Laplace Deep Level Transient Spectroscopy Techniques Research Articles

Effects of gamma radiation on the electrical properties of InAs/InGaAs quantum dot-based laser structures grown on GaAs and Si substrates by molecular beam epitaxy.

This study investigates the impact of gamma radiation on the electrical properties of InAs/InGaAs quantum dot-based laser structures grown on both GaAs (Sample A) and Si (Sample B) substrates using molecular beam epitaxy. The research explores the electrical characteristics of the lasers before and after being exposed to gamma radiation employing current-voltage (I-V), capacitance-voltage (C-V), deep level transient spectroscopy (DLTS) and Laplace DLTS techniques. The results show that the electrical properties of the lasers change due to gamma radiation exposure, and the extent of the change depends on the substrate used for growth. The I-V results revealed that the ideality factor (n) and built-in voltage were increased in Sample A and Sample B after radiation. Nonetheless, the series resistance (Rs) at room temperature decreased in both samples after radiation. Overall, this study provides valuable insights into the effects of gamma radiation on the electrical properties of InAs/InGaAs quantum dot lasers and highlights the importance of considering substrate materials in the design of radiation-hardened electronic devices.

Investigation of the effects of GaAs substrate orientations on the electrical properties of sulfonated polyaniline based heterostructures

In this work we present a detailed study of the influence of the GaAs substrate orientation on the electrical properties of heterojunctions based on GaAs and sulfonated polyaniline (SPAN) using Current-Voltage (I-V), Capacitance-Voltage (C-V), Deep-Level Transient Spectroscopy (DLTS) and Laplace DLTS techniques. Three different GaAs substrate orientations have been investigated, namely (1 0 0), (3 1 1)A and (3 1 1)B. The I-V results revealed that the turn-on voltage (Von) of SPAN/(3 1 1)B GaAs heterojunction is higher than that for SPAN/(1 0 0) GaAs and SPAN/(3 1 1)A GaAs heterojunctions. The DLTS results showed that the number of electrically active defects present in devices based on the lower index (1 0 0) plane of GaAs substrate is higher than those of higher index (3 1 1)A and (3 1 1)B GaAs substrates, corroborating with I-V results. In order to investigate the role of interface states, capacitance-frequency measurements were performed in forward bias on all three devices.

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.

Thermal stability of defects introduced by electron beam deposition in p-type silicon

The electronic and thermal properties of defects introduced during electron beam deposition (EBD) followed by isochronal annealing of titanium (Ti) contacts on p-Si were investigated. In this work, EBD-deposited Ti Schottky contacts were annealed within a temperature range of 200–400°C. Current-voltage (I-V) measurements were conducted to monitor the change in electrical characteristics with every annealing step. A barrier height of 0.55eV was measured on the as-deposited sample. Deep level transient spectroscopy (DLTS) and Laplace-DLTS techniques were employed to identify the defects introduced after EBD and isochronal annealing of the Ti Schottky contacts. DLTS revealed that the main defects introduced during metallization were hole traps H(0.05), H(0.23) and H(0.38). Annealing at 300°C removed the two hole traps H(0.05) and (0.38). Atomic force microscopy (AFM) was performed on the contacts to monitor their surface topology. The surface of the contacts became rougher as the annealing temperature increased. The slight increase in root-mean-square roughness of the contacts with increasing annealing temperature may be attributed to outdiffusion of Si into Ti layers.

Characterization of deep-level defects in GaNAs/GaAs heterostructures grown by APMOVPE

AbstractConventional deep level transient spectroscopy (DLTS) and high-resolution Laplace DLTS techniques were used to study electrical properties of deep-level defects in dilute GaNAs epitaxial layers grown by atmospheric-pressure metalorganic vapourphase epitaxy (APMOVPE) on the GaAs substrate. Three samples with nitrogen concentrations of 1.2 %, 1.6 % and 2.7 % were investigated. In DLTS and LDLTS spectra of the samples, four predominant electron traps were observed. On the basis of the obtained electrical parameters and previously published results, one of the traps was associated with N-related complex defects, while the other traps with common GaAs-like native defects and impurities, called EL6, EL3 and EL2.

Carbon-Hydrogen Complexes in <i>n</i>- and <i>p</i>-Type SiGe-Alloys Studied by Laplace Deep Level Transient Spectroscopy

A deep level transient spectroscopy (DLTS) study on n- and p-type diluted Si1-xGex alloys (x=0, 0.011, 0.026, 0.046, and 0.070) is presented. Defect levels of several carbon-hydrogen (CH) complexes are observed. The high-resolution Laplace-DLTS technique allows us to detect configurations of defects which contain different numbers of Ge atoms in the first and second-nearest neighbourhood of the CH complexes. The electrical properties of the defects will be analysed and their origin will be discussed.

