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 of ZnSe epilayers grown by metalorganic vapour phase epitaxy (MOVPE) on (100)GaAs using dimethylzinc.triethylamine (DMZn.TEN), diethylselenium (DESe) and trimethylsilylazide (TMSiN3) as the Zn, Se and N precursors, respectively. Both pyrolytic and photoassisted MOVPE (PA-MOVPE) experiments have been carried out to identify the conditions for high purity growth. Characterization included both secondary ion mass spectrometry (SIMS) analysis to assess the incorporation of H, N and halogen impurities in the epilayers and 10 K photoluminescence (PL) measurements. 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 nominally 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. The 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 along with its LO-phonon replica and weaker bound exciton features in the near band-edge region. Finally, intentionally nitrogen doped ZnSe samples were grown by using TMSiN3 under PA-MOVPE conditions at 380 degrees C. SIMS analysis shows an efficient N incorporation up to 1 x 10(20) cm(-3) but increasing the N precursor partial pressure causes the growth rate to decrease together with an increase of the H content in the layers. 10 K PL spectra of doped ZnSe show a sharp nitrogen bound exciton 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.