Papers by Keyword: Deep Level Transient Spectroscopy

Abstract: Solid State Detectors (SSD) are crucial for fast neutron detection and spectroscopy in tokamaks due to their solid structure, neutron-gamma discrimination, and magnetic field resistance. They provide high energy resolutions without external conversion stages, enabling compact array installations in the harsh environment of a tokamak. Research comparing diamond and 4H-SiC detectors highlights thickness as a key efficiency factor. A 250 μm SiC epilayer with low doping, grown using a high-growth-rate process, exhibits sharp interfaces and minimal defects, essential for neutron detectors. The study evaluates detector designs, and performance using a 4H-SiC substrate. Various detector designs, such as Schottky diodes and p/n diodes, are assessed via I-V and C-V measurements, addressing high depletion voltage challenges. Preliminary neutron irradiation tests validate detector functionality, energy resolution and confirming detector reliability.

Abstract: Silicon carbide (SiC) is a wide band-gap semiconductor of great technological importance, showing promise for application areas ranging from quantum computing and communication to power devices. Vital in both the contexts of power devices and quantum technology is the understanding of intrinsic defects that are introduced during various device processing steps, both immediately after their formation and over the course of defect evolution with temperature. Here we monitor the formation and evolution of intrinsic point defects in n-type 4H-SiC after proton irradiation at room temperature and subsequent annealing in the temperature range 300-1000 °C, and discuss the nature and origin of the EH₄ and EH₅ deep level defects observed by deep level transient spectroscopy around 400-500 K. In particular, the controversy on the nature of the EH5 trap in particular is addressed, where we propose the presence of two overlapping defect peaks: one metastable level that appears after low energy electron irradiation below the silicon displacement limit, and one more stable level that gradually decreases in concentration until an annealing temperature of 1000°C. We argue that the former is likely related to carbon interstitials, while the latter was recently tentatively attributed to the carbon antisite-vacancy pair.

Abstract: A deep level transient spectroscopy (DLTS) study on n- and p-type diluted Si_1-xGe_x alloys (x=0, 0.011, 0.026, 0.046, and 0.070) is presented. Defect levels of several carbon-hydrogen (CH) complexes are observed. The high-resolution Laplace-DLTS technique allows us to detect configurations of defects which contain different numbers of Ge atoms in the first and second-nearest neighbourhood of the CH complexes. The electrical properties of the defects will be analysed and their origin will be discussed.

Abstract: It is argued in this work that a DLTS signal associated with hole emission from a radiation-induced defect with an energy level at E_v + 0.09 eV is related to a complex of silicon di-interstitial with an oxygen atom (I₂O). This signal has been observed in the DLTS spectra of p-type Si:O samples irradiated with either 4-6 MeV electrons or alpha particles. Isochronal and isothermal annealing studies of the samples have shown that the defect responsible for the DLTS signal from the E_v + 0.09 eV level disappears upon heat-treatments in the temperature range 75-100 °C and its formation and annealing behavior is similar to that of a center giving rise to the infrared absorption band at 936 cm^-1 previously assigned to a local vibrational mode (LVM) due to the I₂O complex. Possible configurations of the I₂O complex have been found by ab-initio modeling and analyzed. Formation and binding energies, energy levels and LVMs for different configurations have been determined. It has been found that the minimum energy configuration of the I₂O complex consists of the compact I₂ to which a divalent interstitial oxygen atom is attached. Calculated values of the strongest LVM (ν = 971 см^-1 ) and position of the donor level {E_v + (0.11-0.13) eV} for the minimum energy configuration are very close to those assigned to the I₂O defect in the infrared absorption and DLTS experiments.

Abstract: Deep level transient spectroscopy (DLTS) was used to characterize the defects introduced in n-type, N-doped, 4H-SiC while being exposed to electron beam evaporation conditions. This was done by heating a tungsten source using an electron beam current of 100 mA, which was not sufficient to evaporate tungsten. Two new defects were introduced during the exposure of 4H-SiC samples to electron beam deposition conditions (without metal deposition) after resistively evaporated nickel Schottky contacts. We established the identity of these defects by comparing their signatures to those of high energy particle irradiation induced defects of the same materials. The defect E_0.42 had acceptor-like behaviour and could be attributed to be a silicon or carbon vacancy. The E_0.71 had intrinsic nature and was linked to a carbon vacancy and/or carbon interstials.

