Deep Level Transient Spectroscopy Technique Research Articles

The effect of alpha particle irradiation on electrical properties and defects of ZnO thin films prepared by sol-gel spin coating

ZnO thin films were prepared using the sol-gel spin coating technique. The structure was investigated using X-ray diffraction (XRD). The XRD spectra exhibited typical randomly orientated structure with a slight preference for growth along the (002) plane and a crystallite size of ∼ 48 nm. The Schottky barrier diodes were fabricated on the synthesized ZnO thin films. The electrical properties before and after irradiating the devices with alpha particle irradiation were characterized using current-voltage (I-V), capacitance-voltage (C-V), deep-level transient spectroscopy (DLTS) and Laplace-transform deep-level transient spectroscopy (L-DLTS) techniques. Pd/ZnO/n-Si/AuSb Schottky diodes exhibited good rectifying properties. Before irradiation, the DLTS spectra revealed one defect E4 with activation enthalpy 0.41 eV. After irradiation, there is a new defect Eα with the activation enthalpy 0.35 eV. Laplace-transform deep-level transient spectroscopy (L-DLTS) revealed the fine structure of the Eα to be made up of 0.53 eV and 0.36 eV defects.

DLTS study of extended defects in HgCdTe photodiodes

Extended electrically active defects have been investigated in Short Wave InfraRed (SWIR) HgCdTe n on p photodiodes, using the Deep Level Transient Spectroscopy (DLTS) technique. Three localized defects have been found in the dislocations core or in their close environment. DLTS studies have also been performed before and after indentation, a technique which generates dislocations in the material. DLTS spectra are discussed and dislocations generated by indentation have been found to be electrically active only after annealing.

Low-Frequency Noises and DLTS Studies in HgCdTe MWIR Photodiodes

Both low-frequency noises and electrically active defects have been investigated for two technological variants, i.e. optimized and non-optimized, of the HgCdTe p on n technology applied to the mid-wave infrared blue band with a cut-off wavelength of 4.2 μm. This has been achieved using electro-optical characterizations and the deep level transient spectroscopy (DLTS) technique. The results show that the impact of extra 1/f and random telegraph signal noises has been reduced with the optimization of the technology. Furthermore, a broadened DLTS peak, probably related to dislocations in the material, has been found for both variants, the relative amplitude of which is reduced in the optimized case. The potential correlation between low-frequency noises and this broadened peak is discussed.

Peak shape analysis of deep level transient spectra: An alternative to the Arrhenius plot

Abstract

Hole trap, leakage current and barrier inhomogeneity in (Pt/Au)[sbnd]Al0.2Ga0.8N/GaN heterostructures

In this work, we report on the electrical characteristics of Pt/Au Schottky contacts to Al0.2Ga0.8N/GaN heterostructures. Indeed, we have realized gate current-voltage I(V) and deep level transient spectroscopy (DLTS) measurements. The behavior study of series resistance RS, ideality factor n, the effective barrier height Фb and leakage current with the temperature have emphasize barrier height inhomogeneity and extended defect in the (Pt/Au)Al0.2Ga0.8N/GaN system. The abnormal behavior of all these parameters can be attributed to the presence of traps thermally activated. Using the DLTS technique, we have detected one hole trap having an activation energy of 0.28eV and a capture cross-section of 1.9 × 10−19cm2. This trap should be a threading dislocation extending from the GaN layer to the surface.

Evaluation of electron traps in SiNx by discharge current transient spectroscopy: verification of validity by comparing with conventional DLTS

Discharge current transient spectroscopy (DCTS) is a promising technique for detecting the trap level and density in dielectrics because it is based on a simple emission process. In order to confirm the validity of DCTS, we compare the results from the conventional deep-level transient spectroscopy (DLTS) technique for samples of CVD-grown silicon nitride (SiNx) films. Results indicated that a trap level, about 0.6 eV below the energy level of the conduction band edge in the SiNx thin films estimated by DCTS is in good agreement with that obtained from DLTS analysis, and it is found that the trap density increases with the decreasing N/Si ratio in the SiNx film. As a proposed estimation for energy level in defects, it will be originated from hydrogen-incorporated defects in the SiNx matrix. This study demonstrates that the DCTS method will be a useful electrical method for the evaluation of defects.

Deep-Level Defects in a Photovoltaic Converter with an Antireflection Porous Silicon Film Formed by Chemical Stain Etching

Defects in the semiconductor structure of a photovoltaic converter (PVC) with a p–n junction and antireflection film of porous silicon manufactured using chemical stain etching were studied by the current deep-level transient spectroscopy technique. The influence of the regime of porous silicon film formation on the transformation of deep-level defects and the main PVC characteristics is explained.

