Hole capture at acceptors inp-type germanium

Abstract

Hole capture data obtained by capacitance transient spectroscopy on eleven different acceptors in high-purity germanium are presented over the temperature range 8–160 K. Capture invariably proceeded faster than predicted by the cascade theory and did not follow theZ ³ T ⁻³ dependence predicted by cascade theory, whereZ is the acceptor charge andT is the temperature. Instead it was found that capture followed the phenomenological relationship

$$\frac{{N_\upsilon }}{{gp\tau _c }} = kT/h\{ \eta exp (---E_a /kT) \} $$

whereN _υ is the effective density of states at the valence band edge,g is the degeneracy of the ground state (four),p is the hole concentration,τ _c is the mean capture time for the acceptor,k is Boltzman’s constant, andh is Planck’s constant.η is a dimensionless efficiency factor and exp (—E _α /kT) is an activation term required to fit the data of some centers. The authors propose that transitions to the electronic ground state from band states or from bound excited states must be faster than previously considered.