The implantation of donor ions into gallium arsenide for field effect transistors.

The purpose of the work described in this dissertation was to investigate the use of donor ion implantation into GaAs for the production of doped layers suitable for the manufacture of Schottky gated field effect transistors or MESFETs. The project had four main aims: (i) The establishment of a reliable method of encapsulation. (ii) A study of the use of short thermal pulse annealing to activate donor ions implanted into GaAs. (iii) An investigation of various ion implantation schedules to determine the most suitable for producing layers for MESFETs. (iv) The manufacture and characterisation of MESFETs on ion implanted material. This area of the project was performed at the Allen Clark Research Centre (Plessey Research, Caswell). Two sets of apparatus were constructed to achieve the rapid deposition of Si3N4 encapsulating layers. Both sets of equipment allowed the deposition of reliable encapsulating layers which protected the GaAs from decomposition during high temperature (900°C) annealing. With the second apparatus uniform layers of Si3N4 could be deposited over one inch diameter slices. The rapid thermal pulse annealing was also performed in the Si3N4 deposition equipment. The annealing temperature (900°C) was reached in less than 10 seconds. It was found, by examining the degree of electrical activation of implanted ions, that a total of 30 seconds annealing was sufficient to achieve the maximum number of implanted ions that could be activated at 900°C. Several species of ions, implanted at various energies, were studied as suitable donors, using thermal pulse annealing. These included selenium, tellurium, germanium, tin and silicon. Additionally the implantation of dual ion combinations, and the co-implantation of selenium ions at two energies was investigated. The results of Hall measurements and profiling achieved in this study compare favourably with those reported in the literature for similar implants annealed in more conventional furnace annealing schedules. The characterisation of MESFETs produced on implanted layers compare favourably with those manufactured on epitaxially grown material, both in terms of gain and noise figure. It was found also that characteristics of these MESFETs depended on the type of substrate used. The I-V characteristics of devices produced on bulk semi-insulating material were slightly inferior to those produced on epitaxial buffer layers, although the microwave performance was not significantly worse