Deep Level Transient Spectroscopy Spectra Research Articles

DLTS SPECTRA OF SILICON DIODES WITH P+—N–JUNCTION IRRADIATED WITH HIGH ENERGY KRYPTON IONS

p +- n -Diodes have been studied. The diodes were manufactured on wafers (thickness 460 μm, (111) plane) of uniformly phosphorus doped float–zone–grown single–crystal silicon. The resistivity of silicon was 90 Ohm · cm and the phosphorus concentration was 5 · 1013 cm–3. The diodes were irradiated with 250 MeV krypton ions. The irradiation fluence was 108 cm–2. Deep–level transient spectroscopy (DLTS) was used to examine the defects induced by high energy krypton ion implantation. The DLTS spectra were recorded at a frequency of 1 MHz in the 78—290 K temperature range. The capacity–voltage characteristics have been measured at a reverse bias voltage from 0 to –19 V at a frequency of 1 MHz. We show that the main irradiation–induced defects are A–centers and divacancies. The behavior of DLTS spectra in the 150—260 K temperature range depends essentially on the emission voltage U e. The variation of U e allows us to separate the contributions of different defects into the DLTS spectrum in the 150—260 K temperature range. We show that, in addition to A–centers and divacancies, irradiation produces multivacancy complexes with the energy level E t = E c – (0.5 ± 0.02) eV and an electron capture cross section of ~4 · 10–13 cm2.

Electrical characteristics and deep level traps study of Au/ZnO:H Schottky diodes

The electrical characteristics and the deep level traps of Au Schottky contacts on ZnO:H films have been investigated by temperature-dependent current–voltage (I–V) and deep level transient spectroscopy (DLTS) measurements. The films were deposited with the DC-sputtering, varying the H flow rate in the Ar/H sputtering gas, so that the hydrogen per volume concentration [H2] was 0%, 20%, 33.3%, 50% and 66.6%. We found that for the Schottky diodes with [H2]=33.3% thermionic emission is the dominant current transport process at low forward voltage, taking into consideration the lateral fluctuations of the barrier height described by a Gaussian distribution model. The domination of trap-assisted current transport mechanisms is possible in the diodes with [H2]=0%, 20%, 50% and 66.6%. DLTS spectra revealed two electron traps, with activation energies of 0.29 and 0.21eV, often observed in ZnO and related to intrinsic defects. The trap concentrations are significantly lower in the 33.3% H2 diodes compared to the 0% H2 ones, indicating an interaction of these traps with hydrogen.

Mn Related Defect Levels in Germanium

1. Introduction. Mn doped germanium was studied almost 60 years ago by means of Hall effect [1] and photo conductivity [2] measurements. Based on the temperature dependence of the resistivity and carrier concentration, two levels, one at 0.37eV from the conduction band and one at 0.16eV from the valence band have been assigned to Mn impurities[1]. In agreement with the valence bond model and similar observations by counterdoping with donors for Fe, Co and Ni, these impurities have been assigned to double acceptors. Moreover, the presence of a double acceptor level was confirmed by the observation of the Mn2- state with Electron Paramagnetic Resonance (EPR). [3] However it was also noted in the early studies that the presence of contamination with acceptor impurities may cast doubt on the charge transition assignment. Since the availability of Deep Level Transient Spectroscopy (DLTS), which is a more reliable technique to study deep levels in semiconductors, the electronic properties of most of the 3d transition metals have already been studied with a higher energy resolution. Metal in-diffusion was successful to introduce Cu and Ni[4]. More recently the defect levels of Ti, Cr, Fe and Co have been identified with DLTS on metal-implanted Ge [5,6]. The present study reports on results obtained on Mn doped Ge. 2. Experimental conditions. The source material are single crystal germanium wafers, supplied by Umicore, with a shallow dopant concentration of 1014 cm-3 Ga and Sb for p- and n-type, respectively. To introduce Mn impurities, 99.995% pure Mn was thermally evaporated on the Ge surface. Afterwards the specimens were placed in a resistive furnace under Ar atmosphere for 10 minutes at 700°C. Finally, the residual Mn on the surface was removed by etching with a mixture of HNO3 and HF (3:1?). Schottky diodes for DLTS were prepared by evaporation of Au (n-type) or In (p-type) barriers immediately after etching. To identify the contamination introduced during the processing, Schottky diodes were also prepared on parts of the specimens outside the Mn covered areas. Schottky diodes on n-Ge were also prepared by annealing the n-Ge:Mn samples (after indiffusion at 700°C) to 400°C for 20 min in order to form a MnGe metallic alloy contact. 3. Results and discussion. Fig. 1 a shows the DLTS spectrum of n-Ge:Mn with a MnGe Schottky contact. A similar spectrum was recorded on the specimen with an Au-Schottky barrier. Conventional DLTS shows one electron trap (Mn-E1), while injection of minority carriers (Vp>0) reveals two additional levels (Mn-H1 and Mn-H2). Fig. 1 b shows the DLTS spectrum of p-type Ge, with presence of Mn-H1 and Mn-H2 only after Mn diffusion.Figure 1: DLTS spectrum of a) n-Ge/MnGe diode. b) p-type Ge with and without Mn-difussion. The electron trap Mn-E1 (E=0.36eV) and the hole trap Mn-H1 (E=0.14eV) correspond with the two levels reported before [1,2]. The Mn-H2 peak (E=0.34eV) has to our knowledge not been reported before in the context of transition metal impurities. Nonetheless, its appearance only in Mn diffused samples, its almost equal amplitude and concentration profile to Mn-H1 suggests that it is also related to substitutional Mn in Ge. This may indicate that the substitutional Mn defect can adopt 4 charge states in Ge, one of which certainly corresponds with 2-, as identified with EPR. 4. Conclusions. Three Mn related defect levels have been identified with DLTS. The striking similarity with previously published results for two of the observed levels suggest the assignment to substitutional Mn in germanium. The third level was not reported before but can most probably also be assigned to Mn.

