Laplace Deep Level Transient Spectroscopy Research Articles

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.

Electrical Characterization of Metastable Defects Introduced in GaN by Eu-Ion Implantation

Gallium nitride (GaN), grown by HVPE, was implanted with 300 keV Eu ions and then annealed at 1000 oC . Deep level transient spectroscopy (DLTS) and Laplace DLTS (L-DLTS) were used to characterise the ion implantation induced defects in GaN. Two of the implantation induced defects, E1 and E2, with DLTS peaks in the 100 – 200 K temperature range, had DLTS signals that could be studied with L-DLTS. We show that these two defects, with energy levels of 0.18 eV and 0.27 eV below the conduction band, respectively, are two configurations of a metastable defect. These two defect states can be reproducibly removed and re-introduced by changing the pulse, bias and temperature conditions, and the transformation processes follow first order kinetics.

Electrical characterization of as-grown and H plasma treated CdTe epitaxial layers

In the present work deep level transient spectroscopy (DLTS) and high-resolution Laplace DLTS were employed to study the electrical properties of defects in as-grown and H-plasma treated CdTe thin films grown by the molecular beam epitaxy technique. We demonstrate that two dominant deep states in as-grown CdTe have the activation energy close to the midgap level and, therefore, could act as recombination centres in these crystals. Both traps are donor-like defects. However, their concentration was found to be too small to influence the electrical properties of devices based on this semiconductor. On the other hand, another dominant midgap trap was observed in H-plasma treated CdTe. The question as to the origin of these defects will be addressed.

Structure and electronic properties of trivacancy and trivacancy‐oxygen complexes in silicon

AbstractWe have recently found that the silicon trivacancy (V3) is a bistable defect that can occur in fourfold coordinated and (110) planar configurations for both the neutral and singly negative charge states [V. P. Markevich et al., Phys. Rev. B 80, 235207 (2009)]. Acceptor levels of V3 in both these configurations have been determined. It has also been shown that at T > 200 °C, the interaction of mobile trivacancies with interstitial oxygen atoms results in the formation of V3O complex with the first and second acceptor levels at Ec −0.46 and −0.34 eV. In the present work we identify donor levels arising from V3 and V3O complexes by means of deep level transient spectroscopy (DLTS) and high‐resolution Laplace DLTS on n+p silicon structures irradiated with 6 MeV electrons, combined with density functional modeling studies. It is found that both defects possess two donor levels in the (110) planar configurations. First donor levels at Ev +0.19 and +0.235 eV, and the second donor levels at Ev +0.105 and +0.12 eV are found for the V3 and V3O complexes, respectively.

Deep-level Transient Spectroscopy of GaAs/AlGaAs Multi-Quantum Wells Grown on (100) and (311)B GaAs Substrates

Si-doped GaAs/AlGaAs multi-quantum wells structures grown by molecular beam epitaxy on (100) and (311)B GaAs substrates have been studied by using conventional deep-level transient spectroscopy (DLTS) and high-resolution Laplace DLTS techniques. One dominant electron-emitting level is observed in the quantum wells structure grown on (100) plane whose activation energy varies from 0.47 to 1.3 eV as junction electric field varies from zero field (edge of the depletion region) to 4.7 × 106 V/m. Two defect states with activation energies of 0.24 and 0.80 eV are detected in the structures grown on (311)B plane. The Ec-0.24 eV trap shows that its capture cross-section is strongly temperature dependent, whilst the other two traps show no such dependence. The value of the capture barrier energy of the trap at Ec-0.24 eV is 0.39 eV.

Revealing substructures of H4 and H5 hole traps in p-type InP using Laplace deep-level transient spectroscopy

New substructures of H4 and H5 hole traps have been revealed using Laplace deep-level transient spectroscopy. Our measurements show that the hole traps H4 and H5 can have at least three components for each. Moreover, the activation energies are deduced and the microscopic nature of these substructures is discussed.

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.

