Discharge Current Transient Spectroscopy Research Articles

A high-precision current measurement platform applied for statistical measurement of discharge current transient spectroscopy of traps in SiN dielectrics

This paper presents a current measurement platform to measure current across dielectrics with a high-precision of 10−17 A from a large number of small capacitors at high speed. The developed platform consists of a common readout circuit part and a dielectric part formed on the circuit part by a simple process. A platform chip with 10 μm pitch 384H × 360V cells was fabricated using a 0.18 μm CMOS technology and silicon nitride (SiN) films were formed by plasma-enhanced CVD (PECVD) as a measurement target. The trap property of SiN films in metal–insulator–metal (MIM) capacitors was statistically measured by discharge current transient spectroscopy (DCTS) using the developed platform. The measured average energy levels of traps (E c –E t ) were 0.21–0.25 eV, which is in good agreement with that of the discrete samples. The distributions of energy levels and densities of traps measured with different film thicknesses and areas are also presented and discussed.

Evaluation of electron traps in SiNx by discharge current transient spectroscopy: verification of validity by comparing with conventional DLTS

Discharge current transient spectroscopy (DCTS) is a promising technique for detecting the trap level and density in dielectrics because it is based on a simple emission process. In order to confirm the validity of DCTS, we compare the results from the conventional deep-level transient spectroscopy (DLTS) technique for samples of CVD-grown silicon nitride (SiNx) films. Results indicated that a trap level, about 0.6 eV below the energy level of the conduction band edge in the SiNx thin films estimated by DCTS is in good agreement with that obtained from DLTS analysis, and it is found that the trap density increases with the decreasing N/Si ratio in the SiNx film. As a proposed estimation for energy level in defects, it will be originated from hydrogen-incorporated defects in the SiNx matrix. This study demonstrates that the DCTS method will be a useful electrical method for the evaluation of defects.

Effects of Sacrifice Oxidation on Characterization of Defects in High-Purity Semi-Insulating 4H-SiC by Discharge Current Transient Spectroscopy

To determine the energy levels of intrinsic defects in high-purity semi-insulating 4H-SiC, we apply discharge current transient spectroscopy (DCTS) that is a graphical peak analysis method based on the transient reverse current of a Schottky barrier diode, because transient capacitance methods such as deep level transient spectroscopy and isothermal capacitance transient spectroscopy are feasible only in low-resistivity semiconductors. The reverse current consists the reverse current through the balk and the surface leakage current of the diode. It is elucidated that the sacrifice oxidation could dramatically reduce the surface currents of diodes in the case of high-purity semi-insulating 4H-SiC, suggesting that the densities and emission rates of traps in the bulk of the SiC can be determined from the transient reverse current.

Effect of Intrinsic Defects in High-Purity Semi-Insulating 4H-SiC on Reverse Current–Voltage Characteristics of Schottky Barrier Diodes

Schottky barrier diodes are fabricated using high-purity semi-insulating 4H-SiC. Under certain measurement conditions, the reverse current–voltage (IR–V) characteristics of the diodes exhibit a peak, with the diodes appearing to behave as negative resistance diodes. To investigate the effect of intrinsic defects in the 4H-SiC on the IR–V characteristics, the transient reverse currents of the diodes are measured. Without any assumptions regarding defects, a graphical peak analysis method, discharge current transient spectroscopy (DCTS), which uses the isothermal transient reverse current, can determine the densities and emission rates of defects. From simulation of the IR–V characteristics using the densities and emission rates of intrinsic defects determined by DCTS, the effect of the intrinsic defects in high-purity semi-insulating 4H-SiC on the IR–V characteristics of its Schottky barrier diodes is elucidated. It is found that DCTS is suitable for determining the densities and emission rates of electrically active defects in semi-insulating semiconductors.

Determination of Intrinsic Defects in High-Purity Semi-Insulating 4H-SiC by Discharge Current Transient Spectroscopy

To determine the energy levels of intrinsic defects in high-purity semi-insulating 4H-SiC, we apply discharge current transient spectroscopy (DCTS) that is a graphical peak analysis method based on the transient reverse current of a Schottky barrier diode, because transient capacitance methods such as deep level transient spectroscopy and isothermal capacitance transient spectroscopy are feasible only in low-resistivity semiconductors. Seven intrinsic defects are detected in the high-purity semi-insulating 4H-SiC. From the temperature dependence of the emission rate of each intrinsic defect, its activation energy is approximately determined.

Characterization of Traps in Semi-Insulating 4H-SiC by Discharge Current Transient Spectroscopy

In order to characterize traps in semi-insulating 4H-SiC that is regarded as an attractive semiconductor for X-ray detectors, we apply discharge current transient spectroscopy (DCTS) that is a graphical peak analysis method based on the transient reverse current of a diode. We have found at least three types of traps whose emission rates at 373 K are 4.9×10-3, 8.3×10-3 and 8.0×10-2 s-1. Since it is difficult to characterize traps in semi-insulating semiconductors by transient capacitance methods, it is demonstrated that DCTS is a powerful method for determining the densities and emission rates of traps in semi-insulating semiconductors.

