Positive Fixed Charge Density Research Articles

POx/Al2O3 stacks for surface passivation of Si and InP

Passivation of semiconductor surfaces is crucial to reduce carrier recombination losses and thereby enhance the device performance of solar cells and other semiconductor devices. Thin-film stacks of phosphorus oxide (PO x ) and aluminum oxide (Al 2 O 3 ) have recently been shown to provide excellent passivation of semiconductor surfaces, including crystalline silicon and indium phosphide, and can also be highly interesting for passivation of other semiconductor materials such as Ge and III-V semiconductors. On silicon, the excellent passivation is attributed to the combination of a high positive fixed charge and a very low interface defect density. On InP nanowires, application of the PO x /Al 2 O 3 stacks improves charge carrier lifetime threefold as compared to unpassivated nanowires. In this work, we review and summarize recent results obtained on PO x /Al 2 O 3 stacks for semiconductor surface passivation. Several topics are discussed, including the passivation performance on various semiconductor surfaces, the processing of the PO x and Al 2 O 3 layers, the role of the capping layer, and aspects related to device integration. The PO x /Al 2 O 3 stacks feature some unique properties, including an unusually high positive fixed charge density, a low interface defect density, and can be prepared over a wide deposition temperature range. These unique properties arise in part from the mixing process that occurs between the PO x and Al 2 O 3 layers, which upon post-deposition annealing leads to the formation of AlPO 4 . The surface passivation provided by PO x /Al 2 O 3 stacks is highly stable and the stack can be used to conformally coat high-aspect-ratio structures such as nanowires, showing their promise for use in semiconductor devices. • PO x /Al 2 O 3 stacks provide excellent surface passivation on Si and InP. • PO x /Al 2 O 3 has a unique high positive fixed charge density (10 12 -10 13 cm −2 ) on Si. • PO x /Al 2 O 3 has low interface defect density down to 10 10 -10 11 eV −1 cm −2 on Si. • The Al 2 O 3 layer mixes with PO x during deposition, leading to AlPO 4 upon annealing. • The surface passivation quality provided by PO x /Al 2 O 3 is stable for over 1000 days.

Interface engineering of β-Ga2O3 MOS-type Schottky barrier diode using an ultrathin HfO2 interlayer

Low leakage current and high breakdown voltage are critically important to design high performance Schottky barrier diodes. In this work, a low leakage current was reported by studying the effect of inserting an ultrathin HfO2 layer using atomic-layer deposition with different cycle number at the interface between Ni and β-Ga2O3 for different annealing temperatures. A remarkable decrease in leakage current from 5.68 × 10−3 to 2.97 × 10−6 A/cm² at -300 V and a breakdown voltage increase from -467 to -556 V, were achieved when two cycles of HfO2 are inserted and annealed at 400°C. The leakage current decreases from 9.87 × 10−5 to 2.14 × 10−5 A/cm² for 200°C annealing temperature and from 1.035 × 10−4 to 2.56 × 10−6 A/cm² for as-deposited Metal-oxide semiconductor based Schottky barrier diode (MOSSBD) only after 2-cycles (∼2 Å) HfO2 is inserted. As the number of HfO2 cycles was increased (2–8 cycles) and the annealing temperature is varied, leakage current and breakdown voltage are affected. To investigate these variations in leakage current and breakdown voltage, Silvaco TCAD simulator is used. Good agreement is obtained between experiment and simulation by considering the fixed charge density in HfO2 (positive fixed charge density is related to oxygen vacancy density in HfO2 and the interfacial trap (reduced by annealing), and, where necessary, also considering the inhomogeneity of the Schottky barrier height to understand the main reason for the abrupt increase in leakage current at a specific reverse voltage.