Transition metals (Ti and Co) in silicon and their complexes with hydrogen: A Laplace DLTS study

The electrical properties of transition metals (TM) in Si were often determined by means of the conventional deep level transient spectroscopy (DLTS) technique. In the present study we demonstrate that the poor resolution of the conventional DLTS technique could lead to the wrong interpretation of the experimental data. On the example of well-known lifetime killers such as titanium and cobalt we show that the dominant defects appeared in samples doped with these impurities were previously wrongly attributed to different charged states of interstitial Ti and substitutional Co. Applying the high-resolution Laplace DLTS technique we re-examine the origin of these defects. Some of these defects will be shown to react with H and shallow acceptors leading to the appearance of new complex defects in the band gap of Si. Their nature will also be discussed in the present paper.

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.

Deep level transient spectroscopy characterisation of defects in AlGaN/Si dual‐band (UV/IR) detectors grown by MBE

AbstractThis paper is based on the investigation of electrically active defects in dual band UV/IR photodiodes using Deep Level Transient Spectroscopy (DLTS). The UV/IR photodiodes were fabricated by growing Al0.7Ga0.3N layers on silicon substrate to obtain UV‐ sensitive photodiode structures on the front side, whereas on the back side of silicon IR‐sensitive photodiode structures were fabricated. Our studies reveal the existence of two defect levels in each detector. In order to determine accurately the position of these levels within the band gap of the respective layers, Laplace DLTS has been employed. The activation energies of defects in the UV photodetectors are 0.11±0.01 eV, and 0.31±0.01 eV, whereas, those in the IR detector are 0.25±0.01 eV and 0.47±0.02 eV. These energies are with respect to the conduction band energy of each detector. The effect of the junction electric field on the carrier emission rates of the deep traps was investigated by applying the double pulse Laplace DLTS technique. In particular it is found that the activation energy of the defect in the IR detector (0.47±0.02 eV) changes with electric field. Therefore, in this paper we will present detailed DLTS and Laplace DLTS investigations of deep traps in detectors based on AlGaN/Si (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Investigation of deep-level defects in conductive polymer on n-type 4H- and 6H-silicon carbide substrates using I-V and deep level transient spectroscopy techniques

The current-voltage (I–V) characteristics of Au/sulfonated polyaniline (SPAN)/n-SiC heterojunctions have been investigated in detail over a wide range of temperatures between 20 and 440 K. The measured I–V characteristics of all devices show a good rectification behavior at all temperatures. The room temperature rectification ratios (forward to reverse currents ratio, IF/IR) at 0.6 V for SPAN/n-type 4H-SiC and SPAN/n-type 6H-SiC heterojunctions are 2 × 104 and 7 × 106, respectively. The value of rectification of SPAN/6H-SiC heterojunction is four orders of magnitutude higher than the state-of-the art sulfonated polyaniline thin films deposited on n-type silicon substrates. A self-assembly technique and copolymerization were used to fabricate a self-doped polyaniline films on SiC substrates. The experimental I–V data were analysed using the Werner model, which includes the series resistance of the heterojunctions. The diode parameters such as the ideality factor and the barrier height are determined from the experimental data using I–V analysis method. The effect of the temperature on these parameters is presented. Deep level transient spectroscopy (DLTS) and Laplace DLTS techniques were used to investigate the electrically active defects present in these heterostructure devices.

Effect of epitaxial layer thickness on the deep level defects in MBE grown n‐type Al0.33Ga0.67As

AbstractThe effect of the epitaxial layer thickness on the deep level defects in MBE grown n‐Al0.33Ga0.67As is investigated for the first time using current‐voltage‐temperature (I‐V‐T), deep level transient spectroscopy (DLTS) and Laplace DLTS techniques. The epitaxial layer thickness is found to have profound effects on the room temperature I‐V characteristics, the number of defects detected by DLTS and their concentrations. In this investigation we compare n‐Al0.33Ga0.67As samples having epitaxial layer thicknesses of 2 µm and 1.5 µm. Our results reveal that by increasing the layer thickness (1) the reverse current increases; (2) the number of electrically active deep defects increases from two to six; (3) the concentration of the traps increases.The I‐V‐T and DLTS measurements carried out from 20 K to 300 K show that there is a dominant trap with an activation energy of ∼0.48 eV in both samples but with different concentrations (8.59 × 1014cm‐3 and 1.48 × 1014 cm‐3 for 2 µm and 1.5 µm samples, respectively). The reduction in the reverse current is directly related to the number of defects and their concentration. Our findings have important implications on the performances of electronic and optoelectronic devices. An attempt to explain the effect of the layer thickness on the deep traps in n‐Al0.33Ga0.67As will be given (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Electrical characterisation of GaN and AlGaN layers grown by plasma‐assisted MBE

