Deep Level Transient Spectroscopy Analysis Research Articles

Deep Electronic Levels of AlxGa1-xN with a Wide Range of Al Composition Grown by Metal–Organic Vapor Phase Epitaxy

Deep electronic levels of AlxGa1-xN (0.25<x<0.60) were investigated by deep level transient spectroscopy (DLTS) and photocapacitance methods. Si-doped AlGaN layers were grown on an AlN/sapphire template by metal–organic vapor phase epitaxy. DLTS analysis using a sampling time window of up to 100 s showed two dominant deep levels with activation energies (ΔE) higher than 1.0 eV in AlxGa1-xN with x=0.25 and 0.37. The densities of those levels were higher than 1×1016 cm-3. For the Al0.60Ga0.40N sample, the deeper levels (ΔE>1.5 eV) were detected by photocapacitance measurement. It was found that the energy position of the dominant deep level closely followed the Fermi level stabilization energy reported by Walukiewicz et al. [J. Cryst. Growth 269 (2004) 119], indicating that the origin of the dominant deep level in AlGaN is related to a defect complex including anti-site defects and divacancies.

Current deep level transient spectroscopy analysis of AlInN/GaN high electron mobility transistors: Mechanism of gate leakage

In order to assess possible mechanisms of gate reverse-bias leakage current in AlInN/GaN high electron mobility transistors (HEMTs) grown by metalorganic chemical-vapor deposition on SiC substrates, temperature-dependent current-voltage measurements combined with Fourier transform current deep level transient spectroscopy (FT-CDLTS) are performed in the temperature range of 200–400 K. In this range of temperature reverse-bias leakage current flow is found to be dominated by Poole–Frenkel emission. Based on CDLTS measurements, a model of leakage current transport via a trap state located at the AlInN/metal interface with an activation energy of 0.37 eV is suggested. The trap nature is shown to be an extended trap, most probably associated with dislocations in the AlInN barrier layer.

Investigation of defects introduced by static and dynamic hot carrier stress on SOI partially depleted body-contact MOSFETs

SOI partially depleted body-contact MOSFETs were subjected to static and dynamic hot carrier stress. Drain current was investigated by means of Deep Level Transient Spectroscopy and switch-ON transient analysis in a wide temperature range. Under static degradation regime, drain current behaviour was determined by the creation of two discrete traps most likely located in the drain vicinity; a hole trap cited in the literature and a defect of metastable nature. Under dynamic degradation regime, drain current behaviour was determined by body–Si/SiO 2 interface-state generation. Experimental data and fitting results based on stretched exponential law are in accordance.

Formation and annealing behavior of prominent point defects in MeV ion implanted n-type epitaxial Si

Samples of epitaxially grown n-type Si have been implanted with low doses (<1 × 10 9 cm −2) of He, C, Si, and I ions using energies from 2.75 to 48 MeV. Deep level transient spectroscopy (DLTS) analysis of the implanted samples reveals a stronger signal for the signature of the singly negative charge state of the divacancy (V 2(–/0)) as compared to that of the doubly negative charge state of the divacancy (V 2(=/–)). Isochronal annealing for 20 min ranging from 150 to 400 °C results in a gradual decrease in the DLTS peak amplitude of the V 2(–/0) signature, accompanied by an increase in the peak amplitudes of both the vacancy oxygen pair (VO) and the V 2(=/–) levels, as well as an increase in the carrier capture rates for the levels. A model based on local compensation of charge carriers from individual ion tracks is proposed in order to explain the results, involving two fractions of V 2: (1) V 2 centers localized in regions with high defect density around the ion track ( V 2 dense ) and (2) V 2 centers located in regions with a low defect density ( V 2 dilute ) .

Optimization of 660-nm-Band AlGaInP Laser Diodes by Using Deep-Level Transient Spectroscopy Analyses

We report high power and high temperature operation of 660-nm-band AlGaInP laser diodes. The double-channel ridge waveguide structure was used, and the growth conditions for each layer of the AlGaInP laser were optimized to have the lowest defect density by using deep-level transient spectroscopy (DLTS) analyses. The optimized AlGaInP lasers showed better performance than those fabricated without optimization. One of the optimized AlGaInP lasers showed a very stable fundamental transverse mode even at 200 mW and 70 ◦C, a typical threshold current of 64 mA at 660 nm, a slope efficiency of 1.0 W/A, and a characteristic temperature of 212 K. The beam divergences perpendicular and parallel to the junction plane were 15.3◦ and 8.6◦, respectively, at 80 mW CW, which is small enough for a DVD-R/RW system.

