Thermally Stimulated Capacitance Research Articles

Investigation of the Boron removal effect induced by 5.5 MeV electrons on highly doped EPI- and Cz-silicon

This study focuses on the properties of the BiOi (interstitial Boron–interstitial Oxygen) and CiOi (interstitial Carbon–interstitial Oxygen) defect complexes by 5.5MeV electrons in low resistivity silicon. Two different types of diodes manufactured on p-type epitaxial and Czochralski silicon with a resistivity of about 10 Ω⋅cm were irradiated with fluence values between 1 × 1015cm-2 and 6 × 1015cm-2. Such diodes cannot be fully depleted and thus the accurate evaluation of defect concentrations and properties (activation energy, capture cross-section, concentration) from Thermally Stimulated Currents (TSC) experiments alone is not possible. In this study we demonstrate that by performing Thermally Stimulated Capacitance (TS-Cap) experiments in similar conditions to TSC measurements and developing theoretical models for simulating both types of BiOi signals generated in TSC and TS-Cap measurements, accurate evaluations can be performed. The changes of the position-dependent electric field, the effective space charge density Neff profile as well as the occupation of the BiOi defect during the electric field dependent electron emission, are simulated as a function of temperature. The macroscopic properties (leakage current and Neff) extracted from current–voltage and capacitance–voltage measurements at 20°C are also presented and discussed.

Deep Level Transient Fourier Spectroscopy (DLTFS) and Isothermal Transient Spectroscopy (ITS) in vertical GaN-on-GaN Schottky barrier diodes

The paper explores the Deep Level Transient Fourier Spectroscopy (DLTFS) capabilities in characterizing electrically active traps in vertical GaN-on-GaN Schottky barrier diodes (SBDs). The capacitance-DLTFS (C-DLTFS) experiments reveal a prominent electron trap T2 at EC – 0.56 eV with a density (NT2) of 8 × 1014 cm−3 and a weak presence of another trap at EC – 0.18 eV (T1) with NT1 = 3.8 × 1013 cm−3 in the SBDs. The C-DLTFS acquired with two emission transients (TE = 20.48 ms and 2.048 s) has resulted in identical trap signatures for T1 and T2. Due to the high NT, the trap T2 at EC - 0.56 eV is identified from the current-DLTFS (I-DLTFS) and thermally stimulated capacitance (TSCAP) measurements. Especially the TSCAP results indicate the carrier freeze-out temperature (T < 75 K) in the GaN material. Furthermore, the carrier emission kinetics of the trap T2 is evaluated by performing isothermal transient spectroscopy at a stabilized temperature. The capture time constant of T2 is estimated from the isothermal transients attained with shorter trap-filling pulse widths (<100 ns).

Thermally annealed gamma irradiated Ni/4H-SiC Schottky barrier diode characteristics

Thermal annealing effects on gamma irradiated Ni/4H-SiC Schottky barrier diode (SBD) characteristics are analyzed over a wide range of temperatures (400–1100 °C). The annealing induced variations in the concentration of deep level traps in the SBDs are identified by thermally stimulated capacitance (TSCAP). A little decrease in the trap density at EC – 0.63 eV and EC – 1.13 eV is observed up to the annealing temperature of 600 °C. Whereas, a gamma induced trap at EC – 0.89 eV disappeared after annealing at 500 °C, revealing that its concentration (< 1013 cm−3) is reduced below the detection limit of the TSCAP technique. The electrical characteristics of irradiated SBDs are considerably changed at each annealing temperature. To understand the anomalous variations in the post-annealing characteristics, the interface state density distribution in the annealed SBDs is extracted. The electrical properties are improved at 400 °C due to the reduction in the interface trap density. However, from 500 °C, the electrical parameters are found to degrade with the annealing temperature because of the increase in the interface trap density. From the results, it is noted that the rectifying nature of the SBDs vanishes at or above 800 °C.

