DLTS Technique Research Articles

Electrically Active Defects Induced by α‐Particle Irradiation in p‐Type Si Surface Barrier Detector

Herein, the investigation of radiation‐induced defects generated in the Al/SiO2/p‐type FZ Si surface barrier detector upon irradiation with α‐particles at room temperature using capacitance−voltage (C−V) and current deep‐level transient spectroscopy (IDLTS) methods is conducted. The carried out C−V measurements indicate the formation of at least 8 × 1012 cm−3 radiation‐induced acceptor traps at the depth fairly close to that where, according to TRIM simulations, the highest concentration of vacancy‐interstitial pairs is created by the incoming α‐particles. The studies conducted by the current DLTS technique allow to relate the observed increase in the acceptor concentration with the near‐midgap level at E V + 0.56 eV. This level can apparently be associated with V2O defects recognized previously to be responsible for the space−charge sign inversion in the irradiated n‐type Si detectors.

Study of Radiation-Induced Defects in p-Type Si1-xGex Diodes before and after Annealing.

In this work, electrically active defects of pristine and 5.5 MeV electron irradiated p-type silicon–germanium (Si1−xGex)-based diodes were examined by combining regular capacitance deep-level transient spectroscopy (C-DLTS) and Laplace DLTS (L-DLTS) techniques. The p-type SiGe alloys with slightly different Ge contents were examined. It was deduced from C-DLTS and L-DLTS spectra that the carbon/oxygen-associated complexes prevailed in the pristine Si0.949Ge0.051 alloys. Irradiation with 5.5 MeV electrons led to a considerable change in the DLT spectrum containing up to seven spectral peaks due to the introduction of radiation defects. These defects were identified using activation energy values reported in the literature. The double interstitial and oxygen complexes and the vacancy, di-vacancy and tri-vacancy ascribed traps were revealed in the irradiated samples. The interstitial carbon and the metastable as well as stable forms of carbon–oxygen (CiOi* and CiOi) complexes were also identified for the electron-irradiated SiGe alloys. It was found that the unstable form of the carbon–oxygen complex became a stable complex in the irradiated and the subsequently annealed (at 125 °C) SiGe samples. The activation energy shifts in the radiation-induced deep traps to lower values were defined when increasing Ge content in the SiGe alloy.

Depth Profile Analysis of Deep Level Defects in 4H-SiC Introduced by Radiation

Deep level defects created by implantation of light-helium and medium heavy carbon ions in the single ion regime and neutron irradiation in n-type 4H-SiC are characterized by the DLTS technique. Two deep levels with energies 0.4 eV (EH1) and 0.7 eV (EH3) below the conduction band minimum are created in either ion implanted and neutron irradiated material beside carbon vacancies (Z1/2). In our study, we analyze components of EH1 and EH3 deep levels based on their concentration depth profiles, in addition to (−3/=) and (=/−) transition levels of silicon vacancy. A higher EH3 deep level concentration compared to the EH1 deep level concentration and a slight shift of the EH3 concentration depth profile to larger depths indicate that an additional deep level contributes to the DLTS signal of the EH3 deep level, most probably the defect complex involving interstitials. We report on the introduction of metastable M-center by light/medium heavy ion implantation and neutron irradiation, previously reported in cases of proton and electron irradiation. Contribution of M-center to the EH1 concentration profile is presented.

Investigation of deep defects in nanocrystalline-Si/Si interfaces using acoustic spectroscopy

Abstract A set of structures with nanocrystalline-Si/Si interfaces formed on p-type Si substrate appropriated for photovoltaic application was prepared. The Acoustic DLTS technique based on the acoustoelectric response signal produced by the structure when a longitudinal acoustic wave propagates through the structure was used together with electric characterization to determine deep defects and the role of both individual layers. Several kinds of interface deep centers with activation energies typical for dangling bonds, oxygen participated Si or point defects were observed as well as a particular influence of individual layers on the interface states. The obtained results are analyzed, discussed and subsequently compared.

