Systematic studies of impurities and nitrogen doping of photo-assisted MOVPE grown ZnSe using DESe, DMZn, TEN and TMSiN₃

Abstract

We present a study on the impurity incorporation and nitrogen doping of ZnSe epilayers grown by metalorganic vapour phase epitaxy (MOVPE) on (1 0 0)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 1×1015 cm-3, whilst the hydrogen concentration is about 2×1017 cm-3. In nominally undoped ZnSe epilayers an unexpectedly high level of nitrogen, ranging between 3×1016 cm-3 and 1×1018 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 °C. SIMS analysis shows an efficient N incorporation up to 1×1020 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. © 1998 Chapman & Hall