Polycrystalline Silicon Films Research Articles

High Reliability Tungsten-Doped Indium Zinc Oxide Thin Film Transistors for Display Applications

Recently, flat panel display technologies are based on amorphous silicon (a-Si), polycrystalline silicon (poly-Si) or amorphous oxide semiconductor (AOS) thin film transistors (TFTs) technology. In order to reach higher performance for ultra-high resolution display applications, the material selection for the channel layer is vital. AOS TFTs drawn lots of attention because of its advantages such as low leakage current, high driving current and high uniformity [1,3]. In this work, we presented a novel amorphous oxide semiconductor (AOS) material of gallium-free a-InWZnO thin film transistors (IWZO TFTs) which is very promising to be applied for ultra-high resolution display technology. Experiment In this work, we demonstrated the structure of a-IWZO TFTs processes. Figure 1 shows the schematic of the TFT cross-section. After growing a 550 nm thermal oxide layer as buffer layer, a 25-nm-thick of molybdenum was deposited by DC-sputter as the bottom gate electrode. A 10-nm-HfO2 was deposited by plasma-enhanced atomic layer deposition (PEALD) system as high-κ gate dielectric (GI). Then, post deposition annealing (PDA) was carried out to enhance the quality of the insulator layer. Next, an ultra-thin body a-IWZO was deposited by RF-sputter as channel layer. Finally, source and drain were defined by lift-off process and the gate contact via was etched by dry etching to finish the device fabrication. Result and Discussion Figure 1(b) shows the negative gate bias stress (NGBS) transfer curve (ID-VG) of a-IWZO TFTs with passivation layer. The experimental results have shown that passivation layer could keep the back channel of IWZO channel from exposing to oxygen and hydrogen from the atmosphere. Without the passivation layer, the back channel would contact moisture leading the diffused hydrogen atoms to fill oxygen vacancy sites and de-trap free carriers, causing the VTH shifts negatively. The ultra-thin a-IWZO TFTs with passivation layer exhibited a low subthreshold swing (S.S.) of 89.7 mV/dec, high on/off current ratio (ION/IOFF) of 2.1×107 and small threshold voltage shift (ΔVth) of -0.097 V during NGBS of -2MV/cm with 2000s. To sum up, the passivation layer could enhance the a-IWZO TFTs reliability. Reference [1] Kamiya, H. Hosono, NPG Asia Mater., vol. 2, pp. 15, 2010.[2] Nomura, H. Ohta, A. Takagi, T. Kamiya, M. Hirano, and H. Hosono, nature, vol. 432, no. 7016, pp. 488-492, 2004.[3] Y. Kuo, C. M. Chang, I. H. Liu, and P. T. Liu, Scientific reports, vol. 9, no. 1, pp. 1-7, 2019. Figure 1

3D Neuromorphic Hardware with Single Thin-Film Transistor Synapses Over Single Thin-Body Transistor Neurons by Monolithic Vertical Integration.

Neuromorphic hardware with a spiking neural network (SNN) can significantly enhance the energy efficiency for artificial intelligence (AI) functions owing to its event-driven and spatiotemporally sparse operations. However, an artificial neuron and synapse based on complex complementary metal-oxide-semiconductor (CMOS) circuits limit the scalability and energy efficiency of neuromorphic hardware. In this work, a neuromorphic module is demonstrated composed of synapses over neurons realized by monolithic vertical integration. The synapse at top is a single thin-film transistor (1TFT-synapse) made of poly-crystalline silicon film and the neuron at bottom is another single transistor (1T-neuron) made of single-crystalline silicon. Excimer laser annealing (ELA) is applied to activate dopants for the 1TFT-synapse at the top and rapid thermal annealing (RTA) is applied to do so for the 1T-neuron at the bottom. Internal electro-thermal annealing (ETA) via the generation of Joule heat is also used to enhance the endurance of the 1TFT-synapse without transferring heat to the 1T-neuron at the bottom. As neuromorphic vision sensing, classification of American Sign Language (ASL) is conducted with the fabricated neuromorphic module. Its classification accuracy on ASL is ≈92.3% even after 204800 update pulses.