Deep-level transient spectroscopy characterization of In(Ga)As quantum dots fabricated using Bi as a surfactant

In recent years, deep-level transient spectroscopy (DLTS) has been used to evaluate the electrical characteristics of quantum dots (QDs) for evaluating not only defects around QDs, but also the capture and emission properties of carriers in QDs. In this report, the electrical characteristics of 10-layer QDs grown using a Bi surfactant were evaluated mainly by DLTS. The DLTS spectra show unique dependences on the bias voltage, and it is shown that the characteristics can be explained by considering the tunneling of carriers captured in QDs. From our discussion, all of the DLTS peaks except the EL2-like signal are due to carrier emission from the electron and hole levels in QDs.

Defects Induced by Reactive Ion Etching in Ge Substrate

We investigated impacts of the Ar and CF4 plasma during reactive ion etching (RIE) on defect formation in the Ge substrates using the deep-level-transient-spectroscopy (DLTS) technique. It was found that the Ar plasma causes the roughening of the Ge surface. Moreover, the Ar plasma induces a defect with an energy level of 0.31 eV from the conduction band minimum in the Ge substrate, confirming by DLTS spectra. On the other hand, the CF4 plasma hardly induces the surface roughness of Ge. However, the CF4 plasma induces many kinds of electron and hole traps. It should be noted that the defects associated with Sb and interstitials are widely distributed to around 3-µm.

Effects of sodium ions on trapping and transport of electrons at the SiO2/4H-SiC interface

Capacitance-voltage (C-V) and Deep-Level-Transient Spectroscopy (DLTS) measurements were performed on Metal-Oxide-Semiconductor (MOS) capacitors fabricated on 4H-SiC with the SiO2 layer grown by Sodium-Enhanced Oxidation. This technique has yielded 4H-SiC MOS transistors with record channel mobility, although with poor bias stability. The effects of the mobile positive charge on the C-V characteristics and DLTS spectra were investigated by applying a sequence of positive and negative bias-temperature stresses, which drifted the sodium ions toward and away from the SiO2/4H-SiC interface, respectively. Analytical modeling of the C-V curves shows that the drift of sodium ions in the SiO2 layer during the voltage sweep can explain the temperature dependence of the C-V curves. The effects of lateral fluctuations of the surface potential (due to a non-uniform charge distribution) on the inversion layer mobility of MOS transistors are discussed within a two-dimensional percolation model.

