Browsing by Author "LIAO, K"

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ANALYTICAL MODELING OF POLYCRYSTALLINE SILICON EMITTER BIPOLAR-TRANSISTORS UNDER HIGH-LEVEL INJECTION
(1994-08-01)
CHYAN, YF
;
CHANG, CY
;
SZE, SM
;
LIN, MJ
;
LIAO, K
We derived an analytical model, focused on injected charge storage, for electron current density J(n), hole current density J(ps), current gain beta, and forward transit time tau(f), for heavily doped base and emitter with non-uniform band structures. This model can apply in high-level injection regions before the onset of the Kirk effect. By comparing with those results obtained from Sukuki's low-level injection model, it is observed that a new high-level injection term, proportional to the square of the hole current density, appears in the injected hole concentration in the polycrystalline silicon emitter and this term vanishes in the limit of low-level injection. As bias increases, J(n) and J(ps) of high-level injection model are less than those of the low-level injection model. In addition. for low-level injection model, beta, tau(f), the base transit time tau(b), the crystalline silicon emitter transit time tau(se), and the polycrystalline silicon emitter transit time tau(pe) keep constant for all injection region. However, for high-level injection model, beta and tau(b) decreases as bias increases, while tau(se) and tau(pe) increase with increasing bias. Tau(f) reaches a minimum and then increases. We conclude that the high-level injection model offers significant information for device operations at various electron current levels.
TEMPERATURE INFLUENCE ON THE GENERALIZED EINSTEIN RELATION FOR DEGENERATE SEMICONDUCTORS WITH ARBITRARY BAND STRUCTURES
(1994-05-01)
CHYAN, YF
;
SZE, SM
;
CHANG, CY
;
LIAO, K
;
REIF, R
We present a systematic study of the temperature influence on the generalized Einstein relation for degenerate semiconductors with different band structures. The conventional Einstein relation is still a good approximation at very high temperatures for most carrier concentrations but becomes invalid at low temperatures for highly degenerate semiconductors. As the temperature rises, higher energy bands with small minimum energy separations (e.g., from GAMMA band to L band) and large density-of-state effective masses will have a larger fraction of carriers, because the minimum energy separations become comparable to the thermal energy. Thus, from 500 K to 1200 K, in n-type GaAs and n-type Ge, we observe kinks in the D/mu versus carrier concentration curves. However, no such kinks are observed in n-type Si due to its large minimum energy separations. Similarly, p-type Ge and p-type GaAs show no kinks, because the energy of the spin-orbit splitting in these semiconductors is large compared to the thermal energy.