Carbon‐hydrogen related defects in SiGe observed after dc H plasma treatment

In the present study, the electrical and structural properties of two carbon‐hydrogen related DLTS levels (E42 and E262) that appear after hydrogen plasma treatment are investigated in diluted Si1−xGex alloys. E42 and E262 were previously observed in pure Si after hydrogenation by a dc hydrogen plasma. They were correlated with different charge states of a carbon–hydrogen complex, where H is located on the anti‐bonding position at the carbon atom (CH1AB). By utilizing the Laplace DLTS technique we show that the DLTS peaks E42 and E262 consist of several components in Si1−xGex. These components can be quantitatively explained by the presence of Ge atoms in the first and second nearest‐neighborhood of the CH1AB complex. The observed Laplace DLTS spectra indicate a preference of hydrogen to bond to carbon with a Ge atom in its first nearest‐neighborhood.

Investigation of Mobility Transient on Organic Transistor by Means of DLTS Technique

We analyzed the transient response of organic transistors by means of the deep-level transient spectroscopy technique. We showed how the current transient can be related to a mobility transient from which we estimated two different kinds of activation energies as well as information to the density of states.

Effect of Interface Trap States on Optical Barrier Height of NiSi/Si Infrared Detector

In this paper, influence of interface trap states on barrier height of NiSi/Si Schottky diode is presented. The proposed study is important in view of its application potential as an infrared detector. This involves preparation of silicide by depositing 10 nm thick nickel on n-Si, followed by rapid thermal annealing at 500 0C in argon ambience. The thickness of the silicide was measured by cross-sectional HRTEM and found to be 24 nm. The zero bias barrier heights were measured by current-voltage and optical techniques, and were found to be 0.62 eV and 0.54 eV respectively. This discrepancy in barrier height is attributed to the presence of acceptor like interface trap state which was identified by DLTS technique.

Investigation of Interface States in Si/NAOS-SiO2/HfO2 Structures Using Complete Acoustic Spectroscopy

The set of MOS structures formed on n-type Si substrate with (NAOS)-SiO2/HfO2 gate dielectric layers was prepared and annealed in N2 atmosphere at various temperatures to stabilize the structure and to decrease the interface states density. Two Acoustic DLTS techniques using both surface (SAW) and longitudinal (LAW) acoustic waves including acoustoelectric response signal versus gate voltage dependence (Uac-Ug characteristics) were used to characterize the interface states and the role of annealing treatment. The main interface deep centers with activation energies about 0.30 and 0.20 eV, typical for dangling bonds were observed as well as a particular influence of annealing treatment on the interface states. The obtained results are analyzed, discussed and mutually compared.

New Results on the Electrical Activity of <i>3d</i>-Transition Metal Impurities in Silicon

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.

A re‐examination of the interstitial Ti levels in Si

AbstractUsing high‐resolution Laplace DLTS studies we demonstrate that three Ti‐related levels (E40, E150 and H180) previously assigned to the different charge states of the interstitial Ti belong to different Ti defects. The enhancement of the emission rates of E40 and H180 as a function of the electric field (Poole‐Frenkel effect) shows that these defects are charged before they capture a majority carrier in n‐ and p‐type Si, respectively. In contrast to the previous studies we did not observe the Poole‐Frenkel effect for E150. The inconsistence is correlated with the presence of H‐related defects close to E150, which cannot be distinguished by using the conventional DLTS technique. The absence of the Poole‐Frenkel effect for E150 indicates that the defect is an acceptor in n‐type Si. The origin of the defects will be discussed. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

DLTS Study of Pd-H Complexes in Si

We have observed five electron traps with energy levels at 0.16, 0.30, 0.40, 0.53 and 0.67 eV below the conduction band in Pd and H doped Si by DLTS technique. Successive annealing at 373 K and 473 K for 30 min respectively caused two levels at Ec-0.16 eV and Ec-0.67 eV to disappear and simultaneously a new level to emerge at Ec-0.19 eV. From such annealing behavior and the comparison of the energy levels observed in the present study with those in the literature, we assign them to various Pd and H related defects as follows, Pd-H2: Ec-0.16 eV and Ec-0.67 eV, Pd acceptor: Ec-0.19 eV, Pd-H3: Ec-0.30 eV, Pd-H1: Ec-0.40 eV.