Electrical activation of the Fe2+∕3+ trap in Fe-implanted InP

We have studied the electrical activation of the Fe2+∕3+ trap in Fe-implanted InP by means of capacitance-voltage and deep level transient spectroscopy analyses. Five deep traps have been identified and we have characterized the concentration and depth distribution of the Fe2+∕3+ deep trap, located at EC–0.66eV. The InP substrate background doping, i.e., the Fermi-level position, plays a crucial role in the Fe activation process by setting an upper limit to the amount of Fe centers electrically activated as deep acceptor traps.

Alloy splitting of Te-DX in AlxGa1−xAs analysis using the deep level transient spectroscopy technique

The paper reports on a deep level transient spectroscopy analysis of Te-related DX centers in AlxGa1−xAs with aluminum composition x=0.40. As was shown from experimental results, the state energy of this trap shows a microscopic structure due to an alloy effect. A theoretical analysis based on a multi-step scheme has been made to explain the electron emission from a multiconfigurate center. Using this model, we derived the binding energies of the splitted Te-DX states in the alloy material studied.

Continuous wave operation of a 250 mW AlGaAs laser diode

We report a record high continuous wave (CW) output power of 250 mW for the 780 nm band AlGaAs laser. The selectively buried ridge (SBR) structure was used and each layer of the laser was designed to have the lowest defect density by using the deep level transient spectroscopy (DLTS) analyses. The laser operated at a peak wavelength of 783 nm with a threshold current of 38 mA. The stable fundamental transverse mode was observed at 100 mW, 70 °C for more than 3000 h. The far-field aspect ratio, a ratio of far-field vertical angle over far-field parallel angle to the junction plane, was measured to be 1.8, which is small enough for the high density CD-R system.

Meyer-Neldel rule and the influence of entropy on capture cross-section determination in Cu(In,Ga)Se2

We use deep-level transient spectroscopy (DLTS) to investigate the electronic properties of ZnO∕CdS∕CuxIn1−yGaySe2∕Mo∕soda-lime glass thin-film solar cells. We deposited films with different x and y values using elemental evaporation. Devices made from these films exhibit more than 40 hole and electron traps, with activation energies ranging from 0.07to1.17eV. Standard DLTS analysis (which assumes that entropy changes can be neglected) gives apparent capture cross sections that vary by 18 orders of magnitude over this energy range. All our data show that the charge-carrier emission rate obeys the Meyer-Neldel rule (MNR) with an isokinetic temperature of 340±30K. By including the MNR relation in detailed balance, we show that there is a single cross section for all the traps.

Deep level transient spectroscopy and TEM analysis of defects in Eu implanted GaN

Deep level transient spectroscopy (DLTS) and transmission electron microscopy (TEM) are used to study europium implanted gallium nitride layers. The implantation was realised at room temperature in the random and channeled geometries. From DLTS, we determine intrinsic defects with associated levels located in the band gap (below the conduction band). Besides, we point out a new electron trap named Eu2. Its associated level is located at about Ec –0.36 eV and the defect is probably related to the europium rare-earth ion. TEM investigation shows a difference in structure caused by changing the geometry of implantation. The random implanted sample contains numerous planar defects. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Giant traps associated with extended defects in GaN and SiC

Extended defects in semiconductors can trap charge and lead to changes in carrier concentration and mobility. Here we consider the trapping effects of pores, microcracks, and dislocations in GaN and SiC, as analyzed by deep level transient spectroscopy (DLTS), transmission electron microscopy (TEM), and scanning surface potential microscopy (SSPM). The defect structures are modeled as spheres, plates, and cylinders for pores, cracks, and dislocations, respectively, and their potentials are directly compared with those measured by holographic TEM and SSPV. The dynamics of the capture and emission processes are investigated by DLTS, although the standard DLTS analysis framework is not applicable here and must be replaced by a more general formalism. As an example, 40-nm-dia. nanopores in SiC can each hold more than 100 electrons, and they exhibit anomalous capture and emission properties.

