Capture Activation Energy Research Articles

Extensive assessment of the charge-trapping kinetics in InGaAs MOS gate-stacks for the demonstration of improved BTI reliability

Gate-stack reliability has been a major roadblock in the realization of InGaAs-channel based logic technology. Excessive charge trapping in the gate-oxide causes time-dependent drift in transistor threshold voltage (Vth). The extent to which Vth drifts under certain stress conditions depends on (i) the defect ground-state energy distributions in the oxide bandgap, and (ii) the specific activation energy distributions for charge capture/emission process. In this work, semi-empirical modelling of ground-state defect energy distributions is revisited to determine the Total Operating Voltage Range of InGaAs-based MOSFETs for a DC-BTI lifetime of 10 years under DC operating conditions. Non-radiative Multiphonon (NMP) theory is subsequently used to describe the microscopic physics of charge (de-)trapping kinetics in terms of activation energy barriers for charge capture (EAc) and emission (EAe) into/from gate-stack defects. These activation energy barriers are visualized using Capture/Emission Time (CET) maps, which are efficient and powerful tools to predict the BTI degradation under different AC operating conditions as well. We demonstrate that the enhanced BTI reliability of a gate-stack with a novel ASM interfacial layer (ASM-IL), as compared to the bilayer gate-stack of Al2O3/HfO2, results from the favorable reconfiguration of the defect energy distribution in the oxide bandgap, as well as their activation energies for capture and emission process.

Random telegraph signals originating from unrelaxed neutral oxygen vacancy centres in SiO 2

Unrelaxed neutral oxygen deficiency centres (ODCs) (V0 ODC II) in SiO2 have been identified as the cause of random telegraph signals (RTSs) in highly scaled n-type metal–oxide–semiconductor field-effect transistors. Variable temperature RTS measurements were performed to extract trap capture cross-sections, capture activation energy, relaxation energy associated with the gate oxide defects, and the trap energy in the SiO2 bandgap to determine the trap species and type. The results indicate that the electron is captured by a neutral ODC that is transformed into a negatively charged vacancy (V−). This is the first time V0 ODC II centre is confirmed to be the source of electron switching through RTS measurements defining four different trap characteristics.

Impact of Uniaxial Strain on Random Telegraph Noise in High-<inline-formula> <tex-math notation="LaTeX">$k$ </tex-math></inline-formula>/Metal Gate pMOSFETs

The random telegraph noise (RTN) characteristics of high- $k$ (HK)/metal gate (MG) pMOSFETs with uniaxial compressive strain have been investigated. The configuration-coordinate diagram and band diagram are both established by extracting trap parameters, including capture and emission time, activation energy for capture and emission, trap energy level, and trap location in gate dielectric. Through a comparison of RTN results and gate-leakage current density ( $J_{G})$ between HK/MG pMOSFETs with and without uniaxial compressive strain in channel, it is found that the trap position from the insulator/semiconductor interface is reduced in the uniaxial compressive strained HK/MG pMOSFETs. This is reasonably attributed to the strain-increased tunneling barrier height and out-of-plane effective mass, which brings about the reduction in the tunneling attenuation length. Meanwhile, it can also be demonstrated by the lower $J_{G}$ in uniaxial compressive strained HK/MG pMOSFETs.

Investigation of trap properties in high-k/metal gate p-type metal-oxide-semiconductor field-effect-transistors with aluminum ion implantation using random telegraph noise analysis

In this study, the impact of aluminum ion implantation (Al I/I) on random telegraph noise (RTN) in high-k/metal gate (HK/MG) p-type metal-oxide-semiconductor field-effect-transistors (pMOSFETs) was investigated. The trap parameters of HK/MG pMOSFETs with Al I/I, such as trap energy level, capture time and emission time, activation energies for capture and emission, and trap location in the gate dielectric, were determined. The configuration coordinate diagram was also established. It was observed that the implanted Al could fill defects and form a thin Al2O3 layer and thus increase the tunneling barrier height for holes. It was also observed that the trap position in the Al I/I samples was lower due to the Al I/I-induced dipole at the HfO2/SiO2 interface.