Analysis of Deep Level Centers in GaAs pin-Diode Structures

This paper presents an analysis of the DLTS (Deep Level Transient Spectroscopy) spectra of GaAs p+-pin-n+ diodes. It is shown that the background spectrum of the deep levels is reproducible and depends on the liquid-phase epitaxy mode (LPE). The temperature dependence of the capacitance-voltage characteristics showed that the i layer is formed by compensation involving deep levels. The space charge covers the width of the i layer and spreads into the depletion p and n regions of the diode structures. DOI: http://dx.doi.org/10.5755/j01.eee.19.10.5903

In-growth of an electrically active defect in high-purity silicon after proton irradiation

Defect-related energy levels in the lower half of the band gap of silicon have been studied with transient-capacitance techniques in high-purity, carbon and oxygen lean, plasma-enhanced chemical-vapor deposition grown, n-and p-type silicon layers after 2-MeV proton irradiations at temperatures at or just below room temperature. The in-growth of a distinct line in deep-level transient spectroscopy spectra, corresponding to a level in the band gap at EV + 0.357 eV where EV is the energy of the valence band edge, takes place for anneal temperatures at around room temperature with an activation energy of 0.95 ± 0.08 eV. The line disappears at an anneal temperature of around 450 K. The corresponding defect is demonstrated not to contain boron, carbon, oxygen, or phosphorus. Possible defect candidates are discussed.

Electrical and optical characterization of extended defects induced in p‐type Si after Si ion implantation

AbstractIn this work we present the analysis of small interstitial clusters (ICs) introduced in p‐type Si after ion implantation using deep level transient spectroscopy (DLTS) and photoluminescence. Silicon ions with energy 380 keV and fluence of 1.0 x 1012 cm‐2 have been implanted into bulk p‐type Si and post‐implant annealing at temperatures between 500 oC and 800 oC specifically to create small interstitial cluster (ICs) defects. In the samples annealed at 500 oC, DLTS spectra show deep level hole traps at EV + 0.20 eV, EV + 0.25 eV, EV + 0.36 eV, and EV + 0.50 eV. The hole traps EV + 0.36 eV and EV + 0.50 eV have been attributed to the small Si self‐interstitial clusters. After increasing the post‐implant anneals to 600 oC there is a significant decrease in defect concentration and all the defects are annealed‐out at 700 oC. Photoluminescence (PL) spectroscopy of the samples reveals optical band levels, at 1218 nm (1.019 eV), and 1233 nm (1.007 eV) which have both been attributed to interstitial cluster defects. The interstitial cluster‐related optical band levels have been observed in the samples annealed at 500 oC which correlate well with DLTS measurements. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Electrical characterization of defects introduced in n-Ge during electron beam deposition or exposure

Schottky barrier diodes prepared by electron beam deposition (EBD) on Sb-doped n-type Ge were characterized using deep level transient spectroscopy (DLTS). Pt EBD diodes manufactured with forming gas in the chamber had two defects, E0.28 and E0.31, which were not previously observed after EBD. By shielding the samples mechanically during EBD, superior diodes were produced with no measureable deep levels, establishing that energetic ions created in the electron beam path were responsible for the majority of defects observed in the unshielded sample. Ge samples that were first exposed to the conditions of EBD, without metal deposition (called electron beam exposure herein), introduced a number of new defects not seen after EBD with only the E-center being common to both processes. Substantial differences were noted when these DLTS spectra were compared to those obtained using diodes irradiated by MeV electrons or alpha particles indicating that very different defect creation mechanisms are at play when too little energy is available to form Frenkel pairs. These observations suggest that when EBD ions and energetic particles collide with the sample surface, inducing intrinsic non-localised lattice excitations, they modify defects deeper in the semiconductor thus rendering them observable.

Annealing effects and DLTS study on PNP silicon bipolar junction transistors irradiated by 20 MeV Br ions

Isochronal anneal sequences have been carried out on 3CG130 silicon PNP bipolar junction transistors (BJTs) irradiated with 20MeV bromine (Br) heavy ions. The Gummel curve was utilized to characterize the annealing behavior of defects in both the emitter-base depletion region and the neutral base. The results show that the base current (IB) decreases with the increasing annealing temperature, while the collector current (IC) keeps invariably. The current gain varies slightly, when the annealing temperature (TA) is lower than 500K, while varies rapidly at TA>550K, and the current gain of the 3CG130 BJT annealing at 700K almost restore to that of the pre-radiation transistor. The deep level transient spectroscopy (DLTS) data was used to assign the relative magnitude of each of the important defects. Based on the in situ electrical measurement and DLTS spectra, it is clear that the V2(+/0) trap is the main contribution to the degradation of current gain after the 20MeV Br ions irradiation. The V2(+/0) peak has many characteristics expected for the current gain degradation.

