Ion implantation techniques for the fabrication of gallium arsenide multilayer microwave devices.

This thesis presents a study of the potential for ion implantation to play a more significant role in the manufacture and fabrication of commercially available multilayer microwave devices. Two different applications for ion implantation in device manufacture are investigated. Firstly, implant isolation as an alternative to wet chemical etching for the planar doped barrier diode, and low and high power versions of the graded gap Gunn diode are attempted. It is demonstrated that the technique is an excellent method of lateral device isolation for the current generation of these devices, having little or no effect on the performance of the planar doped barrier diode, but with significant improvements in across wafer uniformity of device area, and hence, improvements in uniformity of device characteristics. Implant isolation of the graded gap Gunn diode has been met with mixed success. It has been shown that implant isolation has no detrimental effect on the ability of the device to emit microwaves at 77GHz, despite encapsulation of the active regions of the device in ion implanted GaAs. Problems have, however, been encountered with the geometry of the integral heat sink device (high power version), resulting in parasitic capacitance to the extent that the device experiences a shift in output frequency and power. Secondly, doping of GaAs by ion implantation of the dopants magnesium and zinc, for the production of p-type layers relevant to GaAs multilayer microwave device manufacture is studied. Attempts are made to emulate the MBE grown planar doped banier buried p-type spike using ion implantation of magnesium through a n-type contact region, and into a 'n-i-n' MBE grown structure. The result is a working bulk unipolar diode, with barrier height dependent on magnesium implanted energy and dose. A p-type dopant diffusion control experiment is also conducted whereby the depth of the diffusion-controlling phosphorus co-implant is varied to yield different p-type doping profiles. It is demonstrated that using this method it is possible to achieve a p-n junction with a gradually decaying p-type surface region, or an extremely abrupt junction. This technique is then used to produce and study varactor diodes, focusing on their rest capacitances, and their capacitance ratios. SIMS analysis and differential Hall effect measurements are also performed