Probing the Gate−Voltage-Dependent Surface Potential of Individual InAs Nanowires Using Random Telegraph Signals

We report a novel method for probing the gate-voltage dependence of the surface potential of individual semiconductor nanowires. The statistics of electronic occupation of a single defect on the surface of the nanowire, determined from a random telegraph signal, is used as a measure for the local potential. The method is demonstrated for the case of one or two switching defects in indium arsenide (InAs) nanowire field effect transistors at temperatures T=25-77 K. Comparison with a self-consistent model shows that surface potential variation is retarded in the conducting regime due to screening by surface states with density Dss≈10(12) cm(-2) eV(-1). Temperature-dependent dynamics of electron capture and emission producing the random telegraph signals are also analyzed, and multiphonon emission is identified as the process responsible for capture and emission of electrons from the surface traps. Two defects studied in detail had capture activation energies of EB≈50 meV and EB≈110 meV and cross sections of σ∞≈3×10(-19) cm2 and σ∞≈2×10(-17) cm2, respectively. A lattice relaxation energy of Sℏω=187±15 meV was found for the first defect.

Direct observation of charge-carrier capture in an array of self-assembled InAs/GaAs quantum dots

In this work, charge-carrier capture by an array of self-assembled InAs/GaAs quantum dots was directly observed for the first time by capacitance recharge. It is proposed to process the obtained transient-capture data by a similar method to that used for emission, by the box-car method. The capture activation energies are determined and compared with the emission activation energies.

Extraction of oxide trap properties using temperature dependence of random telegraph signals in submicron metal–oxide–semiconductor field-effect transistors

Random telegraph signals (RTS) in the drain voltage of light-doped drain n-metal–oxide–semiconductor field effect transistors with W×L=0.5×0.35 μm2 were investigated in the 300–230 K temperature range. The mean capture and emission times were studied as a function of gate voltage as well as temperature in the RTS. A method was developed where several trap characteristics can be extracted, including the position, barrier energy for capture, enthalpy, and entropy associated with emission of an electron, as well as screened scattering coefficient for carrier mobility as a function of temperature. This article reports on a single trap as an example. The position of the trap in the oxide (Tox=70 Å) was found to be 12 Å and, as expected, independent of temperature. The mean capture and emission times exhibited an increase as the temperature is decreased, following a thermally activated process. Utilizing these observations and the temperature dependence of the drain current, the gate voltage dependence of the trap binding energy, and capture activation energy was evaluated. The capture cross-section prefactor (σ0) was calculated using temperature dependence of capture and emission times. These two independent calculations showed almost two orders of magnitude difference in σ0, which is unrealistic. In order to remedy this, the trap binding energy was resolved into entropy and enthalpy components, which were evaluated as a function of gate voltage using the RTS data. The relative contributions of charge carrier mobility and number fluctuations on RTS amplitude were studied as a function of temperature. The mobility fluctuations were found to dominate over number fluctuations over the whole temperature range, and this dominance was found to be more pronounced at higher temperatures. The scattering coefficient due to screened Coulomb scattering effect was computed from the measured RTS data as a function of channel carrier density.

Effects of traps on the dark current transients in GaAs/AlGaAs quantum-well infrared photodetectors

In this work, experimental results showing very slow (up to 10 4 s) dark current transients in n-type GaAs/Al 0.27Ga 0.73As quantum-well photodetectors (QWIPs) are reported. The transients with amplitudes of 0.1% to 65% of the steady-state current have been observed at 77 K. These effects are believed to be associated with initially ionized deep levels acting as traps reducing the positive charge in the structure. The time constant of the dark current (transient) decreases with increasing temperature with an experimentally determined activation energy ∼75 meV . A fitting of the capture cross section to σ(T)=σ 0 exp(E c /k B T) gives an estimate for the capture activation energy of E c∼35 meV.

Experimental evidence of surface conduction contributing to transconductance dispersion in GaAs MESFETs

Low-frequency transconductance dispersion in GaAs metal semiconductor field effect transistors (MESFET's) is commonly attributed to the presence of a high density of surface states under the passivated source-gate and gate-drain separation regions. In this paper, we have found that they also contribute to a temperature dependent surface reverse leakage current with a thermal activation energy of 0.43 eV and a surface electron concentration (2.5/spl times/10/sup 12/ cm/sup 2/). Conductance deep-level transient spectroscopy (DLTS) spectra of these MESFETs have shown apparent hole-like peaks with emission energy of 0.48 eV and capture activation energy of 0.05 eV. These data were used for a model-based simulation and the results were compared with those obtained from experimental transconductance versus temperature measurements performed at various frequencies. A close agreement between these provides conclusive proof that the surface conduction at the GaAs-passivant interface is the major cause of the low-frequency transconductance dispersion observed. Finally, a possible explanation for the characteristic activation energy of 0.43 eV for Si/sub 3/N/sub 4/ passivant film on GaAs has been presented.

