the noise due to donors in n-channel silicon JFETs at temperatures near liquid nitrogen temperature. The noise showed an activation energy of about 1.3E₀, where E₀ is the activation energy of the donor centers. This is compatible with theory.     

Investigation of the transition from tunneling to impact ionization multiplication in silicon p-n junctions

White noise spectra of diodes breaking down between 1·5 and 5 V have been used to investigate the details of the transition from tunneling to avalanche breakdown in silicon p-n junctions. It is found that the transition and carrier multiplication in these junctions is dominated by the influence of the threshold energies for ionization. Because this influence is not explicitly taken into account in the existing theories of carrier multiplication and noise, they are not applicable to low breakdown voltage diodes. Consequently, a multiplication onset model and alternate schemes for calculating the DC multiplication and noise in low breakdown voltage diodes are developed.Analysis of the noise data indicates that the threshold energies for ionization depend slightly on junction widths and, for the diodes employed in this study, range between 1·66–1·9 eV for electrons and 1·79–2·04 eV for holes. The minimum distance between ionizing collisions is found to range from 190 to 240 A for electrons and 200 to 250 A for holes.Application of the threshold energies for ionization to the multiplication onset model permits evaluation of the doping densities on both sides of the step junctions. From it, it is determined that the solubility of aluminum in silicon is N_A = 9·5 ± 0·5 × 10¹⁸ cm^?3.