DLTS Study Research Articles

A Laterally Resolved DLTS Study of Intrinsic Defect Diffusion in 4H-SiC after Low Energy Focused Proton Beam Irradiation

4H-SiC has been irradiated with 10 keV protons and a laterally resolved DLTS study performed to study the diffusion of irradiation induced intrinsic point defects. It is found that the defects migrate on the order of hundreds of μm laterally and carbon interstitials (CI) are believed to be involved in the defect formation. However, the vertical diffusion lengths are revealed to be several orders of magnitude shorter, on the order of hundreds of nm. Specifically, the Z1,2, S1,2 and EH6,7 levels are found to be generated significant distances from the irradiated area, suggesting that CI or another highly mobile species are involved in the formation of these defects.

Interstitial-related defect reactions in electron-irradiated oxygen-rich Ge crystals: A DLTS study

Interstitial-related defect reactions in electron-irradiated oxygen-rich Ge crystals: A DLTS study

Trivacancy in silicon: A combined DLTS and ab-initio modeling study

Trivacancy in silicon: A combined DLTS and ab-initio modeling study

DLTS study of the oxygen dimer formation kinetics in silicon

DLTS study of the oxygen dimer formation kinetics in silicon

Identification and carrier dynamics of the dominant lifetime limiting defect in n– 4H‐SiC epitaxial layers

AbstractThe identity and characteristics of the lifetime limiting defects in n‐type 4H‐SiC epitaxial layers are of particular current interest, due to the suitability of this material for high‐power, solid‐state switching devices. Much work has been done in the past decade to identify the spectral signature and the local atomic structure of the defect that controls the lifetime in this material. Until recently, it was concluded that two dominant electron traps, Z1/2 and EH6/7, both associated with a carbon vacancy, were controlling the lifetime. DLTS and optical studies show, however, that EH6/7 is not an important minority carrier trap, due to its small capture cross section for holes. Thus, Z1/2 acts alone as the lifetime limiting defect. The details of recombination at this trap have been studied through the injection level and temperature dependence of the carrier lifetime and through carrier dynamics simulations that take into account the complex nature of the defect. The simulations shed light on the processes that dominate the recombination at Z1/2 over a large range of injection level and temperature. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

DLTS Studies of Carbon Related Complexes in Irradiated N- and P-Silicon

DLTS studies of transformation kinetics of different carbon–related complexes in electron irradiated n- and p-type silicon have been performed. It has been found that silicon self-interstitials have very low mobility even at room temperature in p-Si, but become extremely mobile under elec-tron injection. It is shown that upon annealing of interstitial carbon in p-Si a metastable state for interstitial carbon-interstitial oxygen complex is formed. This state has an energy level of about Еv+0.36 eV. The formation of the stable and metastable states takes place concurrently. The observed features of the carbon-related complexes formation are likely related to the existence of different crystallographic orientation of the equiprobable pathways through which the interstitial carbon and oxygen atoms can approach each other.

DLTS Study of InGaAs/InGaAsP Double-layered QDs with VariousSpacer Layers

sizes, with the QD layers being separated by spacer layers with thicknesses of 20 nm and 100 nm. In the DLTS measurement for the QD samples, two signals obtained from discrete energy levels of the QDs were analyzed. For the 100-nm-spacer layered QD system, the activation energies of the signals were 0.35 eV and 0.42 eV while for the 20-nm-spacer layered QD system, the activation energies of the signals were 0.36 eV and 0.43 eV, respectively. These activation energies of the QD signals could be varied by changing applied voltage during DLTS measurement.

DLTS study of the oxygen dimer formation kinetics in silicon

The introduction rates of radiation defects, in particular the X- and M-centers for which the oxygen dimer is a precursor, are investigated as a function of duration of the pre-irradiation heat treatment at 480∘C in Czochralski-grown silicon both of n- and p-types. The characteristic annealing time to grow the X-center concentration in the n-type crystal is found to be about 1 h in accordance with the model which implies no significant barrier for the dimer formation. The M-center concentration in the p-type crystal is found to be nearly independent of duration of the pre-irradiation annealing after a few minutes transient period. This behavior is ascribed to the stabilization of dimer concentration due to an effective dimer trapping in these samples.

