Effective passivation of c-Si by intrinsic a-Si:H layer for hit solar cells

The influence of HF solution etching on surface roughness of c-Si wafer was investigated using AFM. Ultra thin(2-3 nm) intrinsic a-Si:H is necessary to achieve high VOC and Fill factor, as it effectively passivates the defects on the surface of c-Si and increase tunneling probability of minority charge carriers. However, to achieve control over ultra-thin intrinsic a-Si:H layer thickness and passivation properties, the films were deposited by Hot-wire CVD. We used tantalum filament and silane (SiH4) as a precursor gas, where as the deposition parameter such as filament temperature temperature was varied. The deposition rate, Dark and Photoconductivity were measured for all the films. The optimized intrinsic a-Si:H layer was inserted between p typed doped layers and n type c-Si wafers to fabricate HIT solar cells. The Current-Voltage characteristics were studied to understand the passivation effect of intrinsic layer on c-Si surface. The high saturation current density (Jsat > 10–7 A/cm2) and Ideality factor (n > 2) were observed. We achieved the efficiency of 3.28 % with the optimized intrinsic and doped a-Si:H layers using HWCVD technique. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/2794

Study of Electrical, Optical and Structural Properties of Al- Doped ZnO Thin Films on PEN Substrates

Aluminum-doped zinc oxide (AZO), as one of the most promising transparent conducting oxide (TCO) material, has now been widely used in thin film solar cells. Most of the study of AZO films till date has been done on glass substrates but nowadays there is a growing interest in replacing glass with polymer substrate for the thin-film solar cell technology and many other flexible optoelectronic devices. In this study, AZO thin films were deposited at room temperature by RF magnetron sputtering on flexible substrates from a 3 inch diameter target of 2 wt % Al2O3 in zinc oxide. The effect of RF power on the structural, optical and electrical properties of AZO films was investigated by X-ray Diffraction (XRD), Hall measurement, and UV-visible spectrophotometery. The XRD data indicates a preferential c-axis orientation for all the films. All films exhibit high transmittance ( 85%) in visible region. Films deposited at 60 W power exhibit lowest resistivity of 1.2 10 – 3 Ωcm. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3102

Preliminary results on a-SiC:H based thin film light emitting diode by hot wire CVD

Preliminary results on the first hot wire deposited a-SiC:H based thin film light emitting p–i–n diode having the structure glass/TCO(SnO2:F)/p-a-SiC:H/i-SiC:H/n-a-SiC:H/Al are reported. The paper discusses the results of our attempts to optimize the p-, i- and the n-layers for the desired electrical and optical properties. The optimized p-layers have a bandgap Eg∼2 eV and conductivity a little lower than 10−5 (Ω cm)−1. On the other hand, the optimized n-type a-SiC:H show a conductivity of ∼10−4 (Ω cm)−1 with bandgap 2.06 eV. The highest bandgap of the intrinsic layer is approximately 3.4 eV and shows room temperature photoluminescence peak at approximately 2.21 eV. Thin film p–i–n diodes having i-layers with Eg from 2.7 to 3.4 eV show white light emission at room temperature under forward bias of >5 V. However, the 50-nm thick devices show appreciable reverse leakage current and a low emission intensity, which we attribute to the contamination across the p–i interface since these devices are made in a single chamber with the same filament

Revisiting the B-factor variation in a-SiC:H deposited by HWCVD

In order to understand material properties in a better way, it is always desirable to come up with new variables that might be related to the film properties. The B-parameter is such a variable, which relates to the quality of a-SiC:H films both in terms of electronic and optical properties. B (scaling factor) is essentially the slope of the straight-line part of the (αE)1/2–E (Tauc plot). Due to dependence on a large number of parameters and no detailed research, many previous authors have surmised that B has an ambiguous correlation with carbon content. We have made an attempt to establish the relation between the B-parameter as a quality-indicating factor of a-SiC:H films in both carbon- and silicon-rich material. For this we studied a-SiC:H films deposited by the HWCVD method with broad deposition parameters of substrate temperature (Ts), filament temperature (TF) and C2H2 fraction. Our results indicate that the B-parameter varies considerably with process conditions such as TF, total gas pressure and carbon content. An attempt is made to correlate the B-parameter with an opto-electronic parameter, such as the mobility edge, which has relevance to the device-quality aspects of a-SiC:H films prepared by HWCVD

Reliability Issues of Ultra Thin Silicon Nitride (a-SiN: H) by Hot Wire CVD for Deep Sub-Micron CMOS Technologies

