Gunter Ebest

Evidence of a high density of fixed negative charges in an insulation layer compound on silicon

Abstract For drift field generation, IS structures with a positive interface charge in an insulator compound were developed in the 1980s and employed mainly on field effect solar cells. While there has been a large number of publications about the positively biased insulator–semiconductor structure there has been very little interest in its antipolar counterpart — the negatively biased insulator–semiconductor structure — so far. However, by using that structure as a second drift field source for field effect solar cells their conversion efficiency could be improved. The conventional rear surface passivation of silicon active layers by shallow ultrahigh aluminium doping in order to form a back surface field involves a high density of lattice and surface defects which increase recombination rates. The structure introduced herein is put onto a silicon layer and acts thus as an external negative drift field source, thereby avoiding the drawbacks of ultrahigh doping. The layer arrangement aluminiumfluoride–silicon dioxide on silicon seems to be a good candidate for a negative drift field source. Experimental results which led to a fixed interface charge of up to −1.6×10 12 cm −2 at the interface aluminiumfluoride∣∣silicon dioxide are presented and an interpretation of the fixed negative charge is given.

Time Dependent Isolation Capability of High Voltage Deep Trench Isolation

The long term isolation properties of deep trenches in thick SOI have been investigated by current-voltage- characteristics. A strong change of the measured trench leakage current was observed depending on the applied voltage. Further on a marked decrease of the leakage current was observed depending on the duration and polarity of the applied stress. The improvement of the formatted trench isolation was found to be irreversible with time, temperature and voltage polarity. This so-called formation effect can be described by a theoretical simulation model assuming a tunneling process of electrons through the oxide barrier, taking into account the charging and discharging of traps within the trench sidewall oxides. The observed formation effect leads to improved reliability results, wherein the trench is either damaged at the start of the stressing or no dielectric breakdown occurs at all.

High-Voltage Amplifier Design for MEMS based Switching Arrays in Wavelength-Division Multiplexing Networks

The paper describes the design requirements of integrated high-voltage amplifiers for large MEMS based arrays which consist of electrostatically driven actuators. Such actuators are applied in optical switching arrays for cross connects in wavelength-division multiplexing (WDM) networks. Besides a new calculation approach for the efficiency of amplifier operation modes a new concept of level-shifter circuitry for switching output stages of high-voltage amplifiers is presented and compared with conventionally level-shifter circuits.

Evidence for high negative charge densities in AlF3 coatings on oxidized silicon: a promising source for large drift fields

Abstract Fixed negative charges in coatings of silicon solar cells can serve as an efficient source for large drift fields, thereby passivating the silicon surface and improving charge separation of the electron–hole pairs. In the present work, we report on the evidence for a high negative charge density in AlF 3 coatings on oxidized silicon. The existence of these charges is related to sub-stoichiometric Fluorine content close to the AlF 3 /SiO 2 interface, as evidenced both in measurements and density functional calculations of an electron trapped in a fluorine vacancy.

Comparison of different emitter diffusion methods for MINP solar cells: Thermal diffusion and RTP

A solar cell technology with an extremely small thermal budget was developed for MINP cells. MINP solar cells with efficiencies of up to 15.3% have been achieved by rapid thermal processing (RTP). An emitter diffusion process was simulated and developed that yields a doping profile with a tunnelling oxide in a single furnace step. The P concentration profile was investigated by SIMS measurements and compared to the calculated profile. The SIMS results of the 850°C processing temperature differ from the calculated profile, but the 800°C values showed an excellent conformity. The surface passivation can be improved by an increase of the deposition temperature of the antireflection film. The maximum temperature was appointed with 400°C for MINP and 300°C for pn cells. In comparison with pn cells the temperature stability of MINP cells is significantly higher.

Modeling the Leakage Current of Dielectric Isolation Structures in a High-Voltage Semiconductor Technology

System-in-package integration becomes more and more important in the growing market of micromechanical sensors and actuators. The most important group of actuators are those based on the electrostatic working principle. Because of the high voltages used to drive these actuators, new methods of isolation need to be introduced. In this paper we will characterize and model the electrical behavior of such an isolation technology. A simple device model to regard parasitic effects of this isolation during the process of circuit design will be introduced.

Novel external field source by localization of electrons for improvement of solar cells

For drift field generation IS structures with a fixed positive charge were developed in the 1970s and employed on solar cells. While many papers were published about the positively charged IS structure there has been little interest in a negatively charged IS structure (Proceedings of the 18th IEEE PVSC, Las Vegas, 1985, p. 1752). In comparison to solar cells with back surface field such structures could improve conversion efficiency more significantly. They also open the way to novel-field-effect-supported solar cells on n-type silicon. The paper represents results of the preparation and characterization of the IS structure on Silicon (Si) consisting of a layer compound AlF 3 6||SiO 2 on Si, a discussion of the phenomena encountered and respective conclusions.

Novel thin film solar cell model with two antipolar MIS structures

In this article we introduce a new thin film solar cell model which uses the properties of two antipolar MIS structures. The active layer consists of unipolar polycrystalline silicon. We employed silicon dioxide as insulator. The back- and top electrode consist of indium tin oxide (ITO). The solar cell model was developed under consideration of the low-temperature chemical vapour deposition (i.e. PECVD). As oxide and ITO are optical transparent media and in compound with the planned process technology the solar cell concept would be very suitable for a stack arrangement which would increase the device conversion efficiency. Currently the preparation of silicon dioxide with a sufficiently large fixed negative charge seems to be out of technological facilities. Nevertheless, we consider the concept introduced herein as an important contribution to novel ways of efficient low-cost thin-film solar cells.

A new method and system for the simulation of modular inverters in solar facades

The paper shows a method of simulation of the stationary and dynamic behaviour of the grid connection of a large number (100...300 and more) of parallel-connected modular inverters which are used in solar facades. Furthermore, it describes the models and their parameters and the results of many simulations by modifying these parameters. It shows the properties of the simulation system used and the significant simulation results (for any number of modular inverters): the time behaviour (transients) of the mains current and the mains voltage; the harmonic spectra by online FFT; and the dependence of the harmonic content on the tolerance range.