Thin SiO2 Interlayer Research Articles

On the hydrogenation of Poly-Si passivating contacts by Al2O3 and SiNx thin films

Doped polycrystalline silicon (poly-Si), when coupled with a thin SiO2 interlayer, is of large interest for crystalline silicon (c-Si) solar cells due to its outstanding passivating contact properties. To reach high levels of surface passivation, it is pivotal to hydrogenate the poly-Si and the underlying c-Si/SiO2 interface. This can be done by capping the poly-Si with a hydrogen-containing dielectric layer such as Al2O3 or SiNx, followed by a thermal anneal. On the basis of recent research, this work addresses several aspects of such hydrogenation by dielectric materials, including the effect of the annealing ambient, the thermal stability and reversibility of hydrogenation, the poly-Si doping level and c-Si surface texture. Additionally, the implementation of hydrogenation of poly-Si by dielectric materials in solar cells is discussed.

Optimized waveguide coupling of an integrated III-V nanowire laser on silicon

The recent integration of III-V semiconductor nanowire (NW) lasers on silicon waveguides marked a key step toward their usage as coherent light sources for future silicon photonics applications. However, the low index contrast between III-V semiconductors and silicon results in a weak modal reflectivity, calling for improved design structures that enable both low-threshold lasing and good in-coupling efficiency into waveguides. Here, we perform numerical simulations to explore how the alternating refractive index of a silicon waveguide with a thin SiO2 interlayer can be used to significantly improve the reflectivity at the III-V–silicon interface to values of up to 83%. We further investigate the frequency dependencies of the end-facet reflectivity and in-coupling efficiency as a function of the nanowire and waveguide dimensions. Our results are kept general by the normalization to the nanowire radius R and show for a waveguide width of 2.75⋅R a maximum coupling efficiency of 50%. Variations in waveguide height or SiO2 interlayer thickness by ±0.1⋅R increase the coupling efficiency by a factor of 2, with little effect on the end-facet reflectivity. Ultimately, a prototypical NW-laser structure consisting of a 1.3-μm emitting InGaAs MQW active region in a core-multishell structure was simulated, showing an optimized low-threshold gain of <500 cm−1 for a TE01 mode with a coupling efficiency of ∼13%. By simplified approximations, we illustrate that these analyses can be adapted to a variety of material systems and serve as guidelines in the construction of optimized nanowire lasers on silicon-on-insulator waveguides for future on-chip optical interconnects.

Analysis of Zr<sub>x</sub>Si<sub>y</sub>O<sub>z</sub> as High-k Dielectric for 4H-SiC MOSFETs

This paper deals with investigation and fabrication of 4H-SiC MOSFETs with a high-k dielectric close to ZrSiO4. We are looking for the optimal stochiometry in order to obtain full benefits of its large bandgap, a k value higher than that of SiO2, thermodynamic stability on SiC, a good interface quality and process compatibility with SiC technology. Several Si/Zr ratios have been tested with the purpose of obtaining the most favorable dielectric configuration. The first test devices have been manufactured successfully with a stack gate dielectric consisting of a thin SiO2 interlayer and a ZrxSiyOz (theoretical Si/Z=0.7) layer on top.

Formation and Characterization of Hybrid Nanodots Floating Gate for Optoelectronic Application

ABSTRACTWe have fabricated a hybrid nanodots floating gate (FG) in which Si quantum dots (QDs) and silicide nanodots (NDs) are stacked with a very thin SiO2 interlayer in order to satisfy both multiple valued capability and charge storage capacity for a sufficient memory window and to open up novel functionality for optoelectronic application. In electron charging and discharging characteristics measured with application of pulsed gate biases to MOS capacitors with a hybrid NDs FG, stepwise changes in the rates for electron injection and emission were revealed with increasing pulse width at room temperature. Also, nMOSFETs with a hybrid NDs FG show unique hysteresis with stepwise changes in the drain current - gate voltage characteristics. The observed characteristics can be interpreted in terms that the electron injection and storage into silicide-NDs proceed through the discrete charged states of Si-QDs. For MOS capacitors with a triple-stacked hybrid NDs FG fabricated by adding another Si-QDs, by subgap light irradiation from the back side of the Si substrate, a distinct infrared optical response in C-V characteristics was detected at room temperature. The result is attributable to the shift of charge centroid in the hybrid NDs FG as a result of transfer of photoexcited electrons from silicide NDs to Si-QDs.