Дефекты с глубокими уровнями в фотоэлектрическом преобразователе с антиотражающей пленкой пористого кремния, сформированной окрашивающим химическим травлением

AbstractDefects in the semiconductor structure of a photovoltaic converter (PVC) with a p – n junction and antireflection film of porous silicon manufactured using chemical stain etching were studied by the current deep-level transient spectroscopy technique. The influence of the regime of porous silicon film formation on the transformation of deep-level defects and the main PVC characteristics is explained.

The Effect of Defects with Deep Levels on the C–V Characteristics of High-Power AlGaN/GaN/SiC HEMTs

This study deals with the capacity–voltage (С–V) characteristics of the gate–drain regions of crystals of high-power microwave HEMT transistors with a large gate periphery of the S and Х bands and a source–drain breakdown voltage VDS ranging from 30 to 150 V, as well as test Schottky diodes formed in a single technological cycle together with HEMTs. Capacitance deep-level transient spectroscopy (DLTS) was used to investigate the structural defects creating deep levels. During the investigations, it was shown that the С–V curves of HEMT crystals always had two areas of change in capacitance with differing slope angles, while there were no such knees in the curves for the test Schottky barriers (SBs). The DLTS technique revealed that НЕМТs and test SBs contained electron-like and hole-like traps, occurring, most probably, in the buffer layer, and also a hole-type peak behaving anomalously. The knee in the С–V curves of НЕМТs is due to the strong electric fields arising at the edge of the gate of the transistor structures.

Trapping Effects in Si -Doped -Ga2O3 MESFETs on an Fe-Doped -Ga2O3 Substrate

Threshold voltage instability was observed on $\beta $ -Ga2O3 transistors using double-pulsed current–voltage and constant drain current deep level transient spectroscopy (DLTS) measurements. A total instability of 0.78 V was attributed to two distinct trap levels, at ${E}_{C}$ -0.70 and ${E}_{C}$ -0.77 eV, which need to be mitigated for future applications. The traps are likely located near the gate–drain edge and below the delta-doped layer, which is determined through the DLTS technique and an understanding of the fill and empty biasing conditions. The trap modulation was consistent with a gate leakage-based trap filling mechanism, which was demonstrated. It is likely that Fe is playing a role in the observed dispersion due to the close proximity of the Fe substrate.

Catastrophic Optical Bulk Damage – A New Failure Mode in High-Power InGaAs-AlGaAs Strained Quantum Well Lasers

ABSTRACTHigh-power single-mode (SM) and multi-mode (MM) InGaAs-AlGaAs strained quantum well (QW) lasers with emission wavelengths of 910 − 980 nm are extensively used in various fiber lasers and amplifiers for both telecom and defense applications. In particular, underseas and satellite communication systems require stringent reliability from these lasers. Since these lasers predominantly fail by catastrophic and sudden degradation due to COD, it is crucial especially for space satellite applications to investigate reliability, failure modes, and degradation mechanisms of these lasers. Catastrophic optical mirror damage (COMD) was known to be the only failure mode until our group reported a new failure mode in MM and SM InGaAs-AlGaAs strained QW lasers in 2009 and 2016, respectively. Our group reported that bulk failure due to catastrophic optical bulk damage (COBD) has become the dominant failure mode of both SM and MM lasers. Since there have been limited reports on COBD compared to COMD, the intent of this paper is to introduce our studies on COBD that have spanned the last decade. We investigated reliability, failure modes, and degradation processes in SM and MM InGaAs-AlGaAs strained QW lasers by performing short-term step-stress tests and long-term accelerated life-tests as well as failure mode analyses using various nondestructive and destructive micro-analytical techniques including electron beam induced current (EBIC), time-resolved electroluminescence (EL), deep level transient spectroscopy (DLTS), focused ion beam (FIB), and high-resolution TEM. EBIC and EL techniques were employed to study dark line defects generated in degraded lasers stressed under different test conditions. Time-resolved EL techniques were employed to study initiation and progressions of dark spots and dark lines in real time as lasers were aged. DLTS techniques were employed to study electron traps in both pristine and degraded lasers. Lastly, FIB and high-resolution TEM were employed to prepare cross sectional and plan view TEM specimens to study DLD areas in post-aged lasers. We also report our current understanding on degradation mechanisms responsible for COBD in both SM and MM lasers.