Thermal annealing studies in epitaxial 4H-SiC Schottky barrier diodes over wide temperature range

Thermal annealing effects on electrical characteristics of Ni/4H-SiC and Ti/4H-SiC Schottky barrier diodes (SBDs) are investigated in the temperature range of 400–1100 °C. The thermal evolution of deep level traps in annealed SBDs is also analyzed by thermally stimulated capacitance (TSCAP) spectroscopy. As-deposited Ni/4H-SiC SBDs exhibited non-ideal electrical properties compared to Ti/4H-SiC SBDs. The electrical parameters of the Ni/4H-SiC SBDs are improved upon annealing at 400 °C for 30 min. in Ar ambient. However, deterioration in the SBD characteristics is observed from the temperature of 500 °C, so optimal annealing temperature for our Ni/4H-SiC SBDs is 400 °C. On the other hand, electrical properties of the Ti/4H-SiC SBDs are found to degrade even from the annealing temperature of 400 °C and hence as-deposited Ti/4H-SiC SBDs have the better properties. No considerable changes in the trap concentrations at Ec-0.63 eV and Ec-1.13 eV are identified in the SBDs up to the annealing temperature of 600 °C. The heat treatment on or above 800 °C results in poor rectifying behavior in both the SBDs, therefore the diode rectification is disappeared from 800 °C.

Thermally stimulated capacitance in gamma irradiated epitaxial 4H-SiC Schottky barrier diodes

Deep level defects in 4H-SiC Schottky barrier diodes (SBDs) fabricated on n-type epitaxial 4H-SiC have been identified by thermally stimulated capacitance (TSCAP) spectroscopy prior to and after 60Co-gamma irradiation. The TSCAP measurements on the non-irradiated SBDs reveal two electron traps at Ec-0.63 eV (∼250 K) and Ec-1.13 eV (∼525 K), whereas only one trap at Ec-0.63 eV is identified by conventional thermally stimulated current (TSC) measurements. Hence, TSCAP spectroscopy is more effective in identifying deep level defects in epitaxial 4 H-SiC SBDs as compared to the TSC spectroscopy. Upon exposure to 60Co-gamma rays up to a dose of 100 Mrad, significant changes in the concentration of the traps at Ec-0.63 eV, Ec-1.13 eV, and one new trap at Ec-0.89 eV (∼420 K) are observed. The electrical characteristics of the SBDs are considerably changed after gamma irradiation. The dominant mechanisms responsible for the irradiation induced changes in the SBD electrical characteristics are analyzed by incorporating the trap signatures in the commercial Silvaco® TCAD device simulator. The extracted trap parameters of the irradiated SBDs may be helpful in predicting the survival of 4H-SiC SBD detectors at higher irradiation levels.

Annealing mechanisms of self-interstitial related defect E1=Ec−0.39 eV in irradiated silicon

DLTS and thermally stimulated capacitance (TSCap) studies of α-particle irradiated p-Si were undertaken to obtain additional information about the self-interstitial related defect E1=Ec−0.39eV. The E1 defect can be retained frozen up to room temperature without any minority carrier injection, but under injection conditions at 77–300K the E1 becomes mobile. As a result of annealing of the E1 defect, the carbon interstitial concentration grows. The E1 defect production rate under reverse bias as well as thermal annealing behavior depends strongly on the temperature and impurity concentration. Numerical estimates of the E1 migration via a Bourgoin–Corbett mechanism are in good agreement with the experimental data obtained.

Two FeH pairs inn-type Si and their implications: A theoretical study

Experimental evidence for interstitial {FeH} pairs in $n$-type Si stems from thermally stimulated capacitance (TSCAP). Electron-paramagnetic resonance (EPR) data have also been interpreted in terms of {FeH} pairs. We present theoretical studies of two {FeH} pairs. The properties of the first match those of the TSCAP center but are incompatible with the EPR center. The second is a possible candidate for the EPR center. If true, this suggests that high-temperature anneals can introduce substitutional Fe in concentrations higher than commonly believed.

Electrical characterisation of hole traps in n-type GaN

We have used thermally stimulated capacitance (TSCAP) and optical deep level transient spectroscopy (O-DLTS) to detect and characterise hole traps in n-type GaN grown by epitaxial lateral overgrowth (ELOG) organo-metallic vapour phase epitaxy (OMVPE). Semi-transparent Ni Schottky barrier diodes (SBDs) were used to probe the space charge region of the GaN layer. Optical excitation was achieved using an ultraviolet light emitting diode with sub-bandgap energy photons at a wavelength of 380 nm. Two hole traps with activation enthalpies of 0.25 eV and 0.85 eV with respect to the valence band were found to be present in concentrations of 5 × 10 14 and 2 × 10 15 cm -3 . This is almost two orders of magnitude higher than the concentration of the electron traps present in this material. We have also found that 1.8 MeV proton implantation introduced additional shallow level hole traps with activation enthalpies of 0.19 eV and 0.23 eV, respectively.

