Apparent Capture Cross Section Research Articles

Charge Carrier Capture by Prominent Defect Centers in 4H-SiC

The knowledge of capture properties of electrically active defects is of primary importance as it helps to understand which deep states are effective in controlling the excess free carriers’ lifetime. Combining DLTS capture experiments with thermal emission measurements enables an overall thermodynamic description of deep states, thus making it possible to characterize recombination centers in semiconductor-based devices. In the present study, junction DLTS capture rate measurements were employed to extract the true capture cross-sections (inversely proportional to the carrier lifetime) and capture energy barriers for the main lifetime limiting defects in 4H-SiC (silicon carbide). A peculiar forward bias dependence of the capture parameters was observed for the shallow boron (B) hole trap. Capture rate measurements on the deep boron (D-center) trap also evidenced the presence of two capture mechanisms, thus allowing discrimination of D1 and D2 deep states within the D-center DLTS peak. The results were combined with activation energies and apparent capture cross-sections to obtain the free energy (ΔG) of electronic activation for the analysed deep states.

Observation of temperature-dependent capture cross section for main deep-levels in β-Ga2O3

Direct observation of the capture cross section is challenging due to the need for extremely short filling pulses in the two-gate Deep-Level Transient Spectroscopy (DLTS). Simple estimation of the cross section can be done from DLTS and admittance spectroscopy data but it is not feasible to distinguish temperature dependence of pre-exponential and exponential parts of the emission rate equation with sufficient precision conducting a single experiment. This paper presents experimental data of deep levels in β-Ga2O3 that has been gathered by our group since 2017. Based on the gathered data, we propose a derivation of apparent activation energy (Eam) and capture cross section (σnm) assuming the temperature dependent capture via the multiphonon emission model, which resulted in a strong correlation between Eam and σnm according to the Meyer–Neldel rule, which allowed us to estimate low- and high-temperature capture coefficients C0 and C1 as well as capture barrier Eb. It also has been shown that without considering the temperature dependence of capture cross section, the experimental values of σn are overestimated by 1–3 orders of magnitude. A careful consideration of the data also allows to be more certain identifying deep levels by their “fingerprints” (Ea and σn) considering two additional parameters (EMN and σ00) and to verify the density functional theory computation of deep-level recombination properties.

On the nature of thermally activated defects in n-type FZ silicon grown in nitrogen atmosphere

n-type float-zone silicon grown in a nitrogen atmosphere contains defects which are activated by temperatures between 450 and 700 °C. We use deep level transient spectroscopy (DLTS) to study the nature of these defects and the impact of the nitrogen content and the polysilicon feed stock type. We find four dominant DLTS peaks with activation energies of Ena = 0.16 eV (E1), Ena = 0.21 eV (E2), Ena = 0.34 eV (E4), and Ena = 0.64 eV (E6). We tentatively assign the two DLTS peaks E1 and E2 to single acceptor and single donor levels of the same defect, a complex of nitrogen with an impurity. Furthermore, we tentatively assign the two DLTS peaks labeled E4 and E6 to two levels of the off-center substitutional nitrogen. Based on the apparent electron capture cross sections and an analysis of the electric field effect on the emission rates, we propose them to be double and single acceptor levels, respectively. Due to its position at midgap and the competing electron and hole emission, the apparent concentration of E6 is reduced to one fifth of the total defect concentration. Correcting for these processes, we find the activation energies for electron and hole emission to be En = 0.50 eV and Ep = 0.68 eV.

Evolution of Deep Traps in GaN‐Based RF High Electron Mobility Transistors under High Voltage OFF‐State Stress

An unrecoverable degradation of gate leakage is observed in AlGaN/GaN high electron mobility transistors (HEMTs) under high OFF‐state drain bias stress up to 200 V. Current‐mode deep‐level transient spectroscopy is developed for in situ observation of evolution of traps in the HEMTs before and after stress. It is revealed that two discrete traps, with activation energy of 0.54 and 0.69 eV, have converted into a deeper and broader trap (0.86 eV) after the stress, along with an increased apparent capture cross section (from 1.71 × 10−17–1.11 × 10−15 cm2 to 9.05 × 10−15 cm2). The conversion lowers down the tunneling barrier between metal and the AlGaN barrier, which facilitates trap‐assisted gate leakage in reversed biased AlGaN/GaN HEMTs. Engineering of deep traps in the AlGaN/GaN epilayers is essential for promoting and upgrading of power capability of GaN‐based RF HEMTs.

