Abstract
This thesis presents the results of implanting He[+] plus Zn[+] into GaAs. The effects of He[+] implantation prior to implanting the Zn[+] and the behavior at high annealing temperatures (700°C ~ 900°C) have been investigated using the van der Pauw technique to measure electical properties and Rutherford backsecttering to measure the residual disorder. The doses and energy for the zinc implantation were 10[15] cm[-2] & 5 x 10[15] cm[-2] and 150 keV respectively. Also for the helium implantation, the doses and energies were 10[11] cm[-2] to 10[16] cm[-2] and 35 keV & 50 keV respectively. The reordering rates of the disordered layers produced by the implantations ara changed for the dual implanted and for the zinc singly implanted samples depending upon anneal temperatures, below 700°C or the higher temperatures (700°C ~ 800°C). The reordering of the lattice disorder occurs at an earlier time for the He[+] plus Zn[+] implanted samples when annealed at 800°C. The prebombardment at a dose of 10[16] He[+] cm[-2] enhances the lattice reorder; the recrystallization occurs in 5 min as compared with 15 min required for the sample implanted with 10[15] He[+] cm[-2] plus 10[15] Zn[+] cm[-2]. Some residual lattice disorder remained after all the annealings in this experiment for the samples implanted with zinc alone. After annealing in the temperature range of 800°C to 850°C a marked change in the depth profiles resulted. This may indicate that the thermal energy of this temperature corresponds to the formation of interstitial Zn in GaAs. Above 850°C a significant zinc diffusion is observed (e.g. junction depth over 1.5 mu, after 900°C. 5 min annealing). The use of dual implantation is in most cases effective in restricting diffusion in short time annealings. Also, the encapsulants (Al and Si[3]N[4]) influence the lattice re crystallization and the depth profile significantly.