Solution-processed tin oxide thin film for normally-off hydrogen terminated diamond field effect transistor

The solution processed method has been wildly used in the thin film fabrication because of the advantages of low cost, high efficiency, large scale for production, and long-term stability. In this paper, a normally-off hydrogen-terminated diamond field-effect transistor (FET) has been realized by using a solution processed SnO2 (sp-SnO2) film as an insulator layer. X-ray photoelectron spectroscopy results demonstrated the stoichiometry of the sp-SnO2 film, which shows good insulator properties with leakage current density less than 2.1 × 10−5 A·cm−2 at gate voltages from −6.0 to 6.0 V. The drain–source current maximum, threshold voltage, extrinsic transconductance maximum, and effective mobility of the FET with a gate length of 10 μm are −17.6 mA·mm−1, −0.5 V, 5.7 mS·mm−1, and 41.3 cm2/V s, respectively. According to the capacitance voltage characteristic, the enhancement mode could be ascribed to the high positive fixed charge density in the sp-SnO2 film, which will repel the hole in the channel. This paper provides a simple method and a low temperature process to fabricate an insulator layer.

Detection of stable positive fixed charges in AlOx activated during annealing with in situ modulated PhotoLuminescence

An in situ Modulated Photoluminescence (MPL) measurement setup mounted on a Plasma Enhanced Chemical Vapor Deposition (PECVD) reactor is described. A method for deriving the actual minority carrier lifetime at the specific injection level of 1.1015 cm−3 is presented. This tool was used in a case study to monitor the passivation properties of aluminum oxide (AlOx) thin films upon annealing. Interesting kinetics, such as a drop of lifetime at temperatures higher than 250 °C along with a recovery of the lifetime during the cooling phase, are shown. Moreover, these in situ results combined with ex situ studies allowed us to demonstrate the formation a stable high positive fixed charge density in the AlOx layer (+1.1012 cm−2) as a consequence of the combination of annealing and light exposure.

Excellent Passivation of n‐Type Silicon Surfaces Enabled by Pulsed‐Flow Plasma‐Enhanced Chemical Vapor Deposition of Phosphorus Oxide Capped by Aluminum Oxide

Phosphorus oxide (POx) capped by aluminum oxide (Al2O3), prepared by atomic layer deposition (ALD), has recently been introduced as a surface passivation scheme for planar n‐type FZ silicon. In this work, a fast pulsed‐flow plasma‐enhanced chemical vapor deposition (PECVD) process for the POx layer is introduced, making it possible to increase the POx deposition rate significantly while maintaining the POx/Al2O3 passivation quality. An excellent surface passivation is realized on n‐type planar FZ and Cz substrates (J0 = 3.0 fA cm−2). Furthermore, it is demonstrated that the POx/Al2O3 stack can passivate textured surfaces and that the application of an additional PECVD SiNx capping layer renders the stack stable to a firing treatment that is typically used in fire‐through contact formation (J0 = 12 fA cm−2). The excellent surface passivation is enabled by a high positive fixed charge density (Qf ≈ 4 × 1012 cm−2) and an ultralow interface defect density (Dit ≈ 5 × 1010 eV−1 cm−2). Finally, outstanding passivation is demonstrated on textured silicon with a heavy n+ surface doping, as is used in solar cells, on par with alnealed SiO2. These findings indicate that POx/Al2O3 is a highly suited passivation scheme for n‐type silicon surfaces in typical industrial solar cells.

Electrical Properties of Al2O3/ZnO Metal–Insulator–Semiconductor Capacitors

An Al2O3 thin film is assembled on an unin- tentionally doped ZnO for metal–insulator–semiconductor (MIS) capacitors. Leakage current density ( ${J}$ ), capacitance–voltage ( ${C} - {V}$ ) properties, and their thermal stabilities are investigated. The ${J}$ -values for the MIS capacitors before and after annealing at 300 °C are lower than $2.0 \times 10^{-7}$ A/cm2 at a gate voltage of −10.0~10.0V. Frequency-dependent ${C}-{V}$ characteristic shows a stable maximum capacitance for the MIS capacitor before annealing. However, it decreases dramatically at 1 MHz for that after annealing at 300 C, which is attributed to the change of ZnO channel resistance. Flat band voltage shifts in the–curves after annealing at 300 C are one order lower than those before annealing, indicating the decrease of positive fixed charge density in the Al2O3 film. There are ledge phenomena for hysteresis characteristics in the curves, which result possibly from the delayed evacuation of minority carriers in deep depletion region. By considering the Fowler–Nordheim tunneling model, band configurations of the Al2O3/ZnO heterojunctions are clarified to be straddling gap structures with conduction band offsets larger than 1.3 eV.

