Ismail Atilgan

Temperature dependence of the capture cross section determined by DLTS on an MOS structure

An energy-resolved DLTS technique was used to determine the distributions of both interface trap density and thermal capture cross section along the bandgap of an MOS structure. The resulting experimental values are criticized and tested in comparison with those obtained from a conventional a.c. conductance technique applied on the same diode. In this respect, incomplete filling of traps has an important effect on the interface trap density distribution. Furthermore, experimental measurements indicate that the capture cross section strongly depends on temperature, which might be interpreted as being due to a multiphonon emission process.

Transport studies of carbon-rich a-SiCx:H film through admittance and deep-level transient spectroscopy measurements

An intrinsic, carbon-rich a-SiC x :H thin film, prepared by the plasma-enhanced chemical vapour deposition (PECVD) technique, has been studied mainly by AC admittance and small-pulse deep-level transient spectroscopy (DLTS) measurements on an Al/a-SiC x :H/p-Si metal–insulator–semiconductor (MIS) structure. The effects of measurement temperature, voltage and small-signal AC modulation frequency on the MIS capacitor are qualitatively and quantitatively described. The kinetics of charge injection from the silicon substrate into the a-SiC x :H film, as a function of temperature and voltage bias stresses, are reported. Nearest-neighbour and variable-range hopping mechanisms are considered. An activation energy of ∼ 0.09 eV, and a density of states (DOS) of about 1019 cm−3/eV were found. The value of the DOS is in agreement with the effective interface DOS of above 1012 cm−2/eV assessed by both capacitance and DLTS measurements. The frequency (or temperature) dependence of the MIS capacitor over the whole DC voltage range is considered in detail. Single- and double-step carrier exchange mechanisms between the a-SiC x :H film and the silicon substrate, in the accumulation and depletion voltage regimes, respectively, are proposed.

Admittance analysis of an MIS structure made with PECVD deposited a-SiNx:H thin films

a-SiNx:H thin films, prepared by the PECVD technique, were optically and electrically characterized. The frequency dependent trap admittance derived for the MIS structure in the accumulation gate voltage regime was revised. Based on these results an omitted multiplying factor was included into the derivation. An extension of the tunnelling model in the depletion bias regime was used in comparison with the widely accepted statistical model and finally, the more general feature of the tunnelling-based approaches was discussed.

Electroforming of Amorphous Silicon Nitride Heterojunction

The deposition parameters of doped hydrogenated nanocrystalline silicon grown by plasma-enhanced chemical vapor deposition were scanned to obtain highly conductive films. The optimized p+ and n+ nc-Si:H films were used as injecting layers in the fabrication of Si-rich hydrogenated amorphous silicon nitride (a-SiNx:H)-based heterojunction p+in+ diode. The as-grown diode was subjected to a Joule-heating-assisted forming process (FP) via the application of a high electric field. The modifications in the luminescent, electrical, and structural properties of the diode subsequent to the FP were investigated. Although the energy distribution of electroluminescence remains almost the same when compared with that of the fresh diode, its intensity is enhanced by at least 30 times with an orange-red emission easily perceived by the naked eye. Parallelly, the low field-current density drastically increases, presumably due to the Si-nanocrystallite formation within the a-SiNx:H layer. This formation, triggered by the neighboring nanocrystalline-doped layers, was confirmed by the X-ray diffraction measurements indicating the rise in the local temperature during FP.

pin

Abstract The effects of positive and negative bias stresses on plasma enhanced chemical vapor deposited (PECVD) hydrogenated amorphous silicon nitride/crystal silicon (a-SiNx/c-Si) structures were investigated as a function of both time and temperature. It was shown that the bias stress induces forward (positive) or backward (negative) shift of the capacitance–voltage ( C – V ) characteristic along the voltage axis according to the polarity of this applied stress voltage. The injection of charge carriers from the semiconductor substrate and their eventual dispersive hopping process, limiting the redistribution of charges throughout the insulator, seem consistent with the time evolution of both dc current and flat band voltage of the metal insulator semiconductor structure.