Low-temperature irradiation-induced defects inp-type germanium

Besides two well-known dominant peaks, which have been earlier correlated with the single monovacancy and gallium interstitial defect, a number of small lines appear in deep level transient spectroscopy (DLTS) spectra measured in situ after particle irradiation at low temperatures in p-type germanium. Three of the most pronounced have been studied to some detail in the present investigation by combining DLTS and high-resolution Laplace DLTS. These three lines are called H70, H280 and H290, where the H refers to their hole-trap nature, and the numbers to their apparent enthalpy for hole emission relative to the valence-band edge. The H70 trap is most probably a primary defect, and its observed energy level is found to be an acceptor level. Possible defects related to these DLTS lines are discussed with special emphasis on the divacancy defect in germanium.

Energy state distributions at oxide–semiconductor interfaces investigated by Laplace DLTS

Energy state distributions at oxide–semiconductor interfaces investigated by Laplace DLTS

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 &amp; 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 &amp; Co. KGaA, Weinheim)

Formation of Radiation-Induced Defects in Si Crystals Irradiated with Electrons at Elevated Temperatures

Defects induced in silicon crystals by irradiations with 6 MeV electrons in the temperature range 60 to 500 oC have been studied by means of deep level transient spectroscopy (DLTS) and high-resolution Laplace DLTS. Diodes for the study were fabricated on n-type epitaxially grown Si wafers. The DLTS spectra for the samples irradiated at elevated temperatures were compared with those for samples, which were subjected to irradiation at 60 oC and subsequent isochronal anneals in a furnace. The dominant radiation-induced defects in the samples irradiated at temperatures lower than 400 oC were found to be vacancy-oxygen (VO) and interstitial carbon – interstitial oxygen (CiOi) complexes. The introduction rates of the VO and CiOi centers increased about twice upon raising the irradiation temperature from 50 to 400 oC. It is argued that this effect is associated with either a) the suppression of the annihilation rate of Frenkel pairs or b) a decrease in the threshold energy for displacement of a host Si atom upon increase in the irradiation temperature. Transformations of deep level traps due to divacancies (V2) and trivacancies (V3) to V2-oxygen and V3-oxygen complexes were found to occur upon irradiation or annealing at temperatures exceeding 250 oC. A clear anti-correlation between changes in the minority carrier life time induced in the p+-n diodes by irradiation at different temperatures and changes in the concentrations of radiation-induced vacancy- and vacancy-oxygen-related complexes was found.

Donor level of interstitial hydrogen in semiconductors: Deep level transient spectroscopy

Abstract The behaviour of hydrogen in crystalline semiconductors has attracted considerable interest during several decades. Due to its high diffusion rate and ability to react with a wide variety of lattice imperfections such as intrinsic point defects, impurities, interfaces and surfaces, hydrogen is an impurity of fundamental importance in semiconductor materials. It has been already evidenced in previous investigations that the most fundamental hydrogen-related defects in-group IV semiconductors are interstitial hydrogen atoms occupying the bond-centre site (BC) or the interstitial tetrahedral site (T). Using first-principles calculations Van de Walle predicted similar properties of isolated hydrogen in other II–VI and III–V semiconductors. Another interesting prediction shown in that work was the existence of a universal alignment for the hydrogen electronic (−/+) level. Until now there is no direct experimental information regarding the individual isolated hydrogen states in compound semiconductors and most reported properties have been inferred indirectly. In the present work in-situ conventional deep level transient spectroscopy (DLTS) and high-resolution Laplace DLTS techniques are used to analyse hydrogen-related levels after low-temperature proton implantation in different II–VI and III–V semiconductors including GaAs, ZnO and CdTe. From these experimental observations the donor level of isolated hydrogen is found to keep almost a constant value in the absolute energy scale taking into account different band-offsets calculated for the whole group of semiconductors.

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.

Energy state distributions at oxide–semiconductor interfaces investigated by Laplace DLTS

Abstract At disordered Si/SiO 2 interfaces the lattice mismatching results in dangling bond P b centres forming a rather broad distribution of energy states. In this study these energy distributions have been determined using isothermal current Laplace deep level transient spectroscopy (DLTS) for the (1 0 0) and (1 1 1) interface orientations. The (1 1 1) distribution is 0.08 eV broad and centred at 0.38 eV below the silicon conduction band. This is consistent with only P b0 states being present. While for the (1 0 0) orientation this distribution is broader (0.1 eV) and deeper (0.43 eV) on the energy scale. Detailed studies revealed two types of the interface states in this broad distribution: one similar to the (1 1 1) orientation while the other has a negative-U character in which the emission rate versus surface potential dependence is qualitatively different from that observed for P b0 and is presumed to be P b1 . Discrepancies between P b states energy distributions obtained with a use of the isothermal Laplace and conventional DLTS measurements are discussed. The presented experimental procedure can be used for analysis of interface states observed at interfaces of other semiconductor–oxide/dielectric systems.