Engineering aluminum oxide/polysilicon hole selective passivated contacts for high efficiency solar cells

Tunnel layer passivated contact technology is already highly efficient in case of selective electron extraction but not as efficient in case of selective hole extraction. Thus far, SiOx/p+-poly-Si contacts have resulted only in efficiencies above ~20.1% for rear-side deployed hole selective contacts. We investigate if hole extraction selectivity can be further improved by substituting the ‘conventionally’ used SiOx tunnel layer exhibiting moderate or even high positive fixed charge density by AlOx tunnel layers, exhibiting high negative fixed charge density. The merits of using atomic layer deposited ultrathin AlOx tunnel layers are investigated and compared with wet chemically formed SiOx tunnel layers to form AlOx/p+-poly-Si and SiOx/p+-poly-Si hole selective passivated contacts respectively. The AlOx thickness (0.13–2 nm) and its thermal budget including annealing time, temperature and ambient were varied. The quality of the resulting AlOx/p+-poly-Si passivated contacts was determined by measuring the recombination current density (Jc) and the effective contact resistivity (ρc). Finally, using the measured values of Jc and ρc, we predict the efficiency potential and selectivity of the passivated contact using Brendel's model. We show that for 425 °C annealed AlOx samples prior to poly-Si capping, there is an improvement in passivation quality due to the high negative AlOx interface charge, which forms only for “thick” tunnel layers (≥1.5 nm). However, after high-temperature poly-Si capping, enhanced boron in-diffusion and charge compensation are degrading the overall passivation quality of “thick” AlOx/p+-poly-Si passivated contacts. The best AlOx/p+-poly-Si passivated contacts use ultra-thin AlOx tunnel layers (efficiency potential of 26.9%), which is only marginally better than the SiOx reference samples, but still improves hole selectivity.

Improving Performances of Enhancement-Mode AlGaN/GaN MIS-HEMTs on 6-inch Si Substrate Utilizing SiON/Al2O3 Stack Dielectrics

Enhancement-mode (E-mode) GaN-based MIS-HEMTs still suffer from undeniable gate leakage or low gate breakdown voltage due to the low quality of gate dielectrics, resulting in a notorious tailing effect of the off-state current. In this letter, a gate scheme featuring SiON/Al2O3 stack dielectrics and partially recessed gate barrier has been employed in the AlGaN/GaN MIS-HEMTs. A high on/off current ratio over $10^{{9}}$ and a small threshold voltage ( ${V} _{\text {th}}$ ) hysteresis less than 20 mV are achieved in the fabricated E-mode devices with a ${V} _{\text {th}}$ around 2.5 V, mainly owing to the reduction of the net positive fixed charge density in the SiON/Al2O3 gate stack confirmed by the ${C}$ - ${V}$ measurements. Meanwhile, a good performance uniformity on 6-inch wafer is achieved which demonstrates the promising scheme for fabricating GaN-based E-mode MIS-HEMT products.

Effect of post-deposition annealing on atomic layer deposited SiO2 film for silicon surface passivation

We have investigated the passivation performance of atomic layer deposited silicon dioxide (ALD-SiO2) films on crystalline silicon surface with various post-annealing temperatures. A maximum effective lifetime of 2157 μs can be achieved at the optimized annealing temperature of 650 °C on 3 Ω cm n-type silicon wafers. The improved passivation quality can be attributed to the low interface defect density and extremely high positive fixed charge density. Especially, the high positive fixed charge density of over 4 × 1012 cm-2 can be observed after annealing at high temperature. Therefore, it is inferred that the passivation mechanism for ALD-SiO2 films is based on not only chemical passivation but also field-effect passivation, which is more similar with the ALD-Al2O3 films rather than the thermally grown SiO2 films. X-ray photoelectron spectroscopy, secondary ion mass spectroscopy and thermal effusion measurement revealed the variation of elements content and distribution of silicon, oxygen, hydrogen and carbon during the post-deposition thermal treatment process, indicating that the rearrangement and release of these elements create more oxygen vacancies and result in the improvement of interface quality and positive fixed charge density of ALD-SiO2 films.