Outdoor Experimental Investigation of the Temperature Effect on the Performance of Different PV Modules Materials

Desert locations are of great interest for photovoltaic applications due to their high solar availability. However, in these regions, harsh climatic conditions can have a significant impact on the performance and reliability of photovoltaic panels. In the present study, the effect of temperature on the performance of the two PV technologies, Polycrystalline Silicon (pc-Si) and thin film Cadmium Telluride (CdTe), in a hot desert climate was investigated. To accomplish this, one module from each technology was installed in Benguerir city and exposed to outdoor conditions during the hot season of the year (May to October). Results indicate that although pc-Si exhibits higher module efficiency than CdTe, the latter was less temperature-sensitive under high ambient temperature values. In fact, during the monitoring period, CdTe technology demonstrated lower module temperatures than pc-Si, with a daily average temperature deviation of 1.75°C. In addition, the performance ratio and conversion efficiency for pc-Si were reduced by 8.7% and 1.35%, respectively, when the daily average ambient temperature increased from 25°C to 40°C. While with the thin film CdTe technology, the decline in these performance parameters did not exceed 6.8% and 1.05%, respectively.

REMOTE MEASUREMENTS OF WATER SURFACE POLLUTION BY THE METHOD OF LASER LOCATION

As it was shown in the nature investigations,the most area of water in the Azerbaijan shore of Caspian Sea is covered by oil film, the square of which depends on direction of wind. The research of pollution's of environment by the mean of optical apparatus of remote sounding, mounted on the board of flying apparatus or space satellites is one of intensely developing directions. The theory of measuring of oil film's thickens by the help of laser location in detail described. The principles of straight¬-line spreading of electromagnetic waves, reflecting of electromagnetic energy by objects and constant speed of their propagation are laid in the basic of location. We have developed lidar for controlling of pollutions of water surface, where helium-neon laser “LGI-102” having power 3mW working in the pulse regime is used as beam radiator. During the experiment the laser was mounted on the plain ground on the distance 1-meter from water surface. The prism was placed in the road of propagation of laser beam and used for direction of radiation under the angle 45 on water surface. Integral photo transducer on the base of local mono-and polycrystalline silicon films with linear output was used in the photo detector device. Photo transducer was made in hybrid form on the base of two crystals: photo sensitive poly-silicon film and unpack operational amplifier 740UD4. Keywords: Pollution, water surface, oil film, laser location, lidar, photo detector.

Self‐Regulating Process for Large Area Nanowire Solar Cells Based on Thin Polycrystalline Silicon Films Prepared on Glass

Herein, a process for the large‐area passivating and contacting of nanowire‐based solar cells is demonstrated. The nanowire‐based solar cells are prepared on layered laser crystallization (LLC) polycrystalline silicon (pc‐Si) thin films with thickness less than 2 μm. It is demonstrated that the space between the nanowires can be filled with a passivating dielectrics Al2O3 layer, and the nanowire tips can be exposed by a self‐regulating selective etching of the Al2O3 deposited on the tips and that on the sidewalls. The exposed tips of the nanowires can be connected by a transparent conducting aluminum‐doped zinc oxide (Al:ZnO or AZO) layer deposited by atomic layer deposition (ALD). The laser beam‐induced current mapping (LBIC) demonstrates that the current density can increase up to 63% at 633 nm due to light trapping and the superior passivation of the nanowires with an thin pc‐Si film of only 1.73 μm.

