Papers by Keyword: DLTS

Abstract: The deep levels ON₁ and ON_2a/b introduced by oxidation into 4H-SiC are characterized via standard DLTS and via filling pulse dependent DLTS measurements. Separation of the closely spaced ON_2a/b defect is achieved by using a higher resolution correlation function (Gaver-Stehfest 4) and apparent energy level, apparent electron capture cross section and filling pulse measurement derived capture cross sections are given.

Abstract: The electrically active deep levels in a graphene / silicon carbide field effect transistor (FET) were investigated by drain-current deep level transient spectroscopy (I_D-DLTS). An evaluation procedure for I_D-DLTS is developed in order to obtain the activation energy, the capture cross section and the trap concentration. We observed three defect centers corresponding to the intrinsic defects E₁/E₂, E_i and Z₁/Z₂ in n-type 6H-SiC. The determined parameters have been verified by conventional capacitance DLTS.

Abstract: A total of nine electrically active levels have been detected in as-grown and electron irradiated p-type 4H-SiC epilayers. These traps are found in the 0.32-2.26 eV energy range, above the valence band edge (E_V). Of these, six are majority carrier traps whereas three are minority carrier traps. We found that thermal oxidation affects the concentrations of two midgap levels, the majority carrier trap, labeled HK4 and the minority carrier trap identified as EH_6/7. The analysis of the irradiation energy and dose dependence of the concentration of these two traps, rules out the possibility that they may share the same origin.

Abstract: We have investigated the electrical properties of n-type 4H-SiC in-situ germanium-doped homoepitaxial layers grown by chemical vapor deposition. Germanium is an isoelectronic impurity and, therefore, not expected to contribute to the conductivity. However, Hall effect measurements taken on samples with and without germanium revealed an enhanced mobility by a factor of ≈2 at T ≈ 55 K in the germanium-doped sample despite equal free electron concentration and equal compensation. Deep level transient spectroscopy (DLTS) measurements taken on germanium-doped samples reveal negative peaks indicating the presence of charged extended defects.

Abstract: Using Deep Level Transient Spectroscopy (DLTS) on n-type MOS capacitors we find that thermal oxidation of 4H-SiC produces deep traps at or near the SiO₂/SiC interface with two well defined DLTS peaks. The traps are located ~ 0.85 V and ~ 1.0 eV below the SiC conduction band edge and are present in wet and dry oxides as well as oxides produced by sodium enhanced oxidation and oxides grown in N₂O. The deep traps are located at the SiO/SiC interface after oxidation at 1150°C but do extend further into the SiC epilayer after oxidation at 1240°C. We identify these traps as ON1 and ON2 which been observed in epitaxial layers after oxidation at very high temperatures (1200-1500°C) [.

Abstract: Constant-capacitance deep-level transient spectroscopy was carried out to characterize in detail interface states close to the conduction band edge in SiO₂/SiC structures. The measured results are summarized as follows: (1) The capture of electrons by the interface states proceeds logarithmically with time. (2) The emission of electrons accelerates slightly with increasing density of captured electrons. The oxide trap model explains the logarithmic change in capture with time but not the phenomenon of accelerated emissions. This prompted us to formulate a new model that replicates the logarithmic capture process with time. In this model, we postulated the electron density at the interface decreases exponentially as the trapped electron density increases owing to the interaction between the trapped electrons and the free electrons. In this case, the capture process is almost the same as with the oxide trap model except for the definition of parameters. Further, we do not need to take into account the delay of the emission process caused by tunneling. The phenomenon of accelerated emissions may be explained by interactions among captured electrons in this model.

Abstract: Photoluminescence (PL) and deep level transient spectroscopy (DLTS) have been used to investigate carbon related defects in p–type Cz–Si induced by proton irradiation. The interstitial carbon–interstitial oxygen (C_iO_i) level in DLTS and the corresponding C–line (789.5 meV) in PL spectra are detected in as–irradiated samples. Formations of the so–called P–line at 767 meV in PL and a new defect level at about 0.39 eV above the valence band edge, E_v, in the DLTS spectra are observed in the annealed samples. The evolution of the C_iO_i and E_v+0.39 eV levels in DLTS and also the C– and P– lines in PL upon post–irradiation heat–treatment is investigated, showing that the intensity of the C_iO_i level decreases with heat–treatment, which is consistent with the PL data for the C–line. The intensity of the E_v+0.39 eV level is enhanced and then saturates with annealing duration. We tentatively assign this level to the interstitial carbon–oxygen dimer (C_iO_2i).

Abstract: In silicon several electronic levels are known which can be attributed to transition metals. Ignorance persists however about the specific nature of the defect centers. Some progress was made recently on identifying electronic levels from substitutional or interstitial lattice sites and on identifying levels from defect complexes. The sensitive Laplace DLTS technique allows us to determine depth profiles or the influence of the electrical field on the emission rate with unparalleled accuracy. Three examples will be discussed in this short review: The identification of the CoB pair, a reinterpretation of the Ti DLTS spectrum and the complex formation of interstitial Cu with substitutional Cu as the nucleation site.

Abstract: Shallow dislocation-related electronic states near the bottom of the conduction band in n-type Si bonded sample have been investigated with deep-level transient spectroscopy (DLTS), isothermal transient spectroscopy (ITS) and energy-resolved DLTS. The effect of thermoemission (TE) enhancement in external electric field was found and the dependence of the TE activation energy reduction as a function of the filling grade was obtained for these states. A new model of dislocation-strain-related Poole-Frenkel effect that accounts for the own electric field of internal charge of dislocation line is suggested and compared with the experimental data.

Abstract: We report on a specific defect, which may form during the growth of Stranski-Krastanov surfactant-mediated Ge/Si (100) islands. Transmission electron microscopy reveals that these loop-like defects are local and could be represented by a missing plane of Ge atoms inside some of Ge islands. This specific defect may generate an electrically active trap within the Si band gap at about 0.3 eV above the Si valence band edge. Deep level transient spectroscopy reveals that at least 1 % of Ge islands may include such defects.