Growth of Highly Doped P-Type Znte Films by Pulsed Laser ablation in Molecular Nitrogen

Abstract

is DISCLAIMERPortions of this document may be illegible in electronic image products. Images are produced from the best available original document. GROWTH OF HIGHLY DOPED i-TYPE ZnTe FILMS BY PULSED LASER ABLATION IN MOLECULAR NITROGEN ABSTRACTHighly p-doped ZnTe films have been grown on semi-insulating GaAs (001) substrates by pulsed-laser ablation (PLA) of a stoichiometric ZnTe target in a high-purity N2 ambient without the use o any assisting (DC or AC) plasma source. Free hole concentrations in the mid-1019 cm-3 to >IO& cm-3 range were obtained for a range of nitrogen pressures The maximum hole concentration equals the highest hole doping reported to date for any wide band gap II-VI compound. The highest hole mobilities were attained for nitrogen pressures of 50-100 mTorr (-6.5-13 Pa). Unlike recent experiments in which atomic nitrogen beams, extracted from RF and DC plasma sources, were used to produce p-type doping during molecular beam epitaxy deposition, spectroscopic measurements carried out during PLA of ZnTe in N2 do not reveal the presence of atomic nitrogen. This suggests that the high hole concentrations in laser ablated ZnTe are produced by a new and different mechanism, possibly energetic beam-induced reactions with excited molecular nitrogen adsorbed on the growing film surface, or transient formation of Zn-N complexes in the energetic ablation plume. This appears to be thefirst time that any wide bund gap (Eg > 2 eV) II-VI compound (or other) semiconductor has been impurity-dopedfrorn the gas phase by laser ablation. In combination with the recent discovery that epitaxial ZnSel-xSx films and heterostructures with continuously variable composition can be grown by ablation from a single target of fixed composition, these results appear to open the way to explore PLA growth and doping of compound semiconductors as a possible alternative to molecular beam epitaxy.

Pulsed Laser Ablation Growth and Doping of Epitaxial Compound Semiconductor Films

“…On the other hand, when a nitrogen glow discharge was established between parallel Cu plates in the same chamber, strong near-infrared N+ atomic emission lines and an N2+ emission band were seen. 7 The lack of atomic N emission from the PLA plasma in our experiments contrasts with the recent observation by Vaudo et al22 of strong near-IR atomic N lines emitted from the nitrogen plasma produced by an F W source that is used for N-doping during MBE growth. They concluded that atomic N (not molecular N2) is responsible for RF plasma p-type doping of ZnSe (and ZnTe) under MBE growth conditions.22 Our experiments do not directly rule out the presence of atomic N in the ground state during PLA, but this seems unlikely.…”

“…This striking correlation suggests that the fast (vacuum) pulse of unscattered ions and atoms has sufficient kinetic energy to produce lattice displacement damage and point defects that reduce the hole mobility. 7 In another paper of this symposium19 Rouleau et al characteristic velocity and amplitude, were required to fit the ion probe data. For mode 1 (the vacuum or collision-free ion pulse in Fig.…”

Time-resolved RHEED Studies of the Growth of Epitaxial ZnSe Films on GaAs by Pulsed Laser Deposition

“…The formation of Ga compounds (e.g., Ga 2 Se 3 ) at the ZnSe/GaAs interface is thermodynamically favored and has been reported [16,17]. Further, it is known that Ga diffusion during the growth of ZnTe on GaSb leads to autodoping during PLD growth [18]. If this is occurring during the growth of our films, then the presence of Ga in the region near the ZnSe/GaAs interface may be responsible for the observed reduction in in-plane order.…”