DX centers in indium-doped Cd0.9Mn0.1Te

Abstract Deep levels in indium-doped Cd0.9Mn0.1Te material were studied by DLTS, thermally stimulated capacitance (TSC) and photocapacitance measurements. The persistent photoeffects observed at low temperature indicate existence of metastable centers in the material. One of the trap related to metastable defects has been identified: the level with activation energy obtained from DLTS studies equal to 0.22 eV, a very high concentration of the associated traps (higher than 10% of the concentration of the shallow levels) and energy barrier for capture equal to 0.1 eV. Stokes shift for this level has been found to be equal to 0.58 eV.

Dopant redistribution and formation of electrically active complexes in SiGe

A review of our recent experimental investigations of dopant diffusion and characterization of electrically active defect complexes in strained and relaxed epitaxial SiGe/Si heterostructures is given. Three topics: (i) Sb and P diffusion, (ii) properties of divacancy and P-vacancy complexes, and (iii) thermal donor generation in SiGe are discussed in detail. High resolution X-ray diffraction (HRXRD), secondary ion mass spectrometry (SIMS), deep-level transient spectroscopy (DLTS), admittance spectroscopy (ADSPEC) and thermally stimulated capacitance (TSCAP) have been employed for the relaxation control, tracer profiling, deep- and shallow-level characterization in our samples. A part of the electrical measurements is performed in MOS Si/SiGe/Si components.

The evolution of interstitial-type defects in silicon during platinum diffusion from 400 to 600°C following 2-MeV electron irradiation

Platinum has been diffused into epitaxial n-type silicon for 30 min at temperatures from 400 to 600°C following room temperature irradiation with 2-MeV electrons at a dose of 1×10 17 e − cm −2. Platinum has only been detected by deep level transient spectroscopy (DLTS) following the highest diffusion temperature. For lower temperatures defects, not previously reported, arise which are thought to be of interstitial nature. The two principal defect levels are determined to be located at 0.29 and 0. 41 eV below the conduction band. The compensation for the two lowest diffusion temperatures is observed to be extremely strong as manifested by a strong reduction of the steady state reverse bias capacitance during the DLTS measurements. Following thermal treatment at 500°C this capacitance, however, increases. DLTS measurements down to 20 K detected thermal donors as well as a number of other defects not previously reported. Their signatures have been determined by DLTS and TSCap (thermally stimulated capacitance) measurements. The nature of the observed defects is discussed with reference to recent results concerning interstitial defects.

Electrical Study of Dislocated Si- and C-Faces of n-Type 6H-SiC

The (0001)Si and (000-1)C faces of n-type 6H-SiC have been scratched and annealed to introduce fresh dislocations. TEM investigations on the as-deformed C-face show that this leads predominantly to the nucleation of partial dislocations of both core natures depending on the distance from scratches whereas on the Si-face predominantly partial Si(g) dislocations are created. By Thermally Stimulated Capacitance (TSC), it was found that the majority carrier traps resulting from the deformation are mainly located in the upper third of the band-gap whatever the deformed face may be. However, the rather low dislocation density is not sufficient to explain the observed large compensation, and other defects generated by the deformation step must be taken into account.

Dislocations in 6H-SiC and their influence on electrical properties of n-type crystals

By scratching the (0001)Si surface of 6H-SiC followed by annealing, dislocations were introduced in the crystal that were subsequently characterized by Transmission Electron Microscopy (TEM). Schottky diodes were then manufactured from the dislocated crystal and their electrical properties were studied by capacitance-voltage (C-V), current-voltage (I-V), and thermally-stimulated capacitance (TSCap) measurements. It was found that the deformation introduces deep traps mainly located in the upper third of the bandgap promoting a significant increase in the series resistance of the diodes. The as-introduced dislocations were predominantly 30° partials and their core nature was determined to be Si(g) by the technique of Large Angle Convergent Beam Electron Diffraction (LACBED). The compensation effects observed after deformation are presumed to be caused not only by Si(g) dislocations but also by the other defects generated during the deformation step.

