Investigation Of Deep Levels Research Articles

Investigation of deep levels in semi-insulating vanadium-doped 4H-SiC by photocurrent spectroscopy

We measured spectral-resolved photocurrent in a wide range of photon energies from 0.68 eV to 4.10 eV, current-voltage characteristics, and mid to near-infrared transmittance spectra on a semi-insulating 4H-SiC wafer at room temperature. We identified four deep levels, their energies, and localization radii. The model considers the defects' wavefunction as a linear combination of s- and p-states. Such a linear combination leads to the mixture of dipole allowed and forbidden transitions. The forbidden transitions contribute to a broad photocurrent spectrum, and the allowed transitions appear as sharp photocurrent peaks. The width of photocurrent peaks is related to the localization radius of deep levels.

Low-Frequency Noise Characterization in GaN HEMTs: Investigation of Deep Levels and Their Physical Properties

In this letter, traps-related dispersion phenomenon of GaN/AlGaN/GaN high electron mobility transistor grown on the SiC substrate is investigated through low-frequency noisemeasurements. Low-frequency drain noise measurements are performed over the frequency range of 20 Hz–1MHz and for varying chuck temperatures ( ${T}_{\text {chuck}})$ ranging between 25 °C and 125 °C. This letter demonstrates that two prominent deep levels are present in the device-under-testwith apparent activation energies ( ${E}_{a})$ of 0.51 and 0.57 eV, respectively. Moreover, signatures of deep level with ${E}_{a}$ of 0.57 eV become visible only at higher operating temperatures, due to the fact that traps dispersion occurs at very low frequencies, which is confirmed through TCAD physical simulations.

Investigation of electrically-active deep levels in single-crystalline diamond by particle-induced charge transient spectroscopy

To investigate electrically-active deep levels in high-resistivity single-crystalline diamond, particle-induced charge transient spectroscopy (QTS) techniques were performed using 5.5MeV alpha particles and 9MeV carbon focused microprobes. For unintentionally-doped (UID) chemical vapor deposition (CVD) diamond, deep levels with activation energies of 0.35eV and 0.43eV were detected which correspond to the activation energy of boron acceptors in diamond. The results suggested that alpha particle and heavy ion induced QTS techniques are the promising candidate for in-situ investigation of deep levels in high-resistivity semiconductors.

Investigation of deep levels in bulk GaN material grown by halide vapor phase epitaxy

Electron traps in thick free standing GaN grown by halide vapor phase epitaxy were characterized by deep level transient spectroscopy. The measurements revealed six electron traps with activation energy of 0.252 (E1), 0.53 (E2), 0.65 (E4), 0.69 (E3), 1.40 (E5), and 1.55 eV (E6), respectively. Among the observed levels, trap E6 has not been previously reported. The filling pulse method was employed to determine the temperature dependence of the capture cross section and to distinguish between point defects and extended defects. From these measurements, we have determined the capture cross section for level E1, E2, and E4 to 3.2 × 10−16 cm2, 2.2 × 10−17 cm2, and 1.9 × 10−17 cm2, respectively. All of the measured capture cross sections were temperature independent in the measured temperature range. From the electron capturing kinetic, we conclude that trap E1, E2, and E3 are associated with point defects. From the defect concentration profile obtained by double correlated deep level transient spectroscopy, we suggest that trap E4 and E6 are introduced by the polishing process.

Investigation of deep levels in nitrogen doped 4H–SiC epitaxial layers grown on 4° and 8° off-axis substrates

Intentionally doped n-type 4H–SiC films were grown on 4° and 8° off-axis substrates to investigate the influence of electron concentration on the incorporation of electron traps Z1/2 and EH6/7. No discernible change was seen in the Z1/2 and EH6/7 trap concentrations for films grown on both orientations with electron concentrations in the range of 1×1014 to 1×1016 cm−3, suggesting that the Z1/2 and EH6/7 traps are not associated with isolated carbon vacancies. The defect concentrations did not correlate with the measured carrier lifetimes, which is consistent with a carrier lifetime controlled by other recombination centers. Observed decreases in lifetime were related to increases in doping levels, with similar trends seen for both orientations. Carrier lifetimes in 8° material were slightly longer than in 4° films for similar doping concentrations, most likely being associated with surface recombination and/or extended defects.

Deep level transient spectroscopy investigation of deep levels in CdS/CdTe thin film solar cells with Te:Cu back contact

Deep levels in Cds/CdTe thin film solar cells have a potent influence on the electrical property of these devices. As an essential layer in the solar cell device structure, back contact is believed to induce some deep defects in the CdTe thin film. With the help of deep level transient spectroscopy (DLTS), we study the deep levels in CdS/CdTe thin film solar cells with Te:Cu back contact. One hole trap and one electron trap are observed. The hole trap H1, localized at Ev + 0.128 eV, originates from the vacancy of Cd (VCd). The electron trap E1, found at Ec −0.178 eV, is considered to be correlated with the interstitial Cuj+ in CdTe.