Influence of current density on constant current electric field enhanced aluminum induced crystallization of amorphous silicon thin films

In this study, electric field-enhanced aluminum-induced crystallization (AIC) of amorphous silicon (a-Si) thin films was investigated considering various current densities. Constant electric currents of 4, 5, and 6 A were applied to assess the Joule heating characteristics during specific durations (40, 15.5, and 9 s). The samples were prepared by depositing a 200-nm thick a-Si layer on a glass substrate and sputtering a 300-nm thick aluminum (Al) layer onto the a-Si layer. During the AIC process, layer exchange occured via the diffusion of silicon (Si) into the Al layer. This phenomenon was verified by the in-situ reflectivity, which was in excellent agreement with thin-film optics calculations. During the annealing, processing temperatures were lower than 470 °C, which is less than the Al-Si eutectic temperature of 577 °C. The Raman peak observed near a wavenumber of 519 cm−1 revealed the formation of polycrystalline silicon films through Joule heating processes. Field-effect scanning electron microscopy images were captured and analyzed to investigate the surface morphology of the samples, specifically focusing on grain growth.

P‐11: A Novel AMOLED Pixel Circuit using Double‐Gate LTPO TFTs for Variable Refresh Rate with Low Power Consumption

This paper proposes an Active Matrix Organic Light Emitting Diode (AMOLED) pixel circuit for Variable Refresh Rate (VRR) driving from 1Hz to 240Hz. The circuit is based on a double‐gate Low Temperature Polycrystalline Silicon and Oxide (LTPO) Thin Film Transistor (TFT) backplane. For low frame rate driving we used oxide TFTs as the Switching (SW) TFTs. Moreover, we applied double‐gate Low Temperature Polycrystalline Silicon (LTPS) process to the Driving (DR) TFT for compensation of the Threshold Voltage (Vth) by controlling the bottom gate bias at a high refresh rate. In this paper, operation principle and simulation results will be illustrated to demonstrate the performance of the proposed circuit.

Single-shot selective femtosecond and picosecond infrared laser crystallization of an amorphous Ge/Si multilayer stack

Pulsed laser crystallization is an efficient annealing technique to obtain polycrystalline silicon or germanium films on non-refractory substrates. This is important for creating “flexible electronics” and can also be used to fabricate thin-film solar cells. In this work, near- and mid-infrared femtosecond and picosecond laser pulses were used to crystallize a Ge/Si multilayer stack consisting of alternating amorphous thin films of silicon and germanium. The use of infrared radiation at wavelengths of 1030 and 1500 nm with photon energies lower than the optical absorption edge in amorphous silicon allowed obtaining selective crystallization of germanium layers with a single laser shot. The phase composition of the irradiated stack was investigated by the Raman scattering technique. Several non-ablative regimes of ultrashort-pulse laser crystallization were found, from partial crystallization of germanium without intermixing the Ge/Si layers to complete intermixing of the layers with formation of GexSi1-x solid alloys. The roles of single- and two-photon absorption, thermal and non-thermal (ultrafast) melting processes, and laser-induced stresses in selective pico- and femtosecond laser annealing are discussed. It is concluded that, due to a mismatch of the thermal expansion coefficients between the adjacent stack layers, efficient explosive solid-phase crystallization of the Ge layers is possible at relatively low temperatures, well below the melting point.

On the presence of oxyphosphorus bonds in TOPCon solar cell polycrystalline silicon films

The presence of silicon oxyphosphorus bonds in the heavily phosphorus (P)-doped n+-type polycrystalline silicon film (n+-poly Si) of TOPCon solar cell has been mainly revealed through a depth-profile X-ray photoelectron spectroscopy (XPS) characterization of chemical components. X-ray diffraction (XRD) pattern is applied to the verification of recrystallized phases in the n+-poly Si film, while high-resolution transmission electron microscopy (HR-TEM) with energy dispersive X-ray (EDX) pattern is used for distinguishing the crystallinity and the elemental segregation. The test sample is of a typical rear passivation contact stacks of c-Si/SiOx/n+-poly Si/SiO2, in which the n+-poly Si layer is heavily phosphorus-doped by ion implantation of as-deposited intrinsic thin film through low-pressure chemical vapor deposition (LPCVD) and recrystallization at 900 °C afterward. In the whole n+-poly Si layer, XPS P 2p electronic states at 129.8, 133.4 and 136.8 eV have been detected and assigned to be Si–P (or P–P), O–P and P–O–P bonds, respectively. In addition, the thermodynamic functions, such as the Gibbs free energy and mole formation energy of likely chemical bonds under the lowest energy as well as temperature-composition fraction (T-CF) phase diagram, are also implemented in the verification of the derivatives of phosphorus oxides.

