EXCITATION AND NONRADIATIVE DEEXCITATION PROCESSES OF ER3+ IN CRYSTALLINE SI

A detailed investigation on the excitation and deexcitation processes of Er3+ in Si is reported. In particular, we explored Er pumping throu gh electron-hole pair recombination and Er deexcitation through Auger processes transferring energy to either free or bound electrons and ho les. Since Er donor behavior would result in a free-carrier concentrat ion varying along its profile, experiments have been performed by embe dding the whole Er profile within previously prepared n-doped or p-dop ed regions. Multiple P (B) implants were performed in n-type (p-type) Czochralski Si samples in order to realize uniform dopant concentratio ns from 4 x 10(16) to 1.2 x 10(18)/cm(3) at depths between 0.5 and 2.5 mu m below the surface. These samples have been subsequently implante d with 4 MeV 3.3 x 10(13) Er/cm(2) and annealed at 900 degrees C for 3 0 min. Free electrons or holes concentrations in the region where Er s its were measured by spreading resistance profiling. It has been found that the release of electrons or holes from shallow donors and accept ers, occurring at temperatures between 15 and 100 K, produces a strong reduction of both time decay and luminescence intensity at 1.54 mu m. These phenomena are produced by Auger deexcitation of the Er3+ intra- 4f electrons with energy transfer to free carriers. The Auger coeffici ent of this process has been measured to be C-A similar to 5 x 10(-13) cm(3) s(-1) for both free electrons and free holes. Moreover, at 15 K (when the free carriers are frozen and the donor and acceptor levels occupied) the Er3+ time decay has been found to depend on the P (or B) concentrations. This is attributed to an impurity Auger deexcitation to electrons (or holes) bound to shallow donors (accepters): the effic iency of this process has been determined to be two orders of magnitud e smaller with respect to the Auger deexcitation with free carriers. F urthermore, at temperatures above 100 K a nonradiative back-transfer d ecay process, characterized by an activation energy of 0.15 eV, is see n to set in for both p-type and n-type samples. This suggests that the back-transfer process, which severely limits the high-temperature lum inescence efficiency, is always completed by a thermalization of an el ectron trapped at an Er-related level to the conduction band. Finally, by analysis of the pump power dependence of time decay and luminescen ce yield at 15 K, we have found that excitation of Er through the reco mbination of an electron-hole pair is a very efficient process, charac terized by an effective cross section of 3 x 10(-15) cm(2) and able to provide an internal quantum efficiency as high as 10% at low temperat ures (15 K) and pump powers (below 1 mW). This efficiency is significa ntly reduced when, at higher temperatures and/or high pump powers, str ong nonradiative decay processes set in. These phenomena are investiga ted in detail and their impact on device operation perspectives are an alyzed and discussed. [S0163-1829(98)01008-X].