Characterization of deep centers in semi-insulating SiC and HgI2: Application of discharge current transient spectroscopy

In order to characterize traps in semi-insulating 4H-SiC and HgI2 regarded as an attractive semiconductor for X-ray detectors, we apply discharge current transient spectroscopy (DCTS), which is a graphical peak analysis method based on the transient reverse current of a diode. In high-purity semi-insulating 4H-SiC whose diode may detect X-rays or γ-rays, DCTS can detect two types of trap species, and can determine those densities and emission rates. The emission rates of detected traps are close to each other, suggesting that thermally stimulated current (TSC) may not distinguish between these two types of traps. In semi-insulating HgI2, the densities and emission rates of two types of trap species are also determined by DCTS. Therefore, it is demonstrated that DCTS is a powerful method for determining the densities and emission rates of traps in semi-insulating semiconductors

Analysis of Carrier Traps in Silicon Nitride Film with Discharge Current Transient Spectroscopy, Photoluminescence, and Electron Spin Resonance

Electrical characteristics and an origin of traps in silicon nitride film were investigated using discharge current transient spectroscopy (DCTS), electron spin resonance (ESR), and photoluminescence (PL). It was found from DCTS that the density of traps of 1.1 eV from the conduction band edge increased with the increase of the gas-mixture ratio of SiH2Cl2 over NH3 for the fabrication of silicon nitride film. The energy levels of traps in silicon nitride film of 0.25, 0.68, 0.83–0.91, and 1.25–1.3 eV from the conduction band edge were found from photoluminescence observation. The ESR signals of the K-center that indicated a silicon dangling-bond increased with the increase of the gas-mixture ratio of SiH2Cl2 over NH3. It is suggested that the origin of traps of 1.1 eV from the conduction band in silicon nitride film is the silicon dangling-bond.

Graphical peak analysis method for determining densities and emission rates of traps in dielectric film from transient discharge current

The purpose of this study is to propose and test the graphical peak analysis method [discharge current transient spectroscopy (DCTS)] for determining the densities and emission rates of traps in a dielectric thin film from the transient discharge current Idis(t) in a capacitor at a constant temperature, different from thermally stimulated current (TSC). It is theoretically demonstrated that DCTS can distinguish among traps with close emission rates. Experimentally, the densities and emission rates of five traps in Pb(Zr, Ti)O3 thin films are determined using DCTS. Here, these five emission rates are between 1×10−3 s−1 and 7×10−2 s−1. One kind of trap, which was determined by TSC under the assumption of one emission rate, is found to be distinguished into five kinds of traps with close emission rates by DCTS.

Difference between Traps Determined from Transient Capacitance and Transient Reverse Current

The densities and energy levels of traps in silicon pin diodes are determined using the transient capacitance method (ICTS: isothermal capacitance transient spectroscopy) as well as the transient reverse current method (DCTS: discharge current transient spectroscopy). The traps determined by ICTS are located in the i layer (i.e., the n- region) and affect the steady-state reverse current (i.e., a generation current). Conversely, the traps determined by DCTS are probably located at the surface of the substrate.

Investigation of Transient Reverse Currents in X-Ray Detector Pin Diodes by Discharge Current Transient Spectroscopy

Transient reverse currents flow in X-ray detector diodes when a high reverse bias (operating voltage) is suddenly applied from 0 V, which leads to problems in the X-ray measurements. Discharge current transient spectroscopy (DCTS) was applied to determine the densities, energy levels and capture cross sections of traps related to the transient reverse currents in the diodes. DCTS analysis revealed one type of trap with EC-0.54 eV in our silicon pin diodes, where EC is the energy level at the bottom of the conduction band.

Evaluating Polarization in Dielectrics with Continuously Distributed Dipole Relaxation Time by Discharge Current Transient Spectroscopy

The application of discharge current transient spectroscopy (DCTS) to the evaluation of the steady-state polarization P s(τ) in dielectrics with continuously distributed dipole relaxation time (τ) is discussed. The method proposed in Jpn. J. Appl. Phys. 35 (1996) 2216 can be used to evaluate P s(τ) only in dielectrics with discrete τ. Using the method discussed here, P s(τ) corresponding to the transient discharge current, which obeys a power law with respect to discharge time, can easily be evaluated.

A Simple Graphical Method for Evaluating Dipole Relaxation Time in Dielectric

A simple graphical method for evaluating the dipole relaxation times (τ) in a dielectric is proposed. From isothermal measurements of the transient discharge current due to dipole relaxation, τ can be obtained graphically by means of discharge current transient spectroscopy (DCTS). In other words, the time at which the DCTS signal is a maximum corresponds to τ. Since τ and the steady-state polarization (P s) in dielectrics at electric field (F p) and temperature (T) can be obtained using DCTS, the dependencies of τ and P s on F p or T can be investigated in detail.