Graphical Peak Analysis Method Research Articles

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

A graphical peak analysis method for characterizing impurities in SiC, GaN and diamond from temperature-dependent majority-carrier concentration

A method for uniquely determining the densities and energy levels of impurities from the temperature dependence of the majority-carrier concentration in wide band gap semiconductors (e.g., SiC, GaN, and diamond) is discussed. It is demonstrated that the proposed graphical peak analysis method can evaluate the number of impurity species and can determine those densities and energy levels uniquely and accurately, while fitting a simulation to the experimental temperature-dependent majority-carrier concentration leads to less reliable densities and energy levels of impurities. In the case that the Fermi levels in p-type SiC, GaN and diamond are located between the acceptor level and the valence band maximum, the excited states of acceptors strongly affect the hole concentration. This indicates the distribution function including the influence of the excited states should be applied to determine the densities and energy levels of acceptors from the temperature-dependent hole concentration.

Accurate Determination of Acceptor Densities and Acceptor Levels in Undoped InGaSb from Temperature Dependence of Hole Concentration

Without any assumptions regarding residual impurity species and intrinsic defects in an undoped semiconductor, it is experimentally demonstrated that the densities and energy levels of impurities and defects can be precisely determined by a graphical peak analysis method based on Hall-effect measurements, referred to as free-carrier-concentration spectroscopy (FCCS). By FCCS, the number of acceptor species in p-type undoped In0.2Ga0.8Sb epilayers is determined, and the densities and energy levels of these acceptor species are accurately estimated. Two acceptor species, whose acceptor levels are EV+25 meV and EV+86 meV, are detected, where EV is the valence band maximum. The density of the EV+25 meV acceptor increases with Sb4/(In+Ga) flux beam equivalent pressure (BEP) ratio, whereas the density of the EV+86 meV acceptor decreases with increasing BEP ratio. These observations are not consistent with the conventional assumption that these acceptor species are VSb+ and VSb2+ in GaSb-based semiconductors, where VSb is the Sb vacancy.

Ionization of deep Te donor in Te-doped Al0.6Ga0.4Sb epilayers

The temperature dependence of the electron concentration n(T) for a Te-doped AlxGa1−xSb epilayer with x=0.2 or x=0.6 is obtained from Hall-effect measurements. The density ND and energy level ΔED of Te donors are determined by the graphical peak analysis method (i.e., free-carrier concentration spectroscopy) from the n(T). Since the donor level of Te is shallow in Al0.2Ga0.8Sb, the Fermi–Dirac distribution function, which does not include the influence of the excited states of the Te donors, can be applied to determining ND and ΔED. In Al0.6Ga0.4Sb, on the other hand, a proposed distribution function including this influence is elucidated to be necessary to the determination of ND and ΔED, because Te acts as a deep donor. Moreover, the excited states of the Te donors in Al0.6Ga0.4Sb are found to enhance the ionization efficiency of the Te donors at elevated temperatures.

Determination of densities and energy levels of donors in free-standing undoped 3C–SiC epilayers with thicknesses of 80μm

The densities and energy levels of donors in free-standing undoped 3C–SiC epilayers with the thicknesses of ∼80μm are investigated from the temperature dependence of the electron concentration n(T) obtained by Hall-effect measurements. Although in the analysis of n(T) many researchers usually assume that only one type of donor species is included in n-type 3C–SiC, no one knows whether this assumption is correct or not. In order to determine the densities and energy levels using n(T) without any assumptions regarding donor species, the graphical peak analysis method called free carrier concentration spectroscopy is applied. Three types of donor species are detected in these epilayers. These donor densities can be reduced to <5×1015cm−3 by growing 3C–SiC epilayers on undulant Si substrate. Moreover, the dependence of each donor level on a total donor density is investigated, which is used in 3C–SiC device simulation.

