Electric-field-induced quenching of shallow and deep bound excitons in silicon.

Abstract

A comparative study of photoluminescence (PL) quenching of shallow bound excitons (BE's) associated with shallow donors and acceptors and of deep isoelectronic bound excitons (IBE's) in Si in a weak electric field at liquid-He temperatures is reported. In both cases the photoluminescence is quenched due to impact ionization by field-accelerated hot carriers. A comparison between n- and p-type samples showed no significant difference in quenching rate for the shallow donor- and acceptor-related BE's; the quenching starts around 50 V/cm, and both electrons and holes are released as free carriers in the impact process. The IBE's show a completely different behavior and a different impact mechanism. IBE's first show an increase in PL intensity with applied electric field and are difficult to completely quench before the electrical breakdown of the sample around 400 V/cm. In this case it is concluded that only one carrier is released from the center in the impact process. By impact ionizing the shallow donor- and acceptor-related BE's and the free excitons, an efficient recombination channel for free carriers is removed, and the carrier lifetime is drastically increased. This opens up new recombination channels, such as free-to-bound transitions, which are not seen in the absence of an electric field.