SYSTEMATIC STUDIES OF IMPURITIES AND NITROGEN DOPING OF PHOTO-ASSISTED MOVPE GROWN ZNSE USING DESE2 DMZN, TEN AND TMSIN3

We present a study on the impurity incorporation and nitrogen doping o f ZnSe epilayers grown by metalorganic vapour phase epitaxy (MOVPE) on (100)GaAs using dimethylzinc.triethylamine (DMZn.TEN), diethylseleniu m (DESe) and trimethylsilylazide (TMSiN3) as the Zn, Se and N precurso rs, respectively. Both pyrolytic and photoassisted MOVPE (PA-MOVPE) ex periments have been carried out to identify the conditions for high pu rity growth. Characterization included both secondary ion mass spectro metry (SIMS) analysis to assess the incorporation of H, N and halogen impurities in the epilayers and 10 K photoluminescence (PL) measuremen ts. SIMS elemental analysis of halogens in undoped ZnSe shows that the concentration of these impurities is of the order of 1 x 10(15) cm(-3 ), whilst the hydrogen concentration is about 2 x 10(17) cm(-3). In no minally undoped ZnSe epilayers an unexpectedly high level of nitrogen, ranging between 3 x 10(16) cm(-3) and 1 x 10(18) cm(-3), was found. T he presence of N in undoped epilayers was confirmed by 10 K PL spectra , which are dominated by a N-related donor-acceptor-pair (DAP) band al ong with its LO-phonon replica and weaker bound exciton features in th e near band-edge region. Finally, intentionally nitrogen doped ZnSe sa mples were grown by using TMSiN3 under PA-MOVPE conditions at 380 degr ees C. SIMS analysis shows an efficient N incorporation up to 1 x 10(2 0) cm(-3) but increasing the N precursor partial pressure causes the g rowth rate to decrease together with an increase of the H content in t he layers. 10 K PL spectra of doped ZnSe show a sharp nitrogen bound e xciton peak in the near band-edge region along with dominant features ascribed to a free electron to acceptor transition at 2.710 eV and to a DAP band at around 2.695 eV, followed by their LO-phonon replica. (C ) 1998 Chapman & Hall.