M-center in 4H-SiC: Isothermal DLTS and first principles modeling studies

We report on a bistable defect known as M-center, here introduced in n-type 4H-SiC by 2 MeV He ion implantation. Deep levels of the M-center are investigated by means of junction spectroscopy techniques, namely, deep level transient spectroscopy (DLTS) and isothermal DLTS. In addition to previously reported three deep levels arising from the M-center (labeled as M1, M2, and M3), we provide direct evidence on the existence of a fourth transition (labeled as M4) with an activation energy of 0.86 eV. Activation energies and apparent capture cross sections for all four metastable defects are determined. From first-principles calculations, it is shown that the observed features of the M-center, including the charge state character, transition levels, bi-stability dynamics, and annealing, are all accounted for by a carbon self-interstitial.

Determination of capture barrier energy of the E-center in palladium Schottky barrier diodes of antimony-doped germanium by varying the pulse width

The capture barrier energy of the E-center deep level defect introduced in Pd/Sb-doped Ge by alpha-particle irradiation has been studied. Palladium Schottky barrier diodes (SBDs) fabricated by resistive evaporation technique were successfully characterised by current-voltage (I-V), capacitance-voltage (C-V), conventional and Laplace deep level transient spectroscopy. The rectification quality of Schottky contacts before and after irradiation was confirmed by I-V and C-V results. The ideality factor and doping density were determined to be in the range of 1.23 to 1.46 and 3.55 × 1015 to 5.25 × 1015 cm−3, respectively before and after irradiating the device with alpha-particles. The thermal emission activation energy and the apparent capture cross section of the E-center were determined from the Arrhenius plot to be 0.37 eV and 1.3 × 10−15 cm2, respectively. The capture barrier energyand the true capture cross section of the E-center were calculated to be 0.052 eV and 2.25 × 10−17 cm2, respectively from the experimental findings after varying the pulse width at different temperature range from 145 to 180 K in steps of 5 K.

Impact of interstitial iron on the study of meta-stable B-O defects in Czochralski silicon: Further evidence of a single defect

We explore the influence of interstitial iron (Fei) on lifetime spectroscopy of boron-oxygen (B-O) related degradation in p-type Czochralski silicon. Theoretical and experimental evidence presented in this study indicate that iron-boron pair (Fe-B) related reactions could have influenced several key experimental results used to derive theories on the fundamental properties of the B-O defect. Firstly, the presence of Fei can account for higher apparent capture cross-section ratios (k) of approximately 100 observed in previous studies during early stages of B-O related degradation. Secondly, the association of Fe-B pairs can explain the initial stage of a two-stage recovery of carrier lifetime with dark annealing after partial degradation. Thirdly, Fei can result in high apparent k values after the permanent deactivation of B-O defects. Subsequently, we show that a single k value can describe the recombination properties associated with B-O defects throughout degradation, that the recovery during dark annealing occurs with a single-stage, and both the fast- and slow-stage B-O related degradation can be permanently deactivated during illuminated annealing. Accounting for the recombination activity of Fei provides further evidence that the B-O defect is a single defect, rather than two separate defects normally attributed to fast-forming recombination centers and slow-forming recombination centers. Implications of this finding for the nature of the B-O defect are also discussed.

Recent insights into boron-oxygen related degradation: Evidence of a single defect

Fast and slow boron-oxygen related degradation in p-type Czochralski silicon is often attributed to two separate defects due to the different time constants and the determination of different capture cross section ratios (k). However, recent work has suggested the possible involvement of a single defect [1,2]. This study reviews recent evidence, and provides further evidence/analysis to demonstrate the involvement of a single defect, in four key areas: 1) Identical recombination properties in the fast and slow timescales [1]; 2) The ability to describe a multi-stage degradation of carrier lifetime with a single recombination active defect [1]; 3) The possible involvement of interstitial iron in accounting for higher apparent capture cross-section ratios during early stages of boron-oxygen related degradation and recombination with a high capture cross-section ratio remaining after permanent deactivation; 4) The ability to modulate the fraction of fast and slow degradation by thermal annealing without modulating the total extent of degradation or recombination properties [2]. A revised parameterisation of the B-O related recombination is also presented, which suggests a stronger influence of acceptor-level related recombination than has been previously reported.

Characterisation of Cs ion implanted GaN by DLTS

Deep level transient spectroscopy (DLTS) was used to characterise Cs implanted GaN grown by hydride vapour phase epitaxy (HVPE). This implantation was done at room temperature using energy of 360keV to a fluence of 10–11cm−2. A defect with activation energy of 0.19eV below the conduction band and an apparent capture cross section of 1.1 × 10–15cm2 was induced. This defect has previously been observed after rare earth element (Eu, Er and Pr) implantation. It has also been reported after electron, proton and He ion implantation.