Effect of Post Nitridation Annealing on Thermally Grown Silicon Oxynitride Characteristics

The ability to block the direct current is one of the main requisite for the gate dielectric in a metal-oxide-field-effect-transistor. Since thickness of oxide is inversely related with oxide capacitance, therefore oxide capacitance can be increased as an alternative to oxide thickness to meet the scaling requirements. Oxynitrides and high-k materials as gate dielectric have been considered as promising candidates to overcome the above problems. At greater physical thickness, these materials have the similar capacitance value which avoids tunneling effect. SiON has been used as a substitute for SiO2 because of its high dielectric permittivity and low density of surface states. In this paper, the effect of post nitridation annealing on thermally grown silicon oxynitride characteristics have been investigated by analyzing high-frequency capacitance-voltage (C-V) and current- voltage characteristics (I-V) of n-Si/SiON/Ti-Pt MOS capacitor. Post nitridation annealing was carried out at 800°C for 15 min in Nitrogen (N2) ambient. Ellipsometery, FESEM, Atomic force microscopy (AFM) and Fourier transform infrared spectroscopy (FTIR) was used to study the effect of post nitridation annealing on the physical characteristics of deposited silicon oxynitride film. Cheung’s approach has been used for evaluating barrier height (ϕbo ) and ideality factor (η). We present a comparative study between the as-deposited and annealed film and it was found that the physical and electrical properties (k, η, ϕbo etc) improved by post nitridation annealing is attributed to the improvement in the interface properties of Si/SiON. Moreover, the value of positive fixed charge density (Q f ~1.8×1012 cm−2) is effective for field-effect passivation of n-type Si surfaces. For both as-deposited and annealed SiON film, the maximum current through the Si/SiON/Ti-Pt device never exceeded a value of 10–8A/cm2 which indicates that the film were very good insulators. These results indicate that the obtained SiON film is an appropriate gate insulator for advanced nano electronic devices.

POx/Al2O3 stacks: Highly effective surface passivation of crystalline silicon with a large positive fixed charge

Thin-film stacks of phosphorus oxide (POx) and aluminium oxide (Al2O3) are shown to provide highly effective passivation of crystalline silicon (c-Si) surfaces. Surface recombination velocities as low as 1.7 cm s−1 and saturation current densities J0s as low as 3.3 fA cm−2 are obtained on n-type (100) c-Si surfaces passivated by 6 nm/14 nm thick POx/Al2O3 stacks deposited in an atomic layer deposition system and annealed at 450 °C. This excellent passivation can be attributed in part to an unusually large positive fixed charge density of up to 4.7 × 1012 cm−2, which makes such stacks especially suitable for passivation of n-type Si surfaces.

Comparative study of electrical characteristics for n-type 4H–SiC planar and trench MOS capacitors annealed in ambient NO**Project supported by the National Basic Research Program of China (Grant No. 2015CB759600), the National Natural Science Foundation of China (Grant Nos. 61474113 and 61574140), the Beijing NOVA Program, China (Grant No. Z1611000049161132016071), China Academy of Engineering Physics (CAEP) Microsystem and THz Science and

The interface properties and electrical characteristics of the n-type 4H–SiC planar and trench metal–oxide–semiconductor (MOS) capacitors are investigated by measuring the capacitance voltage and current voltage. The flat-band voltage and interface state density are evaluated by the quasi-static method. It is not effective on further improving the interface properties annealing at 1250°C in NO ambient for above 1 h due to the increasing interface shallow and fast states. These shallow states reduce the effective positive fixed charge density in the oxide. For the vertical MOS capacitors on the () and () faces, the interface state density can be reduced by approximately one order of magnitude, in comparison to the result of the planar MOS capacitors on the (0001) face under the same NO annealing condition. In addition, it is found that Fowler–Nordheim tunneling current occurs at an oxide electric field of 7 MV/cm for the planar MOS device. However, Poole–Frenkel conduction current occurs at a lower electric field of 4 MV/cm for the trench MOS capacitor. This is due to the local field crowded at the trench corner severely causing the electrons to be early captured at or emitted from the SiO2/SiC interface. These results provide a reference for an in-depth understanding of the mobility-limiting factors and long term reliability of the trench and planar SiO2/SiC interfaces.

