Pb-type Defects Research Articles

First-principles calculations of the hole-induced depassivation of SiO2/Si interface defects

The holes induced by ionizing radiation or carrier injection can depassivate saturated interface defects. The depassivation of these defects suggests that the deep levels associated with the defects are reactivated, affecting the performance of devices. This work simulates the depassivation reactions between holes and passivated amorphous-SiO2/Si interface defects (HPb + h → Pb + H+). The climbing image nudged elastic band method is used to calculate the reaction curves and the barriers. In addition, the atomic charges of the initial and final structures are analyzed by the Bader charge method. It is shown that more than one hole is trapped by the defects, which is implied by the reduction in the total number of valence electrons on the active atoms. The results indicate that the depassivation of the defects by the holes actually occurs in three steps. In the first step, a hole is captured by the passivated defect, resulting in the stretching of the Si–H bond. In the second step, the defect captures one more hole, which may contribute to the breaking of the Si–H bond. The H atom is released as a proton and the Si atom is three-coordinated and positively charged. In the third step, an electron is captured by the Si atom, and the Si atom becomes neutral. In this step, a Pb-type defect is reactivated.

Interface nature of oxidized single-crystal arrays of etched Si nanowires on (100)Si

Low temperature electron spin resonance studies have been carried out on single crystalline arrays of sub-10 nm Si nanowires (NWs) manufactured on (100)Si by top down etching and oxidation thinning. This reveals the presence of a substantial inherent density of Pb0 (Si3 ≡ Si•) defects (traps) at the NW Si/SiO2 interfaces, due to particular faceting and enhanced interface strain, leaving NW interfaces of reduced electrical quality. Perusal of the specific properties of the occurring Pb-type defect system points to a nanopillar morphology compatible with NWs predominantly bordered by {110} facets, with cross sectional shape of 〈100〉 truncated {110} squares. The inherent interface quality appears limited by the wire-narrowing thermal oxidation procedure.

Inherent paramagnetic defects in layered Si/SiO2 superstructures with Si nanocrystals

An extensive electron spin resonance (ESR) analysis has been carried out on structures comprised of Si nanoparticles (∼2 nm across) embedded in a regular pattern in an amorphous SiO2 matrix, fabricated by the SiO/SiO2 superlattice approach, with the intent to reveal and quantify occurring paramagnetic defects. The as-grown state is found to exhibit only a Si dangling bond (DB) signal, which through combination of first and second harmonic X-, K-, and Q-band observations in combination with computer spectra simulation, could be conclusively disentangled as solely comprised of overlapping powder pattern spectra of Pb(0) and Pb1 defects, the archetypal intrinsic defects of the Si/SiO2 interface, with no evidence for a D line (Si DBs in disordered Si). This indicates a full crystalline system of randomly oriented Si nanocrystals (NCs). The Pb(0)/Pb1 defect system, pertaining to the NC-Si/SiO2 interfaces, is found to be both qualitatively and quantitatively much alike that of standard (high-quality) thermal Si/SiO2. The system is inherent, remaining unaffected by subsequent UV/vacuum UV irradiations. Relying on the known properties of Pb-type defects in standard microscopic Si/SiO2, the data would comply with Si nanocrystallites, in average, predominantly bordered by (111) and (100) facets, perhaps with morphology, schematically, of [100] truncated (111) octahedrons. Based on independent NC particles counting, there appears a Pb-type center at ∼71% of the Si NCs indicating the latter to be comprised of two subsystems–with or without an incorporated strain relaxing interface defect–which in that case will exhibit drastically different defect-sensitive properties, such as, e.g., photoluminescence (PL). Upon additional optical irradiation, two more defects appear, i.e., the SiO2-associated Eγ′ and EX centers, where the observed density of the former, taken as criterion, indicates the SiO2 matrix to be of standard thermal oxide quality. Thus, the properties of the revealed crucial intrinsic point defects bear out a high quality of both the NC-Si/SiO2 interfaces and the embedding SiO2, alike that of standard thermal Si/SiO2. In combination with H passivation/depassivation treatments, the degrading impact of the optical excitation (∼360 nm) itself used during PL measurements has been studied, revealing weak ESR reactivation of Pb(0), Pb1, and Eγ′ defects.