Deep level of iron-hydrogen complex in silicon

Deep levels related to iron in n-type silicon have been investigated using thermally stimulated capacitance (TSCAP) combined with minority carrier injection. The TSCAP measurement reveals two traps of EV+0.31 and EV+0.41 eV. The trap of EV+0.41 eV is a donor due to interstitial iron. The trap of EV+0.31 eV, due to a complex of interstitial iron and hydrogen, is observed in the sample etched chemically with an acid mixture containing HF and HNO3 and annihilates after annealing at 175 °C for 30 min. It is demonstrated that interstitial 3d transition metals such as vanadium, chromium, and iron tend to form complexes with hydrogen in n-type silicon, and the complexes induce donor levels below the donor levels of the isolated interstitial species. This trend is related to the interaction between the metals and hydrogen in the complexes.

Photogeneration and Carrier Transport in Amorphous Silicon/Crystalline Silicon Devices

ABSTRACTHydrogenated amorphous silicon (a-Si:H)/ crystalline silicon (c-Si) type heterodiodes in solar cell structures have been studied by rf glow discharge, dc magnetron sputtering, and a remote plasma deposition of a-Si:H onto p type c-Si. Carrier transport and photogeneration in such structures have been investigated by current-voltage-temperature, thermally stimulated capacitance (TSCAP), and spectral response experiments. Dark carrier conduction is found to be a combination of tunneling and interface recombination, but is dominated by either one depending on the deposition/sputtering conditions. The conditions investigated include energy of the plasma species, type of plasma cleaning, and substrate preparation techniques. For each of the conditions, the trap type, energy and concentration have been identified by TSCAP. Solar cells fabricated by the optimized fabrication scheme routinely yield 10.5% efficient devices having a short circuit current density (Jsc) of 30 mA/cm2, a open circuit voltage of 0.55 volts and a fill factor (FF) of 0.64, without an AR coating, over 0.3 cm2 area.

Deep-level defects responsible for persistent photoconductivity in Ga-doped Cd1-xMnxTe.

Bulk n-type ${\mathrm{Cd}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Mn}}_{\mathit{x}}$Te crystals heavily doped with Ga are known to exhibit strong persistent photoconductivity (PPC) at low temperatures (below \ensuremath{\sim}100 K). In order to identify the origin of the PPC effect, we investigated the electronic properties of deep-level defects present in this material by deep-level transient spectroscopy (DLTS) and by thermally stimulated capacitance (TSCAP) measurements. We used a ${\mathrm{Cd}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Mn}}_{\mathit{x}}$Te crystal with x=0.03 and a Ga doping level of 1\ifmmode\times\else\texttimes\fi{}${10}^{19}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$. The DLTS measurements revealed the presence of two deep levels, with thermal activation energies for electron emission of 0.25 and 0.43 eV. The electron capture process to the 0.25-eV level was found to be thermally activated, with a thermal energy barrier of 0.11 eV. DLTS measurements performed after sub-band-gap illumination at low temperatures established that, in addition to the PPC effect, the illumination causes also a strong increase in the concentration of the 0.25-eV states, which persist to temperatures as high as T=200 K. This finding indicates that---in addition to the metastability of conduction electrons with respect to the 0.25-eV states, which results in the PPC below 100 K---the 0.25-eV states are also metastable with respect to other (ground) states from which they are created by photoexcitation. Our TSCAP measurements detected also two transitions to two different deep levels, in agreement with these results. The first of these levels is donorlike, with an activation energy of 0.21 eV. The second level is acceptorlike, and the electron transition to this level requires a thermal energy of several hundreds of meV. Because the concentrations of both the 0.25- and the 0.43-eV states found by DLTS appear to be very close to each other, we propose a single defect model with two charge states, attributing the 0.43-eV level to an acceptorlike two-electron ground state of the defect, and the 0.25-eV level to the excited, donorlike one-electron state. According to this model, the defect possesses a positive Hubbard correlation energy (positive-U system). We discuss a configuration coordinate diagram of the defect in the paper.