Deep level investigation of p-type GaN using a simple photocurrent technique

The deep level spectrum of p-type GaN was investigated using time-resolved photocurrent spectroscopy. The spectral dependence of the optical cross section for hole photoemission from a deep level was determined from the initial value of the photocurrent transient. Unlike other implementations of photocurrent, the present method does not require multiple excitation sources or determination of the optical emission rate. A deep level was observed at Ev+1.84 eV, where Ev is the valence band maximum, with a Franck-Condon shift of 0.25 eV. A bias-dependent component of the photocurrent, possibly due to metal-semiconductor interface states, complicated the steady-state response but did not affect the measured spectrum for the Ev+1.84 eV deep level. This photocurrent method is expected to be readily extended to materials with very deep dopants, such as p-type AlGaN, for which many other deep level spectroscopy techniques are unsuited.

Investigation of deep levels in InGaAs channels comprising thin layers of InAs

The generation-recombination noise in doped-channel In0.53Ga0.47As/In0.52Al0.48As/InP micro-Hall devices is characterized using deep level noise spectroscopy. Three noise sources are detected with trap energies of 140, 170 and 40 meV respectively. The levels are likely to be associated with arsenic vacancies.

Investigation of deep levels in n-type 4H-SiC epilayers irradiated with low-energy electrons

Deep levels in n-type 4H-SiC epilayers have been investigated by deep level transient spectroscopy (DLTS). The Z1∕2 and EH6∕7 centers are dominant in as-grown samples. After electron irradiation at 116 keV, by which only carbon atoms may be displaced, the Z1∕2 and EH6∕7 concentrations are significantly increased. The Z1∕2 and EH6∕7 centers are stable up to 1500–1600 °C and their concentrations are decreased by annealing at 1600–1700 °C. In the irradiated samples, the trap concentrations of the Z1∕2 and EH6∕7 centers are increased with the 0.7 power of the electron fluence. The concentrations of the Z1∕2 and EH6∕7 centers are very close to each other in all kinds of samples, as-grown, as-irradiated, and annealed ones, even though the condition of growth, irradiation (energy and fluence), and annealing has been changed. This result suggests that both Z1∕2 and EH6∕7 centers microscopically contain the same defect such as a carbon vacancy.

A technique for the investigation of deep levels on irradiated silicon based on the Lazarus effect

A new technique for the investigation of deep levels on irradiated silicon by measuring the charge collection efficiency (CCE) of samples from 220 K down to 90 K is presented here. The temperature and time dependencies of the CCE have been measured with unprecedented precision and resolution for standard and oxygenated silicon diodes, and the data obtained have been analyzed in the framework of the Lazarus effect and polarization models, extracting information about the radiation-induced deep levels in the materials. Results are presented and discussed in terms of these models and what can be inferred from them when applied to experimental data.

Deep Level Investigation by Current and Capacitance Transient Spectroscopy in 4H-SiC MESFETs on Semi-Insulating Substrates

In this paper we present static measurements fand defects analysis performed on 4H-SiC MESFETs on semi-insulating (SI) substrates containing vanadium. I d-Vds -T and I d-Vgs -T characteristics show anomalies (Threshold voltage shift, leakage current, degradation in saturation current...). Deep defects analysis performed by capacitive transient spectroscopy (C-DLTS) proves the presence of one deep defect called E1 with an activation energy 0.32eV. The studies of C-DLTS signal with pulse duration (t p) and polarization voltage (V r) confirm that E 1 trap is a point defect. Current transient spectroscopy (I-DLTS) performed in the same devices confirm E1 defect and shows the presence of six levels with activation energies ranging from 0.09eV to 1.01eV. The localization and the identification of these defects is presented. Finally, the correlation between the anomalies observed on output characteristics and defects is discussed.

A critical analysis of investigation of deep levels in high-resistivity CdS single crystals by photoelectric transient spectroscopy

The investigation of high-resistivity CdS single crystals by photoelectric deep-level transient spectroscopy (PEDLTS) is discussed. Computer simulation of the experiment is carried out. This simulation enables us to compare the results obtained by the PEDLTS and thermally stimulated conductivity methods. The experimental potentials of these methods are compared.

Nonstoichiometry and point defects in nonlinear optical crystals A 2B 4C 25

Using thermodynamic calculation, the equilibrium concentrations of point defects in ZnGeP 2 and CdGeAs 2 depending on a liquidus temperature are obtained. The conclusion about a high degree of compensation of native donors and acceptors is made. The methods of a model pseudo-potential and large unit cell are used for investigation of deep levels created by vacancies and antisites in the forbidden band of ZnGeP 2. Optical transitions with participation of the defects are defined. It is supposed the possibility of conditions favourable for mid-IR optical absorption, as a result of the interaction of ionized zinc vacancies with GeP clusters.