Neutron-irradiation-induced defects in germanium: A Laplace deep level transient spectroscopy study

Deep level transient spectroscopy (DLTS), high-resolution Laplace DLTS (L-DLTS) and L-DLTS combined with uniaxial stress have been used in this work for characterization and identification of electrically active defects induced in Sb-doped germanium crystals by irradiation with fast neutrons. The samples were irradiated with relatively small doses of neutrons (≤5 × 10 11 cm −2) in order to produce uniformly distributed damage and to detect small defect clusters. It is found that for such low neutron doses in many respects the damage produced is similar to that resulting from electron irradiation. Vacancy–antimony (V–Sb) pairs uniformly distributed in the sample bulk are the dominant defects observed in the DLTS spectra. It is inferred from the L-DLTS measurements under application of uniaxial stress that the V–Sb pair has a trigonal symmetry in the doubly negatively charged state. It is argued that an electron trap with the activation energy for electron emission of 0.1 eV is related to an acceptor state of a small vacancy cluster located in highly damaged regions of the neutron-irradiated samples. L-DLTS measurements under application of uniaxial stress indicate that the symmetry of the defect is low, monoclinic-I, C 1h point group, or lower. Environment-induced broadening of the L-DLTS signal due to this centre prevents precise determination of the defect symmetry.

Gallium interstitial in irradiated germanium: Deep level transient spectroscopy

Two electronic levels at 0.34 eV above the valence band and 0.32 eV below the conduction band, in gallium doped, p-type Ge irradiated with 2 MeV electrons have been studied by deep level transient spectroscopy (DLTS) with both majority- and minority-carrier injections, and Laplace DLTS spectroscopy. It is concluded that these levels, having donor and acceptor characters, respectively, are correlated with interstitial Ga atoms, formed by the Watkins-replacement mechanism via self-interstitials.

Determination of radiation-defect symmetry by high-resolution Laplace DLTS

It has been shown for the first time that implementation of the L-curve approach to choose the regularization parameter for Laplace DLTS significantly increases the reliability of the data obtained. The possibility of considerable reduction of the mechanical stress necessary for energy level splitting in determination of the defect symmetry due to the increase in the Laplace DLTS resolution is shown by the example of the wellknown point radiation defect: oxygen-vacancy complex (A center) in a CzSi crystal.

High resolution Laplace deep level transient spectroscopy of p‐type polycrystalline diamond

AbstractHigh resolution Laplace deep level transient spectroscopy (LDLTS) has been used to characterise deep electronic states in the band gap of polycrystalline p‐type diamond. The thin diamond films were grown by the hot‐filament chemical vapour deposition (HFCVD) technique on p‐type and n‐type Si for the formation of the Schottky and p–n diodes respectively. The B concentration in the diamond films ranged from 7 × 1018 cm–3 to 7 × 1021 cm–3. Conventional capacitance DLTS showed a fairly narrow peak at about 180 K from the diamond grown on p‐type Si, but further analysis with LDLTS shows that this peak originates from a complex defect with up to three hole emission rates. In the case of the Schottky diode, these emission rates do not vary much with temperature which indicates that they may be due to the presence of an extended defect, where the valence band itself is changing its profile as the traps capture more carriers. LDLTS of a similar trap in the diamond grown on n‐type Si also shows three emission rates, which do not vary as expected with temperature. The results are discussed in terms of defects existing in the strain fields of grain boundaries, and exhibiting non point‐defect like properties. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

No trace of divacancies at room temperature in germanium

Alpha-particle irradiated n +p-mesa diodes of Ge were investigated by conventional deep level transient spectroscopy and high-resolution Laplace deep level transient spectroscopy. The electronic and annealing properties of the observed hole traps were studied. It is concluded that none of the observed traps which are stable at room temperature are related to the divacancy. These results are consistent with previous optical studies. They are, however, in disagreement with recent numerical density function calculations which predict a stable divacancy at room temperature with band-gap levels in the lower half of the band gap.