Method for Detecting Defects in Silicon-On-Insulator Using Capacitance Transient Spectroscopy

A method for detecting defects such as interface states and a deep trap in Si-on-insulator (SOI) has been proposed, which is based on deep-level transient spectroscopy (DLTS) analysis of the metal-oxide semiconductor (MOS) structure. It is shown, for a bonded p-type SOI wafer consisting of 5 µm top-Si (T-Si) and 1 µm buried oxide (BOX) layers, that the interface state densities between T-Si/BOX and BOX/back-Si (B-Si) can be measured. Furthermore, the validity of this DLTS technique for the detection of a discrete deep level has been confirmed by using a Fe-doped SOI wafer. It is shown that the Fe concentration in B-Si is consistent with that of bulk Si, while the Fe concentration in T-Si shows significant enhancement. Through these investigations of SOI wafers, the validity of this DLTS method has been demonstrated.

Photocatalytic Property and Deep Levels of Nb-doped Anatase TiO2 Film Grown by Metalorganic Chemical Vapor Depostion

A Nb-doped anatase TiO2 (Nb: 5 at%) film was grown on a SrTiO3(001) substrate by metalorganic chemical vapor deposition. Deep level transient spectroscopy analysis revealed that this film possessed two kinds of deep levels due to the Nb ions, which were found to exist at 0.32 eV and 0.67 eV below the bottom of the conduction band. The photocatalytic activity of this film was low compared with that of the undoped anatase film, suggesting that the deep levels acted as recombination centers of photoexcited electron-hole pairs.

Reverse recovery characteristics and defect distribution in an electron-irradiated silicon p–n junction diode

Electron irradiation was performed to enhance the switching speed and thereby to reduce the energy loss of a p–n junction diode. The reverse recovery time decreased significantly but other electrical deterioration such as leakage current and on-stage voltage drop due to the electron irradiation was found not to be much. Also the defect distribution and the type of the electron irradiation-induced defects are discussed based on the deep level transient spectroscopy (DLTS) analysis results and the secondary ion mass spectrometry (SIMS) depth profiles of the silicon substrate.

Conductance transient, capacitance–voltage and deep-level transient spectroscopy characterization of atomic layer deposited hafnium and zirconium oxide thin films

High-permittivity HfO 2 and ZrO 2 based oxides grown by atomic layer deposition are investigated. Both ZrO 2 and HfO 2 are materials of high chemical stability and may form relatively stable interface with silicon substrate. To amorphize the structure and increase the resistivity of the dielectric layer, the high-permittivity material was mixed with another high band-gap material such as Al 2O 3. This work presents experimental results obtained from electrical characterization of metal–insulator–semiconductor structures based on these dielectrics. Capacitance–voltage, deep-level transient spectroscopy and conductance transient analysis have been used to prove the promising performances of these advanced materials to obtain good interface quality in the incoming CMOS technology. Mixtures of nanolayers of zirconium or hafnium oxide and aluminium oxide yield the best behaviour. They show acceptable density levels of disordered-induced gap states in the insulator level and interface state densities similar to those of stoichiometric oxides.

Post-Annealing Effects on Fixed Charge and Slow/Fast Interface States of TiN/Al2O3/p-Si Metal–Oxide–Semiconductor Capacitor

The fixed charges (Nf) and the “slow” (Nsi) and “fast” (Dit) interface states of TiN/Al2O3/p-Si metal–oxide–semiconductor (MOS) capacitors were investigated by the capacitance–voltage and deep level transient spectroscopy (DLTS) method. In addition, small pulse DLTS (SP-DLTS) analysis was performed for a more precise estimation of energies and capture cross sections of the interface states. The variations in the Nf, Nsi and Dit with various post-annealing conditions were evaluated. Annealing under a H2 atmosphere effectively reduced the Nf, Nsi, and Dit. The Dit at an energy of 0.35 eV from the valence band decreased from 1×1012 cm-2eV-1 at the as-fabricated state to 4×1011 cm-2eV-1 after annealing at 450°C. A large peak related to minority carrier capture was detected in the high temperature region of the DLTS results. The peak intensity also decreased after hydrogen annealing. This suggests that the interface states in the upper half of the Si band-gap decrease with H2 annealing.