Deep level investigation in AlGaAs/InGaAs/GaAs cryoelectronic MODFET

The pseudomorphic AlGaAs/InGaAs/GaAs MODFET, intended for future applications in cryoelectronics, has been investigated. In the temperature range of 10–350 K no collapse nor Kink effect have been detected. However, a threshold shift has been observed which is thought to be associated with electrically active defects in the heterostructure. The related deep levels are directly characterized by two electrical techniques: capacitance deep level transient spectroscopy and drain current transient spectroscopy. Experimental results establish the complementarity of both techniques.

Investigation of deep levels in semi-insulating GaAs by means of a thermally activated piezoelectric photoacoustic measurements

The temperature variation of the piezoelectric photoacoustic (PPA) signal intensity of semi-insulating (SI) GaAs from 20 to 150K was measured. Four peaks at 50, 70, 110 and 125K were observed in the PPA signal. From the theoretical analysis based on the rate equations of electrons in the conduction band and several deep levels, we concluded that the observed four peaks were due to the nonradiative electron recombinations via EL6, EL7, EL15 and an unknown deep level, respectively. Deep levels with extremely low concentrations (1011–1015cm−3) were clearly identified conveniently in SI–GaAs by using the PPA method for the first time.

Investigation of deep levels in semi-insulating GaAs by means of the temperature change piezoelectric photo-thermal measurements

The temperature variation of the piezoelectric photo-thermal (PPT) signal intensity of semi-insulating (SI) GaAs from 20 to 150 K was measured. Four peaks at 50, 70, 110, and 125 K were observed in the PPT signal. From the theoretical analysis based on the rate equations of electrons in the conduction band and deep levels, we concluded that the observed four peaks were due to the nonradiative electron transitions through EL6, EL7, EL15, and an unspecified deep level, respectively. Deep levels with extremely low concentration (1012–1015 cm−3) were clearly identified in SI GaAs by using the PPT method.

Deep Level Investigation of pn-Junctions formed by MeV Aluminum and Boron Implantation into 4H-SiC

Deep Level Investigation of pn-Junctions formed by MeV Aluminum and Boron Implantation into 4H-SiC

Photoinduced current generated by subband gap optical pumping for the investigation of deep levels in semiconductor lasers

It is shown that the measurement of photocurrents induced by optical pumping at subband gap wavelengths may be a useful technique for studying deep-level traps in semiconductor lasers. In this experiment a 1.3 μm wavelength laser is used to probe a 0.78 μm wavelength GaAs laser device. The trap density of a predegraded and postdegraded device was measured. The measurement indicates a significant increase in the trap density for the degraded device over the nondegraded device. Rate equations describing this excitation process are given and are shown to describe the experiment very well.

Investigation of deep levels in rapid thermally annealed SiO2-capped n-GaAs grown by metal-organic chemical vapor deposition

Defects created in rapid thermally annealed (RTA) SiO2-capped epitaxial GaAs layers grown by metal-organic chemical vapor deposition have been investigated by deep level transient spectroscopy. RTA introduced four electron traps S1 (Ec−0.23 eV), S2 (Ec−0.46 eV), S3 (Ec−0.72 eV), and S4 (Ec−0.74 eV). S1 may be the so-called EL9 defect. We propose that S2 is a defect complex involving the Ga vacancy and Si dopant atoms, VGa–SiGa, and associate it with the EL5. S2 is introduced almost uniformly within the first 0.8 μm below the surface with an activation energy of 4.4 eV. S4 is most probably one of the EL2 family. The concentration of S4 decreased exponentially below the surface with a characteristic decay length ∼0.2 μm. The activation energy for the introduction of S4 is 2.5 eV.

Deep-level transient spectroscopy in the depletion zone of boron-doped homoepitaxial diamond films

Abstract Investigation of deep levels in the depletion zone of boron-doped homoepitaxial diamond films is achieved from analysis of the transient responses of Schottky junctions. The active layer consists of a homoepitaxial film grown by microwave plasma decomposition of a very small percentage of B2H6 mixed with CH4 in hydrogen on synthetic Ib diamond substrates. Rectifying contacts are implemented with either aluminium, gold or erbium after suitable pre- and post-treatments. Reverse-current transients due to the thermal emission of holes from deep-level traps into the valence band are recorded and analysed with a Fourier transform deep-level transient spectroscopy (Fourier DLTS) procedure as a function of temperature up to 520°C. At each temperature, a thermal emission time constant is extracted. Arrhenius diagrams are deduced. A deep level at 1.40±0.07 eV above the valence band is detected in samples that have been submitted to a 800°C annealing in ultrahigh vacuum. Another deep level at 1.16±0.03 eV above the valence band exists only if an oxygen radio-frequency plasma treatment is applied to the sample before the Schottky contact deposition. Thermal capture cross-sections are also deduced.