47.1: A 15.6 FHD LTPS Product Display With Wide Refresh Rate from 5Hz to 480Hz

47.1: A 15.6 FHD LTPS Product Display With Wide Refresh Rate from 5Hz to 480Hz

Activation energy of gold-induced crystallization of amorphous silicon suboxide films

• Au-induced crystallization of a-SiO 0.2 films was carried out at 210–275 °C. • The activation energy for AuIC of a-SiO 0.2 was determined for the first time to be 1.7 ± 0.1 eV. • Raman spectroscopy revealed the improvement of crystalline properties of poly-Si films with decreasing annealing temperature. • XRD revealed the formation of poly-Si with (1 1 1) crystallographic orientation. Polycrystalline silicon (poly-Si) films were fabricated by gold-induced crystallization (AuIC) of amorphous silicon suboxide (a-SiO x , x = 0.2) films at temperatures of 210–275 °C. The films were studied by in situ optical microscopy, Raman spectroscopy, and X-ray diffractometry. The activation energy for AuIC of a-SiO 0.2 was determined for the first time to be 1.7 ± 0.1 eV.

Effect of N2-Anneal Temperature on Silicon Nitride Film: (I) Time-Dependent Dielectric Breakdown and ESR Evaluations

Silicon Nitride (SiN) film has been used as insulating material in many electronic devices such as capacitors and memories . In this report, the effect of N2 anneal temperature on charge break down (Qbd) of LP-CVD SiN film was electrically evaluated using the time-dependent dielectric breakdown (TDDB) test method, and the variation and the density of defects which exist in SiN film, in the oxide layer between SiN and Si substrate, and at the surface of Si substrate, were investigated using an Electron Spin Resonance (ESR) to reveal the defect behavior related to the trigger of Qbd.SiN metal-insulator-metal (MIM) capacitors were fabricated to evaluate TDDB. A 54 nm dielectric layer of SiN film was deposited at 700 degree-C, using a mixture of dichlorosilane（SiH2Cl2）and ammonia (NH3) gasses, by a LP-CVD vertical furnace. For the lower and upper electrode, a 400 nm polycrystalline silicon films were deposited using a LP-CVD. In order to evaluate the effect of anneal temperature on SiN film breakdown frequency, these samples were annealed in nitrogen atmosphere at temperatures between 700 and 1150 degree-C for 1 hour, using a vertical furnace.Breakdown voltage was measured with a current-voltage tester (HP4071A, Hewlett Packard) for each SiN MIM capacitor. The breakdown frequency was defined as the ratio of failed capacitors to tested capacitors. For the TDDB measurements, a constant current stress of 1.33 A/cm2 was applied to the MIM capacitors with the area of 0.00375cm2, 0.0075cm2, 0.015cm2 and 0.03cm2. For each area, 100 chips were made from one wafer and measured.In Fig.1, SiN film breakdown frequency increases toward a peak at around the N2 anneal temperature of 900 degree-C, then decreases at 1000 degree-C, and at more than 1100 degree-C, the frequency increases again drastically at 1150 degree-C.SiN films for ESR study were fabricated on Si wafer in the same LP-CVD process, and annealed in nitrogen atmosphere at temperatures between 700 and 1150 degree-C for 1 hour, using a vertical furnace.The ESR measurements were performed at room temperature using an X-band spectrometer (JES-RE1X). To improve the signal-to-noise ratio of an ESR signal waveform, we set the accumulation number of magnetic-field (H) sweep about 300 times. Mn2+/ MgO hyperfine lines were used for the g marker, and spin densities were determined by using the standard of known spin content.In Fig.2, Dangling bond density at silicon interface (Pb center) has a peak at 900 degree-C, and those in SiO2 (E’ center) and SiN film (K center) increase with increasing temperature from 1000 to 1150 degree-C. The former phenomena of Pb center coincides with the peak of SiN film breakdown frequency at 900 degree-C, and the latter one of E’ center and K center coincides with the tendency of increasing Qbd frequency at more than 1000 degree-C. Figure 1

Local Enhancement of Dopant Diffusion from Polycrystalline Silicon Passivating Contacts.