Paramagnetic point defects at SiO2/nanocrystalline Si interfaces

A K- and Q-band electron spin resonance study, combining two detection modes, on structures composed of Si nanoparticles (∼2nm across) embedded in a SiO2 matrix obtained by annealing of SiO∕SiO2 superstructures unveils the observed principal Si dangling bond signal as solely comprised of the intrinsic Pb(0) and Pb1 Si∕SiO2 interface defect spectra, of comparable densities. Based on independent particle density counting, about one Pb-type defect is found at every 1.4 Si nanoparticles. Relying on the known properties of Pb-type defects in standard microscopic Si∕SiO2, the data would comply with Si nanocrystallites with morphology, schematically, of [100] truncated (111) octahedrons. Both types and densities of observed point defects indicate a structure of quality much alike that of standard thermal Si∕SiO2.

Paramagnetic point defects at interfacial layers in biaxial tensile strained (100)Si/SiO2

A comparative electron spin resonance study is reported on (100)Si/SiO2 entities, grown by thermal oxidation of biaxial tensile strained (100)Si (sSi) layers, epitaxially grown on a strain relaxed Si0.8Ge0.2 buffer layer, and standard (100)Si. In the as-oxidized state a significant decrease (∼50%) of inherently incorporated interface defects, Pb0 and Pb1, is observed, i.e., the sSi/SiO2 interface is found to be inherently significantly improved in terms of electrically detrimental interface traps (Pb0). After vacuum-ultraviolet irradiation two more SiO2-associated defects appear, namely Eγ′ (generic entity O3≡Si·) and EX. Interestingly, a decrease (∼50%) of Eγ′ defect density is observed compared to standard Si/SiO2. This reduction in inherent electrically active interface (Pb0) and near-interface (Eγ′) traps would establish sSi/SiO2 as a superior device structure for all electrical properties where (near)-interfacial traps play a detrimental role. For one, the reduction of detrimental (near)-interface defects may be an additional reason for the commonly reported mobility enhancement in sSi/SiO2 based metal–oxide–semiconductor structures over standard Si/SiO2 ones, and at the same time account for the reported reduction of 1/f noise in the former structures. The data also confirm the generally accepted notion that Pb-type defects are mismatch induced defects.

Paramagnetic point defects in (100)Si∕LaAlO3 structures: Nature and stability of the interface

The atomic nature of the interface in (100)Si∕LaAlO3 structures with nanometer-thin amorphous LaAlO3 layers of high dielectric constant (κ), deposited directly on clean (100)Si by molecular beam deposition at ∼100°C, was assessed through probing of paramagnetic point defects. On the as-grown samples K-band electron spin resonance indicated the absence of a Si∕SiO2-type interface in terms of the archetypal Si-dangling bond-type Si∕SiO2 interface defects (Pb0, Pb1). With no Pb-type defects observed, this state is found to persist during subsequent annealing (1atm N2 or 5% O2 in N2 ambient) up to the temperature Tan∼800°C, referring to a thermally stable abrupt Si∕LaAlO3 interface, quite in contrast with other high-κ metal oxide∕Si structures. However, in the range Tan∼800–860°C a Si∕SiO2-type interface starts forming as evidenced by the appearance of Pb0 defects and, with some delay in Tan, the EX center—a SiO2 associated defect, attesting to significant structural∕compositional modification. The peaking of the defect density versus Tan curves indicates the SiOx nature of the interlayer to break up again upon annealing at Tan⩾930°C, possibly related to crystallization and∕or degrading silicate formation. No specific LaAlO3-specific point defects could be traced.

Nature and stability of the (100)Si∕LaAlO3 interface probed by paramagnetic defects

Electron spin resonance analysis of (100)Si∕LaAlO3 structures reveals the absence of a Si∕SiO2-type interface in terms of archetypal Si-dangling bond-type Si∕SiO2 interface defects (Pb0,Pb1). With no Pb-type defects observed, this state is found to persist during subsequent annealing (5% O2+N2 ambient) up to Tan∼800°C, indicating a thermally stable and abrupt Si∕LaAlO3 interface. In the range Tan∼800–860°C, however, a Si∕SiO2-type interface starts forming as evidenced by the appearance of Pb0 defects and, with some delay in Tan, the EX center (a SiO2 associated defect) attesting to significant structural/compositional modification. The peaking of the defect density versus Tan curves indicates that the interlayer with SiOx nature breaks up upon annealing at Tan⩾930°C, possibly related to crystallization and silicate formation. No LaAlO3-specific point defects could be detected.