Effect of Wafer Orientation on Near-Interface Oxide Traps in 4H-SiC Metal-Oxide-Semiconductor Capacitors

4H-Silicon carbide is one of the enabling materials for modern high voltage and high temperature power electronic devices due to its attractive material properties. A significant drawback to SiC MOSFET performance is the low channel conductance due to trapping of carriers by the high-density of near-interface traps (NITs) at the SiO2/4H-SiC interface. These states are spatially located within ~1 nm from the interface and energetically positioned near the conduction band edge of 4H-SiC. Constant capacitance deep level transient spectroscopy (CCDLTS) technique is appropriate for analysis of such defects as it can differentiate between trap types and measure trapped charge emission rates. In this study, we examined SiO2-4HSiC interfaces formed on the polar (0001) Si- face (100% Si) and non-polar (11-20) a-face (50% Si, 50% C) oriented 4H-SiC wafers using CCDLTS. For the NO annealed Si-face interface, there are two main types of NITs detected by CCDLTS, labeled “O1” and “O2” traps by Basile et al. [1]. The physical identities of these defects have been suggested to be carbon dimers substituted for O dimers (CO=CO) and interstitial Silicon atoms in the near interfacial SiO2[2]. In this work, we observed both the O1 and O2 traps in the Si-face with activation energies of about 0.15±0.01 eV and 0.35±0.01 eV respectively, which are consistent with previous results[3]. The original result obtained in this study was that for the a-face; two new NITs (labeled A1 & A2) positioned very close to the O1 peak were observed but the O2 peak was absent. For this study, 4H-SiC MOS capacitors were fabricated on Si-face and a-face oriented wafers. The samples underwent dry oxidation followed by nitridation with NO annealing at 1175°C. After that, circular Al gates were evaporated as gate contact. The oxide thickness was ~62 nm and ~54 nm for Si-face and a-face respectively. CCDLTS was measured on capacitors keeping a constant capacitance in deep depletion in a temperature range of 77 K to 298 K changing pulse voltages and emission rates. Using the analysis method detailed in [1], the activation energies of the A1 and A2 peaks were found to be 0.15±0.01 eV and 0.19±0.01 eV respectively, which is in the same range as the O1 trap in the Si-face. The capture cross-sections for all traps detected was in the 10-16-10-14 cm2 range. Qualitatively, this result is similar to the results reported in [4], which shows that nitrided SiO2 formed on the (000-1) C-face (100% C terminated) also shows only one peak very similar to the O1 trap observed on the Si-face. This result points to the importance of interface structural differences due to different wafer orientation with respect to near-interface oxide traps. Acknowledgement: This work was supported by the II-VI foundation

Comparison of purity in single walled carbon nanotube gas detectors with Pd and Ti electrodes using low frequency noise techniques

This work deals with oxide traps properties of single walled carbon nanotubes (SWCNTs) based gas sensors using Random telegraph signals (RTS) and low frequency (LF) noise techniques. RTS signals are two or more levels switching events that we observe measuring the drain current of transistors with Ti (RTS1) and Pd (RTS2) contacts. RTS noise is analyzed in time and frequency domains. Time domain analysis allows us to identifying slow traps (three traps) responsible to RTS noises (energetic position and cross capture section). These traps undetectable by other techniques, e.g. deep level transient spectroscopy (DLTS) technique, are localized in the gate oxide region. The spatial localization of the three traps in the SWCNT/SiO2 interface are determined using numerical simulations (yTrap1 ≈0.6nm, yTrap2 ≈0.9nm and yTrap3 ≈0.3nm). (RTS1) noise is attributed to trap1 and (RTS2) to traps 2 and 3. From RTS analysis in frequency domain, are able to extract the cut-off frequencies of a single trap even at very low frequencies (for RTS1 noise fc=10Hz (trap1) and for RTS2 noise fc1=4Hz (trap2), fc2=50Hz (trap 3)). These results are in good agreement with those obtained by analysis in time domain and confirm the localization of each trap from the SWCNT/SiO2 interface. This is the first time that this kind of studies is performed on CNTFETs used as gas sensors and gives us some interesting hints on the potential phenomena related to these new generation of carbon based nanomaterials based devices in the field of electronics.

Carbon-related defects in microelectronics

In the present study electrically active carbon and hydrogen-related (CH) defects, which can act as strong recombination centers in high power devices and CMOS photodetectors, are investigated in n-type Si. Several different CH-related defects are observed by using the deep level transient spectroscopy (DLTS) technique on hydrogenated Si samples with different oxygen content. The concentration of these defects is determined as low as 1012–1013cm−3. By comparing samples with different O, C, and H concentrations the origin of the CH-related defects is derived. We show that the concentration of the electrically inactive substitutional C can be estimated by a comparison of the depth profiles of the electrically active CH-related defects in a sample with those in a reference sample which has an identical oxygen and known carbon content. This approach is applicable even for concentrations of substitutional C lower than 1015cm−3.