Defect levels of proton-irradiated silicon with doses ranging from 1 × 10 12 cm −2 to 1 × 10 13 cm −2

Schottky diodes of n-type silicon have been irradiated by 800 keV and 1 MeV protons at doses ranging from 1 × 10 12 cm −2 to 1 × 10 13 cm −2. Thermally Stimulated Capacitance (TSCAP), capacitance-voltage (CV) and Deep Level Transient Spectroscopy (DLTS) have been applied for sample analysis. By TSCAP measurements a strong compensation effect has been observed for irradiation doses up to 5 × 10 12 cm −2. At least five deep levels have been observed in the DLTS spectra, but the E(200) trap, located at E c − 0.36 eV, was only revealed by the fitting procedure. An additional new pure damage level, labelled E(110), with an energy of E c − 0.19 eV and a capture cross section of about 5 × 10 −16 cm 2 has been also observed in the highly damaged region. The variations of the DLTS signal with pulse amplitude of the E c − 0.3 eV level, called E(170), has been found to be different of what is obtained at low dose irradiations: a dip followed by a peak in concentration near the maximum of implanted ions is suggested. A possible explanation of such behavior is discussed. We also report the possibility of an overdoping effect near the proton distribution before thermal annealing.

Donor-related deep level in bulk GaSb

Deep level transient spectroscopy (DLTS) and thermally stimulated capacitance (TSCAP) studies on bulk grown tellurium- selenium-, and sulphur-doped gallium antimonide reveal the presence of deep level intrinsic of the dopant species. The trap densities in Te- and Se-doped samples were found to be at least two orders of magnitude lower than the shallow donor concentration. Interestingly, the DLTS spectrum of S:GaSb exhibits DX-like nature with the trap concentration comparable to that of shallow donor concentration. However, the Te and Se related levels do not exhibit DX-like nature. The DLTS and TSCAP results are in good agreement with each other.

Studies of majority-carrier traps in Zn-doped p-InP by thermally stimulated capacitance techniques

High-barrier Yb/p-InP Schottky diodes were used to study majority-carrier traps in the Zn-doped p-InP single-crystal substrates by thermally stimulated capacitance (TSCAP) techniques. The TSCAP studies involved a forward bias VF=0.6 V, cooling to 90 K, bias switching to reverse bias VR=4.0 V, and then heating at a constant heating rate to 450 K. The junction capacitance was recorded as a function of temperature for various heating rates between 0.05 and 0.5 K/s, and corrected for temperature dependence of the diffusion voltage and the dielectric constant. The trapping parameters of the strong hole trap level were determined from the plots of dΔC/dT vs T at different heating rates, and values of Eh1=EV+0.59 eV and σp1 =3×10−21 cm2 were obtained for the activation energy and capture cross section, respectively, of the hole trap. From the TSCAP data at a constant heating rate and using the Eremin, Strokan, and Turebekov [Sov. Phys. Semicond. 15, 1010 (1981)] method, a hole trap with Eh1=EV+0.62 eV and σp1 =2×10−21 cm2 was also detected. From the amplitude of the steady-state positive capacitance step, a value of NTP =2.7×1014 cm−3 for the concentration of the hole trap level was estimated.

Band Offsets and Anomalous Deep Defect Distribution at the Hydrogenated Amorphous Silicon-Crystalline Silicon Interface via Junction Capacitance Techniques

ABSTRACTA novel a-Si:H/c-Si Schottky diode heterostructure device premits the study of the capacitive response to relatively low temperatures (25 K) and also allows fast pulse filling capture measurements of electrons from the c-Si substrate into a-Si:H defect states. These latter measurements, as well as capacitance vs. temperature measurements on these diodes, indicate a nearly zero conduction band offset (50±50 meV). We also have observed trapping of holes at the a-Si:H/c-Si valence band discontinuity ΔEv. A clear threshold for the subsequent optical release of these trapped holes by sub-bandgap light yields a value of ΔEv = 0.58±0.02 eV. Finally, photocapacitance spectra along with thermally stimulated capacitance (TSCAP) measurements indicate an anomalously large (l×1018/cm3) Gaussian-shaped defect band located a Ec - 0.88 eV with a FWHM of 0.46 eV. Model calculations of the high temperature capacitance-voltage dependence indicate these defects lie predominately within 350 Å of the a-Si:H/c-Si interface.