Passivating contacts consisting of heavily doped polycrystalline silicon (poly-Si) and ultrathin interfacial silicon oxide (SiOx) films enable the fabrication of high-efficiency Si solar cells. The electrical properties and working mechanism of such poly-Si passivating contacts depend on the distribution of dopants at their interface with the underlying Si substrate of solar cells. Therefore, this distribution, particularly in the vicinity of pinholes in the SiOx film, is investigated in this work. Technology computer-aided design (TCAD) simulations were performed to study the diffusion of dopants, both phosphorus (P) and boron (B), from the poly-Si film into the Si substrate during the annealing process typically applied to poly-Si passivating contacts. The simulated 2D doping profiles indicate enhanced diffusion under pinholes, yielding deeper semicircular regions of increased doping compared to regions far removed from the pinholes. Such regions with locally enhanced doping were also experimentally demonstrated using high-resolution (5-10 nm/pixel) scanning spreading resistance microscopy (SSRM) for the first time. The SSRM measurements were performed on a variety of poly-Si passivating contacts, fabricated using different approaches by multiple research institutes, and the regions of doping enhancement were detected on samples where the presence of pinholes had been reported in the related literature. These findings can contribute to a better understanding, more accurate modeling, and optimization of poly-Si passivating contacts, which are increasingly being introduced in the mass production of Si solar cells.

Large-area bifacial n-TOPCon solar cells with in situ phosphorus-doped LPCVD poly-Si passivating contacts

The potential of passivating contacts incorporating in situ phosphorus (P)-doped polycrystalline silicon (poly-Si) films grown by low pressure chemical vapor deposition (LPCVD) is demonstrated in this work by integrating these layers at the rear side of large-area (241.3 cm 2 ) bifacial n-type Tunnel Oxide Passivated Contact (n-TOPCon) solar cells with diffused front emitter and screen-printed contacts. In situ doped poly-Si films are studied as their use could simplify the production of industrial n-TOPCon solar cells compared to the common approach relying on ex situ doping of intrinsic LPCVD poly-Si films. The developed poly-Si passivating contacts exhibited excellent characteristics with low recombination current densities in passivated and screen-printing metallized regions down to 2.3 fA/cm 2 and 65.8 fA/cm 2 , respectively, and a low contact resistivity of 2.0 mΩ⋅cm 2 . For reaching the best passivating contact characteristics and high solar cell efficiencies, a poly-Si film thickness of 150–200 nm was found to be optimal while a polished rear surface morphology was found to be beneficial. The best solar cell reached a certified power conversion efficiency of 23.01% along with a high open circuit voltage of 691.7 mV, enabled by the passivating contacts with the in situ doped poly-Si films. 1-cell glass-glass laminates were also fabricated with the developed solar cells, which showed no loss in their power output both upon 400 thermal cycles and after 1000 h of damp heat testing. Lastly, a roadmap is presented, indicating strategies to achieve efficiencies up to 25.5% with n-TOPCon solar cells incorporating the in situ P-doped LPCVD poly-Si films. • In situ P-doped LPCVD poly-Si passivating contacts integrated in n-TOPCon solar cells. • 241.3 cm 2 -large bifacial n-TOPCon devices with 23.01% certified efficiency demonstrated. • Using ≥ 150 nm of poly-Si and polished rear side improves the solar cell efficiency. • 1-cell glass-glass laminates of the devices pass damp heat and thermal cycling tests. • Roadmap to 25.5% efficiency presented.

