ICTS Measurements of Interface Properties in GaSb MOS Structure

We have investigated the electrical properties of Ru/Ni/n-GaN Schottky structure using current-voltage (I-V) and capacitance-voltage (C-V) measurements at room temperature. The barrier height (Fbo) and ideality factor (n) of Ru/Ni/n-GaN Schottky structure are found to be 0.66 eV and 1.44, respectively. The Fbo and the series resistance (RS) obtained from Cheung's method are compared with modified Norde's method, and it is seen that there is a good agreement with each other. The energy distribution of interface state density (NSS) is determined from the I-V measurements by taking into account the bias dependence of the effective barrier height. Further, the interface state density NSS as determined by Terman's method is found to be 2.14´10 12 cm -2 eV -1 for the Ru/Ni/n-GaN diode. Results show that the interface state density and series resistance has a significant effect on the electrical characteristics of studied diode.

The determination of the interface state density distribution of the Al/methyl red/p-Si Schottky barrier diode by using a capacitance method

Investigation of diode parameters using I– V and C– V characteristics of In/SiO 2/p-Si (MIS) Schottky diodes

Transparent gate structures were fabricated by electron beam evaporation of Sn-doped In2O3 on oxidized p-Si substrates. The samples were oxidized at 1100°C in dry oxygen. No post-oxidation or post-electrode-deposition annealig was carried out. Admittance-voltage-frequency measurements were made under optical illumination. Interface state density distributions and hole and electron capture cross-sections were obtained using the recently developed optical metal-oxide-semiconductor (MOS) admittance technique. The experimental interface state density profile contained two peaked distributions, one near the valence band-edge Ev, and the other near the conduction band-edge Ec, overlying a concave background. The peak near Ec was sharper and the peak density was higher than in the case of the peak near Ev. The capture cross-section vs band-gap energy profile also displayed a peaked distribution for interface states under each of the peaks. With increasing illumination, the state density at the peak increased, the peak energy location moved closer to the respective band-edge, and the capture cross-section decreased. The experimental results show the presence of defects at unpassivated Si-SiO2 interfaces, which exchange electrons/holes with silicon bands under illumination.

Determination of the density of Si-metal interface states and excess capacitance caused by them

A novel charge pumping technique is proposed for measuring the spatial distribution of interface state density N/sub it/ in MOSFETs. Instead of connecting the source and the drain together as is usually done, different reverse bias voltages are applied to the source and the drain separately. The method makes it possible to measure the distribution of N/sub it/ without making any assumptions about it. With this method, one can determine N/sub it/ distribution near the source and the drain of the channel independently. Results show that the interface state distribution of a virgin MOSFET is not constant along the channel. >

TiO2/CuO and TiO2/Cu2O solar cells are promising devices for photovoltaic applications. The power conversion efficiency of these cells, however, remains low. We used the SCAPS-1D program to perform simulations of n-TiO2/p-Cu2O and n-TiO2/p-CuO thin-film solar cells. The short circuit current and efficiency were 13.3 mA cm−2, 28.4 mA cm−2 and 13.7% 22.4%, respectively, Furthermore, we evaluated some specific parameters of n-TiO2/p-CuO heterostructure, such as the influence of temperature, interface state density, metal work function, electron and hole capture cross-section, shallow uniform donor density (ND) for TiO2 with constant uniform acceptor doping density (NA) in CuO and shallow uniform acceptor density (NA) for CuO with constant (ND) in TiO2. Our findings revealed that the efficiency of n-TiO2/p-CuO solar cells can be improved by increasing metal work function of the contact and by decreasing defects and the electron and hole capture cross-section.

