Simultaneous measurement of hole lifetime, hole mobility and bandgap narrowing in heavily doped n-type silicon

Abstract

The hole diffusion length, hole lifetime, hole mobility, and hole equilibrium concentration in epitaxial heavily phosphom-doped silicon have been measured by a combination of steady-state and transient techniques. Steady state measurements were performed on bipolar transistors in which the base was epitaxially grown. The transient measurement relied on the observation of the decay of the photoluminescence radiation after laser excitation. Significant findings are: 1) the hole mobility is about a factor of two larger in heavily doped n-type silicon than in p-type silicon; 2) the apparent bandgap narrowing is smaller than previously thought, with a value of about 90 meV at a doping level of 10'' cm-'.

Polycrystalline silicon-germanium emitters for gain control, with application to SiGe HBTs

“…The strong dependence of on interfacial oxide thickness indicates that the base current is dominated by tunneling through the interfacial oxide layer under these conditions. This can be understood from (11) by noting that decreases exponentially with increasing Ge content, so that at high Ge content in (13). Since and , we than have .…”

“…For 0% Ge and small interfacial oxide thicknesses, saturates at a value of 1.2 10 m/s, which is equal to the value of . This behavior can be understood from (13) by noting that is equal to unity, and so that . In this region of the characteristic is therefore dominated by transport in the polySiGe layer.…”

“…4 shows that varies strongly with interfacial oxide thickness. This behavior can be understood from (13) by noting that and so that . In this region of the characteristic, the base current is therefore dominated by transport through the interfacial oxide layer.…”

“…This equation will be used together with (13) to interpret the competing transport and recombination mechanisms in polySiGe emitters. It should be noted that (14) models the ideal portion of the base characteristic, whereas in practice nonideal base characteristics are often obtained due to recombination in the emitter/base depletion region.…”

“…The hole concentration can then be related to and using (8) (9) Combining (5) to (9) gives (10) where (11) The current density at the edge of the polySiGe emitter is now given by (12) where models recombination at the polysilicon/silicon interface, and is given by an equation analogous to (A8) and is the overall effective surface recombination velocity for the polySiGe emitter, which is given by (13) It is worth noting that holes tunneling through the oxide become hot as they appear in the polySiGe grain, as they pick up kinetic energy of . The holes will quickly thermalize to the valence band edge and continue to diffuse toward the emitter contact.…”