Process–Structure–Properties Relationships of Passivating, Electron‐Selective Contacts Formed by Atmospheric Pressure Chemical Vapor Deposition of Phosphorus‐Doped Polysilicon

Herein, we investigate the process–structure–properties relationships of in situ phosphorus (P)‐doped polycrystalline silicon (poly‐Si) films by atmospheric pressure chemical vapor deposition (APCVD) for fabricating poly‐Si passivating, electron selective contacts. This high‐throughput in‐line APCVD technique enables to achieve a low‐cost, simple manufacturing process for crystalline silicon (c‐Si) solar cells featuring poly‐Si passivating contact by excluding the need for vacuum/plasma environment, and additional post‐deposition doping steps. A thin layer of this P‐doped poly‐Si is deposited on an ultrathin (1.5 nm) silicon oxide (SiO x ) coated c‐Si substrate to fabricate the passivating contact. This is followed by various post‐deposition treatments, including a high‐temperature annealing step and hydrogenation process. The poly‐Si films are characterized to achieve a better understanding of the impacts of deposition process conditions and post‐deposition treatments on the microstructure, electrical conductivity, passivation quality, and carrier selectivity of the contacts which assists to identify the optimal process conditions. In this work, the optimized annealing process with post‐hydrogenation yields passivating contact with a saturation current density (J 0) of 3 fA cm−2 and an implied open‐circuit voltage (iV OC) of 712 mV on planar c‐Si wafer. Junction resistivity values ranging from 50 to 260 mΩ cm2 are realized for the poly‐Si contacts processed in the optimal annealing condition.

Energetic and financial analysis of solar landfill project: a case study in Qingyuan

Abstract Landfilling is the most commonly used option for waste disposal in China but occupies massive land resources and solar landfills could be a win-win solution by installing photovoltaic (PV) systems on the closed landfills. This paper theoretically studies the feasibility of solar landfills and compares two possible PV technologies, which are polycrystalline silicon (p-Si) and thin film PVs, from the aspects of energy and financial performance. Based on the research, the capacity factors of p-Si and thin film PV are 19.706% and 17.825%, while the conversion efficiency of them are 12.52% and 10.05%, respectively. The financial analysis indicates that the discounted payback period of p-Si PV is 13.42 years while that of thin film PV is 18.56 years. From another aspect, the levelized cost of electricities of p-Si and thin film PV are 0.87 and 0.92 CNY. The conclusion that can be drawn from the above research is that solar landfills are feasible for the case in Qingyuan energetic and financially. Compared with the thin film PV, the p-Si PV is the optimal choice for solar landfills no matter from the aspects of performance or financial consideration.

Phosphorus oxides in heavily doped polysilicon films

In tunneling oxide passivation contact (n-TOPCon) photovoltaic devices, poly-Si (n<sup>+</sup>) films with high-concentration phosphorus doping are the key materials for electron selective passivation. Its optical and electronic properties strongly depend on the chemical configuration and physical phase, and also on high temperature annealing and structural relaxation in the recrystallization process. The poly-Si (n<sup>+</sup>) films grown on SiO<sub><i>x</i></sub>/n-Si substrates by low pressure chemical vapor deposition technology are investigated, while the microstructure of the film is studied by using X-ray photoelectron spectroscopy with depth etching, high-resolution transmission electron microscopy and X-ray diffraction analysis. It is found that the binding energy values of the two fitted peaks (O2 and O3) of O 1s state of the thin film are situated at 532.1 and 533.7 eV, corresponding to the bonding of O—Si and O—P, respectively. The binding energy values of the two fitted peaks (P2 and P3) of P 2p state are located at 132.4 and 135.1 eV, corresponding to O—P* bonding with the same origin. Electronic microscopy and light diffraction analyses show that the polycrystalline silicon film has the characteristic of (111) preferential orientation, and the space of crystal plane is 0.313 nm, for which the average grain size is in a range of about 43.6–55.0 nm. However, the mechanical deformation and grain boundaries are generated in the annealing process at 920 ℃ along (111) crystal cluster, resulting in the localized monocrystalline state within large grains. The comprehensive analyses of thermodynamic function parameters of formation enthalpy, reaction entropy, heat capacity, formation energy and Gibbs free energy and energy minimum principle analysis indicate that there exist conditions for forming Si—O and P—O bonds in the polysilicon film, and thus the bonding state of silicon and phosphorus oxides are formed.