Energy band alignment of SiO2/ZnO interface determined by x-ray photoelectron spectroscopy

Thin SiO2 interlayer is the key to improving the electroluminescence characteristics of light emitting diodes based on ZnO heterojunctions, but little is known of the band offsets of SiO2/ZnO. In this letter, energy band alignment of SiO2/ZnO interface was determined by x-ray photoelectron spectroscopy. The valence band offset ΔEV of SiO2/ZnO interface is determined to be 0.93±0.15 eV. According to the relationship between the conduction band offset ΔEC and the valence band offset ΔEV: ΔEC=EgSiO2−EgZnO−ΔEV, and taking the room-temperature band-gaps of 9.0 and 3.37 eV for SiO2 and ZnO, respectively, a type-I band-energy alignment of SiO2/ZnO interface with a conduction band offset of 4.70±0.15 eV is found. The accurate determination of energy band alignment of SiO2/ZnO is helpful for designing of SiO2/ZnO hybrid devices and is also important for understanding their carrier transport properties.

Effects of N2 remote plasma nitridation on the structural and electrical characteristics of the HfO2 gate dielectrics grown using remote plasma atomic layer deposition methods

The characteristics of remote plasma atomic layer deposited HfO2 on Si, which has a very thin SiO2 interlayer with and without remote plasma nitridation (RPN), have been investigated. Small amounts of N atoms were successfully incorporated by RPN pretreatment, in which the dominant emission species were excited atomic nitrogen (N*) and excited molecular nitrogen (N2*), into a very thin SiO2 interlayer for the growth of HfO2 thin film. The thin (∼1.5nm) intermediate layer containing nitrogen, which was prepared by sequential O2 and N2 remote plasma treatment of the Si substrate, can effectively suppress growth of the unintentional interface layer. In addition, it enhances the thermal stability and the resistance to oxygen diffusion during rapid thermal annealing. The HfO2 film containing the remote plasma nitrided SiO2 interlayer annealed at 800°C showed a lower equivalent oxide thickness of ∼1.89nm and a lower leakage current density (3.78×10−7Acm−2 at ∣VG−VFB∣=2V) compared to a non-nitrided sample of the same physical thickness. Also, we compared the characteristics of HfO2 films annealed in two different ambient environments, N2 and O2.

Characteristics of remote plasma atomic layer-deposited HfO2 films on O2 and N2 plasma-pretreated Si substrates

Characteristics of remote plasma atomic layer-deposited HfO2 on Si, which has a very thin SiO2 interlayer with and without remote plasma nitridation, have been investigated. The thin (∼1.5nm) intermediate layer containing nitrogen, which was prepared by sequential O2 and N2 remote plasma treatment of the Si substrate, can effectively suppress growth of the unintentional interface layer. In addition, it enhances the thermal stability and the resistance to oxygen diffusion during rapid thermal annealing. The HfO2 film containing the remote plasma nitrided SiO2 interlayer annealed at 800°C showed a lower equivalent oxide thickness of ∼1.89nm and a lower leakage current density (3.78×10−7Acm−2 at ∣VG−VFB∣=2V) compared to a non-nitrided sample of the same physical thickness. Also, we compared the characteristics of HfO2 films annealed in two different ambient environments, N2 and O2.

