Mathematical details of a two-dimensional semiconductor device simulation program are presented, Applicability of the carrier transport model to shallow junction bipolar transistors is discussed. Use of this program to optimize device structures in new bipolar technology is illustrated by presenting calculated device characteristics for variations in a few selected process conditions, Software links that automatically transfer data from a two-dimensional process simulation program and to a quasi-three-dimensional device equivalent circuit model generation program are also discussed.

Two-dimensional device simulation program: 2DP

The state of the art in self-consistent numerical low-temperature MOS modeling is reviewed. The physical assumptions that are required to describe carrier transport at low ambient temperatures are discussed. Particular emphasis is placed on the models for space charge (impurity freeze-out), carrier mobility (temperature dependence of scattering mechanisms at a semiconductor-insulator interface), and carrier generation-recombination (impact ionization). The differences with regard to the numerical methods required for the solution of low-temperature models compared to room-temperature models are explained. Typical results obtained with the simulator MINIMOS 4 are presented. These include comparisons of short-channel effects and hot-electron phenomena such as energy relaxation and avalanche breakdown at 77 K and 300 K ambient temperatures. >

MOS device modeling at 77 K

Publisher Summary This chapter describes the performance limitations of Si PIN detectors and avalanche photodiodes so that a decision regarding which device to employ can be based on the system requirements. The chapter discusses the basic properties of these devices, for applications that require an avalanche photodiode, and summarizes the performance of avalanche photodiodes in various materials, pointing outareas where further research would be particularly fruitful. This exploration should first be directed toward finding a semiconductor with the appropriate energy gap that has a large asymmetry of the electron and hole ionization coefficients. Only after this is done should additional effort in materials and device technology, which are necessary to obtain high performance avalanche photodiodes, be considered.

Chapter 5 Avalanche Photodiodes

The high levels of substrate doping needed in deep-submicrometer MOS devices affect device properties strongly. The authors present a detailed experimental study of high-doping effects on the threshold voltage, which is shown to be affected by the quantum-mechanical splitting of the energy levels in the conduction band. A simple expression to account for these effects is proposed and the consequences for device scaling and design are discussed. Furthermore, the increasing levels of substrate doping and high normal electric fields affect the channel mobility through Coulomb and surface-roughness scattering. Several empirical models for the surface mobility are compared with the characteristics of experimental devices. >

Influence of high substrate doping levels on the threshold voltage and the mobility of deep-submicrometer MOSFETs

Photomultiplication, initiated by both pure electron and pure hole injection, has been measured in submicrometer Si p+-i-n+ and n+-i-p+ diodes with intrinsic region thicknesses w between 0.1 and 0.8 mum, at temperatures between 15 and 420 K. A local analysis is used to extract the values of effective ionization coefficients. Values of bulk ionization coefficients, alpha and beta, are then deduced and parameterized in an extended form of Chynoweth's expression to cover their dependence on both electric field and temperature. Multiplication at various temperatures can be recovered from these bulk coefficients by using a simple dead space correction. beta falls faster with temperature than alpha so that the ionization coefficient ratio, k=beta/alpha, decreases with temperature. Decreasing w reduces this temperature sensitivity, which is weaker than in GaAs, possibly because of the softer ionization threshold in Si

Temperature Dependence of Impact Ionization in Submicrometer Silicon Devices

The temperature dependencies of the carrier ionization rates and saturated drift velocities in silicon have been extracted from microwave admittance and breakdown voltage data of avalanche diodes. The avalanche voltage and broadband (2–8 GHz) microwave small-signal admittance were measured for junction temperatures in the range 280 to 590 K. An accurate model of the diode was used to calculate the admittance characteristic and voltage for each junction temperature. Subsequently, the values of ionization coefficients and saturated velocities were determined at each temperature by a numerical minimization routine to obtain the best fit between the calculated values and measured data.

C. N. Dunn

Papers

Temperature dependence of carrier ionization rates and saturated velocities in silicon