Capacitance and conductance measurements are presented for dc-driven Au/ZnS:Mn/p-Si electroluminescence metal-insulator-semiconductor (MIS) devices, where the ZnS:Mn films are deposited by radio frequency sputtering. Stable dc operation is achieved by introducing oxygen into the film during deposition and subsequently annealing. The effect of the post-deposition annealing upon the density of states at the ZnS:Mn/p-Si interface is investigated. As deposited, the devices show unusual MIS C-V characteristics, that indicate a very high interface state density. Annealing at 700 °C, normal C-V characteristics are observed, indicating that the very high density of states is greatly reduced. For these films the conductance technique has been used to measure the density of states at the interface between the ZnS:Mn and p-Si. The statistical model is found to describe most accurately the interface state conductance response. The interface state density consists of a tail of states that varies between 3.7×1013 cm−2 eV−1 at the silicon Fermi level and 1.1×1013 cm−2 eV−1 at the silicon mid-gap. A small peak is superimposed upon this tail at (−0.16±0.01) eV below mid-gap. The tail of states is believed to be intrinsic to the ZnS:Mn/p-Si interface, but evidence suggests that the small peak is due to the presence of oxygen, which is shown by secondary-ion mass spectrometry analysis to accumulate at the interface after annealing at 700 °C. It seems likely that the very high density of interface states in as deposited devices is a consequence of a plasma damage to the silicon surface during growth, creating defects such as silicon dangling bonds. One possible explanation for the decrease in this density is that by annealing at 700 °C, oxygen in the bulk of the film diffuses to the interface, where it mops up these defects by forming compounds such as SiOx. A simpler model of interface recrystallization is also suggested. The doping density in the depletion region of the silicon is calculated as (7.5±0.5)×1014 cm−3, and the interface state capture cross section for holes is found to have mean value of approximately 10−15 cm−2.

The effect of Pt‐diffusion on the electrical properties in the Pt‐diffused MOS structure has been investigated. In these structures, the Pt‐diffusion ambient has a direct effect on the electrical properties;, the samples which were Pt‐diffused in oxygen ambient show a large positive flatband voltage shift, and those which were Pt‐diffused in nitrogen ambient show little flatband voltage shift but have a memory effect. We measured the dependence of flatband voltage on the oxide thickness and evaluated the distribution of the Si‐SiO2 interface state density. We also measured the oxide charge density. From these experimental results, we show that the large shift of the flatband voltage is caused mainly by the charges generated within the oxide film and that the Si‐SiO2 interface state density distribution varies reversibly according to the memory effect.

Differential isothermal capacitance transient spectroscopy (DICTS) and normalized isothermal capacitance transient spectroscopy (NICTS) were proposed to improve the resolution of the conventional isothermal capacitance transient spectroscopy (ICTS) which could characterize the deep levels in semiconductors isothermally. The resolution of the methods was studied for the closely spaced energy levels by the numerical simulation. Though the resolvable emission rate ratio R (R=λ2/λ1, where λ1 and λ2 are each thermal emission rate for two levels) of ICTS was around 5, R of DICTS was around 4. Moreover, R of NICTS reached 3.5 which is less than that of any other conventional methods. The error ratio of the estimation is almost the same as ICTS. The new method was applied to study the deep levels in a Si:Au system as an example and found two closely spaced energy levels explicitly.

An ICTS (Isothermal Capacitance Transient Spectroscopy) theory for a system of continuously-distributed gap states is given and experimental data by the ICTS applied to P-doped a-Si:H Schottky barrier diode are presented. It is shown that the ICTS is a useful tool for the study of gap states of a-Si:H whose material parameters are strongly temperature-dependent.

We propose and demonstrate that temperature-dependent curve-fitting error values of the Schottky diode I-V curve in the forward regime can be an auxiliary diagnostic signal as the temperature-scan Capacitance DLTS (CDLTS) signals and helps to work time-efficiently with high accuracy when using the Laplace Transform (LT)-DLTS or Isothermal Capacitance transient spectroscopy (ICTS) method. Using Be-doped GaAs showing overlapping DLTS signals, we verify that the LT-DLTS or ICTS analysis within a specific temperature range around the characteristic temperature Tpeak coincides well with the results of the CDLTS and Fourier Transform DLTS performed within the whole temperature range. In particular, we found that the LT-DLTS signals appeared intensively around Tpeak, and we confirmed it with the ICTS result. The occurrence of the curve fitting error signal is attributed to the relatively increased misfit error by the increased thermal emission from the deep-level trap in the case near the Tpeak, because the applied transport model excludes defect characteristics.

Photoconduction of natural cinnabar (α-HgS)

Current transport mechanism in Al/Si 3N 4/p-Si (MIS) Schottky barrier diodes at low temperatures

We demonstrate our new local deep level spectroscopy system improved for more accurate analysis of trap states at SiO2/4H-SiC interfaces. Full waveforms of the local capacitance transient with the amplitude of attofarads and the time scale of microseconds were obtained and quantitatively analyzed. The local energy distribution of interface state density in the energy range of EC − Eit = 0.31–0.38 eV was obtained. Two-dimensional mapping of the interface states showed inhomogeneous contrasts with the lateral spatial scale of several hundreds of nanometers, suggesting that the physical origin of the trap states at SiO2/SiC interfaces is likely to be microscopically clustered.