Electrically active defects in as-implanted, deep buried layers in p-type silicon

We have studied electrically active defects in buried layers, produced by heavy ion implantation in silicon, using both conventional deep level transient spectroscopy (DLTS) and an isothermal spectroscopic technique called time analyzed transient spectroscopy operated in constant capacitance mode (CC-TATS). We show that CC-TATS is a more reliable method than DLTS for characterization of the heavily damaged buried layers. The major trap produced in the buried layers in p-type Si by MeV Ar+ implantation is found to have an energy level at Ev+0.52 eV. This trap, believed to be responsible for compensation in the damaged layer, shows exponential capture dynamics. We observed an unusually high thermal activation energy for capture, which is attributed to a macroscopic energy barrier for carriers to reach the buried layer. We observe two other majority carrier traps, and also a minority carrier trap possibly due to inversion within the depletion layer.

A simple and inexpensive circuit for emission and capture deep level transient spectroscopy

A simple and inexpensive circuit for deep level transient spectroscopy is described, which allows rapid characterization of emission as well as capture activation energies of deep levels. This flexibility of making capture activation studies affords more information on defect morphology than the more standard emission activation studies. This is demonstrated by making a representative capture activation energy measurement on the EL6 level in undoped n-type GaAs of 0.484±0.005 eV. Also the spectrometer has shown better performance than earlier reported systems by its ability to resolve the side peaks of the EL6 level, for which emission activation energies of 0.29 and 0.4 eV are assigned. Constructed around a commercially available capacitance meter and pulse generator, the control circuitry is designed and developed using inexpensive and off-the-shelf integrated circuits.

A deep-level spectroscopic technique for determining capture cross-section activation energy of Si-related DX centers in AlxGa1−xAs

A deep-level transient spectroscopy (DLTS) technique is reported for determining the capture cross-section activation energy directly. Conventionally, the capture activation energy is obtained from the temperature dependence of the capture cross section. Capture cross-section measurement is often very doubtful due to many intrinsic errors and is more critical for nonexponential capture kinetics. The essence of this technique is to use an emission pulse to allow the defects to emit electrons and the transient signal from capture process due to a large capture barrier was analyzed, in contrast with the emission signal in conventional DLTS. This technique has been applied for determining the capture barrier for silicon-related DX centers in AlxGa1−xAs for different AlAs mole fractions.

Deep donor levels in Sn-doped AlxGa1−xAs

The properties of the Sn-doped AlxGa1−xAs alloys with various compositions have been studied by deep level transient spectroscopy and photocapacitance methods. Two deep donor levels with the thermal activation energies of 0.19 and 0.32 eV are found in all of the samples. Detailed data for the thermal emission and capture activation energies, optical ionization energies, and their composition dependence are given for the first time. Because their electronic properties are similar to that of the typical Si DX level in AlxGa1−xAs, it is concluded that both Sn-related levels are the DX-like levels.

DX centers in AlAs and GaAs-AlAs selectively doped superlattices

Dx centers have been investigated using deep level transient spectroscopy (DLTS) in Si doped AlAs and in selectively doped GaAs-AlAs superlattices (SLS) grown by molecular beam epitaxy. The activation energy for thermal emission is E~ = 0.42 eV in both the SLS and AlAs layers. For the first time a study of the capture in a SL reveals a capture activation energy E~~ = 0.36 eV, which locates the Dx at E, m 60 mev below the conduction nfiniband. Taking into account the measured energies and trap concentrations, we show that the Dx observed in the SLS lies in the AlAs layers.

Experimental analysis of temperature dependence of deep-level capture cross-section properties at the Au oxidized InP interface

Deep levels in unintentionally doped InP liquid encapsulated Czochralsky material have been studied by deep-level transient spectroscopy (DLTS) technique. Five electron traps are observed between 80 and 270 K labeled T1, T3, T4A, T4B, and T5. Trap concentrations are generally below 1013 cm−3. The capture cross sections for levels T1, T3, and T5, determined assuming an exponential time dependence of the capacitance transient, show a quite large variation with temperature which is consistent with the multiphonon emission process. In each case under this process, the binding energy term is much lower than the capture activation energy term. An unusual increase of the DLTS peak magnitude as the emission rate decreases leads us to analyze the capacitance signal as a multi-exponential transient. Each DLTS peak is then decomposed into two components from which the specific parameters have been extracted, activation energy, binding energy, and the experimental dependence of the capture cross section versus temperature for each contribution. The agreement between the theoretical model and experimental results is very good for the three levels T1, T3, and T5 under all experimental conditions, including the incomplete capture.

