Time-Resolved Recombination Dynamics of Photoionized Hydrogenlike Impurities

Abstract

The dynamics of recombination of photoionized shallow impurities is investigated on a nanosecond time scale, by monitoring the photoconductive decay of high-purity n-InP illuminated with fast, high-power far-infrared pulses. The classical rate equation is found to break down due to the population and impact ionization of excited states. At higher carrier densities and bias electric fields Auger-like recombination is found to strongly affect the decay process.Recombination of electrons a t shallow impurities in semiconductors is the prototype of a general class of electron recombination processes at localized states, such as deep traps or surface states. In this letter we report the use of a novel time-resolved far-infrared (FIR) technique to probe shallow-impurity recombination in a 111-V semiconductor. This enables us to obtain, for the first time, clear evidence of the population of excited impurity states during recombination and direct insight into the mechanisms involved in the electron energy relaxation processes.The shallow donor in many 111-V semiconductors is known to be a good analogue of the hydrogen atom [l, 21. It is known that the shallow donors in indium phosphide (InP), which are predominantly silicon and sulphur, exhibit model hydrogenic behaviour. It is generally accepted [3] that carriers optically excited to higher bound impurity states are further thermally excited into continuum states (thereby giving rise to photoconduction), and that

Nonlinear far-infrared photoionization of shallow acceptors in Germanium

“…With this approximation the optically generated hole density p(Z) as function of intensity is given by (3) in agreement to the experimental results. In this relation rr = (TfN,)-' is the life time of holes in the band which in terms of the model is equal to the capture time in the excited state.…”