Trivacancy in silicon: A combined DLTS and ab-initio modeling study

Abstract Deep level transient spectroscopy and ab-initio modeling have been used for identification of energy levels and structure of trivacancy (V3) in Si. It is found that in the neutral charge state the V3 is bistable, with the “fourfold” configuration being lower in energy than the (1 1 0) planar configuration. V3 in the (1 1 0) planar configuration gives rise to two acceptor levels at Ec−0.36 eV and Ec−0.46 eV in the gap, while in the “fourfold” configuration the defect has trigonal symmetry and an acceptor level at Ec−0.075 eV.

Interstitial-related defect reactions in electron-irradiated oxygen-rich Ge crystals: A DLTS study

Abstract Electrically active defects induced in oxygen-rich Ge:Sb crystals by irradiation with MeV electrons at 80 or 300 K have been studied by means of capacitance transient techniques. Transformations of the defects upon post-irradiation isochronal anneals have also been investigated. It is argued that a radiation-induced electron trap with an energy level at about 110 meV below the conduction band edge (E110) can be associated with electron emission from an energy level of the Ge self-interstitial (IGe). The E110 trap is eliminated in the temperature range 150–200 K upon 15 min isochronal annealing. No other traps in the upper half of the gap emerge simultaneously with the disappearance of the E110 trap. It is argued that Ge self-interstitials become mobile at temperatures higher than 150 K and in oxygen-rich Ge interact with interstitial oxygen atoms (Oi). The resulting IGeOi complexes do not have energy levels in the upper half of the Ge gap. Diffusion and interaction of the IGeOi defects with interstitial oxygen atoms at T>50 °C result in the formation of IGeO2i complexes. In the most stable configuration the IGeO2i complex has orthorhombic (C2v) symmetry.

Temperature Dependence of Electron Transport in CdSe Quantum Dot Films

To elucidate minority carrier transport in CdSe quantum dot films, a detailed DLTS study on TiO2/CdSe quantum dot heterojunctions is performed. Long transient times are found, which are related to tunneling instead of the thermal emission of electrons. Surprisingly, the transient times increase with increasing temperature, which is possibly related to thermal expansion of the tunnel barrier width between quantum dots. This effect can give rise to unexpected behavior of quantum dot devices.

A DLTS study of Pt/Al2O3/InxGa1 - xAs Capacitors

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I-V and DLTS study of generation and annihilation of deep-level defects in an oxygen-ion irradiated bipolar junction transistor

A commercial bipolar junction transistor (2N 2219A, npn) irradiated with 84 MeV O6+-ions with fluence of the order of 1013 ions cm−2 is studied for radiation-induced gain degradation and deep-level defects or recombination centers. I-V measurements are made to study the gain degradation as a function of ion fluence. Properties such as activation energy, trap concentration and capture cross section of deep levels are studied by deep-level transient spectroscopy. Minority carrier trap energy levels with energies ranging from E C −0.17 eV to E C −0.55 eV are observed in the base–collector junction of the transistor. Majority carrier defect levels are also observed with energies ranging from E V +0.26 eV to E V +0.44 eV. The irradiated device is subjected to isothermal and isochronal annealing. The defects are seen to anneal above 250 °C. The defects generated in the base region of the transistor by displacement damage appear to be responsible for an increase in base current through Shockley-Read-Hall or multi-phonon recombination and consequent transistor gain degradation.

DLTS study of n-type GaN grown by MOCVD on GaN substrates

Abstract Electron traps in n-type GaN layers grown homoepitaxially by MOCVD on free-standing GaN substrates have been characterized using DLTS for vertical Schottky diodes. Two free-standing HVPE GaN substrates (A and B), obtained from two different sources, are used. The Si-doped GaN layers with the thickness of 5 μm are grown on an area of 0.9×0.9 cm2 of substrate A and on an area of 1×1 cm2 of substrate B. Two traps labeled B1 ( E c – 0.23 eV ) and B2 ( E c – 0.58 eV ) are observed with trap B2 dominant in GaN on both substrates. There exist no dislocation-related traps which have been previously observed in MOCVD GaN on sapphire. This might be correlated to the reduction in dislocation density due to the homoepitaxial growth. However, it is found that there is a large variation, more than an order of magnitude, in trap B2 concentration and that the B2 spatial distributions are different between the two substrates used.