PL and DLTS Analysis of Carbon-Related Centers in Irradiated P-Type Cz-Si

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 (CiOi) 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, Ev, in the DLTS spectra are observed in the annealed samples. The evolution of the CiOiand Ev+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 CiOilevel decreases with heat–treatment, which is consistent with the PL data for the C–line. The intensity of the Ev+0.39 eV level is enhanced and then saturates with annealing duration. We tentatively assign this level to the interstitial carbon–oxygen dimer (CiO2i).

Annealing effects and DLTS study on NPN silicon bipolar junction transistors irradiated by heavy ions

Isochronal anneal sequences have been carried out on 3DG112 silicon NPN bipolar junction transistors (BJTs) irradiated with 20MeV bromine (Br) heavy ions. The Gummel curve is utilized to characterize the annealing behavior of defects in both the emitter-base depletion region and the neutral base. We find that the base current (IB) decreases with the increasing annealing temperature, while the collector current (IC) remains invariable. The current gain varies slightly, when the annealing temperature (TA) is lower than 400K, while varies rapidly at TA<450K, and the current gain of the 3DG112 BJT annealing at 700K almost restore to that of the pre-radiation transistor. Deep level transient spectroscopy (DLTS) data is used to assign the relative magnitude of each of the important defects. Based on the in situ electrical measurement and DLTS spectra, it is clear that the V2(−/0)+V-P traps are the main contribution to the degradation of current gain after the 20MeV Br ions irradiation. The V2(−/0)+V-P peak has many of the characteristics expected for the current gain degradation.

Temperature-independent slow carrier emission from deep-level defects in p-type germanium

In the deep-level transient spectroscopy (DLTS) spectra of the 3d-transition metals cobalt and chromium in p-type germanium, evidence is obtained that hole emission from defect levels can occur by two parallel paths. Besides classical thermal emission, we observed a second, slower and temperature-independent emission. We show that this extra emission component allows determining unambiguously whether or not multiple DLTS peaks arise from the same defect. Despite similar characteristics, we demonstrate that the origin of the non-thermal emission is not tunnelling but photoionization related to black-body radiation from an insufficiently shielded part of the cryostat.

Effect of surface passivation by SiN/SiO2 of AlGaN/GaN high-electron mobility transistors on Si substrate by deep level transient spectroscopy method

Device performance and defects in AlGaN/GaN high-electron mobility transistors have been correlated. The effect of SiN/SiO2 passivation of the surface of AlGaN/GaN high-electron mobility transistors on Si substrates is reported on DC characteristics. Deep level transient spectroscopy (DLTS) measurements were performed on the device after the passivation by a (50/100 nm) SiN/SiO2 film. The DLTS spectra from these measurements showed the existence of the same electron trap on the surface of the device.

DLTS Study of plastically deformed copper-doped n-type germanium

Classical deep level transient spectroscopy (DLTS) and its modification are used to study the time constants of electron capture by substitutional Cu s 2− atoms and thermal electron emission from Cu s 3− atoms in plastically deformed Cu-doped n-type germanium. The activation energy E σ, the electron capture cross-section, the energy E 3 of the third acceptor level of Cu s/3− atoms, and the ionization entropy are determined. The lack of E 3-level broadening, the exponential capture kinetics for a filling-pulse duration of t p ≲ 1 ms, the fact that the Cu s/2−/3−-atom recombination parameters are independent of the dislocation density, and the low concentration of Cu s/2−/3− atoms in the deformed samples suggest that the DLTS spectra are due to Cu s/2−/3− atoms located outside the Read cylinders.

Electrical characterisation and predictive simulation of defects induced by keV Si+ implantation in n-type Si

In this work, we focused on the analysis of implantation-induced defects, mainly small interstitial clusters (ICs) and {311} defects introduced in n-type Si after ion implantation using deep level transient spectroscopy (DLTS). Silicon ions (at 160 keV or 190 keV) of fluences ranging from (0.1–8.0) × 1013 cm−2 have been implanted into n-type Si and annealed at temperatures between 500 °C and 800 °C specifically to create small ICs or {311}s rod-like defects. In samples dominated by small ICs, DLTS spectra show prominent deep levels at Ec − 0.24 eV and Ec − 0.54 eV. After increasing the fluence and temperature, i.e., reducing the number of small ICs and forming {311} defects, the peak Ec − 0.54 eV is still dominant while other electron traps Ec − 0.26 eV and Ec − 0.46 eV are introduced. There were no observable deep levels in reference, non-implanted samples. The identity and origin of all these traps are interpreted in conjunction with recently developed predictive defect simulation models.