Effect of the Ti/Si ratio of spin coating solutions on surface passivation of crystalline silicon by TiOx–SiOx composite films

Passivation films or antireflection coatings are generally prepared using costly vacuum or high-temperature processes. Thus, we report the preparation of TiOx–SiOx composite films by novel spin coatable solutions for the synthesis of low-cost passivation coating materials. The desired films were formed by varying the mixing ratios of TiOx and SiOx, and the resulting films exhibited excellent surface passivation properties. For the p-type wafer, an optimal effective surface recombination velocity (Seff) of 93 cm/s was achieved at , while a surface recombination current density (J0s) of 195 fA/cm2 was obtained. In contrast, for the n-type wafer, an Seff of 27 cm/s and a J0s of 38 fA/cm2 were achieved at . This excellent surface passivation effect could be attributed to the low interface state density and high positive fixed charge density. Furthermore, the thickness of the interfacial SiOx layer was determined to be important for obtaining the desired surface passivation effect.

Process-Induced Variations of 10-nm Node Bulk nFinFETs Considering Middle-of-Line Parasitics

Process-induced variations of 10-nm node n-type FinFETs considering middle-of-line parasitics were investigated in terms of dc/ac performances using fully calibrated TCAD simulations. Variations of positive fixed oxide charge density at shallow trench isolation interface and source/drain (S/D) height influenced off-state and on-state performance variations, respectively, but slightly on RC delay variations. Fin width variations induced off-state performance and RC delay variations critically due to the fluctuation of short channel effects. But, fin height variations affected them slightly due to the preserved gate-to-channel controllability and the buffered effects by varying drain currents and gate capacitances in the same direction. Gate length, spacer length, and S/D length variations influenced dc/ac performance variations severely; 2-nm-length changes were barely acceptable to satisfy 10% RC delay margin. Thus, the process-induced variability parameters, including fin width, gate length, spacer length, and S/D length, should be controlled tightly under a few nanometers to reduce dc/ac performance variations of the FinFETs.

Three-Dimensional Computational Analysis of Accumulated Body MOSFETs

Accumulated body approach for short- and narrow-channel (10-nm scale) bulk Si MOSFETs is analyzed through 3-D finite-element studies. Accumulation of the side interfaces is achieved by a side-gate structure surrounding the body of the transistor, which leads to the accumulation of the body for narrow structures. A separately controlled top gate is used for transistor action. The simulation results show the suppression of leakage currents by 106 times for no side-interface charges, and by 1010 times for an interface positive fixed charge density of 1012 cm−2. The threshold voltage (VT ) can be dynamically increased by over 1 V with the accumulation of the body ( $V_{{\rm side}} = 0$ to −3 V) for W × $L = 10$ -nm × 15-nm structures, enabling electrostatic VT control and reliable high-temperature (>600 K) operation. Improvements in subthreshold slope and drain-induced barrier lowering are significant for narrower channel devices.

Film properties of alumina passivation layer for silicon solar cells prepared by spin-coating method

We prepared alumina passivation films deposited by a sol-gel wet process for silicon substrates. Aluminum acetylacetonate was used as a precursor, and the solution was spin-coated onto silicon substrates. Calcination temperature dependence of the passivation quality of the films was evaluated mainly by measuring effective lifetime using a photo conductance decay technique and capacitance–voltage measurements. Also, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy were carried out to evaluate film properties. A large amount of negative fixed charge density (Qf=−3.1×1012cm−2) exists in the films calcined at 300°C. On the other hand, a long effective lifetime of 400μs was obtained for the sample calcined at 600°C, and the passivation films had a large amount of positive fixed charge density (Qf=3.6×1012cm−2) with a low interface state density.

The Characterization and Passivation of Fixed Oxide Charges and Interface States in the $\hbox{Al}_{2}\hbox{O}_{3}/ \hbox{InGaAs}$ MOS System