Parameters required to simulate electric characteristics of SiC devices for n-type 4H–SiC

In order to obtain some of the parameters required to simulate the electric characteristics of silicon carbide (SiC) power electronic devices in a wide temperature range from startup temperatures (⩽30°C) to steady-operation temperatures (⩾200°C), we discuss the dependence of the two donor levels on the total donor density (ND) as well as the dependence of the electron mobility on the total impurity density (Nimp) and operating temperature (T) in the n-type 4H–SiC. The temperature-dependent electron concentration n(T) and electron mobility μn(T) in the n-type 4H–SiC epilayers with several nitrogen-doping densities are obtained from the Hall-effect measurements. By the graphical peak analysis method (free carrier concentration spectroscopy: FCCS) without any assumptions regarding the donor species, the two types of donor species are detected from n(T). Moreover, the energy level and density of each donor species are determined by the FCCS. Using these results, we obtain the parameters with which the dependence of each donor level on ND can be simulated. Using μn(T) at T>250K, moreover, we obtain the parameters with which the dependence of the electron mobility on Nimp and T can be simulated.

Dependence of acceptor levels and hole mobility on acceptor density and temperature in Al-doped p-type 4H-SiC epilayers

The temperature-dependent hole concentration p(T) and hole mobility μp(T) are obtained in p-type 4H-SiC epilayers with several Al-doping densities. From p(T), the densities and energy levels of acceptors are determined by the graphical peak analysis method (free carrier concentration spectroscopy: FCCS) without any assumptions regarding the acceptor species. In the heavily Al-doped case, the excited states of acceptors affect p(T) because the Fermi level is located between the valence band maximum and the acceptor level (i.e., the ground state level of the acceptor), indicating that a distribution function for acceptors, which includes the influence of excited states of acceptors, should be required. Here, FCCS can determine acceptor densities and acceptor levels using any distribution function (e.g., the Fermi-Dirac distributing function or the distribution function including the influence of excited states). Two types of acceptor species are detected in the lightly Al-doped epilayers, while only one type of acceptor species is found in the heavily Al-doped epilayer. Some of the parameters required to simulate electric characteristics of 4H-SiC power electronic devices are obtained; (1) the dependence of each acceptor level on a total acceptor density and (2) the dependence of the hole mobility on temperature and total impurity density.

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.

Acceptor Densities and Acceptor Levels in Undoped GaSb Determined by Free Carrier Concentration Spectroscopy

Without any assumptions regarding residual impurity species in an undoped semiconductor, it is experimentally demonstrated that the densities and energy levels of impurities can be precisely determined by the graphical peak analysis method based on Hall-effect measurements, referred to as free carrier concentration spectroscopy (FCCS). Using p-type undoped GaSb epilayers grown by molecular beam epitaxy (MBE), the densities and energy levels of several acceptor species are accurately determined. Five acceptor species are detected in the undoped GaSb epilayers grown by MBE, while two are also found in p-type undoped GaSb wafers. A 21–41 meV acceptor and a 75–99 meV acceptor exist both in the epilayers and in the wafer. On the other hand, a 164–181 meV acceptor is detected in epilayers grown at an Sb4/Ga flux beam equivalent pressure ratio of 8 or 10, while a 259 meV acceptor is found in the epilayer grown at Sb4/Ga = 6. In addition, a very shallow acceptor, which is completely ionized at 80 K, is found in the epilayers. The densities of the very shallow acceptor and the 21–41 meV acceptor are minimum at Sb4/Ga = 8, which makes the hole concentration lowest in the temperature range of the measurement.

Donor Densities and Donor Energy Levels in 3C-SiC Determined by a New Method Based on Hall-Effect Measurements

Without any assumption of the number of donor species, the densities and energy levels of donors in undoped 3C-SiC grown from hexamethyldisilane (HMDS; Si2(CH3)6) are precisely determined by a graphical peak analysis method proposed here, using the temperature dependence of the majority-carrier concentration obtained from Hall-effect measurements.