Charge deep-level transient spectroscopy of SiO2 and Al2O3 layers with embedded Ge nanocrystals

The present study of deep level transient spectroscopy (DLTS) is focused on a comparison of the trap states in two types of Ge nanocrystallites (NCs)-insulator composites. The investigated systems were the dielectric matrices Al2O3 and SiO2 in which the Ge NCs were embedded. We have found couples of traps with related values of activation energies in both the Ge:Al2O3 and the Ge:SiO2 films. In the films with a relatively low Ge content (where only small NCs sized 3–5 nm could have been detected by means of Raman spectroscopy), we observed traps with an energy level ∼50 meV in the Ge:Al2O3 films and 120 and 50 meV in the Ge:SiO2 films. In both systems, we found that the electron traps have a small carrier capture cross-section (10−21–10−23 cm2). We have identified the levels of the traps to be the quantum confinement levels in the small Ge NCs. For samples of higher Ge contents, where the NC size reaches about 20 nm and where an appreciable portion of the dielectric matrix consists of amorphous Ge (α-Ge), we found traps with an energy of 0.22–0.24 eV in the Ge:Al2O3, and 0.26–0.27 eV in the Ge:SiO2 samples. We suggest that this peak in the charge DLTS (Q-DLTS) spectra is associated with a trap at the Ge-NC/α-Ge interface. We have also identified the energy position of a defect level in the Ge:Al2O3 layers, which lies 0.46–0.49 eV below the conduction-band edge of the Si substrate.

Classification of Defective Regions in p-type Multicrystalline Silicon by Comparing Luminescence Images Measured under Different Conditions

In this contribution, we apply three different camera-based luminescence imaging techniques to mc-Si wafers and solar cells, fabricated on neighboring wafers. On wafer level, we determine the spatially-resolved carrier lifetime using calibrated photoluminescence lifetime imaging. On the solar cell level, we use band-to-band electroluminescence and sub-band-gap electroluminescence imaging for the characterisation. We analyze the differences obtained by the different techniques in specific defective areas. Characteristic regions are additionally examined using deep-level transient spectroscopy (DLTS). Comparing different luminescence images, we find different signal correlations in selected regions of the wafers and the neighboring cells presumably caused by different types of defects, which react more or less effective on the phosphorus gettering during the solar cell process. DLTS spectra show that in the edge region of the wafer close to the crucible, FeB pairs are present in the wafer as well as in the cell. However, the FeB concentration in the cell is, due to phosphorus gettering during the cell process, reduced by one order of magnitude. In regions which appear as very recombination-active defect clusters in the solar cell, we detect ZnB pairs by DLTS analysis. Note that the ZnB itself is a shallow centre and therefore expected to be not strong recombination active. However, our measurements reveal that Zn is present in regions with increased recombination activity, which is also in good agreement with the high total Zn concentration measured in the mc-Si ingot. We hence conjecture that dislocation clusters decorated by Zn are responsible for the non-getterable defect regions.

Capacitance transient study of a bistable deep level in e−-irradiated n-type 4H–SiC

Using capacitance transient techniques, a bistable centre, called FB centre here, was observed in electron irradiated 4H–SiC. In configuration A, the deep level known as EH5 (Ea = EC − 1.07 eV) is detected in the deep level transient spectroscopy spectrum, whereas for configuration B no obvious deep level is observed in the accessible part of the band gap. Isochronal annealing revealed the transition temperatures to be TA → B > 730 K and for the opposite process TB → A ≈ 710 K. The energy needed to conduct the transformations were determined to be EA(A → B) = (2.1 ± 0.1) eV and EA(B → A) = (2.3 ± 0.1) eV, respectively. The pre-factor indicated an atomic jump process for the opposite transition A → B and a charge carrier-emission dominated process in the case of B → A. Minority charge carrier injection enhanced the transformation from configuration B to configuration A by lowering the transition barrier by about 1.4 eV. Since the bistable FB centre is already present after low-energy electron irradiation (200 keV), it is likely related to carbon.