DLTS Study on Al<sup>+</sup> Ion Implanted and 1950°C Annealed p-i-n 4H-SiC Vertical Diodes

A vertical 4H-SiC p-i-n diode with 2×1020cm-3 Al+ implanted emitter and 1950°C/5min post implantation annealing has been characterized by deep level transient spectroscopy (DLTS). Majority (electron) and minority (hole) carrier traps have been found. Electron traps with a homogeneous depth profile, are positioned at 0.16, 0.67 and 1.5 eV below the minimum edge of the conduction band, and have 3×10-15, 1.7×1014, and 1.8×10-14 cm2 capture cross section, respectively. A hole trap decreasing in intensity with decreasing pulse voltage occurs at 0.35 eV above the maximum edge of the valence band with 1×1013 cm2 apparent capture cross section. The highest density is observed for the refractory 0.67 eV electron trap that is due to the double negative acceptor states of the carbon vacancy.

Evidence for room-temperature in-diffusion of nickel into silicon

Interstitial nickel in crystalline Si is shown to be a fast diffuser at room temperature. In this study, Ni is incorporated in Si by wet chemical etching in nickel-contaminated alkaline solutions. Nickel in-diffusion is observed by means of detecting the electrically active NiVO defect, which is formed due to Ni capture to the vacancy–oxygen complex in electron-irradiated Si. The depth profiles of the NiVO concentration measured by the deep-level transient spectroscopy technique extend to ∼15 μm in the samples doped with Ni at 35 °C for 30 min. This allows us to get a lower estimate for the nickel diffusivity at this temperature as 10−9 cm2/s. The activation energy for electron emission from the NiVO level and the apparent capture cross section are equal to 371 meV and 3 × 10−15 cm2, respectively. The NiVO complex dissociates at 300 °C reestablishing the initial concentration of the VO centers.

Electrical characterization of deep levels created by bombarding nitrogen-doped 4H-SiC with alpha-particle irradiation

Deep-level transient spectroscopy (DLTS) and Laplace-DLTS were used to investigate the effect of alpha-particle irradiation on the electrical properties of nitrogen-doped 4H-SiC. The samples were bombarded with alpha-particles at room temperature (300K) using an americium-241 (241Am) radionuclide source. DLTS revealed the presence of four deep levels in the as-grown samples, E0.09, E0.11, E0.16 and E0.65. After irradiation with a fluence of 4.1×1010 alpha-particles-cm−2, DLTS measurements indicated the presence of two new deep levels, E0.39 and E0.62 with energy levels, EC – 0.39eV and EC – 0.62eV, with an apparent capture cross sections of 2×10−16 and 2×10−14cm2, respectively. Furthermore, irradiation with fluence of 8.9×1010 alpha-particles-cm−2 resulted in the disappearance of shallow defects due to a lowering of the Fermi level. These defects re-appeared after annealing at 300°C for 20min. Defects, E0.39 and E0.42 with close emission rates were attributed to silicon or carbon vacancy and could only be separated by using high resolution Laplace-DLTS. The DLTS peaks at EC – (0.55–0.70)eV (known as Z1/Z2) were attributed to an isolated carbon vacancy (VC).

Electronic defects in In2 O3 and In2 O3 :Mg thin films on r -plane sapphire

The electrical and structural properties of undoped and Mg-doped pulsed-laser-deposited In2O3 thin films grown on r-plane sapphire were investigated by means of Hall-effect, X-ray diffraction, and space-charge spectroscopic methods, such as thermal admittance spectroscopy and deep-level transient spectroscopy. Undoped thin films are preferentially -oriented but X-ray diffraction also revealed -orientation. The incorporation of Mg promotes growth along the direction. Further, the free electron concentration is reduced from to values below due to incorporation of MgO. We found that a deep-level defect with a thermal activation energy of and an apparent capture cross-section of is exclusively incorporated in Mg-doped thin films.

Oxygen vacancy and EC − 1 eV electron trap in ZnO

Fourier transform deep level transient spectroscopy has been performed between 80 and 550 K in five n-type ZnO samples grown by different techniques. The capture cross section and ionization energy of four electron traps have been deduced from Arrhenius diagrams. A trap 1 eV below the conduction band edge is systematically observed in the five samples with a large apparent capture cross section for electrons (1.6 ± 0.4 × 10−13 cm2) indicating a donor character. The assignment of this deep level to the oxygen vacancy is discussed on the basis of available theoretical predictions.

Characterization of deep electron traps in 4H-SiC Junction Barrier Schottky rectifiers

Conventional deep level transient spectroscopy (DLTS) technique was used to study deep electron traps in 4H-SiC Junction Barrier Schottky (JBS) rectifiers. 4H-SiC epitaxial layers, doped with nitrogen and grown on standard n+−4H-SiC substrates were exposed to low-dose aluminum ion implantation process under the Schottky contact in order to form both JBS grid and junction termination extension (JTE), and assure good rectifying properties of the diodes. Several deep electron traps were revealed and attributed to impurities or intrinsic defects in 4H-SiC epitaxial layers, on the basis of comparison of their electrical parameters (i.e. activation energies, apparent capture cross sections and concentrations) with previously published results.

