Stefan Zukotynski

Determination of the sp3/sp2 ratio of a-C:H by XPS and XAES

Abstract X-ray photoelectron spectroscopy and X-ray excited Auger electron spectroscopy were used to determine some of the properties of diamond like amorphous carbon films deposited using saddle field glow discharge of methane. By applying the chemical shift technique and curve fitting technique to the C1s peak in the X-ray photoelectron spectrum of the film, we were able to determine the sp 3 /sp 2 bonding ratio of the films. The ratio from this method was in agreement (±1%) with that calculated from the X-ray excited Auger electron spectrum of the same film. The method was also applied to a-C:H films doped with different impurities (boron and phosphorus) in amounts varying from 1% to 20%. We found that the sp 3 /sp 2 ratio of the film was dependent on the deposition parameters and on types of impurities and their concentrations.

High-efficiency photonic crystal solar cell architecture

Thin silicon solar cells suffer from low light absorption compared to their thick counterparts, especially in the near infra-red regime. In order to obtain high energy conversion efficiency in thin solar cells, an efficient light trapping scheme is required. In this paper, we theoretically demonstrate significant enhancement in efficiency of thin crystalline silicon solar cells by using photonic crystals as the light absorbing layer. In particular, a relative increase of 11.15% and 3.87% in the energy conversion efficiency compared to the optimized conventional design is achieved for 2 microm and 10 microm thicknesses, respectively.

Disorder and optical absorption in amorphous silicon and amorphous germanium

Abstract The role that disorder plays in shaping the functional form of the optical absorption spectra of both amorphous silicon and amorphous germanium is investigated. Disorder leads to a redistribution of states, which both reduces the empirical optical energy gap and broadens the optical absorption tail. The relationship between the optical gap and the breadth of the absorption tail observed in amorphous semiconductors is thus explained.

CMOS LC-oscillator phase-noise analysis using nonlinear models

In this paper, a second-order stochastic differential equation is used as a tool for the analysis of phase noise in a submicron CMOS LC oscillator. A cross-coupled topology typical of integrated CMOS designs is considered. Nonlinear limiting and mobility degradation effects in the circuit are modeled and used to predict the statistics of the random amplitude and phase deviations in terms of design variables. Assuming Gaussian noise disturbances and describing the phase noise as a random diffusion process, the average phase-noise power spectrum is derived and its accuracy verified with measurement and simulation results. Calculations for phase noise arising from stationary tank noise, nonstationary channel thermal noise, and flicker noise are discussed. The analysis is used to emphasize the fundamental power/performance tradeoff associated with compensation of tank losses via adjustments in the power supply and device size.

Photonic crystal intermediate reflectors for micromorph solar cells: a comparative study

Wave-optics analysis is performed to investigate the benefits of utilizing Bragg-reflectors and inverted ZnO opals as intermediate reflectors in micromorph cells. The Bragg-reflector and the inverted ZnO opal intermediate reflector increase the current generated in a 100 nm thick upper a-Si:H cell within a micromorph cell by as much as 20% and 13%, respectively. The current generated in the bottom muc-Si:H cell within the micromorph is also greater when the Bragg-reflector is used as the intermediate reflector. The Bragg-reflector outperforms the ZnO inverted opal because it has a larger stop-gap, is optically thin, and due to greater absorption losses that occur in the opaline intermediate reflectors.

Infrared vibration spectra of hydrogenated, deuterated, and tritiated amorphous silicon

This article presents infrared absorption data of amorphous silicon alloys in which the hydrogen isotopes deuterium and tritium have been substituted for hydrogen. Silicon–deuterium and silicon–tritium vibration frequencies are related to silicon–hydrogen vibration frequencies by simple mass relationships. The silicon–deuterium wagging vibration is broadened and blueshifted due to strong coupling to the amorphous silicon network vibrations.

Tritiated amorphous silicon films and devices

The dc saddle-field glow discharge system was used to stably bond tritium in hydrogenated amorphous silicon films. A betavoltaic battery is demonstrated using tritiated-hydrogenated amorphous silicon as the intrinsic layer in a p–i–n diode and betaconductivity was observed in a-Si:H:T films. Although the half-life of tritium is 12.5 years, the decay of tritium appeared to rapidly increase the midgap density of states which decreased the excess carrier lifetime and decreased the power from the betavoltaic battery. The betaconductivity properties of the a-Si:H:T film were also affected.

Dependence of optical gap in a-Si:H on bonded hydrogen concentration

Abstract An analysis of new and existing data over a wide range of hydrogen concentrations, from 0.3 to 50 at%, shows that the optical gap of hydrogenated amorphous silicon prepared by various techniques varies linearly with the bonded hydrogen density per unit length. The extrapolated gap for zero hydrogen concentration, (1.23±0.05) eV, is close to the minimum (indirect) gap in crystalline silicon, as would be expected if the electron energy levels in amorphous silicon are determined primarily by the near-neighbour environment.

Betavoltaics using scandium tritide and contact potential difference

Tritium-powered betavoltaic micropower sources using contact potential difference (CPD) are demonstrated. Thermally stable scandium tritide thin films with a surface activity of 15mCi∕cm2 were used as the beta particle source. The electrical field created by the work function difference between the ScT film and a platinum or copper electrode was used to separate the beta-generated electrical charge carriers. Open circuit voltages of 0.5 and 0.16V and short circuit current densities of 2.7 and 5.3nA∕cm2 were achieved for gaseous and solid dielectric media-based CPD cells, respectively.

Study of resonant tunneling structures: A hybrid incremental Airy function plane‐wave approach

A numerical procedure for the calculation of the electron tunneling current through an arbitrary potential profile has been developed. It involves subdividing the profile into a number of strips for which a linear approximation of the potential is appropriate. A solution of the Schrodinger equation in the form of Airy functions is obtained. These functions are linked through boundary conditions at the interface of the strips. An expression for the transmission coefficient of the structure is obtained. The approach is found to accelerate the calculation of the electrical characteristic of resonant tunneling devices. An analysis is performed of tunneling through parabolic quantum‐well and half‐parabolic quantum‐well structures in the presence of an electric field. The room‐temperature current‐voltage characteristic for the half‐parabolic quantum‐well structure is calculated and is found to be rectifying with multiple peaks and regions of negative differential resistance. It is also found to have a relativel...