InGaN/GaN Multi-Quantum Well Metal-Insulator Semiconductor Photodetectors with Photo-CVD SiO2 Layers

InGaN/GaN multiple-quantum well (MQW) structure was epitaxial growth by metal-organic chemical vapor deposition (MOCVD). Their MIS photodiodes with SiO2 interlayer were fabricated successfully using photochemical vapor deposition. The normal undoped-GaN metal-semiconductor-metal (MSM) potodiodes were also prepared to compare with them. It was found that the minimum dark current of InGaN/GaN MQW photodiodes was 4.2×10-13 A with 88 nm-thick SiO2 layer under 5 V reverse bias voltage. Furthermore, it was found that we can significantly reduce the dark current of this photodiodes by inserting a thin SiO2 interlayer in between metal electrode and the underneath InGaN/GaN MQW. With a 53 nm-thick SiO2 interlayer, it was also found that we could achieve a high 1.53×103 photo current to dark current contrast.

Suppression of Auger deexcitation and temperature quenching of the Er-related 1.54 μm emission with an ultrathin oxide interlayer in an Er/SiO2/Si structure

A strong enhancement of the Er3+-related 1.54 μm emission was obtained from Er-doped porous silicon (PSi), when host PSi was slightly oxidized before Er incorporation. Separate measurements of the energy transfer and the Auger deexcitation between carriers in Si crystallites of preoxidized PSi and Er3+ ions were measured as functions of the preoxidized time or the thickness of the SiO2 interlayer, and revealed that a 1 nm order thick SiO2 interlayer between Si crystallites and Er3+ ions suppressed the Auger energy backflow strongly with only a moderate decrease of the carrier mediated Er3+ excitation. A thin SiO2 interlayer was also effective at suppressing the phonon-assisted energy backtransfer at high temperatures, leading to a strong room temperature Er3+-related 1.54 μm emission.

Preferential suppression of Auger energy backflow by separation of Er ions from carriers with a thin oxide interlayer in Er-doped porous silicon

Strong enhancement of the Er-related 1.54μm emission was obtained at room temperature from Er-doped porous silicon (PSi), when host PSi was slightly preoxidized at 900°C before Er incorporation. It was speculated that the formation of the oxide interlayer played an important role. Separate measurements of the energy transfer and the Auger deexcitation between carriers in Si crystallites and Er ions were carried out using a two-beam (cw and pulse) excitation method for various preoxidation time which was supposed to change the oxide interlayer thicknesses from about 1 to 10nm. It was found that a very thin SiO2 interlayer between Si crystallites and Er ions suppressed preferentially the Auger deexcitation to the carrier-mediated Er excitation. A thin SiO2 interlayer was also effective to suppress the phonon-assisted energy backtransfer at high temperatures (so-called temperature quenching). This preferential suppression of the energy backflow (both Auger deexcitation and temperature quenching) by a thin oxide interlayer led to a strong room temperature Er-related emission at 1.54μm in Er-doped porous silicon. The Er/SiO2/Si structure was also formed on a flat Si surface and quite the same result was obtained. The oxide interlayer thickness of ∼2nm was found optimum to suppress the energy backflow sufficiently with only a slight decrease in the carrier-mediated excitation of Er ions.

Secondary ion mass spectrometry depth profiling of Mo/SiO2/Si structural samples

This report describes the influence of surface roughness resulting from the Mo film sputter process on oxygen profiles of the thin SiO2 interlayer in an Mo/SiO2/Si structural sample. The sputter-induced surface roughness causes expansion of oxygen profiles. The expansion increases as the Mo grain size increases. This is why the original surface roughness of an Mo film deposited on an SiO2 surface is almost all proportional to Mo grain size (20–300 nm) and why the sputter-induced surface roughness is developed by the original Mo surface roughness. The relation between sputter-induced inexactness resulting from the Mo film sputter process and an expanded oxygen profile of the thin SiO2 interlayer is obtained. The Mo grain size is controlled by postdeposition heat treatment (800–1100 °C).