The reliability of gate dielectric is of high importance, especially as its thickness is reaching atomic dimensions. The gate leakage currents and the operating fields can be very high in devices with these ultra thin gate dielectrics. Several anomalous degradation mechanisms and breakdown characteristics are observed in these devices. New phenomena such as quasi breakdown and SILC are now considered important for accurate reliability assessment In this work we investigate a systematic reliability evaluation of high quality MNS devices made with ultra thin HWCVD nitride as the gate dielectric by taking into account these newer effects

Photoluminescent, wide-bandgap a-SiC:H alloy films deposited by Cat-CVD using acetylene

Hydrogenated amorphous silicon/carbon films (a-Si-C:H) are deposited from a silane and acetylene gas mixture by the catalytic chemical vapour deposition (Cat-CVD) technique. It is observed that under certain conditions of total gas pressure and filament temperature (TF), the optical bandgap varies non-linearly with the acetylene to silane (C2H2/SiH4) ratio, having a maximum value of 3.6 eV for a C2H2/SiH4 ratio ≥0.8. However, the deposition rate drastically reduces with an increase in acetylene fraction. FTIR spectra indicate that the total hydrogen content is lower compared to samples deposited by PECVD using similar gas mixtures, with hydrogen being preferentially attached to carbon rather than silicon atoms. The photoluminescence (PL) spectra of these films show PL in the visible spectral region at room temperature. The films with larger bandgap (>2.5 eV) exhibit PL at room temperature, with the emission having peak energy in the range 2.0–2.3 eV

Low temperature silicon nitride deposited by Cat-CVD for deep sub-micron metal–oxide–semiconductor devices

Silicon nitride as a gate dielectric can improve the performance of ULSI CMOS devices by decreasing the gate leakage currents. In this paper we report a a-SiN:H gate dielectric fabricated using Cat-CVD at a relatively low substrate temperature of ∼250°C, using silane and ammonia as the source gases. The films were deposited at various gas pressures, (NH3/SiH4) flow rate ratios and at different filament temperatures (TF). The deposition parameters, i.e. total gas pressure and gas composition (silane+ammonia) were optimized to deposit insulating and transparent films with high breakdown strength. The structural properties of these films were studied by Fourier transform infrared (FTIR) spectroscopy and ultraviolet-visible (UV-vis) spectroscopy. Films with bandgap as high as 5.5 eV were obtained. The optimized conditions were used to deposit ultrathin films of the order of 8 nm thickness for deep-submicron CMOS technology. Electrical properties such as C–V and I–V measurements were studied on metal–nitride–semiconductor (MNS) capacitor structures. These characterization results on MNS capacitors show breakdown fields of the order of 10 MV cm−1 and good interface properties

Ultra-thin silicon nitride by hot wire chemical vapor deposition (HWCVD) for deep sub-micron CMOS technologies

Silicon nitride is considered a promising candidate to replace thermal oxide dielectrics, as the latter is reaching its scaling limits due to the excessive increase in the gate tunneling leakage current. The novel hot wire chemical vapor deposition (HWCVD) technique shows promise for gate quality silicon nitride film yields at 250 °C while maintaining their primary advantage of a higher dielectric constant of 7.1. In this paper we report the results of our efforts towards developing ultra-thin HWCVD silicon nitride as an advanced gate dielectric for the replacement of thermal gate oxides in future generations of ultra large scale integration (ULSI) devices

Nitrogen dilution effects on structural and electrical properties of hot-wire-deposited a-SiN:H films for deep-sub-micron CMOS technologies

Hot-wire chemical vapor-deposited silicon nitride is a potential dielectric material compared to glow-discharge-deposited material due to its lower hydrogen content. In several earlier publications we have demonstrated these aspects of the HWCVD nitride. However, to replace SiO2 with a-SiN:H as the gate dielectric, this material needs further improvement. In this paper we report the results of our efforts to achieve this through nitrogen dilution of the SiH4+NH3 gas mixture used for deposition. To understand the electrical behavior of these nitride films, we characterized the films by high-frequency capacitance–voltage (HFCV) and DC J–E measurements. We attempted to evolve a correlation between the breakdown strength, as determined from the J–E curves, and aspects such as the bond density, etching rate, deposition rate and refractive index. From these correlations, we infer that nitrogen dilution of the source gas mixture has a beneficial effect on the physical and electrical properties of the hot-wire a-SiN:H films. For the highest dilution, we obtained a breakdown voltage of 12 MV cm−1