Laplace deep level transient spectroscopy: Embodiment and evolution

This paper is to commemorate the work of Leszek Dobaczewski11Professor Leszek Dobaczewski died in April 2010. who devoted much of his life to the development and application of high resolution DLTS.Under good experimental conditions Laplace DLTS provides an order of magnitude higher energy resolution than conventional DLTS techniques. This has had a profound effect on electrical defect spectroscopy enabling the effect of external probes, such as uniaxial stress, and internal perturbations, such as the proximity of atoms isovalent with the host, to be quantified in terms of electronic behaviour. Laplace DLTS provides a synergy with other techniques that was difficult or impossible to achieve previously. In this paper we present an overview of the development of LDLTS and illustrate some of its uses by describing its application in a number of key areas of defect research.Leszek Dobaczewski was born on 25th December 1954. He received his education in Warsaw taking his PhD in 1986 with Jerzy Langer at the Institute of Physics on “Recombination Processes at defects with the large lattice relaxation”. He held a research position at the institute in Warsaw until he came to Manchester in 1990 and thereafter alternated between Manchester and Warsaw. He worked primarily on the development and application of high resolution DLTS. He was awarded the degree of DSc in 1994 for his work on DX centres and held an appointment as full professor in Warsaw with Visiting Professor posts at Manchester and Aarhus.

Spectroscopic Studies of Iron and Chromium in Germanium

We report on the electronic properties of Fe and Cr in n-type germanium using conventional and Laplace DLTS techniques, which in the case of Schottky barriers, are restricted to levels located in the upper half of the band gap. In this work we present extensive DLTS and Laplace DLTS results, re-examining various basic properties of Fe and Cr in n-type Ge samples. In addition our analysis bring new insights into the microscopic behavior of these two chemical species such as their interactions with hydrogen present as an unwanted contaminant, giving rise to the generation of other related levels in the band gap.

On the Electrical Characterization of Grain Boundaries in Multicrystalline Silicon

Impurity decoration of grain boundaries (GB) introduces deep levels and enhances their recombination activity. In this study we use the standard DLTS technique to investigate the influence of the GB structure on the electrical properties of mc-Si. The detected DLTS spectra have an opposite signal compared to the usually known majority carrier peaks of deep levels, but standard DLTS analysis can yield trap energies and capture cross sections. By comparing the properties between GB and intra-grain regions with similar minority carrier lifetime, it is considered that the DLTS signals might be due to traps generated in the extended defects present both at GBs and grains. It is observed that ∑3 GB has deep level traps at the same energy level as ∑9 GB, while the trap concentration in the former one is lower than the latter. Furthermore, a phosphorous gettering treatment can reduce the recombination activities both in the grains and at the GBs.

Dependence of silicon PIN diode electrical characteristics on proton fluence

A comparative analysis of capacitance–voltage (C–V ) and current–voltage (I–V ) characteristics dependent on proton irradiation fluence in the range from 7·1012 to 7·1014 p/cm2 has been performed in float zone (FZ) silicon PIN diodes. A δ-shape and triangle profiles of radiation induced defects were formed by irradiation with protons having energy in the range from 2.0 to 2.7 MeV. Temperature-dependent variations of current (I–T) at fixed reverse voltage VR enable one to extract the thermal activation parameters. These values are found to be in a quantitative agreement with trap activation parameters measured by DLTS technique. The role of point and extended defects in correlated modifications of C–V and I–V characteristics of the irradiated diodes is discussed. Keywords: radiation defects, Si PIN diodes, capacitance–voltage, current–voltage characteristics

Electrical properties of nitrogen‐related defects in n‐type GaAsN grown by molecular‐beam epitaxy