“Recovery” Effect of Electron Induced Damage in 4H-SiC Schottky Diodes

ABSTRACTThe effects of electron irradiation on the defects associated electronic levels in Schottky diodes on 4H silicon carbide epilayers grown by chemical vapour deposition were investigated by Deep Level Transient Spectroscopy (DLTS) and Capacitance-Voltage (C-V) characteristics. These investigations were performed before and after irradiation with 8.6 MeV electrons at different doses. After irradiation four new traps with enthalpies equal to (Ec-0.23 eV), (Ec-0.39 eV), (Ec-0.63 eV) and (Ec-0.75 eV) were detected. Their thermal stability, a key point to determine their structure on the basis of recent theoretical and experimental results, was carefully investigated since it was earlier observed that during DLTS temperature runs up to 500 K a slight but significant recovery of a few irradiation-induced levels occurs. This effect was previously observed in literature for the level (Ec-0.70 eV) after thermal treatment at 500 °C [1], but the present results indicate that it involves more than a single level and is also effective at lower temperature. DLTS analyses were also performed from room temperature to liquid nitrogen temperature and vice versa up to 500 K.The annealing kinetics is reported and a few conclusions on the structure of the defects involved in the recovery are drawn. The correlation with the diode charge collection efficiency is also reported.

Distribution of Substitutional Nickel Atoms in Dislocation-Free Silicon Studied by Deep Level Transient Spectroscopy and Theoretical Analyses Based on the Dissociative Mechanism of Diffusion

By means of deep level transient spectroscopy (DLTS), the diffusion profiles of substitutional nickel atoms in silicon are investigated in dislocation-free silicon at 980°C for the in-diffusion process and at 950°C for the annealing process. The results are analyzed on the basis of the dissociative mechanisms of diffusion. It is shown that nickel distribution in dislocation-free silicon can be explained by the dissociative mechanism with the model that sinks and sources of vacancies are present in the bulk in addition to the surfaces.

Deep Level Transient Spectroscopy Analysis of 10 MeV Proton and 1 MeV Electron Irradiation-Induced Defects in p-InGaP and InGaP-based Solar Cells

Minority carrier injection annealing under forward-bias conditions is shown to enhance defect annealing in InGaP and to result in the recovery of solar cells properties. Such peculiar recovery of properties affected by radiation damage demonstrates that InGaP-based devices, under minority-carrier injection-mode operation, have superior radiation resistance compared to GaAs and Si. The first example of a recombination-enhanced mechanism in the ternary compound InGaP is also reported. We have performed detailed studies of the stability of the radiation-induced defect H2 in p-InGaP under various biases in order to determine the dependence of the reaction rate on the position of the Fermi level in the absence of minority carrier injection and recombination. Recombination-enhanced defect annealing of H2 causes a reduction of the minority carrier injection annealing activation energy, compared to thermal annealing from 1.69 eV to 0.52 eV. Analysis of the results reveals that the mechanism involved in the minority carrier injection annealing of the defect is the energy release mechanism, in which enhancement is induced by the energy that is released when a minority carrier is trapped at the defect site.

Characterization of Interface States in Degraded ZnO Varistors

The degradation mechanism of ZnO varistors was investigated by using spectral analysis of deep-level transient spectroscopy (SADLTS), and using the current–voltage (I–V) characteristics and the capacitance–voltage (C–V) characteristics before and after AC biasing stress. The interface states in the Pr-type ZnO varistors consist of two adjacent levels: T0 and T1 levels. The activation energy ET and the capture cross section σ of the interface states decrease with increasing degradation induced by AC bias stress. The decrease in ET and σ is related to a decrease in the barrier height caused by the degradation. In order to characterize the change in the interface states with degradation, distribution parameters (ΔET, Δσ) are introduced, where the parameters for each level increase after degradation. The degradation is closely related to the distribution of the emission rate of the interface states. The degradation phenomenon is caused by migrated ions or by adsorbed ions such as oxygen. The increase in the distribution parameters upon degradation suggests activation of the oxygen ions at the grain boundaries and nonuniform migration.