Advanced Generation-Recombination Models
In 1934 Zener [3.118] proposed band-to-band tunneling as explanation for the electrical breakdown. A modified Zener theory was used by McAffee et al. [3.75] in 1951 to describe the breakdown of reversed biased pn-junctions, called Zener diodes since then.
- PDF / 7,055,477 Bytes
- 82 Pages / 481.882 x 691.647 pts Page_size
- 0 Downloads / 218 Views
Advanced Generation-Recombination Models
3.1 Band-to-Band Tunneling In 1934 Zener [3.118J proposed band-to-band tunneling as explanation for the electrical breakdown. A modified Zener theory was used by McAffee et al. [3.75J in 1951 to describe the breakdown of reversed biased pn-junctions, called Zener diodes since then. However, experimental work [3.76-3. 78J in the following years showed that in such diodes with wide junctions the breakdown is not caused by tunneling, but by impact ionization. Only in narrow junctions, where the width of the transition region is less than 50 nm, the necessary field strength for tunneling is reached before the avalanche effect sets in. This was first clearly demonstrated by Chynoweth and McKay [3.22J in 1957 by the absence of microplasma noise and by the temperature coefficients of reverse and forward characteristics of junctions with different breakdown voltages. In the same year Esaki [3.32J discovered that narrow pn-junctions between degenerate regions can have forward characteristics with a portion ofnegative differential conductivity, and that the tunnel "hump" is only weakly temperature dependent. Esaki's work initiated intensive experimental and theoretical investigations. Holonyak et al. [3.53J and Hall [3.45J observed structures in the I (V)-characteristics of heavily doped Sijunctions at 4.2 K, which they attributed to the momentum-conserving phonons in indirect band-to-band tunneling. Various phonon energies could be resolved in these characteristics. Chynoweth et al. [3.19, 3.20J then found evidence that the excess current in silicon Esaki junctions, i.e. the current between the tunnel "hump" and the normal forward injection current, is essentially caused by the process offield ionization of impurity levels. This mechanism had been suggested by Yajima and Esaki [3.117J. It was confirmed by Sah [3.91J, who measured the excess current in gold-doped silicon tunnel diodes and found different onsetvoltages for the various possible tunneling paths via the gold levels. Brody [3.12J suggested another explanation for the excess current. He considered transitions between the tail states of the heavily doped material and tried to find a correlation between tunneling characteristic and DOS shape. Chynoweth et al. [3.19J A. Schenk, Advanced Physical Models for Silicon Device Simulation © Springer-Verlag/Wien 1998
3.1 Band-to-Band Tunneling
171
investigated the dependence of the excess current on radiation damage and observed a linear increase ofthat current with the bombardment dose. Furthermore, phonon-assisted tunneling was correlated to a S-bend shape of the peak currentvs-temperature curve, which did not occur for the excess current. By measuring the derivative of the conductance in silicon Esaki diodes at 4.2 K, Chynoweth et al. [3.21J could reveal twelve phonon and phonon-combination energies, which agreed well with results of neutron scattering studies. In a subsequent paper Logan and Chynoweth [3.71J succeeded to decompose the tunneling current of silicon Esaki juncti
Data Loading...