In this paper, we present a review of experimental results examining charged defect components in the Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.53</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.47</sub> As metal-oxide-semiconductor (MOS) system. For the analysis of fixed oxide charge and interface state density, an approach is described where the flatband voltage for n- and p-type Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.53</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.47</sub> As MOS structures is used to separate and quantify the contributions of fixed oxide charge and interface state density. Based on an Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> thickness series (10-20 nm) for the n- and p-type In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.53</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.47</sub> As layers, the analysis reveals a positive fixed charge density ( ~ 9 ×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">18</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> ) distributed throughout the Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and a negative sheet charge density (- 8 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> ) located near the Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.53</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.47</sub> As interface. The interface state density integrated across the energy gap is ~1 ×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> and is a donor-type (+/0) defect. The density of the fixed oxide charge components is significantly reduced by forming gas (5 % H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> / 95% N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ambient at 350 °C for 30 minutes) annealing. The interface state distribution obtained from multi-frequency capacitance-voltage and conductance-voltage measurements on either MOS structures or MOSFETs indicates a peak density located around the In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.53</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.47</sub> As midgap energy, with a sharp increase in the interface state density toward the valance band and evidence of interface states aligned with the In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.53</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.47</sub> As conduction band. The integrated interface state density obtained from multi-frequency capacitance-voltage and conductance-voltage analysis is in good agreement with the approach of comparing the flatband voltages in n- and p -type Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.53</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.47</sub> As MOS structures. Finally, this paper reviews recent work based on an optimization of the In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.53</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.47</sub> As surface preparation using (NH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> ) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> S, combined with minimizing the transfer time to the atomic layer deposition reactor for Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> , which indicates interface state reduction and genuine surface inversion for both n- and p -type Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.53</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.47</sub> As MOS structures.

Excellent surface passivation of heavily doped p+ silicon by low-temperature plasma-deposited SiOx/SiNy dielectric stacks with optimised antireflective performance for solar cell application

The passivation of p+ Si surfaces is challenging due to the fact that most passivation films have an intrinsically high positive fixed charge. In this work we show experimentally that low-temperature plasma-enhanced chemical vapor deposited SiOx/SiNy stacks with a low positive fixed charge density (+1011cm−2) and very low interface defect density (~3×1010eV−1cm−2) as measured by contactless corona-voltage measurements can effectively passivate p+ surfaces resulting in emitter saturation current density (J0e) values of 25 and 45fA/cm2 on planar and textured 75Ω/sq p+ silicon after industrial firing with a set-temperature of ~800°C, respectively. Based on contactless corona-voltage measurements and advanced device simulations, we explain the mechanism of surface passivation by PECVD SiOx/SiNy dielectric stack to be completely dominated by chemical passivation rather than field-effect passivation. Furthermore, from advanced device simulations we illustrate the role of fixed charge in surface passivation and in the extraction of fundamental surface recombination velocity parameter for p+ silicon surfaces. The fundamental surface recombination velocity parameter for electrons is determined to be about 400cm/s at these c-Si/SiOx interfaces. With excellent optical and passivation properties, SiOx/SiNy dielectric stacks are suitable for high-efficiency and cost-effective industrial n-type silicon wafer solar cells.

Interface properties of SiOxNy layer on Si prepared by atmospheric-pressure plasma oxidation-nitridation

SiOxNy films with a low nitrogen concentration (< 4%) have been prepared on Si substrates at 400°C by atmospheric-pressure plasma oxidation-nitridation process using O2 and N2 as gaseous precursors diluted in He. Interface properties of SiOxNy films have been investigated by analyzing high-frequency and quasistatic capacitance-voltage characteristics of metal-oxide-semiconductor capacitors. It is found that addition of N into the oxide increases both interface state density (Dit) and positive fixed charge density (Qf). After forming gas anneal, Dit decreases largely with decreasing N2/O2 flow ratio from 1 to 0.01 while the change of Qf is insignificant. These results suggest that low N2/O2 flow ratio is a key parameter to achieve a low Dit and relatively high Qf, which is effective for field effect passivation of n-type Si surfaces.

Formation of SiO2/Si structure with low interface state density by atmospheric-pressure VHF plasma oxidation

SiO2/Si structure has been prepared by atmospheric-pressure (AP) plasma oxidation at 400°C using gas mixtures of 0.5–5% O2 and He. From the characterization results of thickness, refractive index, atomic composition and electrical properties of the oxide films, it is found that the properties of SiO2/Si structures formed by AP-plasma oxidation are similar to those of high-temperature grown thermal oxides. By optimizing formation conditions, the SiO2/Si structure with a low interface state density of 1.4×1010cm−2eV−1 is obtained. On the other hand, the positive fixed charge density in the AP-plasma oxide film is relatively high at 5.3×1011cm−2. These characteristics (low interface state density and high fixed charge density) are useful for effective field-effect passivation of Si surfaces for photovoltaic application.