Characterization of D X centers in selectively doped GaAs-AlAs superlattices

Using deep level transient spectroscopy (DLTS), DX center has been characterized in GaAs-AlAs superlattices grown by molecular beam epitaxy and selectively Si-doped either in the AlAs layers or in the middle of the GaAs layers. The activation energy for thermal emission, which is the summation of the binding energy Et and the thermal capture energy Ec, is Ea=0.42 eV in both superlattices. The lowest DX concentration is obtained for the case where the only GaAs layers are doped. For the first time, a study of the capture reveals a capture activation energy Ec=0.36 eV, which locates the DX at Et≊60 meV below the conduction miniband. Taking into account the measured energies and trap concentrations, we show that the only observed DX on such structures is due to the silicon diffusion into AlAs layers.

Hall effect, photoluminescence and DLTS investigation of the DX centre in AlGaAs

The DX centre was observed on MOCVD-grown unintentionally doped Al0.3Ga0.7As by means of the Hall effect involving persistent photoconductivity (PPC), temperature-dependent photoluminescence (PL) and deep-level transient spectroscopy (DLTS). The ionisation energies of the hydrogen-like shallow donor (EaD=23 meV) and of the deep donor (Eadd=120 meV) with regard to the Gamma minimum were observed simultaneously by PL investigations at T=75 K. The value Eadd observed from the difference between the DLTS emission and capture barrier agrees excellently with that found by PL studies. The PL emission due to the transition involving the occupied DX centre was observed in a narrow temperature range (70<or=T<or=140 K). The population of the DX centre by thermally activated electrons which surmount the occupation barrier at these temperatures is indicated by the drop of the PPC and the DLTS capture studies. For the capture activation energy of the deep donor a value of 240 meV is obtained.

DX centers in selectively Si-doped GaAsAlAs superlattices

DX center has been characterized in four GaAsAlAs superlattices grown by MBE at 580°C. The structures are uniformly Si-doped or selectively Si-doped in the AlAs layers or in the middle of the GaAs layers or on both sides of the interfaces. Deep level transient spectroscopy measurements (DLTS) put in evidence one dominant electron trap, with an activation energy for thermal emission of about 0.42eV for all the superlattices. This defect shows a thermally activated capture cross section and a large concentration except for the case where the only GaAs layers are doped. For the first time, a study of the capture reveals a capture activation energy of 0.36-0.37 eV, which allows us to locate the DX level nearly 60 meV below the conduction miniband. From these results, we show that the observed DX center is related to silicon in the AlAs layers. For the case when the AlAs barriers are not doped, the DX level is due to the Si diffusion from the middle of the wells towards the barriers, the Si atoms having diffused during the growth.

Discovery of a new photoinduced electron trap state shallower than the DX center in Si doped AlxGa1−xAs

We have found a new electron trap state in Si-doped AlxGa1−xAs by deep level transient spectroscopy and constant temperature capacitance transient measurements under strong light illumination. This new trap is shallower than the DX center associated with Si impurity in that its emission and capture activation energies are equal to 0.20±0.05 and 0.17±0.05 eV, respectively. Its maximum concentration is comparable to the concentration of the DX center. Possible origins of this new trap and its relationship to the DX center are discussed.

Electrical Properties of Interface-Traps in Selectively Doped AlGaAs/GaAs Heterostructures

A hole-trap-like peak appears in the drain current DLTS spectra recorded from a high-electron-mobility transistor fabricated with a selectively doped AlGaAs/GaAs heterostructure grown by molecular-beam epitaxy. The peak is caused by traps which strongly affect the mobility. The emission and the capture activation energy of the traps increases as the gate bias increases. This shows that the traps which remain ata fixed energy level relative to the GaAs conduction band edge exchange electrons with the sub-bands in the accumulation layer. Based on the above characteristics, an analysis of the spectra indicates that interface-traps with a density of 3.8×1010 cm-2 are located at 0.01 eV above the conduction band edge of GaAs, in the potential well of the accumulation layer.