Luminescent and electrical properties of oxygen‐implanted silicon

Light emitting diodes with an active defect‐rich region produced by oxygen implantation and a subsequent multistep annealing of silicon wafers were investigated by means of transmission electron microscopy, SIMS, capacitance voltage, deep level transient spectroscopy, electroluminescence (EL), and cathodoluminescence (CL) techniques. The properties of two groups of n‐based samples with and without thermal pre‐treatment at 1000 °C for 15 min were compared regarding their defect structure, defects electrical activity, luminescent spectra as well as the impact of prolonged intense electron irradiation. The observed difference in the properties of such groups was explained by a difference in the density and oxygen content of oxygen‐related defects. A significant distinction between EL and CL spectra at low excitation levels was found and interpreted to be due to particular defect kinds in near‐surface and the deepest layers of the implanted region. The blue shift of EL spectra upon excitation increase reported previously is explained by the increase of penetration depth of the holes and specific depth distribution of the defects of different kinds.

Deep level transient spectroscopy characterisation of Xe irradiated GaN

In this study n-type GaN was subjected to irradiation. This irradiation was performed by Xe+26 of 167MeV to a fluence of 1010 cm−2 at room temperature. Irradiation resulted in an increase in the reverse current by about 10 orders of magnitude. This has been explained by the generation/recombination centers formed during irradiation. Using the deep level transient spectroscopy (DLTS) technique, two defects were identified after irradiation with activation energies of 0.07 and 0.48eV below the conduction band. These defects have similar signatures to other defects observed after electron irradiation, thermal annealing and In doping.

Optoelectronic properties of ZnO/ZnMgO multiple quantum wells in ZnMgO nanocolumns grown on Si (111)

Superlattice structures formed using the II-VI family of semiconductors have attracted a great deal of attention due to some unique properties (chemical sensors, UV detectors, lasers, white LED). We present a comparison of optical and electrical measurements of 10-period ZnO/ZnMgO multiple quantum wells (MQWs). The structures have been fabricated on (111) Si by molecular beam epitaxy grown at very high temperatures. The optical properties were analyzed by photoluminescence and cathodoluminescence techniques. Cross-sectional SEM-CL mapping shows that the ZnO/ZnMgO multiple quantum wells are located in ZnMgO nanocolumns. Based on these structures, diodes were processed and characterized by current-voltage (I-V), capacitance-voltage and deep level transient spectroscopy techniques (DLTS). I-V measurements confirm that in both diodes, deep traps govern the conduction mechanisms at a forward bias. DLTS studies yield signatures of these traps as well as those related to the presence of QWs. In particular, DLTS results let us estimate the distance of 30 meV from the QW ground state to the barrier conduction band.

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.

DLTS characterization of defects in GaN induced by electron beam exposure

The deep level transient spectroscopy (DLTS) technique was used to investigate the effects of electron beam exposure (EBE) on n-GaN. A defect with activation energy of 0.12eV and capture cross section of 8.0×10–16cm2 was induced by the exposure. The defect was similar to defects induced by other irradiation techniques such as proton, electron, and gamma irradiation. In comparison to GaN, the EBE induced defects in other materials such as Si and SiC are similar to those induced by other irradiation methods.

Deep-level spectroscopy in metal–insulator–semiconductor structures

In this study we present a method for measuring bulk traps using deep-level spectroscopy techniques in metal–insulator–semiconductor (MIS) structures. We will focus on deep-level transient spectroscopy (DLTS), although this can be extended to deep-level optical spectroscopy (DLOS) and similar techniques. These methods require the modulation of a depletion region either from a Schottky junction or from a highly asymmetric p–n junction, junctions that may not be realizable in many current material systems. This is the case of wide-bandgap semiconductor families that present a doping asymmetry or have a high residual carrier concentration or surface carrier accumulation, such as InGaN or ZnO. By adding a thin insulating layer and forming an MIS structure this problem can be circumvented and DLTS/DLOS can be performed under certain conditions. A model for the measurement of bulk traps in MIS structures is thus presented, focusing on the similarities with standard DLTS, maintaining when possible links to existing knowledge on DLTS and related techniques. The model will be presented from an equivalent circuit point of view. The effect of the insulating layer on DLTS is evaluated by a combination of simulations and experiments, developing methods for the measurement of these type of devices. As a validation, highly doped ZnO:Ga MIS devices have been successfully characterized and compared with a reference undoped sample using the methods described in this work, obtaining the same intrinsic levels previously reported in the literature but in material doped as high as cm−3.