The only II‐VI/II‐VI wide band‐gap heterojunction to provide both good lattice match and p‐ and n‐type dopability is CdSe/ZnTe. We have carried out numerical simulations of several light emitter designs incorporating CdSe, ZnTe, and Mg alloys. In the simulations, Poisson’s equation is solved in conjunction with the hole and electron current and continuity equations. Radiative and nonradiative recombination in bulk material and at interfaces are included in the model. Simulation results show that an n‐CdSe/p‐ZnTe heterostructure is unfavorable for efficient wide band‐gap light emission due to recombination in the CdSe and at the CdSe/ZnTe interface. An n‐CdSe/Mg_(x)Cd_(1−x)Se/p‐ZnTe heterostructure significantly reduces interfacial recombination and facilitates electron injection into the p‐ZnTe layer. The addition of a Mg_(y)Zn_(1−y)Te electron confining layer further improves the efficiency of light emission. Finally, an n‐CdSe/Mg_(x)Cd_(1−x)Se/Mg_(y)Zn_(1−y)Te/p‐ZnTe design allows tunability of the wavelength of light emission from green into the blue wavelength regime.

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n‐CdSe/p‐ZnTe based wide band‐gap light emitters: Numerical simulation and design

A new set of semiconductor equations is proposed here which will be suitable for the numerical study of the carrier transport effects in submicron devices. With simplified models and comprehensive numerical techniques, the relative importance (on the device behavior) of several physical effects, such as velocity overshoot, intracollisional field effect, avalanche breakdown, carrier generation and temperature effect can be determined. The program that is capable of solving this set of equations will become an indispensible CAD tool if the current trend of the decreasing of the device dimensions continues.

A new set of semiconductor equations for computer simulation of submicron devices

GTO thyristor turn-off process is analyzed for a resistive load case by performing an exact two-dimensional time- and temperature-dependent numerical simulation. A newly defined concept "on-region" is introduced to help understanding of the simulation results. Excess carrier plasma (on-region) in the p-base is squeezed finally to as narrow as 60 µm wide, accompanying a large current density increase at the center of the middle junction. The carriers in the n-base are found not to be greatly affected by the initial plasma squeezing in the p-base. After the on-region width in the p-base reaches its final limit, the excess carriers around the middle junction of the final on-region is rapidly reduced, resulting in complete anode current turn-off.

A time- and temperature-dependent 2-D simulation of the GTO thyristor turn-off process

Some experimental observations of the switching characteristics and second breakdown susceptibility of high-voltage, fast-switching power transistors are discussed. A unique test circuit is described which permits devices to be taken into reverse-bias second breakdown many times with little or no apparent degradation. Evidence for the constriction of emitter current to the centers of the emitter fingers during the time associated with the extraction of stored charge is presented, three modes of reverse-bias second breakdown are shown, and reverse-bias safe-operating-area limits which have been nondestructively determined are shown.

Some effects of base current on transistor switching and reverse-bias second breakdown

A computer program for two-dimensional analysis of semiconductor devices has been developed. The basic semiconductor equations are solved using the finite clement method. Results from calculations on short channel MOS transistors arc presented and compared to experimental results.

HALVFEM—a computer program for two-dimensional finite element analysis of semiconductor devices

The current density and temperature distribution in a bi-polar power transistor operating in the switching mode under transient conditions has been computed as a function of circuit environment. A modeling was done of the turnoff of the transistor in a circuit containing resistive and inductive elements. Of particular interest was the study of the local current and temperature distribution achieved in the transistor during turnoff in a circuit with a large inductance; in the process of shutoff this inductance maintains the transistor collector current at a high value as the collector junction undergoes avalanche multiplication due to the high voltage induced across this junction by the inductive load. The length of time that the transistor remains in the high-current high-voltage mode during the turnoff transient determines the extent of current crowding and local heating in the device. The method of computation was to solve numerically the electrical carrier flow as well as Poisson's and the heat-flow equations in a two-dimensional model of an n+-p-n-n+transistor structure, as a function of time. The electrical boundary conditions on the emitter, base, and collector contacts were determined by considering the transistors interaction with its electric circuit environment. This interaction was calculated at each step in time, in an iterative fashion, as the transistor was turned off by extracting current from its base lead. The study permits the evaluation of a given bipolar transistor design with respect to current crowding, heating, and impact ionization in switching circuits containing inductive loads.

Two-dimensional nonisothermal carrier flow in a transistor structure under reactive circuit conditions

The current density and temperature distribution in a bipolar power transistor operating in the switching mode under transient conditions is computed as a function of circuit environment. The method of computation is to solve numerically the electrical carrier flow as well as Poisson and the heat flow equations in a two-dimensional model of an n+-p-n-n-transistor structure, as a function of time. Of particular interest is the behavior of the local current and temperature distribution achieved in the transistor during turn-off in a circuit with a large inductance. The length of time that the transistor remains in the high current, high voltage mode during the turn-off transient determines the extent of current crowding and local heating in the device.

http://ieeexplore.ieee.org/iel5/9943/31771/01479323.pdf

L.J. Turgeon

Papers

Two-dimensional nonisothermal carrier flow in a transistor structure under reactive circuit conditions

Two-dimensional nonisothermal carrier flow in a transistor structure under reactive circuit conditions