DLTS studies of irradiation-induced defects in p-type germanium

In the present investigation, we have made use of our newly produced n +p-mesa diodes on Ga-doped, 2-Ω cm Ge-single crystals to study irradiation-induced defects in p-type Ge. Irradiation with electrons shows five distinct levels introduced. The use of protons and α-particles (and at different doses) for irradiation, reveals four new levels, and allows for the possibility of connecting some of the levels to the divacancy.

Deep electron states in indium‐doped Cd0.93Mn0.07Te DLTS study

AbstractElectron traps in indium doped Cd0.93Mn0.07Te were studied with Deep Level Transient Spectroscopy. Five electron traps were found (labeled as E1 ‐ E5). Energy levels ET of related defects are equal to E T 1 = 0.09 eV, E T 2 = 0.12 eV, E T 3 = 0.18 eV, E T 4 = 0.56 eV and E T 5 = 0.65 eV. Three of them (E1, E2, E3 ) are related to the defects with thermally activated capture cross section. Electric field enhanced electron emission from the trap E4 was observed and described in the terms of the Poole‐Frenkel ‐ mechanism. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

DLTS Study on Deep Levels Formed in Plasma Hydrogenated and Subsequently Annealed Silicon

P-n junctions are created in p-type Czochralski silicon after a low temperature (270°C) hydrogen plasma exposure. This is attributed to the formation of hydrogen-related shallow donors. A deep level (E1) with an activation energy of about EC-0.12 eV is observed by DLTS measurement and assigned to a metastable state of the hydrogen-related shallow donors. At an annealing temperature of 340°C, the E1 centres disappear and oxygen thermal donors appear. The concentrations of the oxygen thermal donors are found typically to be 2-3 decades lower than that required for over-compensating the initial p-type doping and for contributing the excess free carriers.

EBIC and DLTS Study of Deformation Induced Defect Thermal Stability in n-Si

The electrical properties of deformation-induced defects in n-Si with a high dislocation density (10 8 -10 9 cm - 2 ) and their annealing behaviour in the temperature range from 600 to 800°C have been studied. Special attention was paid to revealing the oxygen role in the annealing processes. It is shown that the diffusion length in deformed Si starts to restore at 800°C while the deep level concentration decreases even after 600°C annealing. No direct correlation between oxygen gettering by deformation-induced defects and their electrical property annealing is revealed.

DLTS study of deep centers created by Ar-ion bombardment in n- and p-type MBE AlGaAs

The thermal emission rate of dominant traps in molecular beam epitaxial n- and p-type AlGaAs subjected to Ar-ion beam etching has been studied by deep level transient spectroscopy. Emission signatures were determined and compared with results obtained by other authors for irradiation induced and grown-in defects in GaAs and AlGaAs. The most significant result of this study is the observation that the process-induced defects in n- as well as p-type AlGaAs exhibit emission signatures, which are characteristic of native defects found in GaAs. The effect is discussed in terms of a compensation effect and related band bending.

DLTS study of bonded interface in silicon-on-insulator structures annealed in hydrogen atmosphere

The results of the comparative Charge Deep Level Transient Spectroscopy study of Si/SiO 2 interfaces in silicon-on-insulator structures prepared by wafer bonding and hydrogen slicing and annealed in hydrogen ambient in the temperature range of 430–670 °C are presented in the report. At bonded interface the trap transformations under hydrogen annealing are strongly discriminated from passivation of traps at Si/thermal SiO 2 interface. It was found that heat treatments at T>430 °C inhibit generation of new traps and changes in trap spectra in bonded interface.