Hydrogenation effect on enhancement of photoluminescence of Er and Si nanocrystallites in Er-doped SiO2 synthesized by laser ablation

Significant enhancement of photoluminescence (PL) was attained for Er ions and Si nanocrystallites (nc-Si) in SiO2 films by two kinds of hydrogenation, using H2 molecules or H atoms. Er-doped SiO2 films containing Er impurities and a high density of nc-Si were fabricated by laser ablation of Er films deposited on Si substrate in an O2 gas atmosphere, followed by annealing at high temperatures in flowing Ar gas. Hydrogenation at 300–500 °C was found to effectively increase the PL intensity of Er ions as well as that of nc-Si. In particular, the hydrogen atom treatment dramatically shortens the hydrogenation time for the enhancement of Er PL compared to the hydrogen molecule treatment. Spectra of electron spin resonance showed a decrease in residual defects, namely, Pb-type defects located at the interfaces between nc-Si and SiO2 by hydrogenation. These results clearly show the effectiveness of hydrogen passivation for Si nanostructures; i.e., the increase in the Er PL and nc-Si PL due to hydrogen passivation of the nonradiative recombination centers located at the interfaces between nc-Si and SiO2.

Probing Semiconductor/Insulator Heterostructures Through Electron Spin Resonance of Point Defects: Interfaces, Interlayers, and Stress

AbstractElectron spin resonance (ESR) spectroscopy has become indispensable when it comes to the characterization on atomic-scale of structural, and correlated, electrical properties of actual semiconductor/insulator heterostructures. Through probing of paramagnetic point defects such as the Pb-type defects, E', and EX as a function of VUV irradiation and post deposition heat treatment, basic information as to the nature, quality, and thermal stability of the interface and interfacial regions can be established. This is illustrated by some specific examples of ESR analysis on contemporary Si/insulator structures promising for future developments in integrated circuits. First the impact of strain on the Si/SiO2 entity will be discussed. Through ESR analysis of thermally oxidized (111)Si substrates mechanically stressed in situ during oxidation, and tensile strained (100)sSi/SiO2 structures, it will be pointed out that in-plane tensile stress in Si can significantly improve the interface quality. Next, ESR results for stacks of (100)Si/SiOx/HfO2 and (100)Si/LaAlO3 are presented, revealing the potential to attain a high quality Si/SiO2 interface for the former and an abrupt, thermally stable interface for the latter.

Analysis of defects at the interface between high-k thin films and (1 0 0) silicon

Paramagnetic defects in atomic layer deposition grown aluminium oxide thin films have been studied using electron paramagnetic resonance. Initial spectra indicate the presence of Si-db, Pb0 and Pb1 defects, previously observed in Si/SiO2 structures. We show that the Si-db defect is located in the substrate only. We quantify the unpassivated Pb-type defect density and show that this can be reduced by a pre-deposition nitridation step. However, forming gas annealing at temperatures up to 550°C causes no further reduction in defect density; this may be related to the low deposition temperature, which causes a spread in passivation activation energies.

Electron spin resonance analysis of interfacial Si dangling bond defects in stacks of ultrathin SiO2, Al2O3, and ZrO2 layers on [formula omitted]Si

Paramagnetic point defects were probed by electron spin resonance in stacks of (100)Si with nm-thin SiOx, ZrO2, and Al2O3 layers. After hydrogen photodesorption (8.48 eV; 300 K), the Si dangling bond interface centers Pb0, Pb1 appear as prominent defects at all (100)Si/dielectric interfaces. This Pb0, Pb1 fingerprint, generally unique for the thermal (100)Si/SiO2 interface, indicates that, while reassuring for the Si/SiOx/ZrO2 case, the as-deposited (100)Si/Al2O3 interface is basically Si/SiO2-like. The interfaces are under enhanced stress, typical for low temperature Si/SiO2 growth. Standard quality thermal Si/SiO2 interface properties, as exposed by the Pb-type defects (density ∼1×1012 cm−2), may be approached by appropriate annealing (∼650 °C). A high quality (100)Si/SiO2 type interface, with ultrathin SiO2 interlayer, may be basic to successful application of high-κ metal oxides in Si-based devices.