Effect of annealing temperature on the kinetics of aluminum-induced crystallization of amorphous silicon suboxide thin films

In this work, the kinetics of aluminum-induced crystallization (AIC) of non-stoichiometric silicon oxide a-SiO0.25 was investigated for the case of annealing at temperatures of 370, 385 and 400oC, as a result of which thin films of polycrystalline silicon were obtained. It is shown that, at low annealing temperatures, the surface morphology of the crystalline material is represented by dendritic structures corresponding to the growth model with diffusion-limited aggregation. In addition, with increasing annealing temperature, the nucleation density increases from 3 to 53 mm-2. From the Arrhenius plot, the activation energy of the a-SiO0.25 AIC was obtained for the first time and appeared to be 3.7± 0.4 eV. Keywords: aluminum-induced crystallization, silicon suboxide thin films, polycrystalline silicon, activation energy.

In situ phosphorus-doped polycrystalline silicon films by low pressure chemical vapor deposition for contact passivation of silicon solar cells

In situ phosphorus (P)-doped polycrystalline silicon (poly-Si) films by low pressure chemical vapor deposition (LPCVD) were studied in this work for the fabrication of poly-Si passivating contacts. In situ doping was targeted for enabling the full potential of the high-throughput LPCVD technique, as it could allow leaner fabrication of industrial solar cells featuring poly-Si passivating contacts than the more common ex situ doping routes. By careful optimization of the deposition temperature and the flows of the carrier gas (H2) and the dopant precursor (PH3), high doping in the poly-Si layers was achieved with active P concentrations up to 1.3⋅1020 cm−3. While reduction in the deposition rate (rdep) and thus in the throughput is a known problem when growing in situ P-doped films by LPCVD, this reduction could be limited, and the resulting rdep was equal to 0.078 nm/s. The developed poly-Si films were characterized both structurally and in terms of their passivation potential in poly-Si contacts. The latter yielded recombination current densities down to 1.5 fA/cm2 in passivated (J0,p) and 25.6 fA/cm2 in screen-printing metallized (J0,m) regions on saw-damage removed (SDR) Cz-Si surfaces, accompanied by a contact resistivity (ρc,m) of 4.9 mΩ⋅cm2. On textured Cz-Si surfaces, the corresponding values were J0,p = 3.5 fA/cm2, J0,m = 56.7 fA/cm2, and ρc,m = 1.8 mΩ⋅cm2. Optical impact of the developed poly-Si films was also assessed and a short circuit density loss of 0.41 mA/cm2 is predicted per each 100 nm of poly-Si applied at the rear side of solar cells.

Features of the Morphology and Structure of Thin Silicon Films

Abstract—The surface morphology and structure of LPCVD silicon thin films (with thicknesses of 40 nm or less) obtained at a deposition temperature of T = 550°С, at which amorphous films (a-Si) are usually obtained, and at a deposition temperature of 584°С, at which films of polycrystalline silicon with hemispherical grains (HSG-Si) with a large surface roughness are obtained, are studied. It is found that, at a deposition temperature of 550°С, amorphous films with comparatively smooth surfaces form in the case of thicknesses of 35 nm or more, and granular polycrystalline HSG-Si films with a large surface roughness form in the case of thicknesses of 35 nm or less. It is shown that granular silicon films deposited at T = 550°С (d = 28 nm) have a morphology that is analogous to that of HSG-Si films deposited at T = 584°С (d = 29 nm). It is found that, as the thickness of the deposited Si film decreases to 28 nm, the lower boundary of the temperature range at which HSG-Si films form is shifted toward smaller temperatures to T = 550°C.