Minority Hole Mobility Research Articles

Improved concepts for predicting the electrical behavior of bipolar structures in silicon

Most bipolar device models, based upon doping profiles and upon numerical solutions to coupled, nonlinear equations for semiconductor devices, contain empirical methods for computing the effective intrinsic carrier concentration n <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ie</inf> mobility, and lifetime. These methods usually are based upon electrical measurements, assume that the majority hole (electron) mobility equals the minority hole (electron) mobility at high doping densities, use Boltzmann statistics, and assume that the carrier lifetime is much greater than the carrier transit time. More physically correct concepts are reported in this paper and are applied to bipolar transistors in silicon. These concepts use the perturbed densities of states and nonparabolic bands which arise from a quantum mechanical description of bandgap narrowing to compute separately n <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ie</inf> and the carrier mobility, use minority carrier lifetimes which agree much better with measured lifetimes in processed silicon, and use Fermi-Dirac statistics. When these concepts are incorporated into a device analysis code such as SEDAN <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> and then used to compute the dc common-emitter gain of two n-p-n transistors, the predicted gains agree very well with the measured gains. In addition, these concepts offer potential improvements in predicting the temperature dependence of the gain.

Effective drift current densities in the n-type heavily doped emitter region of p−n + junction silicon solar cells

The effective drift current density components J cp and J cn in the n-type heavily doped emitter region of p−n + junction silicon solar cells at 300 K were investigated using the simplified models of heavily doped semiconductors proposed in our previous papers. It was found that (i) the effective electric field E p acting on the minority holes is lower than the effective electric field E n acting on the majority electrons, (ii) the minority hole mobility μ p is less than the majority electron mobility μ n , (iii) the minority hole concentration p is very much less than the majority electron concentration n and (iv) therefore J cp is appreciably lower than J cn . Our theoretical results for E p and μ p are compared with those obtained using other theories.

Carrier distribution in graded-band-gap semiconductors under asymmetric band-edge gradients

The authors have discussed earlier the photomagnetoelectric effect in graded-band-gap semiconductors assuming symmetrical band-edge gradients. The present paper rewrites the continuity equation under asymmetric band-edge gradients, and includes the effects of position-dependent minority carrier lifetime, electron and hole mobilities, and effective masses. A study of excess minority carriers as a function of position in the direction of graded composition indicates that under steady photoexcitation, minority carrier distribution and total concentration of carriers are markedly dependent on the relative magnitudes of conduction- and valence-band-edge gradients. A plausible physical explanation of the carrier distribution in the graded-band-gap specimen has been attempted.