AbstractIn the present study GaN and Alx Ga1‐x N layers (with x below 5%) grown by plasma‐assisted MBE (PAMBE) were investigated by deep level transient spectroscopy (DLTS) and high‐resolution Laplace DLTS. In GaN a dominant DLTS peak was observed at about 120 K. Using the high‐resolution Laplace DLTS technique we demonstrate that this peak consists of two close components. Defects related to the nitrogen vacancy are the most probable candidates for the origin of these levels. Two other dominant peaks were observed in the DLTS spectra in AlxGa1‐xN layers with x = 1.4% and x = 3%, respectively. The position of the peaks depends on the Al content and shifts towards higher temperatures with Al concentration. The electrical properties of the peaks and their origin will be discussed. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Deep levels in H-irradiated GaAs1-xNx (x < 0.01) grown by molecular beam epitaxy

Dilute nitride GaAs1-xNx layers have been grown by molecular beam epitaxy with nitrogen concentration ranging from 0.2% to 0.8%. These samples have been studied before and after hydrogen irradiation by using standard deep level transient spectroscopy (DLTS) and high resolution Laplace DLTS techniques. The activation energy, capture cross section and density of the electron traps have been estimated and compared with results obtained in N-free as-grown and H-irradiated bulk GaAs.

Spectroscopic studies of iron and chromium in germanium

We report on the electronic properties of Fe and Cr in n-type germanium studied using conventional and Laplace Deep Level Transient Spectroscopy techniques (LDLTS). Using Schottky barriers restricts the studies to levels located in the upper half of the band gap. However, by applying external optical excitation to generate minority carriers, the investigation is extended to the lower half of the band gap. Major findings already published by other authors are in several cases confirmed. However, new insight is revealed on the microscopic behavior of these two chemical species such as their interactions with hydrogen giving rise to the generation of complex-related levels in the band gap. For the Fe case, the small difference in energy of its two levels raises the question as to the possibility of negative-U character.

Electrical characterisation of ruthenium Schottky contacts on n-Ge (1 0 0)

Ruthenium (Ru) Schottky contacts were fabricated on n-Ge (100) by electron beam deposition. Current–voltage (I–V), deep level transient spectroscopy (DLTS), and Laplace-DLTS techniques were used to characterise the as-deposited and annealed Ru/n-Ge (100) Schottky contacts. The variation of the electrical properties of the Ru samples annealed between 25°C and 575°C indicates the formation of two phases of ruthenium germanide. After Ru Schottky contacts fabrication, an electron trap at 0.38eV below the conduction band with capture cross section of 1.0×10−14cm−2 is the only detectable electron trap. The hole traps at 0.09, 0.15, 0.27 and 0.30eV above the valence band with capture cross sections of 7.8×10−13cm−2, 7.1×10−13cm−2, 2.4×10−13cm−2 and 6.2×10−13cm−2, respectively, were observed in the as-deposited Ru Schottky contacts. The hole trap H(0.30) is the prominent single acceptor level of the E-centre, and H(0.09) is the third charge state of the E-centre. H(0.27) shows some reverse annealing and reaches a maximum concentration at 225°C and anneals out after 350°C. This trap is strongly believed to be V–Sb2 complex formed from the annealing of V–Sb defect centre.

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.

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.

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.

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.

Laplace DLTS studies on deep levels coexisted with InAs quantum dots

AbstractSelf‐assembled InAs/GaAs quantum dot structures have been investigated in both conventional and Laplace‐transform deep‐level transient spectroscopy (DLTS) experiments. Laplace DLTS technique provides orders of magnitude better energy resolution than conventional DLTS and hence enables us to study the electronic fine structure of the deep level states that are revealed using the conventional DLTS method. Two well‐separated peaks corresponding to excitation energies of 468 meV and 485 meV are determined in the quantum dot sample, which have energy broadenings of 13.7 meV and 22.9 meV, respectively. A fine structure is also observed in the reference sample, but the ratio between the two peaks differs and the energy broadening is too narrow to be resolved even by the Laplace DLTS. The strain relaxation due to the QD formation is proposed to explain our observations. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)