AbstractDeep Level Transient Spectroscopy (DLTS) and Laplace DLTS (LDLTS) techniques have been employed to characterize electron traps in dilute GaAsN epitaxial layers grown by Molecular Beam Epitaxy (MBE) on n+ GaAs substrates. The GaAsN samples used in this study were silicon doped (n‐type) and contained nitrogen concentrations ranging from 0.2% to 1.2%. The number of electron traps in each sample detected by the DLTS measurements is found to be dependent on the nitrogen contents. Some of the traps have been identified with previously reported (N‐As)spl split interstitial, nitrogen‐split interstitial, EL6‐like interfacial defect and EL3 defect levels. In a control sample without nitrogen we observed only one deep electron emitting level of energy 0.76 eV and no shallow levels have been seen. However, new shallow traps with energies ranging from 0.036 to 0.13 eV have been detected in samples with nitrogen content in the range 0.2% to 0.4%. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Laplace DLTS of molecular beam epitaxy GaAs grown on (100) and (211)B substrates

AbstractDeep Level Transient Spectroscopy (DLTS) and Laplace DLTS (LDLTS) techniques have been employed to study defects in n‐type GaAs grown by MBE on (100) and (211)B GaAs planes. The DLTS spectra were different for the two GaAs substrate orientations. Five and four defect states are found in samples grown on (100) and (211)B GaAs planes, respectively with activation energies ranging from 0.054 eV to 0.570 eV. For all of the traps observed in our samples we obtained small activation energies as compared to the previous data published in literature on n‐GaAs samples grown by MBE. This can be explained by the fact that the emission of the carriers depends on the applied electric field and temperature dependence of the carrier concentration. These two phenomena seem to explain the small trap energies seen in our samples. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Comparative Study of Electrical and Optical Properties of Plastically Deformed Silicon

The Czochralski-grown silicon crystals plastically deformed at 680±C to the residual strain of 5% and subsequently annealed in the temperature range of 650{850±C were studied by the IR absorption and DLTS techniques. The formation and disappearance kinetics were investigated for several weak IR absorption lines around the 1000 cm¡1 wave number, which were previously related to the deformation-induced defects of non-dislocation nature in the dislocation trails. In parallel, the spectrum and concentrations of the deep-level centers in the upper half of the gap were measured by DLTS. It is found that the deep-level centers and op- tically active defects exhibit a common behavior during the post-deformation heat treatments. However, a direct correspondence between the IR and DLTS features cannot be established be- cause of the higher concentration of the deep-level centers as compared to the optically active defects.

Dislocation States and Deformation-Induced Point Defects in Plastically Deformed Germanium

We used the DLTS and photoluminescence (PL) techniques to study the deep states due to dislocations and deformation-induced point defects (PDs) in plastically deformed p-type germanium single crystals containing predominantly 60 dislocations with density ND, ranging from 105 to 106 cm-2. The narrow line near the temperature 140K dominates in the DLTS spectra. The ionization enthalpy and the capture cross section for holes traps indicate that the substitution copper atoms Cus are the main type of PDs. A decrease of the Cus atoms concentration and redistribution of the intensity in the PL spectra after the heat treatment of deformed samples at a temperature 500 °C are attributed to the diffusion of copper atoms to dislocations resulting in the appearance of “dirty” regular segments of 60 dislocations.

Relation between photocurrent and DLTS signals observed for quantum dot systems

The electro-optical properties of InAs/GaAs quantum dots (QD) are presented. It is shown that they can contribute to the photocurrent at temperatures where photo-generated excitons can split. This happens if the carrier binding energies are not too large to prevent the carrier emission process. At lower temperatures, the exciton recombination process can effectively compete with the carrier emission processes and no photocurrent signal is observed. The Laplace DLTS technique has been used in a wide temperature range to analyze the electron and hole emission separately and combine them with the observed temperature dependence of the photocurrent. The photocurrent measurements also showed that with an increase in temperature the dot-related photocurrent peaks shift to lower energies with a rate similar to GaAs band gap shrinkage.