Oxidation Induced ON<sub>1</sub>, ON<sub>2a/b</sub> Defects in 4H-SiC Characterized by DLTS

The deep levels ON1 and ON2a/b introduced by oxidation into 4H-SiC are characterized via standard DLTS and via filling pulse dependent DLTS measurements. Separation of the closely spaced ON2a/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.

Deep traps in n-type GaN epilayers grown by plasma assisted molecular beam epitaxy

In this study, we present the results of investigations on Schottky Au-GaN diodes by means of conventional DLTS and Laplace DLTS methods within the temperature range of 77 K–350 K. Undoped GaN layers were grown using the plasma-assisted molecular beam epitaxy technique on commercial GaN/sapphire templates. The quality of the epilayers was studied by micro-Raman spectroscopy (μ-RS) which proved the hexagonal phase and good crystallinity of GaN epilayers as well as a slight strain. The photoluminescence spectrum confirmed a high crystal quality by intense excitonic emission but it also exhibited a blue emission band of low intensity. DLTS signal spectra revealed the presence of four majority traps: two high-temperature and two low-temperature peaks. Using the Laplace DLTS method and Arrhenius plots, the apparent activation energy and capture cross sections were obtained. For two high-temperature majority traps, they were equal to E1 = 0.65 eV, σ1 = 8.2 × 10−16 cm2 and E2 = 0.58 eV, σ2 = 2.6 × 10−15 cm2 whereas for the two low-temperature majority traps they were equal to E3 = 0.18 eV, σ3 = 9.7 × 10−18 cm2 and E4 = 0.13 eV, σ4 = 9.2 × 10−18 cm2. The possible origin of the traps is discussed and the results are compared with data reported elsewhere.

Modeling Recombination at the Si–Al$_{2}$O $_{3}$ Interface

In this paper, we present a complete set of data on the silicon surface passivation parameters of Al2O3 deposited by atmospheric pressure chemical vapor deposition with triethyldialuminum-tri-( sec-butoxide) and H2O precursors at temperatures between 325 and 520°C. Using measured values of the total interface charge Qtot and of the interface defect density Dit(E), apparent electron capture cross section σn (E), and apparent hole capture cross section σp(E) as a function of the energy within the bandgap E, we calculate surface recombination velocities using the Shockley-Read-Hall (SRH) model and compare these with measured values, finding excellent agreement when Qtot is large and reasonable agreement otherwise. The resulting model is valid for both n- and p-type substrates, under the condition that holes are the majority carrier at the surface, as is generally the case for typical (negative) values of Qtot. It is shown that, under these conditions, recombination is dominated by a single donor-like defect species located just below midgap. These results support the direct correspondence between Qtot, Dit (E), σn, and σp determined by capacitance and conductance measurements of metal-insulator-semiconductor structures and the carrier lifetimes measured by photoconductance.

Electronic Properties and Density of States of Self-Assembled GaSb/GaAs Quantum Dots

The electronic properties of a self-assembled GaSb/GaAs QD ensemble are determined by capacitance-voltage (C-V) and deep-level transient spectroscopy (DLTS). The charging and discharging bias regions of the QDs are determined for different temperatures. With a value of 335 (±15) meV the localization energy is rather small compared to values previously determined for the same material system. Similarly, a very small apparent capture cross section is measured (1·10−16 cm2). DLTS signal analysis yields an equivalent to the ensemble density of states for the individual energies as well as the density function of the confinement energies of the QDs in the ensemble.

Deep levels fine structure in proton implanted p-type GaAs

Proton irradiation related deep levels in p-type GaAs were measured by deep level transient spectroscopy (DLTS) at T < 70 K and Laplace DLTS at 42 K ⩽ T ⩽ 48 K. Besides level H0 (apparent energy Epa = 0.06 eV and apparent hole capture cross section σpa = 1.6 × 10−16 cm2), also present in electron irradiated GaAs, three other levels were identified (Epa = 0.1 eV, σpa = 2.5 × 10−15 cm2; Epa = 0.085 eV, σpa = 1 × 10−14 cm2 and Epa = 0.065 eV, σpa = 3 × 10−16 cm2). Another level (Epa = 0.095 eV and σpa = 2 × 10−15 cm2) became evident after annealing steps at the temperature range 150 °C ⩽ T ⩽ 200 °C. All levels suffered a strong concentration reduction after annealing steps at 250 °C ⩽ T ⩽ 300 °C.