Visible Light Emitter

A plasma enhanced chemical vapor-deposited (PECVD) boron nitride (BN) film on p-type crystalline silicon (p-c-Si) was used to fabricate the metal–insulator–semiconductor (MIS) test structure. The effects of positive (inverting type) and negative (accumulating type) bias stresses on the MIS (Al/BN/p-Si/Al) structure were investigated as a function of time, bias voltage stresses and temperature. Charge injection into the gate dielectric (BN film in this case) was considered as a mechanism to provoke the instability problem that manifested itself as a slow shift of specific voltage (ΔVHH) which symbolizes the whole capacitance–gate bias voltage (C–V) curve. Moreover, the evolution of this shift is followed by monitoring ΔVHH as a function of time, temperature and gate voltage stress and fitted to a functional form for the ΔVHH shift kinetics. Good agreement with the experimental data confirms the charge injection hypothesis behind the shift in C–V curves. Finally, the origin of an eventual defective structure, required by the actual instability, is argued in terms of possible chemical composition of the film. Seemingly BN possesses a turbostratic structure; the first layer at the initial stage in growth is amorphous (even self-doped by a contamination from the underlying silicon substrate) on which a more ordered phase might continue.

Instability evolution within a-SiNx film assessed through MIS structure under bias and temperature stresses

Abstract Two sets of hydrogenated amorphous silicon carbide (a-SiC x :H) thin films were grown on glass and c-Si substrates by Plasma enhanced chemical vapor deposition (PECVD) technique at pressures of 0.5 and 0.1 Torr. The influence of the pressure on the distribution of thicknesses, refractive indices at 632.8 nm and optical gaps from the edge to the center of the bottom electrode of PECVD system is examined by transmission, single wavelength ellipsometry and Fourier transform infrared spectroscopy. A recently introduced optimization method considering some prior knowledge of common optical properties of amorphous semiconductor thin films have been applied to the optical transmission spectra for estimating thickness and optical constants of a-SiC x :H thin films at hand. In addition, spectral characteristics of these constants are analyzed by fitting experimental data through Forouhi–Bloomer, Tauc–Lorentz and single Lorentz oscillator models. The retrieved results show that while the thicknesses and optical band gaps are decreasing towards the center of the electrode, refractive index is slightly increasing in that direction. Chemical processes occurring during the film deposition are discussed. These distributions of the film constants have been interpreted as due to the carbon incorporation whose efficiency might increase towards the edge of the electrode corresponding to a longer residence time of carbon radicals.

Instability phenomenon originated from the disordered layer of the plasma-deposited BN film/c-Si interface assessed through the MIS structure by admittance measurement

The optical constants of plasma-enhanced chemical-vapor-deposited amorphous silicon (a-Si:H) thin film upon a transparent substrate are determined within the UV-visible region by measurement of the transmittance spectrum. Apart from thickness irregularities, the effects of vertical film inhomogeneities (refractive-index distribution) on the spectrum are discussed. In this respect, although consideration of any possible variation in thickness of the film within the area illuminated by the probe beam is sufficient for correcting the modulation of the extrema of interference fringes, including in the model the thin transitional regions at substrate-film and film-air interfaces might be an alternative method for understanding the overall optical behavior of the spectrum.

Thickness and optical constant distributions of PECVD a-SiCx:H thin films along electrode radial direction

We report the transformation of an ordinary hydrogenated amorphous silicon nitride based heterojunction diode into a strong visible light emitting electroluminescent device. This forming process (FP) comprises Joule heating induced crystallization during the application of sufficiently high forward bias to the fresh diode. FP starts at an arbitrary point and continues until the accompanying visible light is uniformly emitted from the whole diode. This remarkable phenomenon is presented by real-time photography of the lateral propagation of the formed region. Finally, both the role of window electrode for a successful FP and the luminescence mechanism after FP are briefly discussed.

Correlation between optical path modulations and transmittance spectra of a-Si:H thin films

Abstract Hydrogenated amorphous silicon nitride-based heterojunction pin diode was electroformed under sufficiently high forward bias stress leading to its instant nanocrystallization at room temperature. In order to investigate the origin of the accompanying bright visible light emission, current-voltage and electroluminescence (EL) characteristics of the electroformed diode were scanned over temperature. Electrical transport mechanism was analysed in the low, medium and high electric field regimes. Temperature and field dependence of thermal activation energy were discussed. EL characteristics were studied using the spectral energy distribution and the injection current dependence of its intensity. Thermal quenching data of EL and photoluminescence intensities were compared. Finally, the relationship between the electrical transport and luminescence phenomena was attempted to be interpreted within the frame of a self-consistent model.