Abstract: We show experimentally that dislocations in Si crystals can generate some unknown vacancy complexes Vx_trail in their slip planes during their motion at 600°C. Most of these “dislocation trail defects” are not electrically active but can be detected by their reaction with gold atoms during in-diffusion experiments. It was also shown that contrary to gold, the Vx_trail-complexes do not react with interstitial Ni atoms. It means that the binding energy E_bind of Vx_trail complexes is quite high (E_bind>2.5eV), higher than the binding energy of vacancy complexes generated during FZ-Si crystal growth. It was also shown that Ni in-diffusion results in a strong increase of electron-hole recombination at dislocations and in a strong increase of dislocation-related DLTS C-line.

Abstract: Deep Level Transient Spectroscopy (DLTS) has been applied to Metal-Insulator-Semiconductor (MIS) capacitors, consisting of a p⁺ or n⁺ a-Si:H gate on an intrinsic i-a-Si:H passivation layer deposited on crystalline silicon n-or p-type substrates. It is shown that the type of gate has a pronounced impact on the obtained spectra, whereby both the kind of defects (dangling bonds at the a-Si:H/(100) c-Si interface (P_b0 defects) or in the amorphous silicon layer (D defects) and their relative importance (peak amplitude) may be varied. The highest trap densities have been found for the p⁺ a-Si:H gate capacitors on an n-type Si substrate. In addition, the spectra may exhibit unexpected negative peaks, suggesting minority carrier capture. These features are tentatively associated with interface states at the p⁺ or n⁺ a-Si:H/i-a-Si:H interface. Their absence in Al-gate capacitors is in support of this hypothesis.

Abstract: Deep Level Transient Spectroscopy (DLTS) and Double-correlated DLTS (DDLTS) measurements have been conducted on Schottky contacts fabricated on n-type 4H-SiC epilayers using different contact metals in order to separate the EH₆- and EH₇-centers, which usually appear as a broad double peak in DLTS spectra. The activation energy of EH₆ (E_C - E_T(EH₆) = 1.203 eV) turns out to be independent of the electric field. As a consequence, EH₆ is acceptor-like according to the missing Poole-Frenkel effect. Therefore, it can be excluded that the EH₆-center and the prominent acceptor-like Z_1/2-center belong to different charge states of the same microscopic defect as theoretically suggested. It is proposed that EH₆ is a complex containing a carbon vacancy and another component available at high concentrations. The activation energy of EH₇ (E_C - E_T(EH₇) = 1.58 eV) has been evaluated indirectly by fitting the DLTS spectra of the EH_6/7 double peak taking the previously determined parameters of EH₆ into account.

Abstract: In this study, deep levels are investigated, which are introduced by reactive ion etching (RIE) of n-type/p-type 4H-SiC. The capacitance of as-etched p-type SiC is remarkably small due to compensation or deactivation of acceptors. These acceptors can be recovered to the initial concentration of the as-grown sample after annealing at 1000oC. However, various kinds of defects remain at a total density of ~5× 1014 cm-3 in a surface-near region from 0.3 μm to 1.0 μm even after annealing at 1000oC. The following defects are detected by Deep Level Transient Spectroscopy (DLTS): IN2 (EC – 0.35 eV), EN (EC – 1.6 eV), IP1 (EV + 0.35 eV), IP2 (HS1: EV + 0.39 eV), IP4 (HK0: EV + 0.72 eV), IP5 (EV + 0.75 eV), IP7 (EV + 1.3 eV), and EP (EV + 1.4 eV). These defects generated by RIE can be significantly reduced by thermal oxidation and subsequent annealing at 1400oC.

Abstract: Intrinsic defects in 3C-SiC are generated by implantation of H+- and He+-ions or irra¬diation with high energy electrons. The defect parameters and the thermal stability of the observed defects are determined. The capture-cross-section of the W6-center is directly measured by variation of the filling pulse length. The charge state of the W6-center is obtained from double-correlated DLTS investigations according to the Poole-Frenkel effect.