A recombination model for device simulation that includes both trap-assisted tunneling (under forward and reverse bias) and band-to-band tunneling (Zener tunneling) is presented. The model is formulated in terms of analytical functions of local variables, which makes it easy to implement in a numerical device simulator. The trap-assisted tunneling effect is described by an expression that for weak electric fields reduces to the conventional Shockley-Read-Hall (SRH) expression for recombination via traps. Compared to the conventional SRH expression, the model has one extra physical parameter, the effective mass m*. For m*=0.25 m/sub 0/ the model correctly describes the experimental observations associated with tunneling. The band-to-band tunneling contribution is found to be important at room temperature for electric fields larger than 7*10/sup 5/ V/cm. For dopant concentrations above 5*10/sup 17/ cm/sup -3/ or, equivalently, for breakdown voltages below approximately 5 V, the reverse characteristics are dominated by band-to-band tunneling. >

A new recombination model for device simulation including tunneling

An analytical model describing reverse and forward DC characteristics is presented. It serves as a basis for a compact model for circuit simulation purposes. The model is based on the solution of the hole continuity equation in the depletion layer of a p-n junction and incorporates the following physical mechanisms: band-to-band tunneling, trap-assisted tunneling (both under forward and reverse bias), Shockley-Read-Hall recombination, and avalanche breakdown. It contains seven parameters which can be determined at one temperature. No additional parameters are needed to describe the temperature dependence. From comparisons with both numerical simulations and measurements it is found that the model gives an adequate description of the DC characteristics in both forward and reverse modes. >

A new analytical diode model including tunneling and avalanche breakdown

The DC design considerations associated with optimizing epitaxial Si- and SiGe-base bipolar transistors for the 77-K environment are examined in detail. Transistors and circuits were fabricated using four different vertical profiles, three with a graded-bandgap SiGe base, and one with a Si base for comparison. All four epitaxial-base profiles yield transistors with DC properties suitable for high-speed logic applications in the 77-K environment. The differences between the low-temperature DC characteristics of Si and SiGe transistors are highlighted both theoretically and experimentally. A performance tradeoff associated with the use of an intrinsic spacer layer to reduce parasitic leakage at low temperatures and the consequent base resistance degradation due to enhanced carrier freeze-out is identified. Evidence that a collector-base heterojunction barrier effect severely degrades the current drive and transconductance of SiGe-base transistors operating at low temperatures is provided. >

On the profile design and optimization of epitaxial Si- and SiGe-base bipolar technology for 77 K applications. I. Transistor DC design considerations

Based on numerical simulation and comparison with measured current characteristics, we show that the current in InGaN/GaN single-quantum-well light-emitting diodes at low forward bias can be accurately described by a standard trap-assisted tunneling model. The qualitative and quantitative differences in the current characteristics of devices with different emission wavelengths are demonstrated to be correlated in a physically consistent way with the tunneling model parameters.

Trap-assisted tunneling in InGaN/GaN single-quantum-well light-emitting diodes

In this work, the temperature impact on the off-state current components is analyzed through numerical simulation and experimentally. First of all, the band-to-band tunneling is studied by varying the underlap in the channel/drain junction, leading to an analysis of the different off-state current components. For pTFET devices, the best behavior for off-state current was obtained for higher values of underlap (reduced BTBT) and at low temperatures (reduced SRH and TAT). At high temperature, an unexpected off-state current occurred due to the thermal leakage current through the drain/channel junction. Besides, these devices presented a good performance when considering the drain current as a function of the drain voltage, making them suitable for analog applications.

Temperature impact on the tunnel fet off-state current components

Measurements on the reverse and nonideal forward currents in heavily doped diodes and in advanced bipolar transistors in the temperature range from 77 K to 300 K are presented. A detailed comparison is made between these measurements and various models. It is shown that models from the literature fail to describe all observed phenomena. A model is proposed which is shown to provide a good description of the measured heavy-doping effects on recombination. The model describes the experimentally observed voltage and temperature dependence of both the nonideal forward and the reverse currents without the introduction of fitting parameters. It is shown that, for zero-bias depletion widths between 300 AA and about 700 AA, trap-assisted tunneling is important for reverse-biased junctions at room temperature. For zero-bias depletion widths less than 300 AA, the tunneling effects increase dramatically. Whereas trap-assisted tunneling has to be taken into account for the forward characteristic, the reverse characteristic is dominated by band-to-band tunneling. >

G.A.M. Hurkx

Papers

A new recombination model describing heavy-doping effects and low-temperature behaviour